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

@entity1 @entity6926 @entity910 @entity2472
AIM: To parse out the impact of advanced ageing and disuse on skeletal muscle function, we utilized both in  vivo and in  vitro techniques to comprehensively assess upper- and lower-limb muscle contractile properties in 8 young (YG; 25      6  years) and 8 oldest-old mobile (OM; 87      5  years) and 8 immobile ( @entity6926 ; 88      4  years) @entity1 . METHODS: In vivo, maximal @entity2472 (MVC), electrically evoked @entity910 ( @entity910 ), and physiological cross-sectional area (PCSA) of the quadriceps and elbow flexors were assessed. Muscle biopsies of the vastus lateralis and biceps brachii facilitated the in  vitro assessment of single fibre-specific tension (Po). RESULTS: In vivo, compared to the young, both the OM and @entity6926 exhibited a more pronounced loss of MVC in the lower limb [OM (-60%) and @entity6926 (-75%)] than the upper limb (OM  =  -51%; @entity6926  =  -47%). Taking into account the reduction in muscle PCSA (OM  =  -10%; @entity6926  =  -18%), only evident in the lower limb, by calculating voluntary muscle-specific force, the lower limb of the @entity6926 (-40%) was more compromised than the OM (-13%). However, in  vivo, @entity910 in both upper and lower limbs (approx. 9.8  N  m  cm(-2) ) and Po (approx. 123  mN  mm(-2) ), assessed in  vitro, implies preserved intrinsic contractile function in all muscles of the oldest-old and were well correlated (r  =  0.81). CONCLUSION: These findings suggest that in the oldest-old, neither advanced ageing nor disuse, per se, impacts intrinsic skeletal muscle function, as assessed in  vitro. However, in  vivo, muscle function is attenuated by age and exacerbated by disuse, implicating factors other than skeletal muscle, such as neuromuscular control, in this diminution of function.
