EFFORT INDEX AS A NOVEL VARIABLE FOR MONITORING THE LEVEL OF EFFORT DURING RESISTANCE EXERCISES DAVID RODRI´GUEZ-ROSELL,1 JUAN M. YA´N˜EZ-GARCI´A,1 JULIO TORRES-TORRELO,1 RICARDO MORACUSTODIO,1 MA´RIO C. MARQUES,2,3 AND JUAN J. GONZA´LEZ-BADILLO1 1
Physical Performance and Sports Research Center, Pablo de Olavide University, Seville, Spain; 2Department of Sport Sciences, University of Beira Interior, UBI, Covilha˜, Portugal; and 3Research Center in Sport Sciences, Health Sciences and Human Development, CIDESD, Portugal ABSTRACT
Rodrı´guez-Rosell, D, Ya´n˜ez-Garcı´a, JM, Torres-Torrelo, J, MoraCustodio, R, Marques, MC, and Gonza´lez-Badillo, JJ. Effort index as a novel variable for monitoring the level of effort during resistance exercises. J Strength Cond Res XX(X): 000–000, 2018—This study aimed to analyze the acute mechanical and metabolic response to resistance exercise protocols (REPs) defined by 2 variables: the first repetition’s mean velocity and the percentage of velocity loss (%VL) over the set. The product of these 2 variables was termed the effort index (EI) and was used as an indicator of the degree of fatigue induced during each REP. Twenty-one resistance-trained men (11 in full squat [SQ] and 10 in bench press [BP]) performed 16 REPs separated by 72 hours. Relative loads used (50, 60, 70, and 80% 1repetition maximum) were determined from the load-velocity relationship for the SQ and BP, whereas volume was objectively determined using the %VL attained over the set (10, 20, 30, and 45% for SQ, and 15, 25, 40, and 55% for BP). Lactate concentration and velocity against the load that elicited a ;1.00 m$s21 (V1 m$s21 load) were measured before and after each REP. Post-exercise velocity with the V1 m$s21 load and lactate concentration were significantly different (P , 0.01–0.001) from pre-exercise after all REPs. A very close relationship was found between the proposed EI and %VL with the V1 m$s21 load (r = 0.92–0.98) and post-exercise lactate concentration (r = 0.91–0.95) in both exercises. The correlations between this new index and fatigue indicators such as VL allow us to gain further insight into the actual degree of effort incurred during resistance exercise. In addition to being a valuable addition for training monitoring, the proposed EI could
Address correspondence to David Rodrı´guez-Rosell,
[email protected]. 00(00)/1–15 Journal of Strength and Conditioning Research 2018 National Strength and Conditioning Association
also be used as an independent variable in training studies by equalizing the effort between different interventions.
KEY WORDS neuromuscular fatigue, velocity loss, lactate concentration, velocity-based resistance training, training prescription
INTRODUCTION
D
esigning a resistance training (RT) program is a complex process, which requires adequate monitoring and manipulation of the variables that define the training stimulus (e.g., intensity, volume, movement velocity, rest periods, exercise type, and order and frequency), because the different combinations of these RT variables directly influence the type and magnitude of acute responses of the neural, endocrine and musculoskeletal systems, and consequently, long-term neuromuscular adaptations (3,16,35). Therefore, knowledge of the mechanical and physiological aspects underlying the different RT protocols is essential to improve our understanding of the processes that cause changes in neuromuscular performance (4,5,26). It is traditionally assumed that RT should always be performed to muscular failure to maximize strength gains (3,7,20). It is for this reason that most studies are analyzing acute mechanical and physiological responses after RT programs in which the maximum number of repetitions have been completed in each training set (1,2,14,19,36). However, increasing evidence seems to indicate that it is uncertain that RT should be performed to muscle failure for muscular strength to be enhanced (7,18,24). In this regard, more recent studies (10,13,23,26) have focused on comparing the effect of manipulating the number of repetitions actually performed in each set with respect to the maximum number that can be completed on mechanical, endocrine, sympathetic, parasympathetic, metabolic, and neuromuscular responses. Although these studies (10,13,23,26) have made it possible to ascertain (a) the physiological meaning of the socalled level of effort and (b) the relevance of velocity loss VOLUME 00 | NUMBER 00 | MONTH 2018 |
Copyright ª 2018 National Strength and Conditioning Association
1
the
Journal of Strength and Conditioning Research
TM
Copyright ª 2018 National Strength and Conditioning Association
Scheduled Sets 3 VL (%) Target MPV (m$s21) Actually performed VL (%) Reference MPV (m$s21) Load used (kg) EI Rep Scheduled Sets 3 VL (%) Target MPV (m$s21) Actually performed VL (%) Reference MPV (m$s21) Load used (kg) EI Rep
50%1RM _10%VL
50%1RM _20%VL
50%1RM _30%VL
50%1RM _45%VL
60%1RM _10%VL
60%1RM _20%VL
60%1RM _30%VL
60%1RM _45%VL
3 3 10% ;1.13 (50% 1RM)
3 3 20% ;1.13 (50% 1RM)
3 3 30% ;1.13 (50% 1RM)
3 3 45% ;1.13 (50% 1RM)
3 3 10% ;0.98 (60% 1RM)
3 3 20% ;0.98 (60% 1RM)
3 3 30% ;0.98 (60% 1RM)
3 3 45% ;0.98 (60% 1RM)
9.9 6 1.0 1.13 6 0.03 (;52% 1RM) 61.6 6 6.8 11.2 6 1.3 5.0 6 1.4
20.0 6 0.9 1.14 6 0.02 (;51% 1RM) 61.2 6 7.9 22.8 6 1.0 8.2 6 2.2
30.8 6 2.2 1.13 6 0.02 (;52% 1RM) 60.3 6 8.6 34.7 6 2.7 10.5 6 2.9
46.9 6 2.5 1.12 6 0.02 (;52% 1RM) 61.5 6 6.3 52.7 6 3.3 13.4 6 3.7
11.5 6 1.6 0.99 6 0.03 (;61% 1RM) 73.0 6 7.5 11.4 6 1.6 3.8 6 1.0
20.2 6 1.7 0.99 6 0.03 (;61% 1RM) 74.1 6 8.1 20.0 6 1.8 5.3 6 1.6
29.7 6 1.7 1.00 6 0.03 (;61% 1RM) 73.2 6 8.0 29.5 6 1.7 6.9 6 1.7
47.4 6 2.4 0.99 6 0.03 (;61% 1RM) 74.7 6 5.6 46.8 6 3.1 9.2 6 2.2
70%1RM _10%VL
70%1RM _20%VL
70%1RM _30%VL
70%1RM _45%VL
80%1RM _10%VL
80%1RM _20%VL
80%1RM _30%VL
80%1RM _45%VL
3 3 10% ;0.82 (70% 1RM)
3 3 20% ;0.82 (70% 1RM)
3 3 30% ;0.82 (70% 1RM)
3 3 45% ;0.82 (70% 1RM)
3 3 10% ;0.68 (80% 1RM)
3 3 20% ;0.68 (80% 1RM)
3 3 30% ;0.68 (80% 1RM)
3 3 45% ;0.68 (80% 1RM)
10.7 6 2.3 0.84 6 0.03 (;70% 1RM) 85.6 6 7.3 9.0 6 1.8 2.5 6 0.6
19.8 6 2.0 0.85 6 0.03 (;70% 1RM) 87.7 6 9.6 16.8 6 1.6 3.5 6 1.0
29.9 6 2.0 0.83 6 0.01 (;71% 1RM) 87.6 6 8.7 24.9 6 1.6 4.4 6 1.0
45.8 6 2.9 0.84 6 0.02 (;70% 1RM) 86.1 6 8.4 38.5 6 2.4 5.8 6 1.1
11.0 6 1.2 0.71 6 0.02 (;78% 1RM) 93.7 6 8.2 7.8 6 0.8 1.9 6 0.2
21.1 6 2.5 0.70 6 0.02 (;79% 1RM) 93.4 6 8.9 14.8 6 1.6 2.5 6 0.7
30.9 6 2.3 0.71 6 0.02 (;78% 1RM) 94.5 6 10.3 22.0 6 1.2 3.2 6 0.6
48.1 6 4.5 0.70 6 0.03 (;79% 1RM) 93.5 6 9.9 33.5 6 3.4 3.8 6 0.9
*RM = repetition maximum; VL = loss of MPV over the set; MPV = mean propulsive velocity; EI = effort index (see text for details); Rep = number of repetitions performed in each
set.
