and Svedenhag 1985; Bailey and Pate 1991; Daniels and. Daniels 1992). However, it has been reported that the variation of ËÐ O2max cannot always explain ...
Eur J Appl Physiol (1998) 77: 320±325
Ó Springer-Verlag 1998
ORIGINAL ARTICLE
Daijiro Abe á Kazumasa Yanagawa Kaoru Yamanobe á Keiji Tamura
Assessment of middle-distance running performance in sub-elite young runners using energy cost of running
Accepted: 19 August 1997
Abstract The purpose of this study was to assess the validity of vamax as an indicator of middle-distance running performance in sub-elite young runners, vamax being de®ned as the quotient maximal oxygen uptake (V_ O2max divided by the net energy cost of running (Cr) on a treadmill at a submaximal running velocity (280 m á min)1). The V_ O2max , ventilatory threshold, vamax , and Cr were assessed in 39 young male sub-elite runners having only small variations in performance level. The relationship between each variable and running performance (at 1500 m, 3000 m, and 5000 m) was evaluated. A trend toward a negative correlation existed between Cr and performance although this was not signi®cant. The V_ O2max and vamax were signi®cantly related to performance. The vamax accounted for around 50% of the variability in performance whereas other physiological variables selected in this study were responsible, at best, for approximately 39%. The results presented in this study suggested that vamax was a useful indicator of middle-distance running performance in sub-elite young runners with similar performance levels as well as in top elite athletes. Key words Energy cost of running á Maximal oxygen uptake á Ventilatory threshold á Running performance á Young runners
D. Abe (&) Doctoral Program in Education, Hiroshima University, 1-1-2 Kagamiyama, Higashi-Hiroshima 739, Japan K. Yanagawa Department of Sports Science, Hiroshima University of Economics, 5-37-1 Gion, Asaminami, Hiroshima 731-01, Japan K. Yamanobe á K. Tamura Laboratory of Physiology and Sports Biomechanics, Faculty of Education, Hiroshima University, 1-1-2 Kagamiyama, Higashi-Hiroshima 739, Japan
Introduction It has been widely accepted that some indices of physical working capacity, such as ventilatory threshold (VT), lactate threshold (LT), onset of blood lactate accumulation (OBLA), and maximal oxygen uptake
V_ O2max , are closely related to distance running performance in groups of subjects with a wide range of performance levels (e.g. Costill et al. 1973). In particular, V_ O2max has been the factor that has received the most attention in identifying promising endurance athletes, because it indicates the maximal aerobic working capacity (SjoÈdin and Svedenhag 1985; Bailey and Pate 1991; Daniels and Daniels 1992). However, it has been reported that the variation of V_ O2max cannot always explain running performance in subjects with a limited range of V_ O2max and/or performance levels (Costill et al. 1976; Conley and Krahenbuhl 1980; Kenney and Hodgson 1985; SjoÈdin and Svedenhag 1985). Recently some researchers have proposed that running economy (RE) in addition to other physiological parameters, such as OBLA, LT, and VT, may be used to predict running performance in athletes with similar performance levels and/or well-trained athletes (Conley and Krahenbuhl 1980; Powers et al. 1983; SjoÈdin and Svedenhag 1985; Morgan et al. 1989a, 1989b; Williams 1990; Daniels and Daniels 1992). Previous studies have evaluated the value of RE using dierent treadmill velocities (Conley and Krahenbuhl 1980; Powers et al. 1983; Williams and Cavanagh 1987; Morgan et al. 1989b; Williams 1990; Yoshida et al. 1990; Daniels and Daniels 1992; Pate et al. 1992) which makes it impossible to compare directly the results obtained. The concept of a combined in¯uence of both V_ O2max and RE, independent of running velocity, has been described by di Prampero (1986). He de®ned the net energy cost of running (Cr) as the ratio of steady-state oxygen consumption (V_ O2 above resting) to the running velocity (v). At a constant velocity during treadmill running, the metabolic power output (E_ r ) necessary to run is
321
derived from the product of the energy spent per unit of distance: E_ r Cr v
1
rearranging Eq. 1 and applying it to the maximal conditions gives vmax E_ rmax Crÿ1
2
vend F V_ O2max Crÿ1
3
In aerobic conditions, E_ rmax can be identi®ed with V_ O2max , and Eq. 2 can be rewritten as: where F is the fraction of V_ O2max , and vend is de®ned as the velocity sustainable during endurance running. Using this concept, Lacour et al. (1990) have de®ned vamax as the running velocity at V_ O2max , and have applied it as follows to top elite middle-distance runners: vamax V_ O2max
Crÿ1
4
These researchers have found that vamax was a good predictor of middle-distance running performance in top elite runners (Lacour et al. 1990, 1991; Padilla et al. 1992). However, less information is available concerning the validity of vamax as an indicator of middle-distance running performance in sub-elite runners with similar performance levels. The purpose of this study was to assess whether vamax could be applied to sub-elite young runners with a small variation in performance levels as an indicator of middle-distance running performance.
