Stance and swing phase costs in human walking

Abstract

Leg swing in human walking has historically been viewed as a passive motion with little metabolic cost. Recent estimates of leg swing costs are equivocal, covering a range from 10 to 33 per cent of the net cost of walking. There has also been a debate as to whether the periods of double-limb support during the stance phase dominate the cost of walking. Part of this uncertainty is because of our inability to measure metabolic energy consumption in individual muscles during locomotion. Therefore, the purpose of this study was to investigate the metabolic cost of walking using a modelling approach that allowed instantaneous energy consumption rates in individual muscles to be estimated over the full gait cycle. At a typical walking speed and stride rate, leg swing represented 29 per cent of the total muscular cost. During the stance phase, the double-limb and single-limb support periods accounted for 27 and 44 per cent of the total cost, respectively. Performing step-to-step transitions, which encompasses more than just the double-support periods, represented 37 per cent of the total cost of walking. Increasing stride rate at a constant speed led to greater double-limb support costs, lower swing phase costs and no change in single-limb support costs. Together, these results provide unique insight as to how metabolic energy is expended over the human gait cycle.

Figure 1.

Still-frame sequences for the simulation model and subjects walking at 1.3 m s⁻¹ at the preferred stride rate (54 stride min⁻¹). DLS, double-limb support; SLS, single-limb support; RHS, right heel strike; LTO, left toe off; LHS, left heel strike; and RTO, right toe off. The stance phase encompassed the two DLS periods and the SLS period. Animations of the model walking at all three stride rates are available in the electronic supplementary material.

Figure 2.

Muscle activation patterns for the walking simulation model at all three stride rates. Horizontal bars indicate on–off timing determined from electromyography data (Knutson & Soderberg 1995). In general, there was good temporal agreement between the bursts of muscle activation and the experimental data at the preferred stride rate (solid line). Most muscles showed some effects across stride rate in timing, amplitude or both. The transitions between stance and swing phases are shown by vertical lines that match the corresponding data line (solid (Pref SR), dashed (−20% SR) or dotted (+20% SR)) for each stride rate.

Figure 3.

Example muscle model outputs for a single muscle (medial hamstrings). Variables shown are (a) contractile element force, (b) contractile element length, (c) contractile element (CE) and musculotendon (MT) mechanical powers, (d) thermal power (i.e. rate of heat production) and (e) muscle metabolic power. CE mechanical and thermal powers were combined to determine metabolic power. Metabolic power was integrated with respect to time over various intervals of the gait cycle to compute muscle energy consumption. (c) Solid line, CE; dashed line, MT.

Figure 4.

(a) Average gross (shaded bars) and net (walking minus resting, open bars) metabolic power in the subjects across stride rates. Error bars indicate the range of experimental values. (b) Average whole body (shaded bars) and summed leg muscle (open bars) metabolic power in the simulation model across stride rates. The general trends in the data were the same between subjects (a) and the model (b). Metabolic power was lowest at the preferred stride rate (Pref SR) and highest at the low (−20% SR) stride rate. However, leg muscle energy expenditure was not as sensitive to stride rate as net metabolic power in the subjects.

Figure 5.

(a) Percentage of total leg muscle energy expenditure consumed during the stance phase (shaded bars) and swing phase (open bars) across stride rates. (b) Same data as in panel (a), but with stance phase energy consumption partitioned into double-limb support (shaded bars) and single-limb support periods (black bars). The shaded and black bars in panel (b) for each stride rate sum to the shaded bar in panel (a) for the corresponding stride rate. Open bars indicate swing phase.

Figure 6.

Instantaneous metabolic power for all of the muscles in a single limb across the gait cycle at the preferred stride rate. Heel strike of the ipsilateral limb corresponds to 0 and 100 per cent of the gait cycle. Therefore, during the first double-limb support period shown in this figure, the limb was in the front of the body centre of mass, while for the second double-limb support period, the limb was behind the body centre of mass (see also figure 1). AE (solid line, ankle extensors) is the sum of gastrocnemius, soleus and other plantarflexors; KE (dashed line, knee extensors) is the sum of vasti and rectus femoris; HE (dotted line, hip extensors) is the sum of glutei, medial hamstrings and biceps femoris longus; FL (dash-dotted line, flexors) is the sum of iliacus, psoas, biceps femoris brevis and dorsiflexors; and total (grey line) is the sum of all muscles.