†Data are mean 6 SD. SQ: full back-squat exercise (n = 11).
Effort Index as an Indicator of Muscle Fatigue
2 TABLE 1. Descriptive characteristics of the resistance exercise protocols performed by the SQ group.*†
TABLE 2. Descriptive characteristics of the resistance exercise protocols performed in each session for the PB group.*†
Sets 3 VL (%) Target MPV (m$s21) Actually performed VL (%) Reference MPV (m$s21) Load used (kg) EI Rep Scheduled
50%1RM _25%VL
50%1RM _40%VL
50%1RM _55%VL
60%1RM _15%VL
60%1RM _25%VL
60%1RM _40%VL
60%1RM _55%VL
3 3 15% ;0.93 (50% 1RM)
3 3 25% ;0.93 (50% 1RM)
3 3 40% ;0.93 (50% 1RM)
3 3 55% ;0.93 (50% 1RM)
3 3 15% ;0.79 (60% 1RM)
3 3 25% ;0.79 (60% 1RM)
3 3 40% ;0.79 (60% 1RM)
3 3 55% ;0.79 (60% 1RM)
15.1 6 1.3 0.92 6 0.03 (;52% 1RM) 44.7 6 9.7 14.0 6 1.4 4.8 6 1.0
25.3 6 0.9 0.93 6 0.03 (;51% 1RM) 44.8 6 9.8 23.4 6 1.1 7.7 6 1.4
40.2 6 1.5 0.93 6 0.02 (;51% 1RM) 45.0 6 10.0 37.2 6 1.8 10.9 6 1.8
54.9 6 1.6 0.93 6 0.02 (;51% 1RM) 45.1 6 10.2 50.9 6 2.0 13.2 6 2.1
15.3 6 0.9 0.80 6 0.02 (;59% 1RM) 51.5 6 11.8 12.3 6 0.9 4.2 6 0.6
25.3 6 1.3 0.80 6 0.02 (;59% 1RM) 52.1 6 11.9 20.3 6 1.3 5.6 6 0.8
40.9 6 1.3 0.80 6 0.02 (;59% 1RM) 52.2 6 12.3 32.9 6 1.3 8.1 6 1.6
55.1 6 1.9 0.79 6 0.02 (;59% 1RM) 53.4 6 12.4 43.7 6 1.6 9.6 6 1.4
70%1RM _15%VL
70%1RM _25%VL
70%1RM _40%VL
70%1RM _55%VL
80%1RM _15%VL
80%1RM _25%VL
80%1RM _40%VL
80%1RM _55%VL
3 3 15% ;0.63 (70% 1RM)
3 3 25% ;0.63 (70% 1RM)
3 3 40% ;0.63 (70% 1RM)
3 3 55% ;0.63 (70% 1RM)
3 3 15% ;0.47 (80% 1RM)
3 3 25% ;0.47 (80% 1RM)
3 3 40% ;0.47 (80% 1RM)
3 3 55% ;0.47 (80% 1RM)
15.5 6 1.8 0.63 6 0.03 (;69% 1RM) 60.7 6 16.5 9.8 6 1.2 3.1 6 0.6
25.2 6 1.4 0.63 6 0.02 (;69% 1RM) 61.2 6 16.9 15.9 6 1.1 4.1 6 0.7
40.0 6 2.8 0.62 6 0.02 (;70% 1RM) 62.0 6 16.9 24.8 6 1.6 6.1 6 1.5
54.1 6 2.5 0.63 6 0.02 (;69% 1RM) 62.1 6 16.4 34.1 6 1.6 7.6 6 1.5
15.3 6 1.7 0.48 6 0.02 (;79% 1RM) 70.5 6 19.2 7.4 6 0.8 2.2 6 0.2
25.0 6 2.7 0.49 6 0.02 (;79% 1RM) 70.2 6 19.2 12.3 6 1.4 3.3 6 0.3
40.3 6 2.5 0.49 6 0.02 (;78% 1RM) 70.9 6 19.1 19.8 6 1.5 4.4 6 0.7
56.8 6 4.0 0.49 6 0.02 (;78% 1RM) 70.6 6 19.1 27.8 6 1.6 5.4 6 1.2
*RM = repetition maximum; VL = loss of MPV over the set; MPV = mean propulsive velocity; EI = effort index (see text for details); Rep = number of repetitions performed in each set; BP = bench press exercise (n = 10). †Data are mean 6 SD.
the
Sets 3 VL (%) Target MPV (m$s21) Actually performed VL (%) Reference MPV (m$s21) Load used (kg) EI Rep
50%1RM _15%VL
Journal of Strength and Conditioning Research
TM
3
| www.nsca.com
VOLUME 00 | NUMBER 00 | MONTH 2018 |
Copyright ª 2018 National Strength and Conditioning Association
Scheduled
the
Journal of Strength and Conditioning Research
SQ
BP
TM
Copyright ª 2018 National Strength and Conditioning Association
MPVBEST (m$s21)
MPVpre (m$s21)
MPVpost (m$s21)
1RM_10% 70.5 6 6.9
1.02 6 0.02
0.98 6 0.02
0.85 6 0.08
1RM_20% 70.2 6 9.4
1.01 6 0.03
0.97 6 0.02
0.82 6 0.06
1RM_30% 69.7 6 11.1
1.01 6 0.03
0.98 6 0.03
0.73 6 0.08
1RM_45% 69.6 6 6.1
1.01 6 0.02
0.97 6 0.03
0.67 6 0.08
1RM_10% 70.7 6 7.2
1.01 6 0.02
0.97 6 0.02
0.83 6 0.06
1RM_20% 73.4 6 7.7
1.00 6 0.01
0.96 6 0.03
0.81 6 0.07
1RM_30% 72.5 6 8.0
1.01 6 0.02
0.96 6 0.03
0.77 6 0.07
1RM_45% 74.0 6 5.3
1.01 6 0.01
0.97 6 0.03
0.74 6 0.10
1RM_10% 74.1 6 5.3
1.01 6 0.02
0.96 6 0.03
0.86 6 0.07
1RM_20% 75.3 6 7.1
1.00 6 0.02
0.96 6 0.03
0.82 6 0.08
1RM_30% 75.2 6 7.1
1.00 6 0.03
0.96 6 0.04
0.80 6 0.07
1RM_45% 74.7 6 6.2
0.99 6 0.02
0.95 6 0.04
0.80 6 0.12
1RM_10% 74.6 6 4.9
1.00 6 0.03
0.96 6 0.03
0.85 6 0.07
1RM_20% 74.4 6 6.2
1.00 6 0.03
0.96 6 0.04
0.81 6 0.06
1RM_30% 74.9 6 8.2
1.00 6 0.02
0.96 6 0.03
0.82 6 0.06
1RM_45% 75.2 6 7.6
1.00 6 0.02
0.97 6 0.03
0.77 6 0.10
REP
Load (kg)
50% VL 50% VL 50% VL 50% VL 60% VL 60% VL 60% VL 60% VL 70% VL 70% VL 70% VL 70% VL 80% VL 80% VL 80% VL 80% VL
REP
Load (kg)
MPVBEST (m$s21)
MPVpre (m$s21)
MPVpost (m$s21)
50% 1RM_15% VL 50% 1RM_25% VL 50% 1RM_40% VL 50% 1RM_55% VL 60% 1RM_15% VL 60% 1RM_25% VL 60% 1RM_40% VL 60% 1RM_55% VL 70% 1RM_15% VL 70% 1RM_25% VL 70% 1RM_40% VL 70% 1RM_55% VL 80% 1RM_15% VL 80% 1RM_25% VL 80% 1RM_40% VL 80% 1RM_55% VL
40.9 6 9.3
1.00 6 0.03
0.96 6 0.04
0.83 6 0.07
41.0 6 9.5
1.00 6 0.03
0.97 6 0.03
0.77 6 0.05
41.4 6 9.2
0.99 6 0.02
0.95 6 0.02
0.59 6 0.10
42.1 6 10.2
1.00 6 0.02
0.95 6 0.04
0.51 6 0.12
41.5 6 9.3
1.00 6 0.03
0.96 6 0.04
0.83 6 0.04
41.8 6 9.2
1.01 6 0.02
0.97 6 0.03
0.79 6 0.05
41.8 6 9.2
1.00 6 0.03
0.97 6 0.03
0.73 6 0.08
42.3 6 9.5
1.00 6 0.03
0.96 6 0.03
0.61 6 0.13
41.1 6 10.2
1.01 6 0.02
0.98 6 0.02