Table 1 Physical and physiological characteristics of the subjects. SD Standard deviation, CV coecient of variance, vamax running velocity at V_ O2max , v1500 , v3000 , and v5000 average velocities of best record during 1995 track season at 1500 m, 3000 m, and 5000 m, respectively Characteristics
Mean
Age (year) Height (cm) Body mass (kg) Body fata (%) Cr (ml á kg)1 á m)1) V_ O2max (ml á kg)1 á min)1) VT (ml á kg)1 á min)1) vamax (m á s)1) v1500 (m á s)1) v3000 (m á s)1) v5000 (m á s)1)
18.1 169.4 55.6 10.2 0.180 75.5 46.2 6.53 5.99 5.47 5.34
SD 2.2 5.0 5.1 1.0 0.013 5.5 4.2 0.68 0.22 0.18 0.21
CV (%) 12.2 3.0 9.2 9.8 7.2 7.3 9.1 10.4 3.7 3.3 3.9
a
The skinfold thickness was measured by using a caliper at the sites of triceps brachii muscle (X, mm) and subscapularis muscle (Y, mm). Body density (Bd) was estimated by Nagamine and Suzuki (1964): Bd = 1.0913 ) 0.00116 (X + Y). Body fat was calculated following the equation of Brozek et al. (1963): body fat = (4.570/Bd ) 4.142) á 100
A group of 39 well-trained young male distance runners participated in this study. They had been running for a mean of 4.9 (SD 2.1) years. The physical characteristics of the subjects are shown in Table 1. After being informed of the purpose and possible risks of this study, the subjects gave their written consents. The average running velocities of the subjects best records during the 1995 track season at 1500 m, 3000 m, and 5000 m have been given as v1500 , v3000 , and v5000 , respectively. Of the subjects, 29 runners had participated in 1500-m competitions, 35 runners in 3000-m competitions, and 38 runners in 5000-m competitions during the track season corresponding to the test period (see Table 1).
(280 m á min)1) because 289.2 m á min)1 was the minimal average running velocity for 5000 m by the subjects and because no signi®cant dierences existed among the Cr values obtained at the four velocities employed in this study (see results). A V_ O2max test was performed using a constant velocity, gradeincremented protocol 10±15 min following the ®nal submaximal run. The treadmill velocity to be used was determined from the subject's running performance over 5000 m (within 15 min 00 s, 280 m á min)1, n = 7; 15 min 1 s to 15 min 30 s, 270 m á min)1, n = 7; 15 min 31 s to 16 min 00 s, 260 m á min)1, n = 11; above 16 min 01 s, 250 m á min)1, n = 14). During the ®rst 2 min of the V_ O2max test, the subjects ran at 0% gradient. Every 1 min the gradient was increased by 1% until the subject felt exhausted. When a given criterion was met (a plateau or a drop in V_ O2 and respiratory exchange ratio (R) greater than 1.10), the highest average value of 1-min V_ O2 was regarded as the individual's V_ O2max . The VT, which has been widely used as an indicator of aerobic working capacity, was systematically determined based on the segmental regression analysis method (V -slope method, Beaver et al. 1986) with respiratory gas exchange parameters during the V_ O2max test. A segmental regression analysis was applied to the V_ O2 -V_ CO2 relationship without the transit phase and above the respiratory compensation of metabolic acidosis. Some additional criteria, i.e. increase in V_ L /V_ O2 without any increase in V_ L /V_ CO2 and a non-linear increase in V_ L and R, were employed to con®rm V -slope based values.
Experiment procedure
Statistics
The treadmill test for the measurement of Cr was based on the methodology of Morgan and Daniels (1994). After a warming-up period of about 10-min with the treadmill running at 200 m á min)1, all the subjects performed a series of submaximal level-grade runs at 220, 240, 260, and 280 m á min)1 for 6 min at each velocity. Each submaximal run was separated by 5-min rest. Oxygen consumption (V_ O2 ), CO2 output (V_ CO2), and ventilation (V_L ) were measured using a gas analyser (Oxyconsigma, Mijnhardt, Holland), which was calibrated before the tests with room air and reference gases of known concentrations. A single sample of average 2-min V_ O2 was calculated to obtain Cr at each velocity. Resting V_ O2 was estimated by extrapolating the linear relationship between running velocity and steady-state V_ O2 for the series of submaximal runs. The Cr was determined at the highest of these velocities
Dierences in the Cr values at each velocity were compared using Schee's multiple comparison test. The relationships between physiological variables and average running velocities of the best records were evaluated using a simple linear regression analysis. Statistical signi®cance was established at the 0.05 probability level.
