Energy expenditure and cardiorespiratory responses at the transition between walking and running

AbstractWe investigated whether the spontaneous transition between walking and running during moving with increasing speed corresponds to the speed at which walking becomes less economical than running. Seven active male subjects [mean age, 23.7 (SEM 0.7) years, mean maximal oxygen uptake ( $$\dot V{\text{O}}_{2\max } $$ ), 57.5 (SEM 3.3) ml·kg −1·min −1, mean ventilatory threshold (VTh), 37.5 (SEM 3) ml·kg −1 ·min −1] participated in this study. Each subject performed four exercise tests separated by 1-week intervals: test 1, $$\dot V{\text{O}}_{2\max } $$ and VTh were determined; test 2, the speed at which the transition between walking and running spontaneously occurs (ST) during increasing speed (increases of 0.5 km·h −1 every 4 min from 5 km·h −1) was determined; test 3, the subjects were constrained to walk for 4 min at ST, at ST ± 0.5 km·h −1 and at ST ± 1 km·h −1; and test 4, the subjects were constrained to run for 4 min at ST, at ST±0.5 km·-h −1 and at ST±1 km·h −1. During exercise, oxygen uptake ( $$\dot V{\text{O}}_2 $$ ), heart rate (HR), ventilation ( $$\dot V_{\text{E}} $$ ), ventilatory equivalents for oxygen and carbon dioxide (% MathType!MTEF!2!1!+-% feaafiart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9% vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x% fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGabmOvayaaca% WaaSbaaSqaaiaabweaaeqaaOGaai4laiqadAfagaGaamaaBaaaleaa% caqGYaaabeaakiaacYcacaqGGaGaaeiiaiqadAfagaGaamaaBaaale% aacaqGfbaabeaakiaac+caceWGwbGbaiaacaqGdbGaae4tamaaBaaa% leaacaaIYaaabeaaaaa!4240!\[\dot V_{\text{E}} /\dot V_{\text{2}} ,{\text{ }}\dot V_{\text{E}} /\dot V{\text{CO}}_2 \]), respiratory exchange ratio (R), stride length (SL), and stride frequency (SF) were measured. The results showed that: ST occurred at 2.16 (SEM 0.04) m·s −1; $$\dot V{\text{O}}_2 $$ , HR and speed at ST were significantly lower than the values measured at VTh (P< 0.001, P< 0.001 and P< 0.05, respectively); $$\dot V{\text{O}}_2 $$ changed significantly with speed (P< 0.001) but was greater during running than walking below ST (ST minus 1 km·h −1, P< 0.001; ST minus 0.5 km·h −1, P< 0.05) with the converse above ST (ST.plus 1 km·h −1, P<0.05), whereas at ST the values of $$\dot V{\text{O}}_2 $$ were very close [23.9 (SEM 1.1) vs 23.7 (SEM 0.8) ml·kg −1 · min −1 not significant, respectively, for walking and running]; SL was significantly greater during walking than running (P<0.001) and SF lower (P<0.001); and HR and $$\dot V_{\text{E}} $$ were significantly greater during running than walking below ST (ST minus 1 km·h −1, P<0.01; ST minus 0.5 km·h −1, P{<0.05) with the converse above ST (ST plus 1 km·h −1, P·< 0.05), whereas no difference appeared for $$\dot V_{\text{E}} /\dot V{\text{O}}_{\text{2}} $$ and R between the two types of locomotion. We concluded from this study that ST corresponded to the speed at which the energy expenditure of running became lower than the energy expenditure of walking but that the mechanism of the link needed further investigation.