Potential for strength and endurance training to amplify endurance

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exercise; maximal oxygen uptake; weight training; heavy re- sistance training .... 3. 5. 11. 15. Cycling 3 daysjwk. Running. 3 days/wk. Cycling 1 day/wk. Running.
Potential for strength and endurance to amplify endurance performance

training

R. C. HICKSON, B. A. DVORAK, E. M. GOROSTIAGA, T. T. KUROWSKI, AND C. FOSTER Department of Physical Education, University of Illinois at Chicago, Chicago, Illinois

60680

HICKSON, R. C.,B. A. DVORAK,E. M. GOROSTIAGA,T. T. KUROWSKI,AND C. FOSTER.Potential for strength and endw-

However, one of the unresolved questions in the area of evaluating the interrelationships of these two methante training to amplify endurance performance. J. Appl. Physodologies is the influence of strength training on enduriol. 65(5): 22852290, 1988.-The impact of adding heavyance performance. Along these lines, it is known that resistance training to increase leg-muscle strength was studied strength types of training do not increase maximal 02 in eight cycling- and running-trained subjects who were already uptake to nearly the same extent as endurance training at a steady-state level of performance. Strength training was (1, 9, 14, 17, 18, 22, 28), and the endurance trainingperformed 3 days/wk for 10 wk, whereas endurance training associated increases in maximal O2 uptake do not appear remained constant during this phase. After 10 wk, leg strength affected by a strength program (14). Nevertheless, in an was increased by an average of 30%, but thigh girth and biopsied vastus lateralis muscle fiber areas (fast and slow twitch) and earlier study from this laboratory (l7), it was found that citrate synthase activities were unchanged. Maximal O2 uptake in untrained subjects who had increased the strength of . training durWO 2 max ) was also unchanged by heavy-resistance their lower extremities, time to exhaustion was enhanced ing cycling (55 ml. kg-‘. min-‘) and treadmill running (60 ml. during high-intensity, short-duration (4-8 min) cycling kg-l. min-l); h owever, short-term endurance (4-8 min) was and treadmill running exercise. By contrast, one of the increased by 11 and 13% (P < 0.05) during cycling and running, adaptations to strength types of exercise is the enlargerespectively. Long-term cycling to exhaustion at 80% VOzrnax increased from 71 to 85 min (P < 0.05) after the addition of ment of the trained muscles (7, 20, 26, 27). This added mass could negate the positive effects of the strength strength training, whereas long-term running (10 km times) improvement, particularly during exercise of long duraresults were inconclusive. These data do not demonstrate any tion (~30 min). These observations provided the impetus negative performance effects of adding heavy-resistance training to ongoing endurance-training regimens. They indicate that to further determine, in greater detail, whether strength certain types of endurance performance, particularly those training produces positive or negative effects on both requiring fast-twitch fiber recruitment, can be improved by short- and, in particular, long-term performance in substrength-training supplementation. jects already well trained in cycling and running. exercise; maximal oxygen uptake; weight training; heavy resistance training; cycling; treadmill running; blood lactate; fiber types; muscle fiber area; citrate synthase; thigh girth; skin fold thickness; body fat

ADAPTATIONS to exercise are considered to be primarily dependent on the specific type of training performed. On a performance basis, endurance training, which represents a type of exercise at one extreme of physical activity, increases the capacity to sustain repetitive highintensity, low-resistance exercise, such as cycling or running. Strength training, which represents a type of exercise at the other extreme of physical activity, increases the capacity to perform high-intensity, high-resistance exercise of a single or few repetitions, such as weight lifting. Although investigations of strength and endurance training interaction on performance have only received limited attention (8, 14), the results have been consistent. The major outcome from these investigations was that the combination of strength and endurance training resulted in an inhibition of optimal strength development that would h ave occurred if strength training were performed alone (8, 14). 0161-7567/M

