Isokinetic Strength Training Protocols: Do They Induce Skeletal Muscle Fiber Hypertrophy?

Isokinetic Strength Training Protocols: Do They Induce Skeletal Muscle Fiber Hypertrophy?

Cote C, Simoneau JA, Lagasse P, et al (The Physical Activity Sciences Laboratory and the Dept of Medicine, Laval University, Ste Foy, Quebec, Canada), Arch Phys Med Rehabil 69:281-285, 1988.

This study examined the morphological, histochemical, and biochemical effects of isokinetic training on skeletal muscle.

Twenty-three sedentary subjects participated in a 10-week isokinetic strength training program consisting of five sessions per week. During each session, the subjects performed 30 repetitions of maximal knee flexion-extension contractions on a Hydra-Fitness series 111-307 exercise machine. The subjects trained at a load that was about 65% of their maximum isometric torque value for the quadriceps femoris muscle group. The peak torque output for the quadriceps femoris was calculated before and after the 10-week training period. To obtain the peak torque value, the mean of three maximal isokinetic knee extensions at a velocity of 90 [degrees]/sec was calculated. Histochemical and biochemical analyses were performed from tissue samples taken from the vastus lateralis muscle of all subjects. In addition, 7 out of the 23 subjects remained inactive for a period of 50 days after the 10-week training period and then began the same isokinetic training program. The same analyses were performed again on these subjects.

The maximal torque output for the quadriceps femoris muscle increased an average of 54% in all subjects after the 10-week training period. A statistically significant increase in the percentage of type IIa muscle fibers was found after this same training period. Significant increases also were found in the activities of several muscle enzymes; however, the isokinetic training program did not produce enlargement of the muscle fibers. The seven subjects who remained relatively inactive for 50 days after the initial 10-week period demonstrated an average decrease of 12% in peak torque output. No change was found after 50 days in percentage of fiber type or fiber area. The results of the second 10-week training period did not differ significantly from the results of the first 10-week period for maximal torque output, fiber-type distribution, or mean fiber area.

The authors concluded that significant increases in muscle performance can be achieved through isokinetic training. According to the authors, the adaptations obtained through isokinetic training slowly reverse if training is not continued. The protocol used in this study was not effective in producing muscle hypertrophy. The authors stated that the effect of eccentric muscle contractions, as a part of a program to enlarge muscle fibers, should be examined.