FRONTERA et al. (1988) demonstrated that older (age 60-72 years) sedentary men have the capacity to significantly increase both the size and strength of their muscles. Using a progressive resistance training (PRT) program (80% of the one repetition maximum, 3 days per week for 12 weeks), we demonstrated that muscle hypertrophy was associated with a significant post-training elevation in urinary 3-methylhistidine/creatinine. This PRT program had a substantial eccentric component, which almost certainly resulted in significant damage in the knee extensor and flexor muscles.
Half of the men who participated in this study were given a daily protein-calorie supplement (S) providing an extra 560 ± 16 kcal/d (16.6% as protein, 43.3% as carbohydrate, and 40.1% as fat) in addition to their normal ad lib diet. The rest of the subjects received no supplement (NS) and consumed an ad lib diet. By the twelfth week of the study, dietary energy (2960 ± 230 in S vs 1620 ± 80 kcal in NS) and protein (118 ± 10 in S vs 72 ± 11 g/d in NS) intake were significantly different between the S and NS groups.
Composition on the midthigh was estimated by computerized tomography and showed that the S group had greater gains in muscle than did the NS men. In addition, urinary creatinine excretion was greater at the end of the training in the S group when compared to that of the men in the NS group (MEREDITH, FRONTERA and EVANS, 1992), indicating a greater muscle mass in the S group. The change in energy and protein intake (beginning vs 12 weeks) was correlated with the change in midthigh muscle area (r=0.69, p=0.019; r=0.63, p=0.039, respectively). There was no difference in strength gains between the two groups. These data suggest that a change in total food intake, or perhaps, selected nutrients, in subjects beginning a strength-training program can affect muscle hypertrophy.
It is clear that exercise-induced muscle damage leads to a long-term increase in protein breakdown and synthesis (FRONTERA et al., 1988; FIELDING et al., 1991; CANNON et al., 1991; EVANS, 1986). Few studies have compared the longitudinal effect of high-intensity eccentric and concentric exercise training. Most progressive resistance training devices and lifting free weight have substantial concentric and eccentric components. KOMI and BUSKIRK (1972) measured arm circumference before and after training either eccentrically or concentrically. They found that arm circumference increased only in the arms of men who trained eccentrically.
CIRIELLO et al. (1983) examined the effects of 4 months of high-intensity strength training on a Cybex isokinetic dynamometer which has little or no eccentric component. Although the strength of the subjects increased significantly, there was no evidence of hypertrophy of Type I or Type II muscle fibers. PEARSON and COSTILL. (1988) examined the effects of a progressive resistance weight-training protocol (with eccentric and concentric components) on one leg and isokinetic training (with no eccentric component) on the contralateral leg. Only the leg trained with a significant eccentric component increased in size as a result of the training.
Recently, a direct comparison of the effects of strength training with eccentric and concentric or concentric exercise alone was made (DUDLEY et al., 1991; COLLIANDER and TESCH, 1990). These studies showed that increases in strength were greater following a program of maximum concentric and eccentric muscle actions than resistance training using concentric muscle actions only. The evidence suggests that eccentric exercise-induced skeletal muscle damage and its subsequent repair are important for increasing muscle fiber size in respone to strength training. Not only can resistance training increase muscle size, but a recent report indicated that long-term resistance training may prevent age-associated changes in histochemical fibre-type distribution, myosin heavy chain isoforms and tropomyosin isoforms (KLITGAARD et al., 1990a; b).
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