Secondary Logo

Effect of commuter cycling on physical performance of male and female employees


Medicine & Science in Sports & Exercise: February 2000 - Volume 32 - Issue 2 - p 504
APPLIED SCIENCES: Physical Fitness and Performance

HENDRIKSEN, I. J. M., B. ZUIDERVELD, H. C. G. KEMPER, and P. D. BEZEMER. Effect of commuter cycling on physical performance of male and female employees. Med. Sci. Sports Exerc., Vol. 32, No. 2, pp. 504–510, 2000.

Purpose: The purpose of this study was to determine the effect of commuter cycling on physical performance. Eighty-seven male and 35 female employees volunteered to cycle regularly to their work.

Methods: Sixty-one participants went commuter cycling for 1 yr (cycling group); the others cycled only in the second half year (control group). A maximal exercise test on a cycle ergometer was carried out at the start of the study, after 6 months, and after 1 yr to measure maximal external power (Wmax) and maximal oxygen uptake (V̇O2max).

Results: After the first 6 months of commuter cycling, with a mean single trip distance of 8.5 km and a mean frequency of more than three times a week, a significant increase of 13% was found in the Wmax per kilogram body weight (Wmax·kg−1) in both sexes of the cycling group. The improvement in V̇O2max·kg−1 was significant for the male participants (6%) but not for the female participants (−2%). At the end of the second half year, the control group also showed a mean gain in Wmax·kg−1 of 13%. Their V̇O2max·kg−1 declined in the first half year, but this was counteracted in the second half year. A dose-response relationship was found between two independent variables and the physical performance; the lower the physical performance at the start of the study and the higher the total amount of kilometers cycled, the higher the gain in Wmax. For subjects with a low initial fitness level, a single trip distance of only 3 km turned out to be enough to improve physical performance.

Conclusion: Commuter cycling can yield much the same improvement in physical performance as specific training programs.

Department of Physiology, Faculty of Medicine, Vrije Universiteit, Amsterdam, THE NETHERLANDS and Institute for Research in Extramural Medicine (EMGO), Faculty of Medicine, Vrije Universiteit, Amsterdam, THE NETHERLANDS

Submitted for publication February 1999.

Accepted for publication August 1999.

Address for correspondence: Ingrid J. M. Hendriksen, Netherlands Aeromedical Institute, Kampweg 3, 3769 DE Soesterberg, The Netherlands. E-mail:

Epidemiological research has demonstrated that physical inactivity is an independent risk factor for coronary heart disease (CHD) (9,18,21,23). Regular exercise can also have a positive influence on some of the other known major risk factors of CHD, especially on hypertension (7,8,14) and an unfavorable lipid profile (5,15,22). A large proportion of the population of the Western industrialized countries is physically inactive. In The Netherlands, for example, 34% of the population aged 16 yr or older is physically inactive (1). Therefore, promoting regular exercise may have a considerable impact on the prevention of CHD.

The greatest health benefits are achieved when the least active individuals become moderately active (2,11). The recommendation is to be physically active for at least one-half hour on most days of the week at moderate intensity (17). If possible, physical exercise should be a part of habitual daily life activities. An excellent way of exercising, which fits well in daily life routines, is commuter cycling. However, the question is whether commuter cycling reaches moderate intensity.

The aim of the present study was to investigate the influence of commuter cycling on physical performance. Physical performance is defined as the maximal external power (Wmax) that is achieved during a maximal exercise test on a cycle ergometer. At the same time we were also interested in the underlying energetic process, represented by the maximal oxygen uptake (V̇O2max). We studied the improvement of the Wmax and the V̇O2max as a result of commuter cycling by comparing an experimental group (commuter cycling group) with a control group (without commuter cycling). We tried to find a dose-response relationship between the aforementioned changes in the Wmax and V̇O2max and the frequency of cycling, the cycling distance, and the intensity of commuter cycling. We also searched for the minimal single trip distance that is necessary to achieve a reasonable improvement in physical performance.

Back to Top | Article Outline



Participants included 122 employees (87 men and 35 women) of two different companies in Amsterdam Southeast with mainly administrative jobs. They were between 25 and 56 yr old and were healthy but untrained, which meant that they did not participate in regular intensive exercise in the last 6 months before the start of this study. Subjects who were already commuter cycling were excluded.

Back to Top | Article Outline

Study design.

