Level of lower limb physical activity may not explain muscle volume reduction in the elderly

Aim: Sarcopenia is commonly defined as a loss of muscle mass and strength associated with aging. The decrease in muscle mass, especially at the lower limbs level, is accompanied by an age-related reduction in physical activity. However, the physiological factors underpinning this muscle mass difference between upper and lower limbs in elderly people is not clear. Therefore, the aim of this study was to evaluate how lower and upper limbs activity contributes to total energy expenditure (TEE) during aging. Methods: Fifteen participants (age: 53.9±31.4 yrs.; body mass: 64.4±10.4 kg; stature: 1.65±0.42 m; mean±standard deviation) volunteered in this study and were divided in three age categories (young, YNG, 20-30 yrs; middle-age, MA, 40-60 yrs; and elderly, ELD, 60-90 yrs). Their upper (UL) and lower limbs (LL) volumes were estimated anthropometrically. Then, participants were equipped with two accelerometers, one on the forearm and the other on the leg, and a wearable device on the chest allowing TEE, UL and LL activity recordings that lasted for two consecutive days. Results: UL volume was similar among the three groups (2208±632, 2646±533 and 2344±466 cm3 for YNG, MA and ELD, respectively). Conversely, LL volume of ELD was lower compared to YNG and MA (8246±1725, 9101±2244 and 6475±1262 cm3 for YNG, MA and ELD, respectively; P<0.05). TEE was significantly lower in ELD compared to YNG and MA (2150±519, 2731±518, 1502±314 kcal for YNG, MA, and ELD, respectively). In ELD both LL and UL activity was lower (-56% and -61% vs YNG and MA, respectively, for the UL; -65% and -64% vs YNG and MA, respectively, for the LL; P<0.05). Conclusion: The lower involvement of upper limbs accompanied by a preserved arm volume in ELD should exclude the hypothesis that the loss in leg volume in ELD may depend on the reduced utilization of the lower-limbs.