Are voluntary muscle activation deficits in older adults meaningful?

The relationship between the central activation ratio (CAR) and contraction force is curvilinear, not linear as was previously believed. Voluntary quadriceps femoris muscle activation from previously collected data sets in 46 older adults (64-84 years) and 46 young adults (18-32 years) were therefore reexamined using a curvilinear model of the voluntary muscle activation-percent maximum voluntary force relationship. This method revealed lower voluntary muscle activation in older adults (0.868 +/- 0.018) than younger subjects (0.978 +/- 0.005). The mean difference between older and younger adults was 11%, which may be more meaningful than previous reports of 2-4% because it could explain the greater rate of strength loss as compared to loss of muscle mass as humans age.