0.86 6 0.04
41.4 6 10.2
1.00 6 0.03
0.95 6 0.03
0.78 6 0.07
41.5 6 10.3
1.01 6 0.02
0.97 6 0.03
0.73 6 0.07
42.1 6 9.9
1.00 6 0.02
0.96 6 0.02
0.66 6 0.07
42.6 6 10.3
1.00 6 0.03
0.96 6 0.03
0.86 6 0.03
42.5 6 10.3
1.01 6 0.03
0.97 6 0.02
0.83 6 0.08
43.0 6 10.6
1.00 6 0.03
0.96 6 0.04
0.79 6 0.08
42.7 6 10.3
1.01 6 0.02
0.96 6 0.02
0.72 6 0.07
*MPV = mean propulsive velocity; SQ = full back-squat exercise (n = 11); BP = bench press exercise (n = 10); REP = resistance exercise protocol; MPVBEST = mean propulsive velocity of the fastest (usually first) repetition in the set; MPVpre = average MPV of 3 repetitions before exercise; MPVpost = average MPV of 3 repetitions after exercise; RM = repetition maximum. †Data are mean 6 SD.
Effort Index as an Indicator of Muscle Fatigue
4 TABLE 3. Load (kg) that elicited a mean propulsive velocity of ;1 m$s21 before each REP in the SQ and BP exercises.*†
the
TM
Journal of Strength and Conditioning Research
| www.nsca.com
Figure 1. Schematic representation of study design: (A) general structure of descriptive study of the acute response to 16 different REPs; (B) scheme of each REP indicating the mechanical and metabolic measurements to analyze the degree of induced fatigue. REP = resistance exercise protocol.
(VL) within the set as a noninvasive indicator of the degree of fatigue induced during resistance exercise, the RT protocols used in these studies (10,13,23,26) were prescribed according to the maximal load (kg) that could be lifted a determined number of maximum repetitions (e.g., 4-, 6-, 8-, 10-, and 12-repetition maximum [RM]). This approach is used under the assumption that all individuals are receiving a similar stimulus on completing the protocol (6). However, it does not take into account that the number of repetitions that can be completed against a given relative load (%1RM) shows a large variability between individuals (12,32,34). This variation means that if different subjects are required to perform the same number of repetitions per set, it is likely that they will be exercising with different levels of effort (12). Therefore, rather than prescribing a given and arbitrary number of repetitions (be it maximal or not) to be completed, training sets should be performed until a certain degree of fatigue is achieved to ensure that a more similar stimulus is applied on the completion of each set for all individuals (6,12,26). Several studies have indicated that exercise intensity and volume are the most important training variables in determining the type and extent of acute and chronic responses to RT (3,8,33). As a consequence, monitoring these variables is
a key factor in configuring optimal training stimuli for improving neuromuscular performance. In this regard, recent studies have highlighted the importance of using movement velocity as a valid and objective method for real-time monitoring of exercise intensity (11,28) and volume (12). Very strong relationships (R2 = 0.94–0.98) have been observed between movement velocity and percentage of 1RM in different exercises (11,27,28,30), as well as between the relative loss of velocity in a set and the percentage of performed repetitions (12,17,30) against different relative loads. As a result, in this context of a velocity-based RT approach, instead of a certain amount of weight to be lifted a given number of repetitions per set, it has been proposed to prescribe resistance exercise in terms of 2 variables: (a) first repetition’s mean velocity and (b) the maximum percentage of VL allowed in each set (26). Therefore, the aim of this study was to analyze the acute mechanical (percentage of VL attained against an individual reference load) and metabolic (blood lactate concentration) response to 16 types of resistance exercise protocols (REPs) defined by the first repetition’s mean velocity and the percentage of VL over the set in 2 popular multijoint RT exercises such as the full back squat (SQ) and the bench press (BP). VOLUME 00 | NUMBER 00 | MONTH 2018 |
Copyright ª 2018 National Strength and Conditioning Association
5
Effort Index as an Indicator of Muscle Fatigue
Figure 2. Example of monitoring velocity loss (VL) during the training sets and quantification of percentage of change in MPV pre-post exercise attained against the V1 m$s21 load after 3 sets with 60% 1RM and 30% VL in the set (3 3 ;0.98 [30%] REP) for a representative participant in the SQ exercise. MPV = mean propulsive velocity; RM = repetition maximum; REP = resistance exercise protocol; SQ = squat.
