Abstract
ObjectiveResistance training (RT) can improve whole muscle strength without increasing muscle fiber size or contractility. Neural adaptations, which lead to greater neural activation of muscle, may mediate some of these improvements, particularly in older adults, where motor neuron denervation is common. The purpose of this study was to explore the relationship of neural adaptations, as reflected by neural cell adhesion molecule (NCAM) expression, to improvements in (1) whole muscle strength and (2) muscle fiber size following RT in older adults with knee osteoarthritis. We performed whole muscle strength measurements and immunohistochemical analysis of fiber size, type, and NCAM expression before and after a 14-week RT program.ResultsRT increased whole-muscle strength as measured by 1-repetition maximum (1-RM) leg press (P = 0.01), leg extension (P = 0.03), and knee extensor peak torque (P = 0.050), but did not alter NCAM expression. Greater NCAM expression in myosin heavy chain (MHC) II fibers was associated with greater whole muscle strength gains (knee extensor peak torque r = 0.93; P < 0.01) and greater MHC II fiber size (r = 0.79; P < 0.01). Our results suggest that training-induced NCAM expression, and neural adaptations more generally, may be important for RT-induced morphological and functional improvements in older adults.Trial registration NCT01190046
Highlights
Progressive resistance training (RT) increases whole muscle strength in older adults by increasing muscle size and improving myofilament function and neural activation [1]
Greater neural cell adhesion molecule (NCAM) expression in myosin heavy chain (MHC) II fibers was associated with greater whole muscle strength gains and greater MHC II fiber size (r = 0.79; P < 0.01)
Our results suggest that training-induced NCAM expression, and neural adaptations more generally, may be important for RT-induced morphological and functional improvements in older adults
Summary
RT increased whole muscle strength (Table 1) measured using 1-RM leg press (t = − 3.685; P = 0.010) and knee extension (t = − 2.784; P = 0.032), and isometric knee extensor peak torque (t = − 2.45; P = 0.050). Increased average NCAM signal in all fibers pooled together (r = 0.79; P = 0.04), and in MHC II fibers alone (r = 0.93; P < 0.01), were associated with greater isometric knee extensor torque (Fig. 1). Increased NCAM signal in MHC II fibers (r = 0.79; P = 0.03) was associated with greater MHC II fiber minimum Feret’s diameter (Fig. 2). Increased NCAM signal in MHC I fibers was not correlated with greater MHC I fiber minimum Feret’s diameter (P > 0.10). No correlations were found between NCAM expression and 1-RM data
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