In vivo and in vitro evidence that intrinsic upper- and lower-limb skeletal muscle function is unaffected by ageing and disuse in oldest-old humans

摘要

Abstract\udAim: To parse out the impact of advanced ageing and disuse on skeletal\udmuscle function, we utilized both in vivo and in vitro techniques to comprehensively\udassess upper- and lower-limb muscle contractile properties in\ud8 young (YG; 25 6 years) and 8 oldest-old mobile (OM; 87 5 years)\udand 8 immobile (OI; 88 4 years) women.\udMethods: In vivo, maximal voluntary contraction (MVC), electrically\udevoked resting twitch force (RT), and physiological cross-sectional area\ud(PCSA) of the quadriceps and elbow flexors were assessed. Muscle biopsies\udof the vastus lateralis and biceps brachii facilitated the in vitro assessment\udof single fibre-specific tension (Po).\udResults: In vivo, compared to the young, both the OM and OI exhibited\uda more pronounced loss of MVC in the lower limb [OM (60%) and OI\ud(75%)] than the upper limb (OM = 51%; OI = 47%). Taking into\udaccount the reduction in muscle PCSA (OM = 10%; OI = 18%), only\udevident in the lower limb, by calculating voluntary muscle-specific force,\udthe lower limb of the OI (40%) was more compromised than the OM\ud(13%). However, in vivo, RT in both upper and lower limbs (approx.\ud9.8 N m cm\ud2) and Po (approx. 123 mN mm\ud2), assessed in vitro, implies\udpreserved intrinsic contractile function in all muscles of the oldest-old and\udwere well correlated (r = 0.81).\udConclusion: These findings suggest that in the oldest-old, neither\udadvanced ageing nor disuse, per se, impacts intrinsic skeletal muscle function,\udas assessed in vitro. However, in vivo, muscle function is attenuated\udby age and exacerbated by disuse, implicating factors other than skeletal\udmuscle, such as neuromuscular control, in this diminution of function.\udKeywords in vitro, in vivo, oldest-old, sarcopenia