Age-related changes in gait biomechanics and their impact on the metabolic cost of walking: Report from a National Institute on Aging workshop

Abstract

Changes in old age that contribute to the complex issue of an increased metabolic cost of walking (mass-specific energy cost per unit distance traveled) in older adults appear to center at least in part on changes in gait biomechanics. However, age-related changes in energy metabolism, neuromuscular function and connective tissue properties also likely contribute to this problem, of which the consequences are poor mobility and increased risk of inactivity-related disease and disability. The U.S. National Institute on Aging convened a workshop in September 2021 with an interdisciplinary group of scientists to address the gaps in research related to the mechanisms and consequences of changes in mobility in old age. The goal of the workshop was to identify promising ways to move the field forward toward improving gait performance, decreasing energy cost, and enhancing mobility for older adults. This report summarizes the workshop and brings multidisciplinary insight into the known and potential causes and consequences of age-related changes in gait biomechanics. We highlight how gait mechanics and energy cost change with aging, the potential neuromuscular mechanisms and role of connective tissue in these changes, and cutting-edge interventions and technologies that may be used to measure and improve gait and mobility in older adults. Key gaps in the literature that warrant targeted research in the future are identified and discussed.

Keywords: Fatigue; Mobility; Muscle energetics; Tendon; Wearable technology.

Figure 1.

A cross-sectional analysis from the Baltimore Longitudinal Study of Aging shows that walking speed remains relatively constant throughout adulthood until the 7^th decade, when usual gait speed begins to decline (left). The curvilinear relationship between Usual gait speed and age is shown with a lowess fit curve. Age-related changes in energy expenditure (right) mirror the changes in walking speed, suggesting an association between usual walking speed and age-related changes in energy use during locomotion. The curvilinear relationship between energy expenditure and age is shown with a lowess fit curve. Figure adapted from Schrack et al., 2012 [5].

Figure 2.

With age, both joint motions (kinematics) and causes of motion (kinetics) differ from those of young adults. Compared with younger adults, older adults, even at speeds matched to the young, walk with shorter strides, cover less distance with each step, have greater double support time and have smaller joint ranges of motion, particularly at the ankle and sometimes the hip. At the end of a step, older adults have greater hip joint moments and powers (large arrows), but smaller ankle moments and powers compared to younger adults (small arrows). Figure based on data from Boyer et al., 2017 [10].

Figure 3.

Musculoskeletal modeling is a powerful approach for testing cause-and-effect relations in human movement. In the context of understanding the causes of age-related changes in gait mechanics and energetics, several model inputs (left box) can be adjusted to predict the relative magnitudes of their effects on model outputs (right box). Figure courtesy of B. Umberger.

Figure 4.

Accumulation of intermuscular fat is an important risk factor for slowing gait speed and loss of mobility in aging. Health, Aging and Body Composition Study participants with the greatest decreases in thigh muscle area but increases in thigh intermuscular fat area experienced the greatest declines in gait speed over a 4 year period. 1^st, 2^nd, and 3^rd refer to tertiles. Figure courtesy of B. Nicklas and [59].

Figure 5.

Knee extensor muscle metabolic economy (size-normalized torque or power produced per mM ATP) is lower in vivo during dynamic, isokinetic (right) but not static, isometric (left), contractions in older compared with younger adults. Dynamic contractions were performed at 120 deg∙s⁻¹. Both conditions involved maximal, single-leg contractions on a magnetic resonance compatible ergometer. The potential impact of lower muscle economy on the increased energy cost of walking in aging remains to be determined. Figure adapted from Fitzgerald et al., 2021 [80].

Figure 6.

Achilles tendon stiffness (left) and Young’s Modulus (center) are both lower in older adults with similar physical activity patterns to younger adults. Notably, tendon cross-sectional area is greater in the old (right), which is suggested to be an adaptation to counter reduced material modulus in the tendon. Figure from Lindemann et al., 2020 [99].

Figure 7.

Measurement of everyday movement can include not only A) how much an individual moves (e.g., step counts, activity intensity, locations) Figure from Lonini et al., 2021 IEEE TNSRE [136], but also B) the pattern of an individual’s movements (e.g., kinematics, muscle coordination) Figure from Slaughter et al., 2020, Sensors [137], and C) the effects of movement on tissue strain patterns Figure from Harper et al., (2020) Sensors [108]. Everyday motions such as walking or chair rising are typically repeated multiple times each day, reducing the barriers to their measurement. In contrast, events such as falls and slips are unique and present a far greater challenge for their identification and study. D) Exoskeleton devices that can switch between assistance and resistance modes may enhance mobility while also acting as a therapeutic intervention to help maintain muscle and tendon function. Figure from Yang et al., 2022 Wearable Technologies.[131]