The subjects were divided at random into an experimental (commuter cycling) group and a control group. Stratification was done for sex and age. Before participation in the study, each individual gave written informed consent to participate. The study started in the spring of 1994. In the first half year of the study the cycling group began commuter cycling, covering a minimal distance of 3 km each way, with a minimal frequency of three times a week. In the same period the subjects in the control group were asked not to change their lifestyle. Each cyclist had to fill in a diary with cycling activities. A distance recorder on their bicycle registered the cycling distance. In these 6 months, a telemetric heart rate recording (Sporttester Polar, Kempele, Finland) of each subject was made twice during a one-way trip of commuter cycling. The results of both measurements were compared and the last of both was used to calculate the relative intensity of commuter cycling. The percentage of the maximal heart rate (% HRmax) for each cyclist was obtained by dividing the heart rate measured during commuter cycling by the maximal heart rate of the subject of the first maximal exercise test. Because the recorder also gave information about the exact time spent on a one-way trip (and from the distance recorder the one-way distance was already known), the average speed of commuter cycling could be calculated. In the second half year (from November 1994 until May 1995) all participants were asked to do commuter cycling as much as possible, with no limits concerning minimal frequency of cycling.

Physical performance was measured by a maximal exercise test on a cycle ergometer. This exercise test was completed by all participants at the start of the study (Test 1), after 6 months (Test 2), and after 1 yr (Test 3). Before each exercise test, a “health profile” of the participant was drawn up, which included the measurement of weight, systolic and diastolic blood pressure at rest, blood cholesterol level, and a description of the lifestyle of the participant (information regarding smoking habits, alcohol intake, and physical activities).

Back to Top | Article Outline

Maximal exercise test.

All tests were executed in the afternoon by the same two investigators. Exercise was performed in the upright position on an electrically braked cycle ergometer (Lode L54, Groningen, The Netherlands). Calibration of the cycle ergometer was carried out at the start of the study, and the saddle and handle bars were repositioned to suit each subject.

The maximal physical performance level of each participant was estimated, taking into account gender, age, physique, and physical activities in the preceding months. The protocol of the maximal exercise test consisted of three phases: 1) a 3-min warm-up at about 30% of the estimated maximal external power (phase 1); 2) followed by 6 min at submaximal workload, which was about 60% of the estimated maximal external power (phase 2); and 3) a stepwise increase until exhaustion in the workload (phase 3). This incremental part of the maximal exercise test was constructed in such a manner that maximal power could be reached in about 6 min. In each minute the resistance of the cycle ergometer was raised by 10–25 W, depending on the characteristics of the subject. The participants were asked to keep the speed of pedaling at 50 rpm in the first phase, 60 rpm in the second, and 70 rpm in the third phase of the test.

The subjects were encouraged to exert themselves until exhaustion. Maximal external power (Wmax) was the highest power output that could be reached during the maximal exercise test. If the final workload was not completed, Wmax was calculated from the amount of time completed in the last workload increment (rounded off to 15, 30, or 45 s). In the last minute of each phase (3rd, 9th, and last minute), the expiratory flow was calculated from the pressure difference between the beginning and the end of a Fleisch pneumotachograph, which was combined with a differential pressure transducer (Validyne MP 45.871). At the same time, the fractional oxygen and carbon dioxide concentrations (FeO2, FeCO2) were measured on a paramagnetic oxygen analyzer (Servomex 570A) and a infrared gas analyzer, respectively (Servomex 1410). Each afternoon before and after the exercise tests, the analyzers were checked with certified calibration gases, and the pneumotachograph was calibrated with a 1-L precision syringe (Vitalograph). The maximal oxygen uptake (V̇O2max) was the mean oxygen uptake calculated during the last 30 s of the maximal exercise test. The recorded values were converted to standard conditions (STPD). The decision to stop the exercise was based on signals of extreme fatigue from the participant and was confirmed by a respiratory exchange ratio above 1.00.

Back to Top | Article Outline

Statistical analysis.