METHODS Experimental Approach to the Problem
A cross-sectional research design was used to analyze the degree of fatigue induced by different REPs in which training intensity and volume were objectively monitored by means of movement velocity. Over a period of approximately 10 weeks, 17 testing sessions were conducted by each participant in the following order: (a) an initial test with increasing loads for the individual determination of full load-velocity relationships in the SQ or BP exercise and (b) 16 REPs determined by the best mean propulsive velocity (MPV, usually the first repetition) over the set (MPVBEST) and the relative magnitude of MPV loss (%VL) within the set (S). For each exercise, 4 different loading magnitudes (;50, ;60, ;70, and ;80% 1RM) and 4 magnitudes of MPV loss (;10, ;20, ;30, and ;45% of VL in the SQ; and ;15, ;25, ;40, and ;55% of VL in the BP exercise) were used. Table 1 and Table 2 show in detail the characteristics of each REP performed in the SQ and BP exercises, respectively. Changes in blood lactate concentration and MPV attained against the individual load that elicited a ;1.00 m$s21 (60.03 m$s21) (V1 m$s21 load) were used to analyze the acute mechanical and metabolic response to each REP. All REPs were randomized for each participant and were conducted on separate days, with at least 72 hours of recovery time between sessions. This period between testing sessions
6
the
was sufficient to ensure that the participants were fully recovered before performing the following REP as indicated by the V1 m$s21 load (Table 3) and load used during each REP (Table 1 and Table 2). Sessions were performed at the same time of day for each participant (61 hour) and under similar environmental conditions (;20–228 C and 55–65% humidity). During the experimental period of this study, participants were asked to refrain from any other RT apart from some abdominal and lower-back strengthening exercises. Subjects
Twenty-one young healthy men (mean 6 SD [age range: ,18 years old]age: 23.5 6 3.6 years, body mass: 77.9 6 14.9 kg, height: 1.78 6 0.07 m) volunteered to take part in this study. Participants were physically active sport science students with RT experience ranging from 2 to 4 years (2–3 sessions per week). They were randomly divided into 2 groups depending on the exercise to be performed: full squat (SQ, n = 11), or BP (n = 10). Initial estimated 1RM (1RMest) strength was 111.5 6 14.2 kg (relative strength ratio: 1.52 6 0.17) for the SQ and 90.7 6 18.0 kg (relative strength ratio: 1.13 6 0.23) for the BP group. No physical limitations, health problems, or musculoskeletal injuries that could affect the testing were reported. None of the participants were taking drugs, medications, or dietary supplements known to influence physical performance. The study was conducted according to the Declaration of Helsinki and was approved
TM
Journal of Strength and Conditioning Research
Copyright ª 2018 National Strength and Conditioning Association
SQ
VL VL VL VL VL VL VL VL VL VL VL VL VL VL VL VL
14.0 16.0 25.1 31.5 14.4 15.9 20.4 24.0 10.2 14.9 16.5 18.0 11.6 15.0 14.6 18.6
6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6
7.7 7.2 8.2§ 8.5§ 5.1 6.7 6.9k 10.1k 5.9 7.5 7.6k 9.3z 6.3 5.4 5.0k 6.7k
3.5 6.7 8.3 9.7 3.9 4.6 5.2 7.5 2.9 4.2 4.6 5.4 2.5 3.2 3.8 4.7
6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6
1.9 2.8z 3.1z 2.7z 1.6k 1.7k 2.1k 2.0z 0.9 1.5k 1.7 1.6 0.8 1.0 2.0 2.0
Loss of MPV with V1 m$s21 load (%)
REP 50% 50% 50% 50% 60% 60% 60% 60% 70% 70% 70% 70% 80% 80% 80% 80%
1RM_15% 1RM_25% 1RM_40% 1RM_55% 1RM_15% 1RM_25% 1RM_40% 1RM_55% 1RM_15% 1RM_25% 1RM_40% 1RM_55% 1RM_15% 1RM_25% 1RM_40% 1RM_55%
VL VL VL VL VL VL VL VL VL VL VL VL VL VL VL VL
14.0 20.5 37.7 46.0 13.1 18.5 24.1 37.1 12.3 18.2 24.5 31.2 10.3 14.2 18.1 25.3
6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6
5.3 5.0 9.9 11.7 5.5 5.9 7.4 12.3 4.0 7.2 7.8 5.6 3.4 7.6 7.9 6.8
Lactate (mmol$L21) 2.6 3.3 4.5 5.4 2.6 3.1 4.0 4.6 2.6 2.9 3.8 4.9 2.4 2.9 3.5 4.5
6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6
0.5 0.9 1.1 0.9 0.4 0.5 0.7 0.9 0.4 0.4 0.5 1.1 0.4 0.6 0.5 0.8
*SQ = full back-squat exercise (n = 11); BP = bench press exercise (n = 10); REP = resistance exercise protocol; MPV = mean propulsive velocity; V1 m$s21 = load that elicited a MPV of ;1 m$s21; RM = repetition maximum. †Data are mean 6 SD. Post-exercise lactate significantly different (P , 0.001) from pre-exercise for all REPs. zSignificantly different than BP: p , 0.001. §Significantly different than BP: p , 0.01. kSignificantly different than BP: p , 0.05.
the
1RM_10% 1RM_20% 1RM_30% 1RM_45% 1RM_10% 1RM_20% 1RM_30% 1RM_45% 1RM_10% 1RM_20% 1RM_30% 1RM_45% 1RM_10% 1RM_20% 1RM_30% 1RM_45%
Lactate (mmol$L21)
Journal of Strength and Conditioning Research
50% 50% 50% 50% 60% 60% 60% 60% 70% 70% 70% 70% 80% 80% 80% 80%
BP
Loss of MPV with V1 m$s21 load (%)
REP
TM
7
| www.nsca.com
VOLUME 00 | NUMBER 00 | MONTH 2018 |
Copyright ª 2018 National Strength and Conditioning Association
TABLE 4. Mechanical and metabolic measurements of fatigue after each REP in the SQ and BP exercises.*†
Effort Index as an Indicator of Muscle Fatigue
Figure 3. Loss of MPV pre-post exercise against the V1 m$s21 load and post-exercise lactate concentration after each REP for the SQ (A and C) and the BP (B and D) exercises. Different symbols are used to differentiate between the different relative intensities analyzed: 50% 1RM (black triangle), 60% 1RM (white circle), 70% 1RM (white triangle), and 80% 1RM (black circle). Statistically significant differences between relative intensities: a50% and 80% 1RM; b50% and 70% 1RM; c50% and 60% 1RM; d60% and 80% 1RM; e60% and 70% 1RM; and f70% and 80% 1RM. MPV = mean propulsive velocity; RM = repetition maximum; REP = resistance exercise protocol; SQ = squat; BP = bench press.
by the Research Ethics Committee of Pablo de Olavide University. After being informed of the purpose and experimental procedures, the participants and their parents/guardians signed a written informed consent form before participation. Procedures
Initial Session and Progressive Loading Test in the Squat and Bench Press Exercises. An introductory session was used for anthropometric assessments, medical examination, and familiarization with testing protocols. In this session, participants arrived at the laboratory in a well-rested condition and a fasted state. After being medically screened and having their standing height and body mass measured, participants performed an exercise session with light loads (;40% 1RM) and a low magnitude of VL over the set (;10–15%), whereas researchers emphasized proper technique to ensure that they were familiarized with the protocol to be used in each testing session. Three days later, individual load-velocity relationships and estimated 1RM (1RMest) strength in the SQ and BP ex-
8
the
ercises were determined for each participant using a progressive loading test. This test was mainly performed (a) to estimate the weight (kg) that each subject had to use so that the lifting velocity of the first repetition matched the specified target MPVof each of the 4 relative loads to be used and (b) to make a description of the subjects’ characteristics. All sessions were performed using a Smith machine (Multipower Fitness Line, Peroga, Murcia, Spain). The BP testing protocol has been detailed elsewhere (11,12,29). The BP was performed imposing a momentary pause (;1.0 seconds) at the chest between the eccentric and concentric actions to minimize the contribution of the rebound effect and allow for more reproducible, consistent measurements (22). Similarly, a detailed description of the SQ testing protocol has been recently provided elsewhere (9,26,28). Participants started from an upright position, descending in a continuous motion until the posterior thighs and calves made contact with each other, then immediately reversed motion and ascended back to the starting position. Unlike the eccentric phase, which was
TM
Journal of Strength and Conditioning Research
Copyright ª 2018 National Strength and Conditioning Association
the
TM
Journal of Strength and Conditioning Research
| www.nsca.com
Figure 4. Relationships between effort index and loss of MPV pre-post exercise against the V1 m$s21 load and post-exercise lactate concentration for the SQ (A and B) and the BP (C and D) exercises. Each data point corresponds to one of the 16 different REPs analyzed. Different symbols are used to differentiate between the different relative intensities analyzed: 50% 1RM (black triangle), 60% 1RM (white circle), 70% 1RM (white triangle), and 80% 1RM (black circle). MPV = mean propulsive velocity; RM = repetition maximum; REP = resistance exercise protocol; SQ = squat; BP = bench press.
performed at a normal, controlled velocity, subjects were required to always execute the concentric phase of either BP or SQ at maximal intended velocity. The individual position for the BP (position on the bench as well as grip widths) and SQ exercise (feet position and placement of the hands on the bar) was measured for each participant, so that they could be reproduced in all testing sessions. The initial load was set at 20 and 30 kg for all participants in the BP and SQ exercise, respectively, and was gradually increased in 10-kg increments. The test ended for each participant when the attained concentric MPV was ,0.4 m$s21 in the BP and ,0.6 m$s21 in the SQ group (which corresponds to ;85% 1RM in both exercises (11,28)). The 1RMest was calculated for each individual from the MPV attained against the heaviest load (kg) lifted in the progressive loading test, as follows: (100 3 load)/ (25.961 3 MPV2) 2 (50.71 3 MPV) + 117 for the SQ (28), and (100 3 load)/(8.4326 3 MPV2) 2 (73.501 3 MPV) + 112.33 for the BP exercise (11).
