Strength of two- and one-leg extension in man

Two- and one-leg extension strengths were compared in 155 female and male, untrained and trained (eight bicyclists, 38 weight-lifters) subjects and in a polio patient with almost no strength in one leg. On average two-leg strength was 82 +/- 1.3% (SE) of the sum of the strength of the right and left legs (leg-strength ratio) with no significant difference between the untrained and trained subjects. In the polio patient two-leg strength was lower than the strength of the strongest leg. A similar leg-strength ratio was found when measurements were made with a knee angle of 150 degrees (n = 128) and 90 degrees (n = 25). The ratio did not change when re-determined after 1 year (n = 9). Moderate changes in the subjects' position during measurements did not affect one-leg strength (n = 13). However, familiarization with the experimental apparatus increased the leg-strength ratio from 80 +/- 2.5% to 97 +/- 2.9% (P less than 0.01) (n = 18). In contrast, two-arm extension strength was similar to the sum of the strength of the right and left arms (n = 15). The results demonstrate that two-leg strength in general is lower than the sum of the strength of the right and left legs, and that this phenomenon is found even after intensive endurance or strength training. However, familiarization with the experimental apparatus can increase the relative two-leg strength which suggests that muscle strength in man may be limited by the central nervous systems' ability to activate maximally all synergistic muscles and/or to control antagonistic muscles.