Data analysis was carried out using the Statistical Package for the Social Sciences (SPSS/PC+ 5.1, Chicago, IL). Results are presented as means and SD. Unpaired Student t-tests were performed to analyze differences between groups for baseline data. A two-way analysis of variance (ANOVA) with repeated measures on one factor (time) was used to test for significant differences between both groups for the most important physiological variables (Wmax, Wmax per kilogram body weight (Wmax·kg1), V̇O2max, and V̇O2max ·kg1). Changes in mean values and mean percentage change within groups were analyzed using paired t-tests. Unpaired t-tests were used to evaluate whether differences in mean percentage change in the different time periods between both groups were significant. Multiple regression analysis was performed to find a dose-response relationship between the amount of commuter cycling and the gain in Wmax·kg1 and V̇O2max·kg1. Stepwise regression analysis with backward selection was used. A two-tailed P- value of 0.05 or less was considered to be significant.

Back to Top | Article Outline


In the first 6 months of the study, four subjects did not keep to the agreement and three women withdrew because they became pregnant, so the results of this first half year are based on 115 subjects (57 cyclists and 58 controls). Their physical characteristics are presented in Table 1. There was no significant difference in physical characteristics between the two groups. Another six participants could not perform the last test, mainly because of illness, which resulted in a total of 13 dropouts (11%) after 1 yr. The characteristics of these dropouts were not different from the participants who remained in the study.

Table 1

Table 1

In the first half year, the average single trip (i.e., one-way) distance in the cycling group was 9.4 km for men and 6.4 km for women, and the mean total distance over these 6 months was also higher for men (1714 km) than for women (1039 km)(Table 2). The mean frequency of cycling was reasonably comparable in both genders. After conversion, the average was 3.3 times a week for men and 3.0 times a week for women (holidays included). Men cycled at a higher average speed than women (respectively, 19.7 km·h1, 17.9 km·h1). The intensity of commuter cycling expressed in percentage of the maximal heart rate (%HRmax) was 68% for the male participants and 75% for the female participants. These values roughly correspond with respectively about 55% and 65% of the V̇O2max (14).

Table 2

Table 2

In the second half year the control group also started with commuter cycling and their mean single trip distance was 8.3 km, which is comparable to the figure of the cycling group in the first half year (8.5 km). In spite of the fact that the control group started commuter cycling in the winter period and that they were not committed to any rules, their total cycling distance was higher (1058 km) than the total distance of the original cycling group in this period (893 km). However, the control group cycled fewer kilometers than the cycling group in their first half year (on average 1524 km).

Small changes were seen in the mean weight of the participants during the study year, but these changes were always within ± 1 kg. At the end of the study year both groups showed no significant changes compared with that at the start of the study.

The result of commuter cycling on the variables of the maximal exercise test is shown in Table 3. At the start of the study both groups were comparable on all these variables.

Table 3

Table 3

Significant differences in time between both groups were seen for maximal external power (Wmax, Wmax·kg1), as well as for maximal oxygen uptake (V̇O2max, V̇O2max·kg1)(all P < 0.01). When comparing the results of both groups for each gender separately, only the V̇O2max·kg1 of the women is not significantly different between the groups.

For each participant the change in Wmax·kg1 and V̇O2max·kg1 from pre- to post-test was calculated and expressed as a percentage (Table 4). After 6 months of commuter cycling, a mean increase of 13% (P < 0.01) was found in the Wmax·kg1 in both sexes of the cycling group, while the mean Wmax·kg1 of the control group remained unchanged in the same period. In the second half year, when the control group started commuter cycling, too, their mean gain in Wmax·kg1 was also 13% (men 12%, women 16%, both P < 0.01).

Table 4

Table 4

The gain in maximal oxygen uptake was less pronounced. In the male part of the cycling group the V̇O2max·kg1 increased significantly (P < 0.01) in the first 6 months (6%), but no change was seen in the female cyclists. In the same period, the mean value of the control group declined significantly (men −5%, women −12%, both P < 0.01), while their Wmax·kg1 remained unchanged. In the second half year the mean V̇O2max·kg1 of the control group increased significantly with 8% (men 7%, women 10%, both P < 0.01).

When comparing the results of the first 6 months of both groups, the mean percentage change is significantly more favorable for the cycling group, both for men and women and for Wmax·kg1 and V̇O2max·kg1. In the second half year, when the control group starts commuter cycling, too, their percentage gain in Wmax·kg1 and V̇O2max·kg1 is significantly higher than the gain of the cycling group in this period.

