Joint-level mechanics of the walk-to-run transition in humans

Abstract

Two commonly proposed mechanical explanations for the walk-to-run transition (WRT) include the prevention of muscular over-exertion (effort) and the minimization of peak musculoskeletal loads and thus injury risk. The purpose of this study was to address these hypotheses at a joint level by analysing the effect of speed on discrete lower-limb joint kinetic parameters in humans across a wide range of walking and running speeds including walking above and running below the WRT speed. Joint work, peak instantaneous joint power, and peak joint moments in the sagittal and frontal plane of the ankle, knee and hip from eight participants were collected for 10 walking speeds (30-120% of their WRT) and 10 running speeds (80-170% of their WRT) on a force plate instrumented treadmill. Of the parameters analysed, three satisfied our statistical criteria of the 'effort-load' hypothesis of the WRT. Mechanical parameters that provide an acute signal (peak moment and peak power) were more strongly associated with the gait transition than parameters that reflect the mechanical function across a portion of the stride. We found that both the ankle (peak instantaneous joint power during swing) and hip mechanics (peak instantaneous joint power and peak joint moments in stance) can influence the transition from walking to running in human locomotion and may represent a cascade of mechanical events beginning at the ankle and leading to an unfavourable compensation at the hip. Both the ankle and hip mechanisms may contribute to gait transition by lowering the muscular effort of running compared with walking at the WRT speed. Although few of the examined joint variables satisfied our hypothesis of the WRT, most showed a general marked increase when switching from walking to running across all speeds where both walking and running are possible, highlighting the fundamental differences in the mechanics of walking and running. While not eliciting the WRT per se, these variables may initiate the transition between stable walking and running patterns. Those variables that were invariant of gait were predominantly found in the swing phase.

Modulation of work and power by the human lower-limb joints with increasing steady-state locomotion speed

“…Previous studies have reported that when humans walk at faster steady-state speeds they do so by increasing hip W þ j (Chen et al, 1997;Teixeira-Salmela et al, 2008;Pires et al, 2014) and knee W À j (Winter, 1983a;Chen et al, 1997;Teixeira-Salmela et al, 2008;Pires et al, 2014), which is consistent with our findings (Fig. 1, left column; Fig.…”

“…The equivalent lower-limb joint in humans is the ankle, and we too found ankle W þ j to increase with faster walking. However, in contrast to what was observed for the horse tarsus by Khumsap et al (2001), ankle W À j during stance seems to remain independent of walking speed (Winter, 1983a;Hreljac et al, 2008;Teixeira-Salmela et al, 2008;Pires et al, 2014). It is possible that enhanced utilization of elastic strain energy with faster walking is less of a priority for the human ankle compared with the horse tarsus.…”

“…4, top row). Several other studies have reported similar findings (Winter, 1983a;Hreljac et al, 2008;TeixeiraSalmela et al, 2008;Pires et al, 2014). Such behavior suggests that the probable source of the increased ankle W þ j during stance with faster walking is greater positive work done by muscles rather than enhanced utilization of elastic strain energy.…”

“…Knee joint work during stance increased ( (Hreljac et al, 2008;Pires et al, 2014). For example, when switching from walking to running at the preferred transition speed, Pires et al (2014) found hip W þ j during stance to decrease from 0.14 to 0.04 J kg −1 and ankle W þ j during stance to increase from 0.45 to 0.80 J kg −1 . These data are virtually identical to the results of the present study (Fig.…”

“…While studies have previously explored how a change in steadystate locomotion speed affects lower-limb joint work and power (Winter, 1983a,b;Ae et al, 1987;Chen et al, 1997;Belli et al, 2002;Teixeira-Salmela et al, 2008;Schache et al, 2011;Farris and Sawicki, 2012a;Pires et al, 2014), no single study has included data for the entire spectrum of speeds that humans can attain. Studies have also quantified the relative contribution from each joint towards the total (sum of hip, knee and ankle) amount of work and power produced by the lower limb during locomotion (TeixeiraSalmela et al, 2008;Rubenson et al, 2011;Farris and Sawicki, 2012a;Stearne et al, 2014); however, locomotion speeds exceeding 4.5 m s −1 have not been considered and some inconsistent results have been reported.…”