Acute Resistance Exercise Protocol. Descriptive characteristics of the 16 REPs for the SQ and BP groups are presented in Table 1 and Table 2, respectively. The 16 types of REPs were always performed using 3 sets and 4-minute interset recovery periods. Relative loads were determined from the loadvelocity relationship for the SQ and BP because it has recently been shown that there is a close relationship between percentage of 1RM and MPV in both exercises (11,28). Thus, a target MPV to be attained in the first (usually the fastest) repetition of the first exercise set in each REP was used as an estimation of percentage of 1RM, as follows: ;1.13 m$s21 (;50% 1RM), ;0.98 m$s21 (;60% 1RM), ;0.82 m$s21 (;70% 1RM), and ;0.68 m$s21 (;80% 1RM) for the SQ exercise; and ;0.93 m$s21 (;50% 1RM), ;0.79 m$s21 (;60% 1RM), ;0.63 m$s21 (;70% 1RM), and ;0.47 m$s21 (;80% 1RM) for the BP exercise. Consequently, before starting each REP, adjustments in the proposed load (kg) were made when needed, VOLUME 00 | NUMBER 00 | MONTH 2018 |
Copyright ª 2018 National Strength and Conditioning Association
9
Effort Index as an Indicator of Muscle Fatigue
Figure 5. Relationships between percentage of MPV loss over 3 training sets and loss of MPV pre-post exercise against the V1 m$s21 load and post-exercise lactate concentration for the SQ (A and B) and the BP (C and D) exercises. Each data point corresponds to one of the 16 different REPs analyzed. Different symbols are used to differentiate between the different relative intensities analyzed: 50% 1RM (black triangle), 60% 1RM (white circle), 70% 1RM (white triangle), and 80% 1RM (black circle). MPV = mean propulsive velocity; RM = repetition maximum; REP = resistance exercise protocol; SQ = squat; BP = bench press.
so that the velocity of the first repetition matched the programmed velocity (60.03 m$s21). Once the load (kg) was adjusted, it was maintained for the 3 training sets. Volume in each training set was objectively determined through the magnitude of VL attained over the set (calculated as the percent loss in MPV from the fastest to the slowest repetition) (12,24). Thus, the training set was terminated when the prescribed VL limit was reached (12,26). For each load magnitude (50, 60, 70, and 80% 1RM), 4 magnitudes of VL in the set were allowed: 10, 20, 30, and 45% for the SQ (Table 1), and 15, 25, 40, and 55% for the BP (Table 2), resulting in 16 REPs being undertaken in each exercise. Different %VLs in the set were used for the SQ and BP exercises because we have recently observed (unpublished data) that a given magnitude of repetition VL over the set results in a greater percentage of repetitions being completed (and, therefore, less
10
the
repetitions left in reserve) in the SQ compared with the BP for loads of 50, 60, 70, and 80% 1RM. Thus, to complete the same percentage of repetitions in both exercises, a greater magnitude of MPV loss over the set should be allowed in the BP compared with the SQ exercise as follows: ;5, ;6, ;8, and ;7% higher VL for 50, 60, 70, and 80% 1RM, respectively. During each REP, participants received immediate movement velocity feedback while being encouraged to perform each repetition at maximal intended velocity. A schematic representation of each REP (both in the SQ and BP groups) is provided in Figure 1. In each testing session, the warm-up consisted of 5 minutes of jogging at a self-selected easy pace and 5 minutes of joint mobilization exercises. This was followed by the determination of the V1 m$s21 load. For this purpose, participants performed 3 sets of 6 down to 3 repetitions (3-minute rests) with increasing
TM
Journal of Strength and Conditioning Research
Copyright ª 2018 National Strength and Conditioning Association
the
TM
Journal of Strength and Conditioning Research
| www.nsca.com
were taken as the immediate post-exercise measures. After a 1-minute rest, capillary blood samples were taken for the analysis of lactate. Quantification of the “Effort Index”. Several studies (3,33) have suggested that the interplay between training intensity and volume is the critical factor in determining the optimal range of training stimuli to promote the neuromuscular adaptations associated with RT. Thus, it is reasonable to assume that any index used to quantify the level of effort (or degree of fatigue) should include both variables. Because movement velocity has been considered a valid and objective method for monitoring exercise intensity (11,28) and volume (12,17,24) during resistance exercises, the effort index (EI) was defined as the product of the fastest MPV of the first exercise set (usually the first repetition) and the average MPV loss (%) over the 3 training sets in each REP (EI = MPVBEST 3 average %VL over 3 sets). The EI was calculated as an indicator of the degree of fatigue induced by each REP.
Figure 6. Comparisons of relationships between effort index and loss of MPV pre-post exercise against the V1 m$s21 load (A) and post-exercise lactate concentration (B) in the BP and the SQ exercises. Each data point corresponds to one of the 16 different REPs analyzed. MPV = mean propulsive velocity; REP = resistance exercise protocol; SQ = squat; BP = bench press.
loads up to V1 m$s21 load (60.03 m$s21). This value was chosen because it is a sufficiently high velocity, which is attained against a medium load (;60% RM in the SQ and ;45% in the BP), and it allows for a good expression of the effect of loading on velocity, besides being a relatively easy to move and well-tolerated load when the subject is fatigued (26). The mean value of 3 repetitions with the V1 m$s21 load (kg) was thus taken as a pre-exercise reference measure against which to compare the VL experienced after the 3 exercise sets. This procedure has been used in several previous studies (10,23,26) to quantify fatigue after different resistance exercise configurations. Finally, adjustments in the proposed load (kg) were made, so that the velocity of the first repetition matched the programmed target velocity (60.03 m$s21). The 3 sets of the corresponding REP were performed next. Immediately after completing the last repetition of the third training set, the participants executed 3 maximal-effort consecutive repetitions against the V1 m$s21 load (the load was changed in less than 10 seconds with the help of trained spotters). The V1 m$s21 load mean values
Measurement of Fatigue and Metabolic Stress. Fatigue was quantified by means of the percent change in MPV prepost exercise attained against the V1 m$s21 reference load. The average MPV of 3 repetitions before exercise was compared with the average MPV of 3 repetitions after exercise, i.e., 100 3 ([average MPVpost 2 average MPVpre]/ average MPVpre). Figure 2 shows an example of this VL for a representative participant and protocol (3 sets with 60% 1RM and 30% VL in the SQ exercise). Blood lactate concentration was used as an indicator of the metabolic stress induced by each REP. Capillary whole blood samples were drawn from the earlobe before exercise and again 1 minute after completing the last repetition of the V1 m$s21 load in each REP. Measurement Equipment and Data Acquisition. Height and body mass were determined using a medical stadiometer and scale (Seca 710, Seca Ltd., Hamburg, Germany) with the participants in a morning fasting state and wearing only underclothes. A Smith machine (Multipower Fitness Line, Peroga, Spain), which ensured a smooth vertical displacement of the bar along a fixed pathway, was used for all sessions. A cable-extension linear velocity transducer (TForce Dynamic Measurement System; Ergotech, Murcia, Spain) was attached to one end of the bar and used to measure bar velocity. Instantaneous velocity was sampled at 1,000 Hz and smoothed using a fourth order low-pass Butterworth filter with no phase shift and 10-Hz cutoff frequency. The system’s software automatically calculated the relevant kinematics of every repetition, provided auditory and visual velocity feedback in real time, and stored data on disk for analysis. The reliability of this system has been reported elsewhere (26). All velocity values reported in this study correspond to the MPV of the concentric phase of each repetition. The propulsive phase was defined as that VOLUME 00 | NUMBER 00 | MONTH 2018 |
Copyright ª 2018 National Strength and Conditioning Association
11
Effort Index as an Indicator of Muscle Fatigue (SQ vs. BP). Statistical significance was accepted at P , 0.05. Analyses were performed using SPSS software version 17.0 (SPSS, Chicago, IL, USA).