A clear relationship has been found between the gain in Wmax and V̇O2max, on the one hand, and (the logarithmic value of) the total amount of kilometers cycled in 6 months and the initial fitness level of the subjects, on the other hand. In Figure 1 this dose-response relationship of the mean percentage change in Wmax·kg1 (ΔWmax) is presented for men. On the x-axis the single trip distance in kilometers is given instead of (the logarithmic value of) the total amount of kilometers cycled in 6 months. Those subjects with the lowest initial fitness levels scored the largest gains, and for them a single trip distance of 3 km was enough to lead to a gain of about 14% in the Wmax.

Figure 1

Figure 1

For all participants there was a diminishing return with higher single trip distances; an increase in the cycling distance from 3 to 6 km produced more gain than increasing the distance from 15 to 18 km. Distances over 20–25 km did not improve the results any further.

Back to Top | Article Outline


Until now most research has been focused on the maximal oxygen uptake (V̇O2max) as performance measure while the achieved maximal external power (Wmax) is seldom mentioned, although the latter is the best measure of physical performance (13). The maximal oxygen uptake represents the aerobic process that underlies the deliverance of maximal external power. It gives us useful additional information, but it also exposes a lot of intra-individual variation. The maximal external power, on the other hand, is more stable and can be measured very accurately on a cycle ergometer. Besides, maximal external power can improve as a result of training without an explicit increase in the maximal oxygen uptake. If maximal oxygen uptake was the only measured parameter, the wrong conclusion, i.e., that the training did not lead to any results, could have been drawn.

In the first half year, a significant increase of the Wmax·kg1 is found in the cycling group, while the Wmax·kg1 of the control group remained unchanged. This mean increase in Wmax·kg1 in the cycling group in the first half year is comparable with the mean increase in Wmax·kg1 in the control group in the second half year of the study (i.e., the period they were allowed to cycle). Both went up significantly with a mean of 13%. Commuter cycling thus clearly seems to have an effect on maximal external power.

There was a significant increase of almost 4% in the mean V̇O2max·kg1 in the cycling group in the first 6 months. In the same period, the V̇O2max·kg1 of the control group declined about 7%, whereas their Wmax·kg1 did not change. It is possible that this relatively small increase in the maximal oxygen uptake in the cycling group and this decrease in the control group is a consequence of a habituation process. Repetition of the test procedures can lead to diminished stress caused by the experimental situation and consequently to a lower oxygen uptake at all levels (10,19,20). So in both groups it is possible that higher initial values of the maximal oxygen uptake were measured at the pretest than would have been found if repetition of the test had taken place. If repetition of the pretest had taken place, a higher percentage change in V̇O2max·kg1 could have been found in the cycling group in the first half year, and no decline could have been found in the control group in the same period. This argument is confirmed when one looks at the results of the control group in the second half year. They are now accustomed to the exercise test, and after 6 months commuter cycling their V̇O2max·kg1 increases almost 8%.

The literature about the effect of cycling on physical performance (Wmax) is limited. Table 5 presents an overview of studies that examined the effect of cycling as a training mode on physical performance and on V̇O2max. A comparison of the results of these studies, in which different populations and different training methods were used, was made even more difficult by the fact that different test methods were used. Only those studies that used cycle ergometry were included. The Wmax in all these studies is reported only as an absolute value attained by a subject (W) and not as per kilogram of body weight (W·kg1), as we did in our study. The percentage change of this absolute variable is calculated, which is not quite comparable with our results.

Table 5

Table 5

The mean gain in Wmax in these studies is 24% (range 12–39%). There were two studies with a remarkable high increase in the Wmax. In the study of Siegel et al. (20) the result of a very low initial value can be seen, that is, a high mean increase in Wmax (39%). The reason for their low initial value was that the subjects were extremely unfit, middle-aged blind men. In the subgroup of young men in the study of Denis et al. (4), the high gain in Wmax (35%) is probably caused by the high training intensity, combined with a high total amount of work achieved during the training program.

Compared with the results of the studies mentioned in Table 5, our gain in the Wmax·kg1 was relatively low. One reason for this lower gain in the Wmax·kg1 is that the Wmax of our subjects at the start of the study (initial Wmax) was fairly good, although they did not participate in regular physical activity. In addition, the intensity of commuter cycling, which was 68% and 75% of the maximal heart rate (HRmax) for men and women, respectively, was relatively low compared with the training intensities of the other studies (between 75% and 85% of the maximal heart rate). Naturally, it is understandable that the intensity of commuter cycling is not so high because people do not wish to become sweaty if they are going to work.

