Strength conditioning in older men: skeletal muscle hypertrophy and improved function
W. R. Frontera, C. N. Meredith, K. P. O'Reilly, H. G. Knuttgen and W. J. Evans
United States Department of Agriculture Human Nutrition Research Center on Aging, Tufts University, Boston, Massachusetts 02111.
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.
THE REDUCED MUSCLE STRENGTH of the elderly has been attributed to aging itself and to lower physical activity that produces a decline in muscle function (15). Loss of strength may have a marked effect on the capacity of elderly men and women to lead independent lives. In the United States, surveys have shown that after the age of 74, 28% of men and 66% of women cannot lift objects weighing >4.5 kg (19). Pan of the decline in strength may be due to a reduction in muscle mass (32). Resistance training in older men has been shown to produce significant gains in strength (2, 21, 27), but the evidence for the role of hypertrophy in strength gain in the elderly is not clear. The present study was designed to determine how a standard rehabilitation program for improving strength in elderly men affected the function, total mass and fiber size of the conditioned muscles, and the rate of actomyosin turnover in the whole body.
Conclusion. A vigorous strength training program, similar in nature to standard rehabilitation techniques, caused a marked gain in strength in older men. Strength training led to muscle hypertrophy, due to an increase in the size of type I and type II fibers. Muscle hypertrophy was accompanied by an increase in the rate of actomyosin protein turnover. These results show that the capacity for increasing muscle mass is retained in old age and that the improvement in strength is partly due to muscle hypertrophy.