$1.50 Copyright

0 1988

METHODS Subjects and experimental design. Eight subjects, six males and two females [ (v02 max)maximal O2uptake 250 ml. kg-‘. min-‘1, volunteered to participate in the study. The subjects’ ages, heights, and weights, as well as their previous training history, are shown in Table 1. Many of the subjects had been endurance training for several years. Before the start of testing for the strength phase of the study, all subjects had been training continuously for a minimum of 3-4 mo after a cycling-running (4miles minimum distance) protocol that has been employed previously in this laboratory (cf. 14, 16). Previous training and injuries caused some minor modifications. Subject B had been running exclusively for many years. Therefore, rather than markedly alter this regime, cycling was included once per week to familiarize him with this type of exercise for the testing procedures. Subject F had a chronic leg problem that resulted in an adjustment in running to 20 min/day,-2 days/wk, and cycling was increased to 4 days/wk. All the subjects maintained constant training work rates a minimum of 6-8 wk before the initiation of strength training. Because a major emphasis of this work was centered 2285 the American Physiological Society

2286 TABLE

STRENGTH

1. Physical

Subject

A

Age, Yr

Sex

and training

Height, cm

history

Weight, kg

Total Training,

Previous Training

Yr

188.0

75.9

29

F

168.4

63.4

Running

D

39

M

191.5

86.5

E

30

M

168.2

62.3

F

30

M

178.8

69.3

G

29

M

179.3

82.5

Cycling Running Recreational Tennis Weight lifting Gymnastics Running Weight lifting Hockey Running Cycling Running

Means t SE * Individual

F

3l.l-tl.2 training

167.5

177.7k3.2 schedule

maintained

66.8

63.0

EFFECTS

ON

ENDURANCE

of subjects before start of strength phase

M

30

180.5

TRAINING

33

H

M

ENDURANCE

Soccer Recreational Running

B

29

characteristics

AND

Most

Current Training,* mo

5

4

12

144

3

5

11

15

11

4

6

3

12

70

9

4

Recent

Training _____~

Protocol

Cycling Running Cycling Running Cycling Running Cycling Running Cycling Running

3 daysjwk 3 days/wk 1 day/wk 5 days/wk 3 days/wk 3 days/wk 3 days/wk 3 days/wk 2 days/wk 2-3 days/wk

Cycling Running

4 days/wk 2 days/wk

Cycling Running Cycling Running

3 days/wk 3 days/wk 3 days/wk 3 days/wk

Duration, mo

4 4 5 15

4

71.2t3.3 without

cessation

before

start

on the long-term performance results, the initial testing procedures were separated by 3-wk intervals. This aspect of the study was conducted to demonstrate that the subjects were in a steady-state level of performance with respect to these testing procedures before the initiation of the strength phase. These data are shown in Table 4 and are discussed later in relation to the long-term performance results. Strength training. This program consisted of weight training 3 days/wk for 10 wk. The following exercises were performed: parallel squats, five sets of five repetitions; knee extensions, three sets of five repetitions; knee flexions, three sets of five repetitions, and toe raises, three sets of 25 repetitions. All exercises were performed with as much weight as possible. With the exception of the toe raises, this resistance initially was -80% of the one-repetition maximum. As strength increased (i.e., performing more than five repetitions/set), additional weights were added to maintain this same relative resistance for the required repetitions. The sets were separated by 2-min rest periods. The parallel squats and toe raises were performed using Olympic-style weights, the knee flexions and extensions on a Universal gym. Strength training was always performed with 1 or 2 days rest between sessionsand was completed >1 h before beginning endurance training. These times remained constant for each subject. No strength training of the leg muscles had been performed at least 6 mo before the start of the strength phase. During the strength phase, each subject continued to endurance train at the same absolute cycling and running intensities that they had been performing for a minimum of 6-8 wk up to several years. Measurement of VOW max. Tjogmax was measured during work on a cycle ergometer (Monark) and during work on a treadmill as described previously (16). For the ~oZ max

of strength

training.

