Body composition in elderly men: effect of dietary modification during strength training.

OBJECTIVE: To assess how dietary change affects gain in strength and muscle mass during heavy resistance training of elderly men. DESIGN: Randomized controlled trial. INTERVENTION: During 12 weeks of resistance training of knee extensors and flexors, a daily supplement of 560 +/- 16 kcal/day (17% energy from protein, 43% from carbohydrate, 40% from fat) was randomly assigned to six men (S) while five men (U) received no supplement. Food intake, strength, whole body composition, and midthigh composition by CT scan were assessed before training and at 6 and 12 weeks. SETTING: The men were outpatients but lived in a Metabolic Research Unit during the three assessments. PARTICIPANTS: Eleven healthy men aged 61 to 72 years. RESULTS: Densitometry showed no change over time in fat or fat-free mass. However, the S men increased (P less than 0.05) weight, skinfold thickness at six sites, subcutaneous midthigh fat, and creatinine excretion; in all men, changes in these values and in midthigh muscle were proportional to changes in reported energy intake (P less than 0.05). There was midthigh muscle hypertrophy in both groups, but it was greater in S than U (P less than 0.01). Both groups gained strength (P less than 0.001) with no effect of diet. CONCLUSIONS: During physical rehabilitation of the elderly, dietary intake may influence the increase in lean as well as adipose tissue without altering strength gain. These preliminary findings should be confirmed by a larger study with sedentary controls.

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.

Enhanced protein breakdown after eccentric exercise in young and older men.

The effects of eccentric exercise on whole body protein metabolism were compared in five young untrained [age 24 +/- 1 yr, maximal O2 uptake (VO2max) = 49 +/- 6 ml.kg-1.min-1] and five older untrained men (age 61 +/- 1 yr, VO2max = 34 +/- 2 ml.kg-1.min-1). They performed 45 min of eccentric exercise on a cycle ergometer at a power output equivalent to 80% VO2max (182 +/- 18 W). Beginning 5 days before exercise and continuing for at least 10 days after exercise, they consumed a eucaloric diet providing 1.5 g.kg-1.day-1 of protein. Leucine metabolism in the fed state was measured before, immediately after, and 10 days after exercise, with intravenous L-[1-13C]leucine as a tracer (0.115 mumol.kg-1.min-1). Leucine flux increased 9% immediately after exercise (P less than 0.011) and remained elevated 10 days later, with no effect of age. Leucine oxidation increased 19% immediately after exercise and remained 15% above baseline 10 days after exercise (P less than 0.0001), with no effect of age. In the young men, urinary excretion of 3-methylhistidine per gram of creatinine did not increase until 10 days postexercise (P less than 0.05), but in the older men, it increased 5 days after exercise and remained high through 10 days postexercise (P less than 0.05), averaging 37% higher than in the young men. These data suggest that eccentric exercise produces a similar increase in whole body protein breakdown in older and young men, but myofibrillar proteolysis may contribute more to whole body protein breakdown in the older group.

Strength training and determinants of VO2max in older men.

The effects of strength training on maximal aerobic power (VO2max) and some of its determinants were studied in 12 healthy older men (60-72 yr). They underwent 12 wk of strength conditioning of extensors and flexors of each knee with eight repetitions per set, three sets per session, and three sessions per week at 80% of the one repetition maximum (1 RM). Left knee extensors showed a 107% increase in 1 RM, a 10% increase in isokinetic strength at 60 degrees/s, and a 23% increase in total work performed during 25 contractions on an isokinetic dynamometer. Strength measurements of the untrained left elbow extensors showed no change. Leg cycle ergometer VO2max per unit fat-free mass increased by an average 1.9 ml (P = 0.034) whereas arm cycle VO2max was unchanged. Pulmonary function, hemoglobin concentration, erythrocyte volume, plasma volume, and total blood volume did not change. Biopsies of the vastus lateralis showed a 28% increase in mean fiber area, no change in fiber type distribution, a 15% increase in capillaries per fiber, and a 38% increase in citrate synthase activity. The data suggest that the small increase in leg cycle VO2max in older men may be due to adaptations in oxidative capacity and increased mass of the strength-trained muscles.

Strength conditioning in older men: skeletal muscle hypertrophy and improved function.

The effects of strength conditioning on skeletal muscle function and mass were determined in older men. Twelve healthy untrained volunteers (age range 60-72 yr) participated in a 12-wk strength training program (8 repetitions/set; 3 sets/day; 3 days/wk) at 80% of the one repetition maximum (1 RM) for extensors and flexors of both knee joints. They were evaluated before the program and after 6 and 12 wk of training. Weekly measurements of 1 RM showed a progressive increase in strength in extensors and flexors. By 12 wk extensor and flexor strength had increased 107.4 (P less than 0.0001) and 226.7% (P less than 0.0001), respectively. Isokinetic peak torque of extensors and flexors measured on a Cybex II dynamometer increased 10.0 and 18.5% (P less than 0.05) at 60 degrees/s and 16.7 and 14.7% (P less than 0.05) at 240 degrees/s. The torque-velocity relationship showed an upward displacement of the curve at the end of training, mainly in the slow-velocity high-torque region. Midthigh composition from computerized tomographic scans showed an increase (P less than 0.01) in total thigh area (4.8%), total muscle area (11.4%), and quadriceps area (9.3%). Biopsies of the vastus lateralis muscle revealed similar increases (P less than 0.001) in type I fiber area (33.5%) and type II fiber area (27.6%). Daily excretion of urinary 3-methyl-L-histidine increased with training (P less than 0.05) by an average 40.8%. Strength gains in older men were associated with significant muscle hypertrophy and an increase in myofibrillar protein turnover.

Eccentric exercise-induced muscle damage impairs muscle glycogen repletion.

Five healthy untrained young male subjects were studied before, immediately after, and 10 days after a 45-min bout of eccentric exercise on a cycle ergometer (201 W). The subjects were sedentary at all other times and consumed a eucaloric meat-free diet. Needle biopsies of the vastus lateralis muscle were examined for intracellular damage and glycogen content. Immediately after exercise, muscle samples showed myofibrillar tearing and edema. At 10 days, there was myofibrillar necrosis, inflammatory cell infiltration, and no evidence of myofibrillar regeneration. Glycogen utilization during the exercise bout was 33 mmol glycosyl units/kg muscle, consistent with the metabolic intensity of 44% of maximal O2 uptake; however, the significant glycogen use by type II fibers contrasted with concentric exercise performed at this intensity. At 10 days after exercise, muscle glycogen was still depleted, in both type I and II fibers. It is possible that the alterations in muscle ultrastructures were related to the lack of repletion of muscle glycogen. Damage produced by eccentric exercise was more persistent than previously reported, indicating that more than 10 days may be necessary for recovery of muscle ultrastructure and carbohydrate reserves.