Black Older Adults Walk Slower Due to Weaker Mitochondria and Lower Fitness, Not Just Socioeconomics
A landmark study finds muscle mitochondrial respiration and cardiorespiratory fitness—not just socioeconomic factors—explain slower walking speeds in older Black adults.
Summary
The SOMMA study examined 879 adults aged 70+ and found that older individuals who identify as Black walk significantly slower than matched White peers, even after controlling for age, BMI, muscle mass, physical activity, and socioeconomic factors. Using propensity score matching, researchers identified that lower mitochondrial respiration (Max OXPHOS) in skeletal muscle and lower cardiorespiratory fitness (VO2 peak) were key biological contributors to this mobility gap. These findings suggest that racial disparities in late-life mobility have a meaningful biological component involving muscle energy metabolism, independent of socioeconomic disadvantage, and may point toward targeted interventions to reduce health inequities in aging.
Detailed Summary
Age-related mobility loss disproportionately affects older Black Americans, yet the biological mechanisms underlying this disparity have been poorly understood. Most prior research attributed racial differences in physical function primarily to socioeconomic factors such as income and educational attainment. This study, using data from the Study of Muscle, Mobility and Aging (SOMMA), sought to determine whether skeletal muscle mitochondrial energetics and cardiorespiratory fitness independently contribute to slower walking speeds in older Black adults compared to White adults.
SOMMA enrolled 879 community-dwelling adults aged 70 or older across two clinical sites (Pittsburgh and Wake Forest), including 116 who self-identified as Black and 745 as White. To isolate the effect of race from confounders, the researchers applied propensity score matching (1:1 ratio), creating matched groups of 90 Black and 90 White participants balanced on age, sex, BMI, muscle mass (D3-creatine dilution method), physical activity, marital status, educational achievement, multimorbidity index, and whether financial needs were met. Mitochondrial oxidative phosphorylation capacity (Max OXPHOS) was measured via high-resolution respirometry in permeabilized fibers from vastus lateralis muscle biopsies. Cardiorespiratory fitness was assessed as VO2 peak via a graded cardiopulmonary exercise test, and mobility was evaluated using 400-meter walk test speed.
Despite excellent matching on socioeconomic and clinical variables, Black participants walked significantly slower than White participants (0.97 vs. 1.03 m/s, p=0.014). They also had meaningfully lower skeletal muscle mitochondrial respiration (Max OXPHOS: 50.8 vs. 60.9 pmol/s/mg, p=0.0002) and lower VO2 peak (1391 vs. 1566 mL/min, p=0.007). Critically, multivariate regression analyses demonstrated that including VO2 peak and Max OXPHOS in the model substantially attenuated the race difference in 400-m walking speed, whereas adding socioeconomic variables did not. Mediation analyses further supported the conclusion that mitochondrial function and cardiorespiratory fitness—not socioeconomic factors—partially mediated the observed mobility disparity.
The findings align with prior work from the same group showing lower mitochondrial respiration in young Black women compared to White women, suggesting this biological difference may persist across the life course and become clinically significant in older age when mitochondrial decline intersects with aging-related mobility loss. The study also corroborates known links between mitochondrial energetics, VO2 peak, and walking performance in older adults more broadly.
Importantly, the authors acknowledge that while race was self-identified and socioeconomic factors were carefully controlled, many unmeasured social determinants of health—including lifetime cumulative disadvantage, stress, neighborhood environment, and healthcare access—could still play roles. The cross-sectional design also prevents causal inference. Nevertheless, identifying mitochondrial respiration and cardiorespiratory fitness as modifiable biological mediators opens potential avenues for exercise-based or mitochondria-targeted interventions to specifically address mobility disparities in aging Black Americans.
Key Findings
- Older Black adults walked 6% slower than matched White peers (0.97 vs. 1.03 m/s) despite similar SES, BMI, and muscle mass.
- Skeletal muscle Max OXPHOS was 17% lower in Black participants (50.8 vs. 60.9 pmol/s/mg, p=0.0002).
- VO2 peak was significantly lower in Black participants (1391 vs. 1566 mL/min, p=0.007).
- VO2 peak and Max OXPHOS—but not socioeconomic variables—statistically attenuated the race difference in walking speed.
- Propensity score matching controlled for age, sex, BMI, muscle mass, physical activity, multimorbidity, and financial resources.
Methodology
Cross-sectional analysis of SOMMA (n=879, age ≥70), with 1:1 propensity score matching of 90 Black and 90 White participants on 9 clinical and socioeconomic variables. Mitochondrial respiration was measured by high-resolution respirometry in permeabilized vastus lateralis fibers; fitness assessed by graded cardiopulmonary exercise test; mobility by 400-m walk test.
Study Limitations
The cross-sectional design prevents causal conclusions about whether improving mitochondrial function or fitness would close the mobility gap. Unmeasured lifetime social exposures (cumulative stress, neighborhood quality, healthcare access) were not captured and may contribute to the observed biological differences. The Black participant sample (n=116 before matching, n=90 after) was relatively small, limiting statistical power for subgroup analyses.
Enjoyed this summary?
Get the latest longevity research delivered to your inbox every week.