tests, the subjects performed exercise bouts of 4- to 8min durations against progressively increasing work loads. In general, for the cycling tests, the work rates were increased at l.-min intervals with the amount varying according to the subject’s exercise capacity, whereas for the treadmill tests, speed and/or grade were increased at 1-min intervals with the amount of work also varying according to each subject’s exercise capacity. There were a minimum of two tests per subject on the bicycle and treadmill. The criterion that ~oZ maxshowed no further increase (“leveling off’) or a decrease with increasing work loads was used to establish maximum values in all of the subjects before beginning strength training and after the lo-wk strength and endurance phase. During the TjOz maxtests, the subject’s expired air was continuously analyzed for volume, 02, and CO2 concentration with a Beckman Metabolic Measurement Cart. Measurement of strength. Leg strength was assessed by determining the maximum amount of weight that could be lifted for one repetition in a parallel squat, knee extension, and knee flexion. The subjects were familiarized with all procedures before testing. They performed multiple single repetitions against increasing resistances with -3-4 min elapsing between lifts. The criterion for determining strength was the inability to continue to perform a single repetition. These determinations were made several times before and at least once after the 10 wk of strength and endurance training. All tests were conducted by the same individual. Long-term endurance. Cycling time to exhaustion was measured on a Schwinn ergometric exerciser (EX2) while pedaling against resistances that required 80-85% of the subject’s VOz max.The subjects were considered exhausted at the point at which they could not keep cycl ing at the preselected work rate. Ru nning performance consisted of completing 10 km as fast as possible. To minimize

STRENGTH

AND

ENDURANCE

TRAINING

environmental conditions on performance, the lo-km testing was perf’ormed on an indoor track. Before the strength training, the subjects were tested at least twice on each measure to verify that their performances were not improving. Each subject ate the same food 2 days preceding and oln the day of all long-term endurance tests. Time of day for testing was kept constant for each subject. No endurance training was performed the day before a long-term endurance test. Short-term endurance. Each subject’s short-term endurance was measured while cycling (Monark) and running at maximal work rates that resulted in exhaustion within 5-8 min as described previously (17). Subjects were tested before the strength phase and at the same absolute intensities after the 10 wk of strength and endurance training. Blood samples were obtained from an antecubital vein 5 min postexercise. One milliliter of blood was deproteinized in 2 ml of 17.5% perchloric acid (PCA), centrifuged, and stored at -20°C until analysis. The PCA extracts were subsequently neutralized and analyzed for lactate (12). Skin fold and body fat analysis. Thigh girth on each leg was measured at the midpoint from the greater trochanter to the superior border of the patella. Skin fold thickness was measured at the following sites: triceps, subscapula, suprailliac, pectoralis, anterior thigh, and axilla. Body density by underwater weighing was determined according to the procedures and calculations described by Pollock et al. (24). All measurements were made in the morning before any exercise and after at least a 12h fast. Measurements were made within 2-3 days before the start of the strength phase, and again immediately after the lo-wk strength program. Muscle sampling and analyses. Muscle samples (30-70 mg) from the lateral portion of the quadriceps muscles (vastus lateralis) were obtained from seven subjects at rest, both before and after the strength and endurance phase, according to the percutaneous needle biopsy procedure of Bergstrom (3). One portion was frozen in 2methylbutane (isopentane), which had been precooled in a liquid Nz bath and later stored at -80°C for histochemical analysis. The samples (-150 fibers/biopsy) were sectioned (10 pm:) and stained histochemically for identification of slow-twitch and fast-twitch fibers by the myofibrillar adenosinetriphosphatase reaction using acid and alkaline preincubation (5). For fiber area determinations, the cross-sectional areas were projected (x240) onto white paper and traced. A minimum of twenty slowtwitch and twenty fast-twitch fibers were measured with a polar plainimeter. Mean values were calculated per section and converted to square micrometers. Four of these samples were accidently destroyed before analysis. Another muscle portion was frozen in liquid Nz and stored at -80°C until analyzed for citrate synthase activity (25). Protein content of these homogenates was determined by the Folin phenol method (19). Statistical procedures. The data were analyzed using the Hotelling mulltivariate t test. Statistical significance was set at the 0.05 level. RESULTS

