Balance on one leg may be the best indicator of neuromuscular aging, new study suggests

By Hugo Francisco de SouzaReviewed by Lily Ramsey, LLMOct 29 2024

Mayo Clinic study identifies unipedal balance as key measure for age-related neuromuscular decline.

Study: Age-related changes in gait, balance, and strength parameters: A cross-sectional study. Image Credit: YAKOBCHUK VIACHESLAV/Shutterstock.com

In a recent study published in the journal PLOS One, researchers investigated sex-specific, age-associated declines in three parameters essential for health aging – gait, dominant-side strength, and balance. The investigation utilized a Mayo Clinical cohort comprising 40 healthy individuals above 50, equally divided into younger (50-65) and elderly (65+) subcohorts.

Introduction

A study using strength tests, single-leg balance duration, and gait metrics captured by a motion system found that balance was most affected by advancing age (per decade). While age significantly impacted both upper (grip) and lower (knee) strength, surprisingly, no association was found between gait and aging.

These insights can help clinicians and caregivers recognize early signs of age-related neuromuscular decline, supporting the development of targeted interventions (e.g., exercises) to slow or prevent the effects of aging.

Background

Advances in medicine and healthcare, particularly over recent decades, have significantly extended human lifespans, resulting in a larger aging population than ever before.

While these benefits are undeniable, evolutionary processes (like natural selection) typically do not favor fitness improvements beyond reproductive maturity, which is reflected in the increased risk of chronic diseases in older age.

One such condition, sarcopenia—a musculoskeletal disorder marked by declines in muscle strength, mass, and function—can severely impact physical and mental well-being, limiting independence.

Though gait, strength, and potentially balance have been identified as key indicators of aging, there is ongoing debate over the order in which these symptoms manifest and the relative impact of each on age-related decline.

“Although gait, muscle strength, and balance decline with age, which of these parameters deteriorates faster and at what rate? Answers to these questions can help healthcare professionals design targeted interventions that more effectively slow down these declines by offering maintenance and training programs. Despite previous studies investigating multiple age-related factors for gait, balance, and strength measures, a hierarchy for the measures has not been discussed, and the rate of declines have not been compared in healthy elderly.”

Understanding these declines in more detail would provide patients and their caregivers the knowledge to prepare to live with existing declines and undertake steps (such as balance training) to arrest further neuromuscular deterioration.

About the study

This cross-sectional study aimed to investigate the effects of aging on baseline strength, balance, and gait metrics in healthy older adults. Researchers examined the rate of age-related declines in these areas to help non-invasively identify the onset and progression of musculoskeletal changes associated with aging, as well as any differences in these metrics across sex and age.

Participants were recruited from the Mayo Clinic’s Rochester-area Older Adult Registry (ROAR) longitudinal cohort between March 2022 and March 2023. The study included individuals over 50 years old, divided into two groups: a younger group (ages 50-64) and an elderly group (65+). Both groups were balanced for cohort size and sex representation. Individuals with obesity or severe age-related disability or chronic (mainly neuromuscular) diseases were excluded.

The International Physical Activity Questionnaire (IPAQ) short form was used to collect data on participants' age, height, weight, trochanteric health, limb dominance, and daily activity levels (including duration and intensity). These data were used to calculate metabolic equivalent (MET) scores, providing an assessment of each participant’s physical fitness level.

The study measured dominant-side strength (upper extremity grip strength and knee strength), standing balance (unilateral stance duration), and gait metrics (using a motion capture system to record level walking). These data were used to create a continuous balance index, known as the "dynamic stability margin (DSM)," which reflects the body's ability to control its center of mass.

Study Findings

The summary statistics for the participant cohort showed no significant differences between the younger and older groups in anthropometric indices, such as body mass index (BMI) and trochanteric height. Additionally, the effect of aging on physical activity levels was minimal, as both age groups reported similar daily activity levels.

The strength measurements showed significant age- and sex-related declines in muscle performance. Muscle strength declined by approximately 3.7% per decade for grip strength and 1.4% for knee strength, with men demonstrating around 30% higher grip strength than women. These findings underscore the value of strength metrics as indicators of aging and highlight the need to consider sex-specific variations when diagnosing age-related musculoskeletal changes.

Unexpectedly, none of the gait parameters showed any association with age. Measures of standing postural sway, such as the root mean square of the center of pressure (RMS(CoP)) and Romberg ratio analyses, also revealed no significant associations between age, sex, and bipedal balance. In contrast, unipedal balance, particularly on the non-dominant side, showed marked age-related decline, with balance time decreasing by 2.2% per decade on the non-dominant side and 1.7% on the dominant side.

“The amount of movement in the CoP increased by 6.3% (m/m) per decade for the eyes-open condition (R² = 0.18, p = 0.028) in both sexes. For the eyes-closed condition, the increase was 10.4% (m/m) per decade (R² = 0.25, p = 0.005) in both sexes. The Romberg ratio (Path(CoP)EC/EO) showed no association with age or sex (R² = 0.06, p = 0.33). Hence, older subjects moved more while standing on both legs compared to younger subjects under both conditions.”

Dynamic balance metrics showed no significant association between aging and dynamic balance loss across sexes. Z-score evaluations confirmed that unipedal balance is a reliable, non-invasive indicator of aging, providing an effective measure for screening and guiding timely interventions.

Conclusions

The present study highlights the effects of aging on humans’ neuromuscular health, demonstrating that advancing years can significantly deteriorate unipedal balance duration and strength (grip > knee). Surprisingly, gait was not observed to be impacted during aging. However, significant impacts on the patient’s center of mass modulation were observed, suggesting gait compensation via other avenues.

 The association between unipedal balance duration and neuromuscular health was observed to be strong enough to consider using the non-invasive test as screening for aging, allowing for accurate assessment and timely intention.

“This study underscores the significance of the unipedal balance test in monitoring elderly subjects in the community, regardless of sex. The duration an individual, whether male or female, can maintain balance on one leg emerges as the most reliable determinant of aging, surpassing strength, gait, and other balance parameters.”