Methods Subjects
Results Table 1 shows the physiological and performance data. Coecients of variance (CV) of the average running velocities ranged from 3.3% to 3.9%. Small variations
322
Fig. 1 Relationship between average running velocity calculated from the best performance and energy cost of running (Cr). There was a trend towards a negative correlation between Cr and performance but this was not signi®cant
revealed that the performance level of the subjects was homogeneous. The average values of Cr at each velocity were 0.180 (SD 0.014), 0.179 (SD 0.013), 0.181 (SD 0.013), and 0.180 (SD 0.013) ml á kg)1 á m)1 at 220, 240, 260, and 280 m á min)1, respectively. There was no signi®cant dierence among them, suggesting that the running velocities used in this study did not aect Cr. This constancy of Cr was in accordance with the results of di Prampero et al. (1986). A large variation in the Cr values existed among the subjects; its range was from 0.153 to 0.212 ml á kg)1 á m)1. The average value of Cr obtained in this study was similar to that previously reported (di Prampero et al. 1986; Lacour et al. 1990, 1991; Brueckner et al. 1991; Padilla et al. 1992; Bourdin et al. 1993; Brisswalter and Legros 1994; Bunc and Heller 1994). Although a simple linear regression analysis indicated that Cr was not signi®cantly related to running performance, a trend towards a negative correlation was noted between Cr and running performance (Fig. 1), with a lower Cr relating to better performance. The average values of V_ O2max , VT, and vamax were 75.5 (SD 5.5) ml á kg)1 á min)1, 46.2 (SD 4.2) ml á kg)1 á min)1, and 6.53 (SD 0.68) m á s)1, respectively. Small variations in both V_ O2max and VT were observed (Table 1). A simple linear regression analysis also revealed that V_ O2max and vamax , but not VT, were signi®cantly related to running performance (Figs. 2, 3, 4).
Discussion Several researchers have considered VT (or LT), re¯ecting an alteration in muscle metabolism during sub-
Fig. 2 Relationship between the average running velocity calculated from the best performance and maximal oxygen uptake (V_ O2max ). The V_ O2max accounted for only 39% of the variability in performance, at best, whereas V_ O2max was signi®cantly correlated with running performance
Fig. 3 Relationship between the average running velocity calculated from the best performance and ventilatory threshold (V T ). There was no signi®cant relationship between them
maximal exercise, to be a good predictor of an athlete's potential for endurance exercise (Kindermann et al. 1979; Kumagai et al. 1982; Powers et al. 1983; Tanaka et al. 1983; Tanaka and Matsuura 1984; Fay et al. 1989; Kreider et al. 1990; Yoshida et al. 1990). For example, Kumagai et al. (1982) have described that, in 17 welltrained runners, VT was positively correlated with 5000 m performance. In contrast to those previous studies, VT was not signi®cantly related to running performance in this study (Fig. 3). The lack of a relationship between VT and performance may have been due to the lower
323
Fig. 4 Relationship between the average running velocity calculated from the best performance and vamax . The vamax is de®ned as the quotient maximal oxygen uptake (V_ O2max ) to energy cost of running (Cr) (Eq. 4 in text)
Fig. 5 Relationship between ventilatory threshold (VT ) expressed as a percentage of individual maximal oxygen uptake (V_ O2max ) and F value as calculated from Eq. 5 in text
percentage of VT relative to V_ O2max observed in this study than that found in previous studies. The average in our study corresponded to 61.2% V_ O2max , while most of the previous studies have reported that well-trained athletes exhibited a high percentage (75%) of VT relative to V_ O2max (Kumagai et al. 1982; Tanaka et al. 1983; Tanaka and Matsuura 1984; Fay et al. 1989; Yoshida et al. 1990). When the following equation
reported that such a relationship was poor with a limited range of levels of performance (Costill et al. 1976; Conley and Krahenbuhl 1980; Lacour et al. 1990). In particular, correlations between V_ O2max and middledistance running performance have seemed to be low in well-trained athletes (see Conley and Krahenbuhl 1980; SjoÈdin and Svedenhag 1985; Morgan et al. 1989b; Daniels and Daniels 1992). Results of the present study demonstrated that V_ O2max could account for only 39% of the variability in performance, at best, whereas V_ O2max was signi®cantly correlated with running performance even in the subjects with a small variation in level of performance (Fig. 2). Although the CV of V_ O2max was similar to that of VT (Table 1), only V_ O2max was signi®cantly related to running performance in this study (Figs. 2, 3). These ®ndings would suggest that whether or not VT is signi®cantly correlated with longand middle-distance running performance may be due not only to a small variation in VT and/or performance levels but also to a low percentage of VT relative to V_ O2max . An ethnic dierence appears to exist with regard to RE. The studies of Coetzer et al. (1993) and Saltin et al. (1995) who investigated South and Eastern Africans, respectively, have implied that these people exhibited lower Cr than Caucasians. In view of the ®nding that, during running, but not walking, Cr of African pygmies was 10% less than that of Caucasian runners. Ferretti et al. (1991) have suggested that the ethnic dierence in running economy might be attributed to dierences in the recoil of elastic energy stored in the stretched tendons. Caucasian runners with various performance levels have been shown to have similar Cr ranging from 0.174 to 0.188 ml á kg)1 á m)1 in previously reported
