Influence of muscle‐belly and tendon gearing on the energy cost of human walking

Abstract

This study combines metabolic and kinematic measurements at the whole‐body level, with EMG and ultrasound measurements to investigate the influence of muscle‐tendon mechanical behavior on the energy cost (Cnet) of walking (from 2 to 8 km·h−1). Belly gearing (Gb = Δmuscle‐belly length/Δfascicles length) and tendon gearing (Gt = ∆muscle‐tendon unit length/∆muscle‐belly length) of vastus lateralis (VL) and gastrocnemius medialis (GM) were calculated based on ultrasound data. Pendular energy recovery (%R) was calculated based on kinematic data, whereas the cumulative activity per distance travelled (CMAPD) was calculated for the VL, GM, tibialis anterior, and biceps femoris as the ratio between their EMG activity and walking speed. Finally, total CAMPD (CMAPDTOT) was calculated as the sum of the CMAPD of all the investigate muscles. Cnet and CMAPDTOT showed a U‐shaped behavior with a minimum at 4.2 and 4.1 km·h−1, respectively; while %R, VL, and GM belly gearing showed an opposite trend, reaching a maximum (60% ± 5%, 1.1 ± 0.1 and 1.5 ± 0.1, respectively), between 4.7 and 5 km·h−1. Gt was unaffected by speed in GM (3.5 ± 0.1) and decreased as a function of it in VL. A multiple stepwise linear regression indicated that %R has the greatest influence on Cnet, followed by CMAPDTOT and GM belly gearing. The role of Gb on Cnet could be attributed to its role in determining muscle work: when Gb increases, fascicles shortening decreases compared with that of the muscle‐belly, thereby reducing the energy cost of contraction.

Achilles Tendon Mechanical Behavior and Ankle Joint Function at the Walk-to-Run Transition

“…We also observed differences in terms of strut function between tasks as a function of speed, which suggests that during walking at speeds > 5.5 km/h the behaviour of the muscle fascicles could be impaired compared to running. This speculation is supported by a recent study of Monte et al [ 8 ], who observed that the operating length of the GM muscle fascicle is, indeed, impaired at high walking speeds.…”

“…Sasaki and Neptune [ 6 ], in their modelling study, revealed that running below the transition speed required more muscle fiber work than walking, and, inversely, walking above the transition speed required more muscle fiber work than running. Furthermore, as recently reported by Monte et al [ 8 ], the neuromuscular system is not able to promote “sustainable” GM fascicle mechanics at walking speeds > 7 km/h. This mechanical disadvantage increases the EMG activity required to sustain muscle contraction, increasing the metabolic energy expenditure at the whole-body level.…”

“…At 7.5 and 8.5 km/h, the energy-saving behaviour of the Achilles tendon is, thus, impaired in walking compared to running; this impairment is expected to be associated with an increase in the mechanical demands of the muscle’s fascicles, leading, ultimately, to an increase in the metabolic demands of walking [ 8 ]. Sasaki and Neptune [ 6 ], in their modelling study, revealed that running below the transition speed required more muscle fiber work than walking, and, inversely, walking above the transition speed required more muscle fiber work than running.…”

“…From a physiological point of view, gait transition is triggered by metabolic energy expenditure at the whole-body level [ 4 ]: above a certain walking speed it is metabolically cheaper to run than to walk. Furthermore, it was observed that spontaneous transition speed is associated with a decrease in plantar flexor muscle fibres’ ability to produce force [ 5 , 6 , 7 ] and a reduction of the gastrocnemius medialis force contraction capacity [ 8 ]. This body of evidence reinforces the idea that the determinants of the walk-to-run transition could be related to mechanical alteration at the ankle level in terms of the contractile capacity of plantar-flexor muscles.…”

Muscle shape changes in Parkinson's disease impair function during rapid contractions

“…In healthy subjects, belly gearing was found to play an important role during rapid movements since it is positively correlated with mechanical power production 18 as well as with the capability to increase force rapidly 15 . More recently, it was observed that belly gearing could play a role in determining the metabolic energy demands during walking at increasing speed 39 and this could partially explain the increase in the metabolic demands during walking in PD patients compared to controls.…”