Age-related neuromuscular adaptation does not affect the mechanical efficiency of lower limbs during walking
Highlights
► Ageing increases the metabolic cost and involves neuromuscular adaptations during locomotion. ► We investigated whether the neuromuscular adaptation increases the mechanical workload. ► Muscle-driven models of locomotion accounting for aged muscle-tendon features were developed. ► Results show that the ageing does not increase the overall mechanical output of locomotion. ► The age-related neuromuscular adaptation is not expected to increase the metabolic consumption.
Introduction
According to recent findings, older individuals increase the workload of proximal muscle groups during walking, in order to compensate for the age-related decline of distal actuators [1], [2]. This strategy basically increases the energetic cost [3], leading to the hypothesis that the age-related neuromuscular adaptation may decrease the mechanical efficiency of locomotion.
Noticeably, although young and elderly people adopt self-selected speeds allowing locomotion to consume as little energy as possible, elderly people use about 15–25% more metabolic energy per kilogram of body mass than younger people, at all speeds [4], [5], [6], [7], [8]. However, neither the sedentary lifestyles [4] nor issues related to locomotion dynamics [5], [6], [7], [8] appears to significantly explain this greater metabolic cost. The literature suggests that greater energy consumption of elderly people could be due to many multifactorial reasons involving greater antagonist muscle contraction, reduced muscle efficiency and a modified relationship between strength and endurance [4], [5], [6], [7], [8].
This study aimed at verifying whether locomotion, in conjunction with age-related modifications of the muscle-tendon actuators, involves greater mechanical energy consumption. To assess this, planar models of muscle-driven locomotion were developed, and related muscle-tendon workloads for young and elderly subjects were estimated. If the aged model consumed more mechanical energy than the young one, it would provide a partial explanation as to the different energetic efficiency between young and elderly people.
Section snippets
Subject and procedure
Ten young and seven elderly healthy subjects were enrolled for the study after providing informed consent. Participants had no evidence or known history of diseases which would have biased experiments, and did not practice competitive sports. Table 1 shows details of the subjects’ anthropometric measurements and age. The protocol was designed in accordance with the Local Ethical Committee.
Subjects walked overground, in a 15 m long room, at self selected speed, while the trajectories of 20
Gait patterns
The groups did not show any significant difference in anthropometric features, spatio-temporal parameters (Table 1), or amplitude of angular excursions (Fig. 1). Young subjects generated an ankle moment (AM1) about 14% greater than older subjects (p = 0.01). Accordingly, older subjects produced less concentric power (about 11%) during push-off than young people (AP2), though this lacked statistical significance (p = 0.17). The other peaks related to kinetic patterns showed no significant
Discussion
This study aimed at verifying whether neuromuscular adaptation due to ageing, in conjunction with age-related modifications of the muscle-tendon actuators, involves greater muscle-tendon workload during walking.
Acknowledgment
We thank Prof. Hugh Herr and his team for valuable and useful suggestions.
Conflict of interest statement
The authors have no conflicts of interest.
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