Elsevier

Gait & Posture

Volume 36, Issue 3, July 2012, Pages 350-355
Gait & Posture

Age-related neuromuscular adaptation does not affect the mechanical efficiency of lower limbs during walking

https://doi.org/10.1016/j.gaitpost.2012.03.031Get rights and content

Abstract

Ageing involves modifications of the locomotor system which is believed to increase energy consumption. 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.

Ten young and 7 elderly healthy subjects were assessed using gait analysis while walking at comparable speed. Planar models of muscle-driven locomotion, accounting for 14 muscles grouped into 9 equivalent actuators, were developed. Muscle-tendon forces were estimated by using the inverse-dynamic based static optimization where cost functions were tuned to capture the different muscle co-activation between groups. Following this, tendon and muscle shortening/lengthening was computed, and muscle-tendon work was estimated and compared between groups.

Results showed that both groups produced comparable muscle mechanical work, though shared differently among muscles. In particular, young subjects showed a greater workload of ankle plantaflexor muscles and older subjects used greater eccentric energy at the knee extensors during stance phase. Moreover, young people used more elastic energy than older people.

These findings suggest that the combination adaptation due to ageing, in conjunction with age-related modifications of the muscle-tendon actuators, do not significantly increase the overall energetic output of locomotion. Moreover, the motor control system appears to be characterised by a degree of adaptation which allows older individuals to achieve biomechanical efficiency comparable to younger subjects.

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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