Effectiveness of the strength program. Strength was increased by 27% in the parallel squats, 37% in knee

EFFECTS

ON

ENDURANCE

2287

extensions, and 25% in knee flexions (Fig. 1). For the three exercises, the overall strength gains averaged 30%. Total body and skeletal muscle effects. After strength and endurance training, body weights remained the same as with endurance training alone (Table 1). There were no changes in body composition or thigh girth after the strength and endurance phase (Table 2). Vastus lateralis muscle fiber composition remained in the same range after strength and endurance training as before, and the lack of change in slow- or fast-twitch fiber areas support the overall thigh girth measurements (Table 2). Citrate synthase activities of the biopsied muscles also remained the same after compared with before the addition of strength training (Table 2). endurance. By the criterion of . v02 max and short-term VO 2 max9 55 ml. kg-‘. min-’ during cycling and 60 ml. kg-lnmin-l during treadmill running, the subjects were considered well trained before incorporation of strength training into their exercise regimen (Table 3). The combined training, however, produced no additional effects on these variables. Short-term performance during the maximal exercise tests was increased by 11% during cycling and 13% during treadmill running after strength and endurance training (Table 3). This was probably not a result of a greater anaerobic glycolytic capacity, since blood lactate levels were not significantly altered during cycling (-13 mM) or during running (lo-12 mM) (Table 3). Long- term endurance. The prestrength and endurance phase testing, which was performed over a minimum of 3-wk intervals, showed essentially the same average performances during cycling and running (Table 4). After strength and endurance training, cycling time to exhaustion was increased by 20% (Table 4). The lo-km run performance means for all subjects were not computed because of strength-related injuries to two individuals who could not effectively complete this testing (cycling testing or short-term running were not compromised). Of the six remaining subjects who ran, average performance was not significantly altered by the combination of training (Table 4). DISCUSSION

Strength increases were not accompanied by any overall changes in muscle girth or fiber area. There are data supporting both a nervous and a muscular system factor in the adaptation to heavy-resistance exercise (cf. 21). Thus the accumulation of strength may reflect learning specific activation and motor unit recruitment patterns rather than significant intramuscular biochemical alterations, although the possibility of an increased contractile protein per cross-sectional area cannot be ruled out. Although it is known that training for strength and endurance are not compatible when optimal levels of strength are the goal (8, 14), much less is known about the role of simultaneously training for strength and endurance on endurance-related performance. Several factors provided the background for undertaking this investigation. 1) When previously untrained individuals undergo strength training, there is little change in aerobic power, an observation consistent with almost all

2288

STRENGTH

AND

ENDURANCE

TRAINING

EFFECTS

ON

ENDURANCE

110 100 90 80

FIG. 1. Strength changes after strength-training addition to endurance training. All values are significantly higher (P < 0.05) after strength and endurance training.

60 50 40 30 20 10

Parallel L//l

Endurance

Squats

Knee

Only

Knas

Extensions

[ay

Strength

h

Endurance

2. Total body and skeletal muscle effects after strength-training

TABLE

Training State

Thigh

Endurance training After strength and endurance training Values subjects.

are means

Girth, cm

52.7t0.8

Skin

& SE; n = 8 observations

for total

%Body

Fat

13.2k1.7 13.0t1.8

body

measurements

3. VO,,,,, short- term endurance, and blood lactate responsesto maximal exercise after strengthtraining addition to endurance training TABLE

Training State

00

Short-Term Endurance,

2 max

l/min

ml. kg-l.

mind1

S

Blood Lactate, mM

- -.

