Figure 3.

(A) Older adults with clinically meaningful leg extensor weakness exhibit indices of neural hypoexcitability (ie, significantly smaller motor evoked potentials) in comparison to nonweak older adults as assayed using transcranial magnetic stimulation. This original figure was generated using data extracted from Clark et al. (29). (B) Older adults (n = 7) exhibit significantly slower motor unit firing rates of the first dorsal interosseous (finger abductor) during a maximal voluntary contraction (n = 7). This finding suggests that reductions in muscle strength in older adults are partially due to an impaired ability to fully drive the surviving motor units. Figure created from data presented by Kamen et al. (48).