RESULTS Descriptive characteristics of each REP actually performed in both the SQ and BP groups are reported in Table 1 and Table 2, respectively. No significant differences were found between the expected or targeted MVP values and the fastest MPV values (MPVBEST) of each REP for any group. Similarly, the average magnitude of MPV loss over the set matched that intended in all REPs performed for both groups. Velocity Loss and Blood Lactate Concentration
Figure 7. Relationships between loss of MPV pre-post exercise against the V1 m$s21 load and post-exercise lactate concentration for the SQ (A) and the BP (B) exercises. Each data point corresponds to one of the 16 different REPs analyzed. Different symbols are used to differentiate between the different relative intensities analyzed: 50% 1RM (black triangle), 60% 1RM (white circle), 70% 1RM (white triangle), and 80% 1RM (black circle). MPV = mean propulsive velocity; RM = repetition maximum; REP = resistance exercise protocol; SQ = squat; BP = bench press.
Post-exercise MPV attained against the V1 m$s21 load, and post-exercise lactate concentration was significantly different (P , 0.01–0.001) from pre-exercise values after all REPs. Both the percent loss of MPV pre-post exercise with the V1 m$s21 load and post-exercise lactate concentration gradually increased as the magnitude of VL in the set increased for all 4 load magnitudes used (Table 4 and Figure 3). For the same percentage of VL in the set, both variables (loss of MPV pre-post exercise with the V1 m$s21 load and post-exercise lactate concentration) were greater as the relative load decreased (Table 4 and Figure 3). Comparison between exercises revealed that the MPV loss against the V1 m$s21 load was significantly greater (P , 0.05–0.001) for BP than SQ in those REPs where the MPV loss over the set was greater than 30% for SQ and 40% for BP exercise (Table 4). Mean post-exercise lactate concentration was significantly greater for the SQ compared with the BP group in those REPs performed against 50 and 60% 1RM (Table 4). Relationship Between the “Effort Index” and Loss of MPV Against the V1 m$s21 Load and Blood Lactate
portion of the concentric phase during which the measured acceleration (a) is greater than acceleration due to gravity (i.e., a $ 29.81 m$s22) (29). The Lactate Pro 2 LT-1730 (Arkray, Kyoto, Japan) portable lactate analyzer was used for lactate measurements. The suitability and reproducibility of this analyzer has been previously established throughout the physiological range of 1.0–18.0 mmol$L21 (25). Statistical Analyses
Standard statistical methods were used for the calculation of mean values and SDs. Correlations are reported using Pearson product-moment correlation coefficients (r). A 1-way repeated-measures analysis of variance was performed for each variable to analyze the VL against the V1 m$s21 load, as well as to compare pre-exercise and post-exercise lactate levels between REPs. Independent sample t-tests were used to compare the percentage of MPV loss against the V1 m$s21 load and lactate concentration between groups
12
the
A very strong relationship was found between EI and relative loss of MPV pre-post exercise against the V1 m$s21 load for both SQ (r = 0.92, P , 0.001; Figure 4A) and BP (r = 0.98, P , 0.001; Figure 4C) exercises. Similarly, the EI showed strong linear correlation coefficients with postexercise lactate concentration for both SQ (r = 0.91, P , 0.001; Figure 4B) and BP (r = 0.95, P , 0.001; Figure 4D) exercises. These correlations were greater than those observed between the percentage VL over the 3 sets and MPV loss with the V1 m$s21 load (r = 0.74 and 0.84 for SQ and BP, respectively) and post-exercise lactate concentration (r = 0.69 and 0.93 for SQ and BP, respectively) in both exercises (Figure 5). Comparisons between both exercises showed that, for a given EI value, the loss of MPV prepost exercise against the V1 m$s21 load was greater in the BP compared with the SQ exercise, whereas the postexercise lactate concentration was greater in the SQ than the BP exercise (Figure 6).
TM
Journal of Strength and Conditioning Research
Copyright ª 2018 National Strength and Conditioning Association
the
TM
Journal of Strength and Conditioning Research Relationship Between Velocity Loss and Blood Lactate Concentration
Very large correlations were also found between the magnitude of MPV loss pre-post exercise and the V1 m$s21 load and post-exercise blood lactate concentration for SQ (r = 0.96, P , 0.001; Figure 7A) and BP (r = 0.95, P , 0.001) (Figure 7B).
DISCUSSION To the best of our knowledge, this is the first study to analyze acute mechanical and metabolic responses to 16 different types of REPs, in which training intensity and volume were objectively quantified and monitored using the fastest MPV (usually the first repetition of each set) and the magnitude of MPV loss within the set, respectively (11,12,26). The main finding of this study was that the proposed EI (the product of the fastest MPV of the first exercise set and the mean percent loss of MPV over the 3 training sets) showed very strong relationships with the mechanical variable (MPV loss attained against V1 m$s21 load) used to estimate the degree of fatigue during each REP. In addition, very large relationships were also found between the EI and the post-exercise lactate concentration in both exercises. The high relationship shown by this new index with a valid fatigue indicator as the relative loss of MPV pre-post exercise against the V1 m$s21 load allows us to advance in our knowledge of the prescribed training load (understood as a degree of effort) and internal load experienced by each individual during resistance exercise. As expected, our results indicated that, for a given relative load, the percent loss of MPV pre-post exercise against the V1 m$s21 load and post-exercise lactate concentration progressively increased as the magnitude of MPV loss in the set increased for both exercises (Table 4 and Figure 3). In accordance with these results, previous studies (10,23,26) have also shown similar pre-post changes in these variables after different types of RT protocols as the number of performed repetitions in a set approached the maximum predicted number (i.e., as the MPV loss experienced during the set increased). However, to the authors’ knowledge, this is the first study in which mechanical and metabolic stress after 15 REPs (50–80% 1RM) were quantified by monitoring repetition velocity and adjusting the loads to be lifted using the load-velocity relationship for the SQ and BP (11,28). Thus, we made sure that all participants used a very similar relative load (%1RM) and degree of effort (VL in the set) in each training session (12,24) (Table 1 and Table 2). The results of this study also showed that, for the same magnitude of MPV loss incurred in the set, the loss of MPV pre-post exercise with the V1 m$s21 load and post-exercise lactate concentration clearly differed between relative loads, with a greater degree of fatigue experienced as loads decreased (Table 4 and Figure 3). These findings complement those of previous studies (10,23,26), which suggested that VL in the set was
| www.nsca.com