Cyclmg Endurance training After strength and endurance training

3.86t0.21

54.4t1.8

3.92t0.19

54.8t1.7

Endurance training After strength and endurance training

4.27t0.27 4.29kO.27

Treadmill

362klO 403t25*

12.8k0.7 12.9tl.l

361kl6 407t21*

11.5-t-0.9

running 60.2t2.2 6O.Ok2.0

Values are means & SE. vo2 max, maximal 02 uptake. different from endurance training (P < 0.05).

addition to endurance training Fiber

Folds, cm

69.3S3.2 63.3k6.8

53.3kl.O

Flexions

9.9t0.6

* Significantly

strength-training studies (1, 9, 14, 17, 18, 22, 28). However, it was observed that the capacity to perform highintensity cycling or running to exhaustion can be improved after a program specifically strengthening the lower-limb musculature (17). These results suggested that the development of strength might be compatible with improving endurance in individuals already well trained in cycling or running. 2) Strength training by

% Slow

50t11 44-c-5

and

Area,

pm2

Twitch*

7 observations

Slow twitch

Fast twitch

6058GG35 59352590

6474t417 6213t417

for citrate

synthase

Citrate Synthase, mm01 . mg protein-l. min-’ 161k17 163k27

activity.

* Means

from

3

itself is known to produce muscular enlargement and increase body mass (7, 20, 26, 27). In particular, the strength program previously employed in our laboratory to strengthen the lower-limb muscles increased thigh girth by several centimeters as well as strength by 4050% (16). Thus the potential contribution of the strengthened muscle mass could be counterbalanced by the increased massitself. This factor would be deleterious to endurance, particularly during long-term exercise when body mass represents a significant negative factor. 3) Competitive endurance athletes are known to incorporate, at various stages of training, some types of strength exercise into their regimen. Yet knowledge of the benefits or hazards of this supplementation to endurance training is completely lacking. The present results demonstrate a complete absence of any negative physiological effects of adding strength training to a regular program of endurance exercise in well-trained subjects. In fact, the performance results generally show a positive effect on short-term endurance and on long-term endurance to some extent. Since the strength training program did not induce any increase in total body mass, thigh girth, or fiber area, the potential negative influences on performance did not represent limiting factors to the results.

STRENGTH TABLE

4. Long-term

AND

ENDURANCE

cycling and running

Method of Testing

Cycling to exhaustion, min lo-km run, min:s (all subjects) lo-km run, min:s (6 subjects)

endurance

~~l___l-

TRAINING

EFFECTS

after addition Endurance

Training

Initial

Final

69t6 43:21-t-1:56 42:49&2:02

70-t-6 43:26-c-1:50 42:40-c-1:52

ON

of strength --

2289

ENDURANCE

training

to endurance

training

After

--Best

time

7lt6 43:12-t-1:53 42:27tl:59

Strength and Endurance Training

85-t-6* NC 41:43-r-1:45

Values are means t SE. NC, not computed because of injuries to 2 subjects. See RESULTS for further details. In some instances, the initial tests were the next to last tests. Prestrength training tests were spaced a minimum of 3 wk apart. Because of chronic injury, subject F ran 5 km; for overall comparisons his times were doubled. * Significantly different from endurance training (P c 0.05).

Short-term endurance was increased approximately equally (U-13%) during cycling and treadmill running after the strength and endurance phase of training. Strength-training programs, particularly those encompassing similar durations (2-3 mo) to that currently used, have been reported to increase the high-energy phosphate (creatine phosphate, ATP) and glycogen content at rest, the enzymatic capacity to rapidly resynthesize ATP, and the fast-twitch to slow-twitch fiber area ratio (7, 20, 27). These adaptations are geared to provide energy quickly, and may play a significant role in explaining part of the short-term performance increases. However, the possibility that these adaptations are compromised when both types of training are performed simultaneously is subject for future study. Other factors, besides those accountable uniquely to the strength training, could have potentially influenced the increase in long-term cycling endurance. Although it was determined, based on performance and VOW max, that the subjects were at a “steady-state” level for 6-8 wk before beginning the strength phase, it was possible that further adaptations (i.e., muscle respiratory capacity) to the endurance training could have occurred during the steady-state phase. For example, Henriksson and Reitman (13) demonstrated a dissociation between VOWmax and muscle respiratory capacity, since they observed a further increase in the activities of the citrate cycle enzyme, succinate dehydrogenase, despite a plateauing OfTjOzmax* Presently, the fact that the subjects were, in some cases, more familiarized with running than cycling, also suggested a greater potential for improvement. Nonetheless, the lack of change after strength and endurance training in the activities of citrate synthase, another mitochondrial marker of the citrate cycle, argues against the concept that further metabolic adaptations had occurred with the continued endurance training. Furthermore, the half-lives of a number of mitochondrial proteins in skeletal muscle have been shown to be on the order of 1-wk (4). In response to a constant training stimulus, the half-time of the increase in VOzrnax is -10 days (15). These results, when taken cumulatively, support the long-term, pre-strength, and endurance performance profiles that the subjects were in steady state with regard to certain biochemical and physiological parameters. At this time, a more likely explanation for the improved long-term cycling performance could be related to the strength-training effects on fiber-type recruitment during exercise. It has been reported that during sub-

