What question did this study set out to answer?

This research aims to compare the effects of isometric and dynamic strength training on muscle strength and size in the quadriceps muscle.

October 1, 1987Open Access

Human muscle strength training: the effects of three different regimens and the nature of the resultant changes.

Key Points

This research aims to compare the effects of isometric and dynamic strength training on muscle strength and size in the quadriceps muscle.
Twelve-week training program with isometric and dynamic exercises.
Quadriceps strength assessed, with isometric force and cross-sectional area measured via X-ray computerized tomography scans.
Sample size of n=6 for each training type.
Isometric training led to a 35% increase in force in the trained leg, with no change in the untrained leg.
Eccentric training increased isometric force by 11% and concentric training by 15%, both with approximately a 5% increase in cross-sectional area.
The strength gain is associated more with force per unit area rather than just muscle size.

Abstract

Increases in strength and size of the quadriceps muscle have been compared during 12 weeks of either isometric or dynamic strength training. 2. Isometric training of one leg resulted in a significant increase in force (35 +/- 19%, mean +/- S.D., n = 6) with no change in the contralateral untrained control leg. 3. Quadriceps cross-sectional area was measured from mid-thigh X-ray computerized tomography (c.t.) scans before and after training. The increase in area (5 +/- 4.6%, mean +/- S.D., n = 6) was smaller than, and not correlated with, the increase in strength. 4. The possibility that the stimulus for gain in strength is the high force developed in the muscle was examined by comparing two training regimes, one where the muscle shortened (concentric) and the other where the muscle was stretched (eccentric) during the training exercise. Forces generated during eccentric training were 45% higher than during concentric training. 5. Similar changes in strength and muscle cross-sectional area were found after the two forms of exercise. Eccentric exercise increased isometric force by 11 +/- 3.6% (mean +/- S.D., n = 6), and concentric training by 15 +/- 8.0% (mean +/- S.D., n = 6). In both cases there was an approximate 5% increase in cross-sectional area. 6. It is concluded that as a result of strength training the main change in the first 12 weeks is an increase in the force generated per unit cross-sectional area of muscle. The stimulus for this is unknown but comparison of the effects of eccentric and concentric training suggest it is unlikely to be solely mechanical stress or metabolic fluxes in the muscle.

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