Low muscle strength in late adolescence and Parkinson disease later in life

To evaluate maximal isometric muscle force at 18 years of age in relation to Parkinson disease (PD) later in life.

The cohort consisted of 1,317,713 men who had their muscle strength measured during conscription (1969-1996). Associations between participants' muscle strength at conscription and PD diagnoses, also in their parents, were examined using multivariate statistical models.

After adjustment for confounders, the lowest compared to the highest fifth of handgrip strength (hazard ratio [HR] 1.38, 95% confidence interval [CI] 1.06-1.79), elbow flexion strength (HR 1.34, 95% CI 1.02-1.76), but not knee extension strength (HR 1.24, 95% CI 0.94-1.62) was associated with an increased risk of PD during follow-up. Furthermore, men whose parents were diagnosed with PD had reduced handgrip (fathers: mean difference [MD] -5.7 N [95% CI -7.3 to -4.0]; mothers: MD -5.0 N [95% CI -7.0 to -2.9]) and elbow flexion (fathers: MD -4.3 N [95% CI -5.7 to -2.9]; mothers: MD -3.9 N [95% CI -5.7 to -2.2]) strength, but not knee extension strength (fathers: MD -1.1 N [95% CI -2.9 to 0.8]; mothers: MD -0.7 N [95% CI -3.1 to 1.6]), than those with no such familial history.

Maximal upper extremity voluntary muscle force was reduced in late adolescence in men diagnosed with PD 30 years later. The findings suggest the presence of subclinical motor deficits 3 decades before the clinical onset of PD.