Your Genes Determine Grip Strength But Exercise Matters More If You Drew a Bad Hand
A polygenic score explains ~5% of grip strength variance, but physical activity benefits are greatest for those with low genetic predisposition.
Summary
Researchers used genetic data from over 5,000 twins across five countries to test whether a polygenic score — a combined measure of many genetic variants — could predict handgrip strength in older adults. The score did predict strength, but only explained about 5% of the variation. Crucially, the study found that leisure-time physical activity had a stronger positive effect on grip strength in people with lower genetic scores. In other words, those who are genetically less predisposed to strong muscles benefit the most from staying active. This suggests that while genetics set a baseline, lifestyle choices like regular exercise can meaningfully compensate for an unfavorable genetic profile — a hopeful finding for anyone worried about age-related muscle loss.
Detailed Summary
Handgrip strength is one of the most reliable biomarkers of healthy aging, predicting mortality, disability, and overall physical function. Understanding how genetics and lifestyle interact to shape this trait could help clinicians identify who is most at risk and who stands to gain the most from targeted interventions.
This study examined a polygenic score for handgrip strength — a single number summarizing the cumulative effect of thousands of genetic variants — in 5,103 older adults (ages 40–96) drawn from eight twin cohorts across Denmark, Sweden, Australia, the United States, and Finland. Researchers tested whether the score predicted measured grip strength and whether age, sex, or leisure-time physical activity modified that relationship.
The polygenic score was significantly associated with grip strength, explaining 4.6% of total variance (5.2% in women, 4.3% in men). Importantly, a statistically significant interaction emerged between the genetic score and physical activity: the grip strength benefit of leisure-time exercise was substantially larger in individuals with lower genetic predisposition. No significant interaction with age was detected, suggesting the gene-strength relationship is relatively stable across the lifespan studied.
These findings carry meaningful implications for personalized medicine and public health. Individuals with low genetic scores for muscle strength are not destined for weakness — they appear to be the very people who respond most robustly to physical activity. This gene-environment interaction supports a precision approach to exercise prescription, where genetic profiling could help prioritize interventions for those most likely to benefit.
Several caveats apply. The polygenic score explained only a modest fraction of grip strength variance, reflecting the complex, polygenic nature of muscle traits. Within-pair twin models offered limited support for an independent environmental effect of physical activity, complicating causal interpretation. Additionally, physical activity was self-reported and assessed cross-sectionally, limiting conclusions about directionality. This summary is based on the abstract only.
Key Findings
- A polygenic score for handgrip strength explained ~5% of grip strength variance across 5,103 older adults in five countries.
- Physical activity benefits on grip strength were significantly greater in individuals with lower genetic predisposition for strength.
- The gene-strength association did not significantly change with age, suggesting stable genetic influence across midlife and older adulthood.
- Women showed slightly higher genetic variance explained (5.2%) than men (4.3%), indicating modest sex differences in genetic architecture.
- Twin within-pair models provided limited evidence for an independent environmental effect of physical activity on grip strength.
Methodology
Cross-sectional study of 5,103 adults (ages 40–96, 44% women) from eight twin cohorts in the IGEMS consortium across five countries. A polygenic score derived from Pan-UK Biobank GWAS data was tested against measured handgrip strength using linear mixed models with interaction terms for age, sex, country, and leisure-time physical activity. Fixed-effect within-pair twin models were used to assess environmental contributions independent of shared genetics.
Study Limitations
The polygenic score explained only ~5% of grip strength variance, indicating that most variation remains unexplained by current genetic data. Physical activity was self-reported and the study design is cross-sectional, preventing causal conclusions about exercise effects. Within-pair twin analyses did not strongly support an independent environmental contribution of physical activity, and this summary is based on the abstract only, as the full text was not available.
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