Elsevier

Journal of Biomechanics

Volume 47, Issue 3, 7 February 2014, Pages 667-674
Journal of Biomechanics

Muscle contributions to recovery from forward loss of balance by stepping

https://doi.org/10.1016/j.jbiomech.2013.11.047Get rights and content

Abstract

The purpose of this study was to determine the muscular contributions to the stepping phase of recovery from forward loss of balance in 5 young and 5 older adults that were able to recover balance in a single step, and 5 older adults that required multiple steps. Forward loss of balance was achieved by releasing participants from a static forward lean angle. All participants were instructed to attempt to recover balance by taking a rapid single step. A scalable anatomical model consisting of 36 degrees-of-freedom was used to compute kinematics and joint moments from motion capture and force plate data. Forces for 94 muscle actuators were computed using static optimisation and induced acceleration analysis was used to compute individual muscle contributions to net lumbar spine joint, and stepping side hip joint and knee joint accelerations during recovery. Older adults that required multiple recovery steps used a significantly shorter and faster initial recovery step and adopted significantly more trunk flexion throughout recovery compared to the older single steppers. Older multiple steppers also produced significantly more force in the stance side hamstrings, which resulted in significantly higher hamstring induced flexion accelerations at the lumbar spine and extension accelerations at the hip. However since the net joint lumbar spine and hip accelerations remained similar between older multiple steppers and older single steppers, we suggest that the recovery strategy adopted by older multiple steppers was less efficient as well as less effective than for older single steppers.

Introduction

While both young and older adults are exposed to potential loss of balance in activities of daily living, older adults are more likely to fall because they have a markedly reduced capacity to recover from loss of balance. For example studies of protective stepping behaviours in response to postural perturbations consistently indicate that older adults are less able to recover balance from the same magnitude of postural perturbation than younger adults (Carty et al., 2011, Karamanidis et al., 2008, Pijnappels et al., 2005b) and that the maximum perturbation magnitude from which older adults can recover balance is lower than for young adults (Carty et al., 2011, Thelen et al., 1997). The practical significance of balance recovery behaviour is further supported by prospective studies which demonstrate that the ability to recover from loss of balance with a single rapid step compared to multiple steps predicts a lower incidence of real world falls in older adults (Hilliard et al., 2008, Mille et al., 2013).

Commonly reported neuro-mechanical mechanisms underlying age-related deficits in recovery from loss of balance by stepping include lower extremity muscle weakness (Carty et al., 2012a), slower reaction and step execution times (Owings et al., 2001, Schillings et al., 2005), reduced muscle activation (Cronin et al., 2013, Pijnappels et al., 2005a) and joint power in the stepping limb (Carty et al., 2012b), inadequate step length (Karamanidis et al., 2008, Schillings et al., 2005), and less effective use of the support limb (Pijnappels et al., 2005b) and trunk (Barrett et al., 2012, Grabiner et al., 2008, Owings et al., 2001) for controlling forward motion of the centre of mass following forward loss of balance. The ability to recover from forward loss of balance has also been shown to be primarily governed by factors associated with the stepping phase of the recovery response, rather than those associated with the period following touchdown of the stepping leg (Arampatzis et al., 2008, Carty et al., 2011). Furthermore, step length and trunk flexion angle and angular velocity were reported to be significantly correlated with whole body dynamic stability at the instant of touchdown of the stepping leg (Carty et al., 2011), and adaptations in the length and speed of the recovery step and enhanced control of upper body motion (Barrett et al., 2012, Bierbaum et al., 2010, Carty et al., 2012c) have been identified as mechanisms underlying improved stability following repeated exposure to forward loss of balance.

While the aforementioned studies have revealed important insights into spatial–temporal, kinematic and joint level kinetic factors affecting successful versus unsuccessful recovery from forward loss of balance, the contribution of individual muscle forces to balance recovery by stepping remain unclear. Muscle-driven dynamics based simulations may be used to reveal how muscles are coordinated during balance recovery, and to help explain differences in muscle coordination between successful and unsuccessful recovery. Because the mechanical effect of a muscle force acting in a multi-joint system is not restricted to the segment/s to which the muscle attaches (Zajac et al., 2002), the ability of older adults to effectively control the amplitude and rate of trunk flexion during balance recovery by stepping could impact upon the accelerations induced in the joints of the lower extremity. Evaluation of muscle forces may also provide insight into the muscular demands of balance recovery and help identify how close muscle groups may be working relative to their force generating limits.

A commonly used criterion to evaluate balance recovery behaviour is whether an individual is able to recover from loss of balance with a single step, or requires multiple steps. The ability to recover from loss of balance using a single recovery step is of practical significance when space available to recover balance may be constrained, and in the case of forward loss of balance has been shown to depend on the ability to rapidly generate a sufficiently large step, primarily through recruitment of the hip flexor and knee extensor muscles, while simultaneously retaining adequate control of trunk motion (Arampatzis et al., 2008, Carty et al., 2011, Carty et al., 2012b). It therefore follows that assessment of muscle contributions to lumbar spine, hip and knee joint accelerations during the rapid stepping response may provide insights into the factors that distinguish the ability to recover balance with a single step response compared to a multiple step response. The purpose of this study was therefore to determine the muscular contributions to the stepping phase of recovery from forward loss of balance in a group of young adults, and older adults that were able to recover balance in a single step, and a group of older adults that required multiple steps. It was hypothesised that older adults that required multiple compared to single recovery steps would exhibit altered patterns of muscle force production, which in turn would adversely influence the accelerations induced at the hip and knee joints of the stepping leg during the recovery step.

Section snippets

Methods

Participants consisted of a random sub-sample of 10 male older adults (age: 70±3.9 years, height: 1.71±0.10 m, mass: 80.6±10 kg) and 5 male young adults (age: 34±2.6 years, height: 1.83±0.9 m, mass: 83.9±8.8 kg) from a previous study that contained 31 older adult and 16 younger adult participants (Carty et al., 2011). All participants had normal or corrected to normal vision. Individuals that reported neurological, cognitive, metabolic or musculoskeletal impairment were excluded. Ethics approval

Results

OMS used a significantly smaller mean step length (F=7.61, p=0.03, d=0.30) and step time (F=6.21, p=0.05, d=1.34) relative to OSS and also adopted a significantly smaller trunk segment angle measured from the right hand horizontal at toe off (F=5.91, p=0.05, d=1.57), mid swing (F=11.39, p=0.02, d=1.90), and foot contact (F=9.82, p=0.02, d=1.52) compared to OSS (see Fig. 1 for representative kinematic data and Table 1 for group summary data). OMS also tended to exert larger mean peak

Discussion

We have described the muscular contributions to the step response recovery from forward loss of balance in a group of young and older adults that were able to recover from forward loss of balance with a single rapid step, and a group of older adults that required multiple steps. We initially demonstrated that the accelerations of the lumbar spine joint and the hip joint and knee joint in the stepping leg during recovery arise due to the complex interaction of trunk muscles together with muscles

Conclusion

This study demonstrated that the trunk extensor and stance limb muscles play an influential role in determining the angular acceleration experienced by the stepping leg joints during recovery from forward loss of balance. The stance leg hip abductors generated the largest relative forces of all muscles and may be a limiting factor in balance recovery. Poor control of trunk motion in OMS was shown to adversely affect the muscular control of the stepping leg. The mechanism of this effect is an

Conflict of Interest

The authors declare that there are no conflicting interests.

Acknowledgement

This work was supported by the Australian National Health and Medical Research Council (Project grant 536508).

The simulations in this study will be made freely available at simtk.org following acceptance of this manuscript.

References (33)

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