It is typically assumed that basic features of human gait are determined by purely biomechanical factors. In two experiments, we test whether gait transition speed and preferred walking speed are also influenced by visual information about the speed of self-motion. The visual flow during treadmill locomotion was manipulated to be slower than, matched to, or faster than the physical gait speed (visual gains of 0.5, 1.0, 2.0). Higher flow rates elicit significantly lower transition speeds for both the Walk-Run and Run-Walk transition, as expected. Similarly, higher flow rates elicit significantly lower preferred walking speeds. These results suggest that visual information becomes calibrated to mechanical or energetic aspects of gait and contributes to the control of locomotor behavior.

/pdf/visual-flow-influences-gait-transition-speed-and-preferred-3wiznuyn9n.pdf

Visual flow influences gait transition speed and preferred walking speed

We investigated the effect of reduced gravity on the human walk-run gait transition speed and interpreted the results using an inverted-pendulum mechanical model. We simulated reduced gravity using an apparatus that applied a nearly constant upward force at the center of mass, and the subjects walked and ran on a motorized treadmill. In the inverted pendulum model for walking, gravity provides the centripetal force needed to keep the pendulum in contact with the ground. The ratio of the centripetal and gravitational forces (mv2/L)/(mg) reduces to the dimensionless Froude number (v2/gL). Applying this model to a walking human, m is body mass, v is forward velocity, L is leg length and g is gravity. In normal gravity, humans and other bipeds with different leg lengths all choose to switch from a walk to a run at different absolute speeds but at approximately the same Froude number (0.5). We found that, at lower levels of gravity, the walk-run transition occurred at progressively slower absolute speeds but at approximately the same Froude number. This supports the hypothesis that the walk-run transition is triggered by the dynamics of an inverted-pendulum system.

/pdf/effect-of-reduced-gravity-on-the-preferred-walk-run-2r5kfs03ok.pdf

Effect of reduced gravity on the preferred walk-run transition speed

The mechanisms that govern the voluntary transition from walking to running as walking speed increases in human gait are not well understood. The objective of this study was to examine the hypothesis that plantar flexor muscle force production is greatly impaired at the preferred transition speed (PTS) due to intrinsic muscle properties and, thus, serves as a determinant for the walk-to-run transition. The plantar flexors have been shown to be important contributors to satisfying the mechanical energetic demands of walking and are the primary contributors to the observed ground reaction forces (GRFs) during the propulsion phase. Thus, if the plantar flexor force production begins to diminish near the PTS despite an increase in muscle activation, then a corresponding decrease in the GRFs during the propulsion phase would be expected. This expectation was supported. Both the peak anterior/posterior and vertical GRFs decreased during the propulsion phase at walking speeds near the PTS. A similar decrease was not observed during the braking phase. Further analysis using forward dynamics simulations of walking at increasing speeds and running at the PTS revealed that all lower extremity muscle forces increased with walking speed, except the ankle plantar flexors. Despite an increase in muscle activation with walking speed, the gastrocnemius muscle force decreased with increasing speed, and the soleus force decreased for walking speeds exceeding 80% PTS. These decreases in force production were attributed to the intrinsic force-length-velocity properties of muscle. In addition, the running simulation analysis revealed that the plantar flexor forces nearly doubled for similar activation levels when the gait switched to a run at the PTS due to improved contractile conditions. These results suggest the plantar flexors may serve as an important determinant for the walk-to-run transition and highlight the important role intrinsic muscle properties play in determining the specific neuromotor strategies used in human locomotion.

/pdf/ankle-plantar-flexor-force-production-is-an-important-2omceyg016.pdf

Ankle plantar flexor force production is an important determinant of the preferred walk-to-run transition speed

SUMMARY There has been no consistent explanation as to why humans prefer changing their gait from walking to running and from running to walking at increasing and decreasing speeds, respectively. This study examined muscle activation as a possible determinant of these gait transitions. Seven subjects walked and ran on a motor-driven treadmill for 40s at speeds of 55, 70, 85, 100, 115, 130 and 145% of the preferred transition speed. The movements of subjects were videotaped, and surface electromyographic activity was recorded from seven major leg muscles. Resultant moments at the leg joints during the swing phase were calculated. During the swing phase of locomotion at preferred running speeds (115, 130, 145%), swing-related activation of the ankle, knee and hip flexors and peaks of flexion moments were typically lower ( P P

Swing- and support-related muscle actions differentially trigger human walk–run and run–walk transitions

We studied nine adult horses spanning an eightfold range in body mass (M(b)) (90-720 kg) and a twofold range in leg length (L) (0.7-1.4 m). We measured the horses' walk-trot transition speeds using step-wise speed increments as they locomoted on a motorized treadmill. We then measured their rates of oxygen consumption over a wide range of walking and trotting speeds. We interpreted the transition speed results using a simple inverted-pendulum model of walking in which gravity provides the centripetal force necessary to keep the leg in contact with the ground. By studying a large size range of horses, we were naturally able to vary the absolute walking speed that would produce the same ratio of centripetal to gravitational forces. This ratio, (M(b)v2/L)/(M(b)g), reduces to the dimensionless Froude number (v2/gL), where v is forward speed, L is leg length and g is gravitational acceleration. We found that the absolute walk-trot transition speed increased with size from 1.6 to 2.3 m s(-1), but it occurred at nearly the same Froude number (0.35). In addition, horses spontaneously switched between gaits in a narrow range of speeds that corresponded to the metabolically optimal transition speed. These results support the hypotheses that the walk-trot transition is triggered by inverted-pendulum dynamics and occurs at the speed that maximizes metabolic economy.

Biomechanical and energetic determinants of the walk-trot transition in horses.

We 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.

Durand M

Papers

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