When comparing the results of the studies mentioned in Table 5 concerning the V̇O2max·kg1, we have to bear in mind the difficulties that arise in measuring the V̇O2max. Although all studies used graded exercise tests, different protocols were used to reach the maximum (different step sizes, test duration, and pedal rates). Also, the criteria used to decide whether a subject was maximally exerted and information regarding the equipment used and the exact space of time in which the V̇O2max was determined were seldom mentioned. Finally, the question of repeated measurements of the V̇O2max at the start of the study to prevent the effect of habituation has to be taken into account. Only in the studies of Davis et al. (3) and Siegel et al. (20) was the V̇O2max determined twice on separate days before the start of the training.

For the most part, the same arguments mentioned to explain the difference in the mean gain of the Wmax·kg1 between our results and the literature probably are also applicable for the mean gain in V̇O2max·kg1, a relatively high initial fitness level and a low intensity of cycling in our study. Finally, a remark has to be made about the small group sizes used in all these studies, which influences the reliability of the test results.

Only one study focused on the effect of commuter cycling on maximal performance capacity and V̇O2max·kg1 (16). In this study of Oja et al. (1991), the gain in the maximal performance capacity was 13.3% and the gain in the V̇O2max·kg1 was 7.3%. These results were accomplished by a group of 26 cyclists (men and women) after 10 wk of commuter cycling with a mean distance of about 10 km and an intensity of approximately 57–65% of the V̇O2max. These figures are reasonably comparable with our data although the subjects’ initial fitness level was somewhat lower. However, no information was given about the exact test protocol that was used on the cycle ergometer and what the results were in terms of Wmax·kg1. Also, it is not clear whether repetition of the test had taken place at the start of the study to prevent habituation.

In our study, the dose-response relationship of the mean percentage change in V̇O2max·kg1 (ΔV̇O2max) for men is reasonably comparable with the results of the mean percentage change in Wmax·kg1 (Fig. 1), although the percentage gain in V̇O2max·kg1 is less high (up to 20%). However, for the subjects with a poor initial fitness level, 3 km is still enough to raise the V̇O2max·kg1 by almost 10%. The regression equations of both the Wmax·kg1 and the V̇O2max·kg1 found for the women were more or less comparable with the male ones. However, because the group of women in our study was quite small and diverse, drawing conclusions about the female dose-response relationship must be done very carefully.

From the dose-response relationship that we found it can be concluded that for subjects with a low initial fitness level, frequently cycling short distances is already enough to improve physical performance. Advising people to participate regularly in low intensity activities will probably be received much better by those who are physically inactive than advising them to do more vigorous exercise. Of course, subjects who regularly participate in vigorous sports have to cycle more frequently and cover higher distances to achieve some results.

It can be concluded that commuter cycling at a relatively low intensity (between 55 and 65% of the V̇O2max) as a part of normal daily activities can increase physical performance in men and women if repeated at least 3 times a week with a minimal daily distance of 6 km.

We are grateful to the women and men who participated as subjects, and we also thank the ING Bank and the Stadsdeel Zuidoost for their collaboration.

This research was supported by a grant from the Dutch Ministry of Transport, Public Works and Water Management (Masterplan Bicycle), the Dutch Ministry of Public Health, Wellness and Sport, the Netherlands Heart Foundation, and the Stichting Fiets.

