engleski

Comparison of VO2 kinetics in walking and running at the ‘energetically optimal’ gait transition speed

Background: The metabolic costs for walking and running intersect at a speed (termed the energetically optimal transition speed, EOTS) that is significantly higher than the preferred gait transition speed (Hreljac, 1993 ; Brisswalter and Mottet, 1996 ; Tseh et al., 2002). None of the studies to date, considered the influence of a slow component of VO2 kinetics for walking and running in the determination of EOTS. Purpose: The aim of this study was to examine VO2 kinetics during walking and running at the energetically optimal gait transition speed. Methods: Twenty-two physical education students (21.4±2.4 y, 182±7 cm), performed three incremental treadmill tests for determination of EOTS, the aerobic gas exchange thresholds (for walking, ATw, and running, ATr) and VO2max. Thereafter, they completed two squarewave 30-minute walking (W30) and running (R30) tests at the EOTS ; VO2 was determined breath-by-breath, and computorised non-linear regression techniques were used to describe either a mono-, bi- exponential or exponential+linear VO2 response. ANOVA for repeated measurements was used to test for differences between walking and running parameters. Results: The VO2 and speed of locomotion at the EOTS were 32.8 ml/kg and 8.2±0.2 km/h, respectively. Four subjects had to discontinue the W30 test before completion, due to fatigue and pain in the shins. All W30 tests were distributed within the heavy and very heavy intensity domains, while all R30 tests were distributed within the moderate and heavy intensity domains. The time constant for the fast VO2 component (tau1) in the 30-minute tests was significantly smaller for running than for walking (29.0±9.1 s vs 33.7±9.8 s, p<0.01), while the amplitudes of the primary VO2 response (A1) did not differ (18.1±1.9 vs 17.9±1.9 ml O2/min/kg). The VO2 slow component was greater for W30 than R30 (275±220 ml/min vs 146±104 ml/min, p<0.05) and more often present (22/22 vs 19/22). A steady-state VO2 was reached by 12/22 subjects in the W30, and by 18/22 in the R30 test. The aerobic energy cost derived from VO2 centered at the 3rd minute of exercise (C3) was significantly lower than the one derived from the steady-state VO2 (Css) in both, W30 (187±17 vs 208±23 ml O2/kg/km) and and R30 (188 vs 199±17 ml O2/kg/km) (p< 0.05). Only in the R30 test, C3 explained effectively the variability of Css (r2 = 0.94 and 0.50, for R30 and W30, respectively). Conclusions: Current methods used for EOTS determination are inadequate, as the slow component of the VO2 kinetics has to be considered. The VO2 kinetics (tau1) are significantly faster in running compared to walking at the energetically optimal gait transition speed in young, healthy subjects. Pain located in the shin region may cause an increased perception of local effort, and cause exhaustion in less than 30 min of walking at the EOTS. References: 1. Barstow TJ, Mole’ PA (1991). Linear and nonlinear characteristics of oxygen uptake kinetics during heavy exercise. J Appl Physiol 71(3):2099-106

walking; running; gait transition speed; energy expenditure

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