Age-related force output changes in the knee extensors are different to those in the arm flexors.

This study examined the effect of age on force output and muscle anthropometric differences in the arm flexor and leg extensor muscles. Seventy-four participants aged 16 to 71 years participated in the study. Peak force output was significantly negatively correlated with increasing age in the leg extensor muscles (r = - 0.46; p = 0.015), while in the arm flexor muscles this relationship was not significant (r = - 0.16; p = 0.181). After adjustment for activity level, age was an independent predictor of arm and leg peak force values (all p < 0.01). Lean muscle volume was also significantly negatively correlated with age in the leg muscles (r = - 0.46, p = 0.01), while in the arm muscles this correlation was not significant (r = 0.04, p = 0.739). Peak force was significantly positively correlated with lean volume in both leg (r = 0.64; p = 0.01) and arm (r = 0.74; p = 0.01) muscles, indicating that loss of muscle mass in the leg may be the main cause of the decrements in force output with increasing age in the legs compared to the arm muscles. These findings suggest that decrements in force output in the knee extensors, which are associated with increasing age, were related to decreases in lean volume of the muscles of the lower limb. These findings identify that leg muscles are more greatly affected by age-related strength losses than in the arm muscles, which has implications for both training in the elderly and precautions against falls when ambulatory using the lower limbs, with the lower limbs perhaps needing more focused strength training to attenuate these age-related effects.