Back to Top | Article Outline


1. Backx, F. J. G., H. Swinkels, and E. Bol. Lichamelijke (in)activiteit in de vrije tijd. Geneeskunde en Sport 28:130–137, 1995.
2. Blair, S. N., H. W. Kohl, R. S. Paffenbarger, D. G. Clark, K. H. Cooper, and L. W. Gibbons. Physical fitness and all-cause mortality. JAMA 262:2395–2401, 1989.
3. Davis, J. A., M. H. Frank, B. J. Whipp, and K. Wasserman. Anaerobic threshold alterations caused by endurance training in middle-aged men. J. Appl. Physiol. 46:1039–1046, 1979.
4. Denis, C., D. Dormois, and J. R. Lacour. Endurance training, V̇O2max, and OBLA: a longitudinal study of two different age groups. Int. J. Sports Med. 5:167–173, 1984.
5. Duncan, J. J., N. F. Gordon, and C. B. Scott. Women walking for health and fitness. JAMA 266:3295–3299, 1991.
6. Ekelund, L. G., W. L. Haskell, J. L. Johnson, F. S. Whaley, M. H. Criqui, and D. S. Sheps. Physical fitness as a predictor of cardiovascular mortality in asymptomatic North American men. N. Engl. J. Med. 319:1379–1384, 1988.
7. Fagard, R. Habitual physical activity, training, and blood pressure in normo- and hypertension. Int. J. Sports Med. 6:57–67, 1985.
8. Fagard, R., D. Duprez, D. Clement, and A. Amery. Physical exercise in the management of hypertension: a consensus statement by the World Hypertension League. J. Hypertens. 9:283–287, 1991.
9. Fletcher, G. F., G. J. Balady, S. N. Blair, et al. Statement on exercise: benefits and recommendations for physical activity programs for all Americans. Circulation 94:857–862, 1996.
10. Froelicher, V. F., H. Brammell, G. Davis, I. Noguera, A. Stewart, and M. C. Lancaster. A comparison of the reproducibility and physiologic response to three maximal treadmill exercise protocols. Chest 65:512–517, 1974.
11. Haskell, W. L. Physical/physiological/biological outcomes of physical activity. In: Toward Active Living: Proc. International Conference on Physical Activity, Fitness, and Health. H. A. Quinney, L. Gauvin and A.E.T. Wall (Eds.). Champaign, IL: Human Kinetics, 1994, pp. 17–24.
12. Jennings, G., L. Nelson, P. Nestel, et al. The effects of change in physical activity on major cardiovascular risk factors, hemodynamics, sympathetic function, and glucose utilization in man: a controlled study of four levels of activity. Circulation 73:30–40, 1986.
13. Kuipers, H. Variability of Physiological Responses to Exercise. Doctoral Dissertation. Maastricht, The Netherlands: Rijksuniversiteit Limburg, Faculteit der Geneeskunde, 1983.
14. McArdle, W. D., F. I. Katch, and V. L. Katch. Exercise Physiology: Energy, Nutrition, and Human Performance, 2nd Ed. Philadelphia, PA: Lea and Febiger, 1986, pp. 250–251.
15. Nilsson, S. Medical examination of and advice to middle-aged persons starting physical training. Scand. J. Soc. Med. 29:(Suppl.)161–169, 1982.
16. Oja, P., A. Mänttäri, A. Heinonen, et al. Physiological effects of walking and cycling to work. Scand. J. Med. Sci. Sports 1:151–157, 1991.
17. Pate, R. R., M. Pratt, S. N. Blair, et al. Physical activity and public health: a recommendation from the Centers for Disease Control and Prevention and the American College of Sports Medicine. JAMA 273:402–407, 1995.
18. Powell, K. E., P. D. Thompson, C. J. Caspersen, and J. S. Kendrick. Physical activity and the incidence of CHD. Ann. Rev. Public Health 8:253–287, 1987.
19. Shephard, R. J. Exercise Physiology. Toronto: B. C. Dekker, Inc., 1987, p. 129.
20. Siegel, W., G. Blomqvist, and J. H. Mitchell. Effects of a quantitated physical training program on middle-aged sedentary men. Circulation 41:19–29, 1970.
21. Taylor, H. L., E. Buskirk, and A. Henschel. Maximal oxygen intake as an objective measure of cardio-respiratory performance. J. Appl. Physiol. 8:73–80, 1955.
22. Tran, Z. V., A. Weltman, G. V. Glass, and D. P. Mood. The effects of exercise on blood lipids and lipoproteins: a meta-analysis of studies. Med. Sci. Sports Exerc. 15:393–402, 1983.
23. U. S. Department of Health and Human Services. Physical Activity and Health: A Report of the Surgeon General. Atlanta, Georgia: Department of Health and Human Services, Public Health Service, CDC, National Center for Chronic Disease Prevention and Health Promotion, 1996.
24. Wilmore, J. H., J. A. Davis, R. S. O’Brien, P. A. Vodak, G. R. Walder, and E. A. Amsterdam. Physiological alterations consequent to 20-week conditioning programs of bicycling, tennis, and jogging. Med. Sci. Sports Exerc. 12:1–8, 1980.


©2000The American College of Sports Medicine