The mechanics and energetics of human walking and running: a joint level perspective

Abstract

Humans walk and run at a range of speeds. While steady locomotion at a given speed requires no net mechanical work, moving faster does demand both more positive and negative mechanical work per stride. Is this increased demand met by increasing power output at all lower limb joints or just some of them? Does running rely on different joints for power output than walking? How does this contribute to the metabolic cost of locomotion? This study examined the effects of walking and running speed on lower limb joint mechanics and metabolic cost of transport in humans. Kinematic and kinetic data for 10 participants were collected for a range of walking (0.75, 1.25, 1.75, 2.0 m s(-1)) and running (2.0, 2.25, 2.75, 3.25 m s(-1)) speeds. Net metabolic power was measured by indirect calorimetry. Within each gait, there was no difference in the proportion of power contributed by each joint (hip, knee, ankle) to total power across speeds. Changing from walking to running resulted in a significant (p = 0.02) shift in power production from the hip to the ankle which may explain the higher efficiency of running at speeds above 2.0 m s(-1) and shed light on a potential mechanism behind the walk-run transition.

Figure 1.

Example plots of knee (solid line) and ankle (dashed line) joint powers for a sample stride of walking at 1.25 m s⁻¹. Dark grey areas are periods when the joint is doing positive work and light grey indicates when negative work is being done. Individual periods of positive and negative work are labelled and or and for the ankle and knee, respectively. Work done during each of these periods was calculated separately by integration using the trapezium rule. Positive and negative work done at each joint per stride was calculated as the sum of individual work values, e.g. .

Figure 2.

(a,d) Group mean instantaneous ankle, (b,e) knee and (c,f) hip joint powers plotted over one complete stride for (a–c) walking and (d–f) running at each speed. Dashed lines are the slowest speed for each gait (walk = 0.75 m s⁻¹, run = 2.0 m s⁻¹); then, in ascending order, dotted lines (1.25 m s⁻¹ and 2.25 m s⁻¹); solid grey lines (1.75 m s⁻¹ and 2.75 m s⁻¹); solid black lines (2.0 m s⁻¹ and 3.25 m s⁻¹).

Figure 3.

Group mean (±s.d.) average positive and negative power (W kg⁻¹) produced at the (a) hip, (b) knee, (c) ankle and (d) total limb (sum of the ankle, knee and hip) for all walking (open circles/diamonds) and running (filled circles/diamonds) speeds.

Figure 4.

Pie charts showing the percentage of total average positive power contributed at the hip (white), knee (grey) and ankle (black) joints. The lines marked with an asterisk indicate between which conditions the ankle and hip contributions were significantly different (p < 0.05). The total area of each pie represents the total average positive power relative to the other conditions. (a) Walking; (b) running.

Figure 5.

Group average (±s.d.). (a) Metabolic cost of transport and (b) efficiency of positive work for all walking (open circles) and running (filled circles) speeds. Data points were fitted with either quadratic (walking) or linear (running) polynomials, the R² values for which are reported in §3.2.