v F vamax
5
was de®ned, where v is the mean velocity, F values obtained in this study were 0.917, 0.838, and 0.818 for v1500 , v3000 , and v5000 , respectively. The increase in v could have been the result of an increase in F and/or V_ O2max and/or a decrease in Cr (see di Prampero et al. 1986). It is worth noting that in sub-elite runners, these F values were low compared to results that have been obtained in adult elite runners (Lacour et al. 1990, 1991; Padilla et al. 1992). These low values of F increase the relative importance of V_ O2max as a factor of performance. In addition to this result, F values were signi®cantly related to VT expressed as %V_ O2max (Fig. 5). The possibility cannot be eliminated that an increase in VT by future training may bring about 1. An increase in F and the relative importance of VT 2. A concomitant decrease in the relative importance of V_ O2max . Most of the previous studies which have documented the existence of a signi®cant relationship between V_ O2max and distance running performance have used subjects with heterogeneous levels of performance (Costill et al. 1973; Foster et al. 1978; Farrell et al. 1979; Maughan and Leiper 1983). In contrast, others have
324
data (di Prampero et al. 1986; Lacour et al. 1990, 1991; Brueckner et al. 1991; Padilla et al. 1992; Bourdin et al. 1993; Brisswalter and Legros 1994; Bunc and Heller 1994). It is likely that Cr is independent of the ability to run and that Cr does not have an in¯uence on running performance. In contrast to the ®ndings provided by previous investigations, we observed a trend towards a negative correlation between Cr and running performance, with more economical runners having better performance (Fig. 1) although its relationship was not signi®cant (P = 0.07±0.16). The de®nitive answer as to the correlation between Cr and performance remains to be elucidated in further studies. The major ®nding of the present study was that there was a statistically signi®cant relationship between vamax and performance (Fig. 4). In top elite runners, it has been established that vamax was a good predictor of performance for 1500, 3000, and 5000-m competitions (Lacour et al. 1990, 1991; Padilla et al. 1992). To our knowledge, the present investigation is the ®rst to indicate that sub-elite runners with small variations in performance level are characterized by a similar relationship to that found in elite runners. We suggest that the results of this study may contribute to a wider use of vamax as an indicator of middle-distance running performance in sub-elite young runners with a small variation in performance. In spite of the subjects with lower performance levels used in this study compared to previous reports, the fact that higher vamax and V_ O2max were obtained is of interest. A high average V_ O2max may have been because of the low body masses of the subjects in this study. SjoÈdin and Svedenhag (1992) have suggested that the observed changes in RE and V_ O2max per body mass in young boys during growth may be due to an overestimation of the V_ O2 dependence on body mass. They have proposed that V_ O2 should be normalised using kg)0.75 rather than kg)1. When V_ O2max was recalculated using kg)0.75 to minimize the in¯uence of body mass, the average V_ O2max in our subjects became 206.1 ml á kg)0.75 á min)1. This gave a similar value to those obtained by Lacour et al. (1990, 1991), i.e. 201.3 and 203.0 ml á kg)0.75 á min)1, respectively. The majority of the subjects
n 26 in this study were high school students, thus, the high V_ O2max per unit of body mass might have been dependent on the low body mass. Whenever V_ O2max is evaluated with the use of kg)0.75, the high value of vamax cannot be explained by low body mass because vamax is independent of body mass (Eq. 4). In conclusion, vamax was con®rmed as a useful indicator of middle-distance running performance in subelite young runners with similar performance levels as well as in top elite athletes. Middle-distance running performance tended to be negatively correlated with Cr although its correlation was not signi®cant. The vamax accounted for around 50% of the variability in performance, whereas other physiological variables selected in this study were responsible, at best, for approximately 39%.
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