a valid, objective, and practical indicator of neuromuscular fatigue during resistance exercise. Thus, based on the results of the current study, it seems that, for the same relative load (% 1RM), VL is the variable that determines the degree of induced fatigue during the exercise sets. However, our results further suggest that the relative load used also influences induced muscle fatigue. For this reason, because the MPV of the first repetition (i.e., relative load) and the magnitude of VL incurred in the set (i.e., volume) seem to have a considerable impact on the degree of fatigue, the main aim of this study was to analyze whether the product of both variables (proposed here as a new variable, the “Effort Index”) showed an association with muscle fatigue, which was quantified by the percent loss of MPV pre-post exercise against the V1 m$s21 load and the post-exercise lactate concentration after each REP. In connection with the above, very strong and significant correlations were found between the EI and relative loss of MPV pre-post exercise with the V1 m$s21 load (Figure 4A, C) and post-exercise blood lactate concentration (Figure 4B, D) for both the SQ and BP exercises. These relationships indicate that, for the same EI, the degree of fatigue induced is equivalent, regardless of the MPV of the first repetition and the percentage of VL incurred in the set. These results represent a novel and important finding for quantifying muscle fatigue during resistance exercise, and consequently, they constitute a considerable advance for the prescription and monitoring of the training load during RT with respect to previous research (10,23,26), which indicated that the muscle fatigue was only determined by percentage VL in the set. Indeed, it can be observed that, when the REPs are configured and monitored by means of repetition velocity so that all participants perform each session with the same relative load, the percent VL over the 3 sets alone showed a lower correlation (and lower percentage of explained variance) with the relative loss of MPV pre-post exercise against the V1 m$s21 load (Figure 5A, C) and post-exercise lactate (Figure 5B, D) when compared with the EI, in both the SQ and BP exercises. In addition, the fact that the EI showed a high correlation with the relative loss of MPV pre-post exercise against the V1 m$s21 load and post-exercise lactate in 2 exercises such as the SQ and BP supports the use of this new index as (a) an indicator of degree of effort or fatigue and (b) an accurate predictor of metabolic stress during resistance exercise. This last proposal is further supported by the high correlations (Figure 7) found between the mechanical variable used to assess the degree of effort induced during each REP (relative loss of MPV pre-post exercise with the V1 m$s21 load) and metabolic stress (lactate concentration). Therefore, by measuring repetition velocity during RT and monitoring these 2 variables (MPV of the first repetition and loss of MPV over the sets), it is possible to obtain an accurate index (EI) for prescribing RT, which represents a substantial improvement on previous procedures. VOLUME 00 | NUMBER 00 | MONTH 2018 |
Copyright ª 2018 National Strength and Conditioning Association
13
Effort Index as an Indicator of Muscle Fatigue Another important finding of this study was that higher correlations between the EI and the loss of MPV against the V1 m$s21 load, as well as between the EI and post-exercise lactate, were observed for the BP compared with the SQ (Figure 4). These results may be related to the greater movement control in the BP (lower range of motion, concentriconly action, and imposed pause between concentric and eccentric phases) compared with the SQ exercise. Another aspect to highlight is that, for the same EI, greater MPV losses against the V1 m$s21 load were experienced in the BP compared with the SQ, whereas post-exercise lactate values were higher in the SQ than the BP (Figure 6). These differences between exercises were evident for EI values higher than ;15 and became greater as the EI value increased. Therefore, these results suggest that the use of the EI as a variable to quantify muscle fatigue is specific to each exercise. Previous studies (10,23,26) analyzing acute responses to manipulating the number of repetitions actually performed in each training set with respect to the maximum number of repetitions that can be completed against a given absolute load in SQ and BP exercise have shown similar results, although neither the exercise intensity nor the volume was matched between exercises in these studies (6,11,12). Therefore, to our knowledge, this is also the first study comparing the acute mechanical and metabolic response in upper- and lower-limb exercises in which, by monitoring movement velocity, the relative load (% 1RM) and volume (the percentage of performed repetitions out of the maximum possible number that can be completed in the set) were very similar for both the SQ and BP exercises (11,12,28). Thus, because the main variables related to training load were matched between exercises, differences in the neuromuscular fatigue between exercises could be explained by (a) the smaller muscle groups involved in the BP exercise (more localized fatigue) compared with the SQ (fatigue distributed among a greater amount of muscle mass) and (b) the greater percentage of type II fibers in upper compared with lower limbs (21,31), which have a higher fatigability index (15). In conclusion, the main finding of the current study was that the proposed EI showed a close relationship with the mechanical and metabolic response to different REP, which supports the use of this index as a variable to objectively quantify muscle fatigue during RT (at least when the MPV of the first repetition ranges between ;1.13–0.68 m$s 21 in the SQ and ;0.93–0.47 m$s21 in the BP, and the MPV loss over the set ranges between ;10–45% in the SQ and ;15–55% in the BP). Other notable findings of this study were (a) for the same MPV loss in the set, the lower the relative load used, the greater the fatigue experienced (the magnitude of MPV loss against the V1 m$s 21 load and post-exercise lactate concentration); (b) for the same EI value, the degree of fatigue induced is equivalent, regardless of the MPV of the first repetition and the percent VL incurred in the set;
14
the
and (c) for the same EI value, the induced fatigue was different between the SQ and BP exercises.
PRACTICAL APPLICATIONS The novel findings of the current study provide several key implications for coaches and strength and conditioning professionals who wish to optimize the monitoring and quantification of RT programs. The strong relationships found between the EI and the pre-post changes in the mechanical and metabolic variables used to estimate the muscle fatigue indicate that, to induce a certain degree of effort, the training load should be prescribed taking as a reference the MPV of the first (fastest) repetition and the percentage VL in the set. In addition to being a valuable addition for RT monitoring, the proposed EI might also serve as an independent variable in training studies. By equalizing the EI between training interventions, a better knowledge could be gained about the acute and chronic effects of a given training design. Finally, our results also showed that the muscle fatigue induced by a given EI is specific to the exercise used. These differences should be taken into account when prescribing training programs because the same EI (even against the same relative load) will probably involve a different training stimulus and thus different neuromuscular adaptations, depending on the exercise used.
ACKNOWLEDGMENTS The authors greatly appreciate the commitment and dedication of all participants of this study who performed maximum efforts in each of the exercise protocols. The authors have no professional relationships with companies or manufacturers that might benefit from the results of this study. There was no financial support for this project. The results of this study do not constitute endorsement of any product by the authors or by the National Strength and Conditioning Association.
REFERENCES 1. Ahtiainen, JP and Hakkinen, K. Strength athletes are capable to produce greater muscle activation and neural fatigue during highintensity resistance exercise than nonathletes. J Strength Cond Res 23: 1129–1134, 2009. 2. Ahtiainen, JP, Pakarinen, A, Kraemer, WJ, and Hakkinen, K. Acute hormonal responses to heavy resistance exercise in strength athletes versus nonathletes. Can J Appl Physiol 29: 527–543, 2004. 3. Bird, SP, Tarpenning, KM, and Marino, FE. Designing resistance training programmes to enhance muscular fitness: A review of the acute programme variables. Sports Med 35: 841–851, 2005. 4. Crewther, B, Cronin, J, and Keogh, J. Possible stimuli for strength and power adaptation: Acute mechanical responses. Sports Med 35: 967–989, 2005. 5. Crewther, B, Keogh, J, Cronin, J, and Cook, C. Possible stimuli for strength and power adaptation: Acute hormonal responses. Sports Med 36: 215–238, 2006.
