Once-weekly muscle endurance and strength training prevents deterioration of muscle oxidative function and attenuates the degree of strength decline during 3-week forearm immobilization

Bioenergetic basis for the increased fatigability with ageing

KEY POINTS

The mechanisms for the age-related increase in fatigability during dynamic exercise remain elusive. We tested whether age-related impairments in muscle oxidative capacity would result in a greater accumulation of fatigue causing metabolites, inorganic phosphate (P_i ), hydrogen (H⁺ ) and diprotonated phosphate (H₂ PO₄ ^- ), in the muscle of old compared to young adults during a dynamic knee extension exercise. The age-related increase in fatigability (reduction in mechanical power) of the knee extensors was closely associated with a greater accumulation of metabolites within the working muscle but could not be explained by age-related differences in muscle oxidative capacity. These data suggest that the increased fatigability in old adults during dynamic exercise is primarily determined by age-related impairments in skeletal muscle bioenergetics that result in a greater accumulation of metabolites.

ABSTRACT

The present study aimed to determine whether the increased fatigability in old adults during dynamic exercise is associated with age-related differences in skeletal muscle bioenergetics. Phosphorus nuclear magnetic resonance spectroscopy was used to quantify concentrations of high-energy phosphates and pH in the knee extensors of seven young (22.7 ± 1.2 years; six women) and eight old adults (76.4 ± 6.0 years; seven women). Muscle oxidative capacity was measured from the phosphocreatine (PCr) recovery kinetics following a 24 s maximal voluntary isometric contraction. The fatiguing exercise consisted of 120 maximal velocity contractions (one contraction per 2 s) against a load equivalent to 20% of the maximal voluntary isometric contraction. The PCr recovery kinetics did not differ between young and old adults (0.023 ± 0.007 s^-1  vs. 0.019 ± 0.004 s^-1 , respectively). Fatigability (reductions in mechanical power) of the knee extensors was ∼1.8-fold greater with age and was accompanied by a greater decrease in pH (young = 6.73 ± 0.09, old = 6.61 ± 0.04) and increases in concentrations of inorganic phosphate, [P_i ], (young = 22.7 ± 4.8 mm, old = 32.3 ± 3.6 mm) and diprotonated phosphate, [H₂ PO₄ ^- ], (young = 11.7 ± 3.6 mm, old = 18.6 ± 2.1 mm) at the end of the exercise in old compared to young adults. The age-related increase in power loss during the fatiguing exercise was strongly associated with intracellular pH (r = -0.837), [P_i ] (r = 0.917) and [H₂ PO₄ ^- ] (r = 0.930) at the end of the exercise. These data suggest that the age-related increase in fatigability during dynamic exercise has a bioenergetic basis and is explained by an increased accumulation of metabolites within the muscle.

Effects of Moderators on Physical Training Programs: A Bayesian Approach

Vetter, RE, Yu, H, and Foose, AK. Effects of moderators on physical training programs: a Bayesian approach. J Strength Cond Res 31(7): 1868-1878, 2017-Creating an optimal physical training program is an important focus in sport and exercise research. The purpose of this research was to examine how different moderators (age, ability level, training weeks, training frequencies, and intensity) impacted the physiological outcomes of specific exercise training programs (muscular strength, speed, power, and cardiorespiratory) using the Bayesian method. A Bayesian approach uses flexible frameworks to determine the pattern of outcomes. This Bayesian analysis combined data generated by 34 previous studies from 1984 to 2015 to improve estimates of effects; these studies rendered 312 cases. The analyses for age were strong in cardiorespiratory and speed but less in power and muscular strength. Ability level was not a predictor of outcomes in each of the 4 areas. Training weeks contributed to power and cardiorespiratory, but not for speed, whereas for strength the effect size (ES) increased only up to the 16th week. Training frequency was a nonsignificant predictor of ES; most of the included studies within this analysis used only training frequencies of 2 or 3 days. Training intensity clearly contributed to the ES. The pattern of influence for intensity level in strength was greatest between 55 and 80%, in power it increased at 65% and continued in a positive linear pattern, in cardiorespiratory it increased up to 65% and then plateaued, and for speed no inferences could be made.