C. N. Meredith

Plasma creatine kinase activity and exercise-induced muscle damage in older men

Plasma creatine kinase (CK) activity has often been used as a marker of exercise-induced skeletal muscle damage. While the pattern of muscle damage following eccentric exercise has been established in young adults, there is little data available on eccentric exercise-induced muscle damage in older individuals. The purpose of this study was to compare ultrastructural changes in skeletal muscle following high intensity eccentric exercise of young and older men and to determine whether CK activity is a reliable predictor of muscle damage. Five young (20-30 yr) and five older untrained men (59-63 yr) performed three 15-min bouts of eccentric exercise at 90, 80, and 70% of maximal concentric power output. There was a prolonged increase in CK up to 10 d following exercise that was not significantly different between groups. Light and electron microscopic examination of needle biopsies obtained from the vastus lateralis showed evidence of focal damage in greater than 90% of the post-exercise fibers examined in the older subjects, compared with values ranging from 5 to 50% reported previously in young subjects. Quantitative analysis using light microscopy showed greater damage in the older subjects than reported previously in young subjects. These data suggest that older adults experience greater muscle damage following eccentric exercise than young subjects, which may be due in part to the smaller muscle mass and lower VO2max seen in older men. In addition, there was no relationship between CK activity and the corresponding amount of muscle damage observed in each subject, suggesting that CK activity may be a poor predictor of exercise-induced muscle damage.

Body Composition in Elderly Men: Effect of Dietary Modification during Strength Training

To assess how dietary change affects gain in strength and muscle mass during heavy resistance training of elderly men.

Effect of suspending exercise training on resting metabolic rate in women

We tested the hypothesis that enhanced resting metabolic rate (RMR) in highly trained endurance athletes is an acute effect of prior exercise induced by catecholamines and not serum thyroxine. RMR and energy-regulating hormones were studied in nine highly trained women runners during habitual training (period I), and suspension of training (period II). Data were collected during the follicular phase of two consecutive menstrual cycles, confirmed by serum progesterone and estradiol. Subjects maintained training between the two periods. Total energy intake and diet composition, body weight, and oral temperature did not change from period I to period II (P greater than 0.05). With suspension of training, urinary epinephrine and nonrepinephrine excretion dropped (P less than 0.022) while serum TSH rose (P = 0.011) and free T4 did not change (P = 0.182). RMR (mean +/- SEM) was 274 +/- 6.2 and 252 +/- 7.8 kJ.h-1 for periods I and II, respectively, with repeated measures ANOVA indicating a drop in RMR occurred with cessation of exercise (P = 0.048). The augmentation of RMR by exercise lasted more than 15 h but less than 39 h post-exercise. The results suggest that the drop in catecholamines may partly explain the lower RMR following suspension of training.

Body composition and aerobic capacity in young and middle-aged endurance-trained men

Aging is associated with increased body fat, decreased muscle mass, lower maximal O2 uptake, and lower energy intake. It has been asserted that these changes are caused in part by decreased activity. In order to determine the effects of aging in men who are habitually active, 6 young men (26.8 +/- 1.2 yr) and 6 middle-aged men (52.0 +/- 1.9 yr) who had been running, cycling, and/or rowing for at least 2 yr were studied in a metabolic ward. The men consumed a diet to maintain constant body weight while keeping to their usual exercise schedule and intensity. Both groups had a similar body mass index and muscle mass, but the middle-aged men had a 77% greater fat mass (P = 0.028). Daily energy requirement was 17% lower in the middle-aged men (P = 0.029) although basal metabolic rate was similar in both groups. Aerobic capacity was 15% lower in the middle-aged men per unit body weight (P = 0.048) but not per unit of lean body mass. The young men exercised for an average 12.3 hr.wk-1 and the middle-aged men for 7.5 hr.wk-1 (P = 0.018). For both young and middle-aged men, weekly hours of exercise were negatively correlated with fat mass, and positively correlated with daily energy requirements and maximal O2 uptake. These findings show that in both young and middle-aged men who habitually exercise aerobically at 65 to 80% maximal O2 uptake, the time spent training was associated with body composition, energy requirements, and aerobic capacity.

Influence of a 3.5 day fast on physical performance

SummaryEight young men were tested for strength, anaerobic capacity and aerobic endurance in a post absorptive state and after a 3.5 day fast. Strength was tested both isokinetically (elbow flexors, 0.52 rad·s−1 and 3.14 rad·s−1) and isometrically. Anaerobic capacity was evaluated by having subjects perform 50 rapidly repeated isokinetic contractions of the elbow flexors at 3.14 rad·s−1. Aerobic endurance was measured as time to volitional fatigue during a cycle ergometer exercise at 45%

High-Intensity Strength Training in Nonagenarians: Effects on Skeletal Muscle

V_{O_{2{\text{max}}} }

Strength training and determinants of VO2max in older men

. Measures of