TM
Journal of Strength and Conditioning Research
Copyright ª 2018 National Strength and Conditioning Association
the
TM
Journal of Strength and Conditioning Research 6. Dankel, SJ, Jessee, MB, Mattocks, KT, Mouser, JG, Counts, BR, Buckner, SL, and Loenneke, JP. Training to fatigue: The answer for standardization when assessing muscle hypertrophy? Sports Med 47: 1021–1027, 2017. 7. Davies, T, Orr, R, Halaki, M, and Hackett, D. Effect of training leading to repetition failure on muscular strength: A systematic review and meta-analysis. Sports Med 46: 487–502, 2016. 8. Fry, AC. The role of resistance exercise intensity on muscle fibre adaptations. Sports Med 34: 663–679, 2004. 9. Gonza´lez-Badillo, JJ, Pareja-Blanco, F, Rodrı´guez-Rosell, D, AbadHerencia, JL, Del Ojo-Lo´pez, JJ, and Sa´nchez-Medina, L. Effects of velocity-based resistance training on young soccer players of different ages. J Strength Cond Res 29: 1329–1338, 2015. 10. Gonza´lez-Badillo, JJ, Rodrı´guez-Rosell, D, Sa´nchez-Medina, L, Ribas, J, Lo´pez-Lo´pez, C, Mora-Custodio, R, Ya´n˜ez-Garcı´a, JM, and Pareja-Blanco, F. Short-term recovery following resistance exercise leading or not to failure. Int J Sports Med 37: 295–304, 2016. 11. Gonza´lez-Badillo, JJ and Sa´nchez-Medina, L. Movement velocity as a measure of loading intensity in resistance training. Int J Sports Med 31: 347–352, 2010. 12. Gonza´lez-Badillo, JJ, Ya´n˜ez-Garcı´a, JM, Mora-Custodio, R, and Rodrı´guez-Rosell, D. Velocity loss as a variable for monitoring resistance exercise. Int J Sports Med 38: 217–225, 2017. 13. Gorostiaga, EM, Navarro-Amezqueta, I, Calbet, JA, Hellsten, Y, Cusso, R, Guerrero, M, Granados, C, Gonza´lez-Izal, M, Iba´n˜ez, J, and Izquierdo, M. Energy metabolism during repeated sets of leg press exercise leading to failure or not. PLoS One 7: e40621, 2012. 14. Hakkinen, K. Neuromuscular fatigue and recovery in women at different ages during heavy resistance loading. Electromyogr Clin Neurophysiol 35: 403–413, 1995. 15. Hamada, T, Sale, DG, MacDougall, JD, and Tarnopolsky, MA. Interaction of fibre type, potentiation and fatigue in human knee extensor muscles. Acta Physiol Scand 178: 165–173, 2003. 16. Hoppeler, H. Molecular networks in skeletal muscle plasticity. J Exp Biol 219: 205–213, 2016. 17. Izquierdo, M, Gonza´lez-Badillo, JJ, Hakkinen, K, Iba´n˜ez, J, Kraemer, WJ, Altadill, A, Eslava, J, and Gorostiaga, EM. Effect of loading on unintentional lifting velocity declines during single sets of repetitions to failure during upper and lower extremity muscle actions. Int J Sports Med 27: 718–724, 2006. 18. Izquierdo, M, Iba´n˜ez, J, Gonza´lez-Badillo, JJ, Hakkinen, K, Ratamess, NA, Kraemer, WJ, French, DN, Eslava, J, Altadill, A, Asiain, X, and Gorostiaga, EM. Differential effects of strength training leading to failure versus not to failure on hormonal responses, strength, and muscle power gains. J Appl Physiol 100: 1647–1656, 2006. 19. Kraemer, WJ, Marchitelli, L, Gordon, SE, Harman, E, Dziados, JE, Mello, R, Frykman, P, McCurry, D, and Fleck, SJ. Hormonal and growth factor responses to heavy resistance exercise protocols. J Appl Physiol 69: 1442–1450, 1990. 20. Kraemer, WJ and Ratamess, NA. Fundamentals of resistance training: Progression and exercise prescription. Med Sci Sports Exerc 36: 674–688, 2004. 21. Mygind, E. Fibre characteristics and enzyme levels of arm and leg muscles in elite cross-country skiers. Scand J Med Sci Sports 5: 76–80, 1995. 22. Pallare´s, JG, Sa´nchez-Medina, L, Pe´rez, CE, De La Cruz-Sa´nchez, E, and Mora-Rodrı´guez, R. Imposing a pause between the eccentric
| www.nsca.com
and concentric phases increases the reliability of isoinertial strength assessments. J Sports Sci 32: 1165–1175, 2014. 23. Pareja-Blanco, F, Rodrı´guez-Rosell, D, Sa´nchez-Medina, L, RibasSerna, J, Lo´pez-Lo´pez, C, Mora-Custodio, R, Ya´n˜ez-Garcı´a, JM, and Gonza´lez-Badillo, JJ. Acute and delayed response to resistance exercise leading or not leading to muscle failure. Clin Physiol Funct Imaging 37: 630–639, 2017. 24. Pareja-Blanco, F, Rodrı´guez-Rosell, D, Sa´nchez-Medina, L, Sanchı´sMoysı´, J, Dorado, C, Mora-Custodio, R, Ya´n˜ez-Garcı´a, JM, Morales´ lamo, D, Pe´rez-Sua´rez, I, Calbet, JAL, and Gonza´lez-Badillo, JJ. A Effects of velocity loss during resistance training on athletic performance, strength gains and muscle adaptations. Scand J Med Sci Sports 27: 724–735, 2017. 25. Pyne, DB, Boston, T, Martin, DT, and Logan, A. Evaluation of the Lactate Pro blood lactate analyser. Eur J Appl Physiol 82: 112–116, 2000. 26. Sa´nchez-Medina, L and Gonza´lez-Badillo, JJ. Velocity loss as an indicator of neuromuscular fatigue during resistance training. Med Sci Sports Exerc 43: 1725–1734, 2011. 27. Sa´nchez-Medina, L, Gonza´lez-Badillo, JJ, Pe´rez, CE, and Pallare´s, JG. Velocity- and power-load relationships of the bench pull vs. bench press exercises. Int J Sports Med 35: 209–216, 2014. 28. Sa´nchez-Medina, L, Pallare´s, JG, Pe´rez, CE, Mora´n-Navarro, R, and Gonza´lez-Badillo, JJ. Estimation of relative load from bar velocity in the full back squat exercise. Sports Med Int Open 1: E80–E88, 2017. 29. Sa´nchez-Medina, L, Pe´rez, CE, and Gonza´lez-Badillo, JJ. Importance of the propulsive phase in strength assessment. Int J Sports Med 31: 123–129, 2010. 30. Sa´nchez-Moreno, M, Rodrı´guez-Rosell, D, Pareja-Blanco, F, Mora-Custodio, R, and Gonza´lez-Badillo, JJ. Movement velocity as indicator of relative intensity and level of effort attained during the set in pull-up exercise. Int J Sports Physiol Perform: 1– 23, 2017. 31. Sanchı´s-Moysı´, J, Idoate, F, Olmedillas, H, Guadalupe-Grau, A, Alayon, S, Carreras, A, Dorado, C, and Calbet, JA. The upper extremity of the professional tennis player: Muscle volumes, fibertype distribution and muscle strength. Scand J Med Sci Sports 20: 524–534, 2010. 32. Shimano, T, Kraemer, WJ, Spiering, BA, Volek, JS, Hatfield, DL, Silvestre, R, Vingren, JL, Fragala, MS, Maresh, CM, Fleck, SJ, Newton, RU, Spreuwenberg, LP, and Hakkinen, K. Relationship between the number of repetitions and selected percentages of one repetition maximum in free weight exercises in trained and untrained men. J Strength Cond Res 20: 819–823, 2006. 33. Tan, B. Manipulating resistance training program variables to optimize maximum strength in men: A review. J Strength Cond Res 13: 289–304, 1999. 34. Terzis, G, Spengos, K, Manta, P, Sarris, N, and Georgiadis, G. Fiber type composition and capillary density in relation to submaximal number of repetitions in resistance exercise. J Strength Cond Res 22: 845–850, 2008. 35. Toigo, M and Boutellier, U. New fundamental resistance exercise determinants of molecular and cellular muscle adaptations. Eur J Appl Physiol 97: 643–663, 2006. 36. Walker, S, Davis, L, Avela, J, and Hakkinen, K. Neuromuscular fatigue during dynamic maximal strength and hypertrophic resistance loadings. J Electromyogr Kinesiol 22: 356–362, 2012.
VOLUME 00 | NUMBER 00 | MONTH 2018 |
Copyright ª 2018 National Strength and Conditioning Association
15
