Elsevier

Journal of Biomechanics

Volume 42, Issue 12, 25 August 2009, Pages 1834-1839
Journal of Biomechanics

Age-related mechanical work expenditure during normal walking: The Baltimore Longitudinal Study of Aging

https://doi.org/10.1016/j.jbiomech.2009.05.037Get rights and content

Abstract

The aim of this cross-sectional study was to delineate age-associated kinematic and kinetic gait patterns of normal walking, and to test the hypothesis that older adults exhibit gait patterns that reduce generative mechanical work expenditures (MWEs). We studied 52 adult Baltimore Longitudinal Study of Aging participants (means age 72±9, from 60 to 92 years) who could walk 4 m unaided. Three-dimensional kinematic and kinetic parameters assessed during rotation-defined gait periods were used to estimate MWEs for the rotation of lower extremities about the medial–lateral (ML) and anterior–posterior (AP) axes of proximal joints, which represent MWEs in the AP and ML sides, respectively. Relationships between gait parameters and age were examined using regression analysis with adjustments for walking speed, sex, height, and weight. Older age was associated with slower self-selected walking speed (p<0.001), shorter stride length (p<0.001), and greater propensity of landing flat-footed (p=0.003). With older age, hip generative MWE for thigh rotation was lower about the AP axis (hip abduction and adduction) during stance (p=0.010) and higher about the ML axis (hip extension and flexion) during late stance (p<0.001). Knee absorptive MWE for shank rotation about the AP axis (knee abduction and adduction) during early stance was also lower with older age (p<0.003). These age-related gait patterns may represent a compensatory effort to maintain balance and may also reflect mobility limitations.

Introduction

Older adults exhibit typical changes in gait patterns that are generally considered compensatory to the loss of motor function that occurs with aging (Polcyn et al., 1998; Lord et al., 1996). Understanding adaptation strategies employed by older adults is important for the development of interventions capable of correcting and preventing age-associated mobility limitations.

Self-preferred walking speed declines with age and is a well-accepted marker of overall mobility performance (Teixeira-Salmela et al., 2008; Alexander, 1996; Kerrigan et al., 2001; Dingwell and Marin, 2006). Walking slower may also be thought of as a compensatory strategy aimed at increasing stability, avoiding falls or reducing the energetic cost of mobility (Pavol et al., 1999; Duff-Raffaele et al., 1996). However, whether the presence of sub-clinical impairments that typically affect older persons stimulates the emergence of less energetically costly walking patterns has not been fully investigated.

Different approaches have been used to study walking energetics. The simple analysis of lower extremity joint moments provides a rough approximation of the amount of muscle activity, but does not assess joint direction or speed. By studying mechanical joint moments and angular velocities together, we can estimate the contribution of muscle group activations to joint acceleration and deceleration during gait (Teixeira-Salmela et al., 2008; Chen et al., 1997; Winter, 1983). Total generated mechanical work during acceleration and deceleration has been reported to predict gait disorders (Winter et al., 1990; Siegel et al., 2004; McGibbon et al., 2001; Teixeira-Salmela et al., 2001). To study mechanical work during normal walking, Winter et al. (1990) divided the gait cycle into periods whose boundaries were identified as the times of peak power. The present study identifies the gait phase based on rotations of lower extremities about the medial–lateral (ML) axes of proximal joints to assess gait phases that reflect well identifiable stages during walking. Dominant muscle group activities are related with the rotations of lower extremities about the ML axes of proximal joints (extension and flexion) during walking. Also, the significant age effects on the rotations of lower extremities about the AP axes of proximal joints (abduction and adduction) were previously reported (Dean et al., 2007; Siegel et al., 2004; McGibbon et al., 2001; Teixeira-Salmela et al., 2001). To understand walking mechanisms referred to as mechanical energy expenditures (MWEs), assessing kinetic gait parameters for the rotations about the ML and AP axes of proximal joints for the lower extremities are necessary. For the specified gait stages, we calculated MWEs for the rotations of lower extremities about the ML and AP axes of proximal joints. These MWEs can be interpreted as muscle group activities of lower extremities in the AP and ML sides during operationalized gait periods. Focus on rotation-based gait phases may be more informative than estimating energy expenditure over the entire gait cycle.

Using data collected in joint kinematically-defined phases of gait during normal walking in a cohort of older adults, we examined the hypothesis that older age is associated with gait patterns that employ less generative MWE.

Section snippets

Study design

The Baltimore Longitudinal Study of Aging (BLSA) is a longitudinal cohort study conducted by the Intramural Research Program of the National Institutes of Health, National Institute on Aging. This study was approved by the Medstar Research Institution Review Board, and was conducted with informed consent obtained from all participants. The present report is based on cross-sectional data that were collected between January and April 2008. During regular study visits, all BLSA participants

Results

The descriptive characteristics of the 52 subjects (19 women and 33 men) that completed the gait test are summarized in Table 1. Participants were of the age 60–92 years, with an average body mass index of 26.1 (±3.1 kg/m2). As summarized in Table 2, older age was significantly associated with slower walking speed, shorter stride length, and shorter stance time (p<0.001, for all), but not with stride width. Of the gait phase parameters, older age was associated with a higher percentage of the

Discussion

Understanding adaptation strategies in response to reduced energy availability which are aimed to increase safety is a prerequisite to the development of intervention strategies of mobility–disability prevention in older persons. In this cross-sectional study we observed specific kinematic and kinetic gait patterns associated with older age probably due to declining generative MWE for the rotation about the AP axis of proximal joints for the lower extremities.

Consistent with previous

Conflict of interest

All the authors declare that no financial or personal relationships were conducted with other people or organizations that could inappropriately influence or bias this work.

Acknowledments

This research was supported entirely by the Intramural Research Program of the NIH, National Institute on Aging. Data for these analyses were obtained from the Baltimore Longitudinal Study of Aging, a study performed by the National Institute on Aging.

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