Hamstrings activity during knee extensor strength testing: effects of burst superimposition.

Quadriceps muscle strength is often used as a criterion for functional progression and return to activity after knee joint injury or surgery. Previous research has demonstrated that noteworthy antagonist activity is present during knee strength testing. the countermoment associated with this antagonist muscle activity may lead to an underestimation of knee strength. the burst superimposition method of strength testing is considered by some to be the current gold standard. the effect of burst super-imposition on antagonist activity is unknown. the purpose of this study was to test the hypothesis that burst superimposition diminishes antagonistic hamstrings activity during knee extensor strength testing. Isometric knee strength testing was performed in 22 (11 males, 11 females) active young people with no history of serious lower extremity injuries using the burst superimposition method. the magnitude of hamstrings muscle activity was assessed just before and after burst superimposition. contrary to our hypothesis, a small, but statistically significant increase in antagonistic medial hamstrings activity was observed with burst superimposition (7.23 vs. 9.62; P < 0.001). Higher lateral hamstrings activity was also observed, but this did not reach statistical significance (15.03 vs. 13.50; P = 0.087). though statistically significant, the small increase in hamstrings activity is unlikely to be clinically meaningful.