maximal continuous exercise on the cycle ergometer (85% VOZ max:, 60 rpm), the peak tension that can be developed with each pedal thrust amounts to 50-60% of the maximal force, which can be exerted on the pedals (2). This implies an asynchronous activation of motor units with a significant recruitment of fast-twitch fibers (11). In this study, strength training increased maximal force in the lower limbs by 30%. On the assumption that a proportional increase occurred in the maximal force that may be exerted on the pedals, the peak tension developed with each pedal thrust would decrease from 50 to 60% of the maximal force before strength training to 35-45% after strength training. These observations suggest an increased participation by slow-twitch fibers and a reduced rate of fast-twitch fiber recruitment with each pedal thrust, resulting in an accompanying decrease in ATP consumption per unit of contractile force (10) by the fast-twitch fibers and a probable glycogen-sparing effect in this fiber type (11). By postponing the contribution of fast-twitch muscle recruitment, fatigue may be delayed and time to exhaustion improved. Although the lo-km run results remained somewhat inconclusive, in part due to injuries, several observations suggest that the weight-training effects on fiber-type recruitment would be markedly less significant during submaximal running exercise. During running at velocities between 3.62 m/s (10 km in 46 min) and 4.5 m/s (10 km in 37 min), the peak vertical force is -2.4-3.0 body wt (total force/subject’s body weight) (cf. 6). These values represent -4O-50% of the peak vertical force developed during sprint running, which, in turn, represents -45% of the peak force developed during a maximal vertical jump (23). Based on these data, estimates of peak vertical force, while running before strength and endurance training (10 km in -42 min), would be -20% of the maximal peak force exerted during the vertical jump. This would involve a low, even negligible recruitment of fast-twitch fibers during each step (11). In this context, the increase in force after strength training might have little effect on the rate of fast-twitch fiber recruitment, and consequently, on performance during the submaximal run. In addition, this last possibility could explain why short-term endurance was improved after strength training during treadmill running. The increasing speed and treadmill incline during this test solicits a high rate of fast-twitch fiber recruitment. In this case, the effects of strength training would decrease the rate of fast-twitch fiber recruitment for the same velocity and consequently

2290

STRENGTH

AND

ENDURANCE

TRAINING

could improve performance. In conclusion, these results provide an initial basis for employing strength training to supplement certain types of endurance performance in individuals already conditioned for these activities. However, based on our results, the potential for injury may also increase with both types of training. The word processing assistance of Kimela Kean is greatly appreciated. We thank Michael winski, and Terry Lewis for technical help. Received

23 December

1987; accepted

in final

Coney and Yin-Ming Falduto, Susan Czerform

17 June

1988.

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ENDURANCE

HENRIKSSON,

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ON

13.

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EFFECTS

VODAK, LESLIE.

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J., R. B. PARR, R. N. GIRANDOLA, P. WARD, P. A. T. J. BARSTOW, T. V. PIPES, G. T. ROMERO, AND P. Physiological alterations consequent to circuit weight Med. Sci. Sports Exercise 10: 79-84, 1978.