Markers of oxidative stress, skeletal muscle mass and function, and their responses to resistance exercise training in older adults.

Background: Oxidative stress (OS) negatively affects skeletal muscle homeostasis in experimental models of ageing. However, little is known about the associations between circulating OS markers and parameters of muscle mass and function, and their responses to exercise training, in humans.
Methods: Maximal voluntary contraction (MVC, primary outcome) and isokinetic torque of the knee extensors at 30° s ^-1 (MIT), muscle cross-sectional area (MCSA) and quality (MQ, secondary outcomes), and plasma concentrations of malondialdehyde (MDA, pro-OS), homocysteine (HCY, pro-OS), taurine (TAU, anti-OS), and protein sulphydryl groups (PSH, anti-OS) were measured in 27 healthy older males and 23 females at baseline and after an 18-week resistance exercise program, with or without a nutritional intervention (fish oil vs. placebo).
Results: After adjusting for age, glomerular filtration rate, and nutritional intervention, there were no significant correlations between baseline OS markers and muscle parameters, barring a positive association between TAU and MIT in females (r = 0.53, P = .035) and between MDA and MCSA in males (r = 0.69, P = .001). Training did not significantly change OS markers, except for a reduction in MDA in females (-0.27 μmol/L, 95% CI -0.51 to -0.02, P = .034). In females, there were significant correlations between baseline MDA and exercise-induced changes in MVC (P = .018), baseline TAU and changes in MCSA (P = .026), and baseline HCY and changes in MCSA (P = .046) and MQ (P = .022). In males, baseline MDA was significantly associated with exercise-induced changes in MVC (P = .040).
Conclusions: Plasma MDA, HCY, and TAU were significantly associated with baseline and/or exercise-induced changes in muscle mass and function in healthy older adults, primarily in females. Pending further confirmation in other populations, specific OS markers, particularly MDA, might predict muscle responses to resistance exercise programs in old age.
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