A novel apparatus to measure knee flexor strength during various hamstring exercises: A reliability and retrospective injury study

Study Design: Reliability and case-control injury study.

Objectives: To establish test re-test reliability of a novel apparatus measuring knee flexor strength during various hamstring exercises; to investigate whether these measures detect between-leg differences in males with and without history of unilateral hamstring strain injury (HSI).

Background: Knee flexor strength is a key variable when dealing with HSI and methodologies of objective measurement are often limited to single exercises.

Methods: Twenty males without and ten males with previous unilateral HSI participated. Isometric knee flexor strength and peak rate of force development (RFD) at 0/0, 45/45 and 90/90 degrees of hip/knee flexion were measured, as well as force impulse during bilateral and unilateral variations of an eccentric slider and hamstring bridge, using a novel apparatus. Intraclass correlation coefficient (ICC), typical error (TE) and typical error as a co-efficient of variation (%TE) were calculated for all measures. The magnitude of between-leg differences within each group were calculated using estimates of effect sizes reported as Cohen’s d with a ± 90% confidence interval (CI).

Results: Moderate to high test re-test reliability was observed for isometric knee flexor strength (ICC = 0.87 to 0.92) and peak RFD (ICC = 0.87 to 0.95) across three positions and mean force impulse during the eccentric slider (ICC = 0.83 to 0.90). In those with prior HSI, large deficits were seen in the previously injured leg compared to the contralateral uninjured leg for mean force impulse during the unilateral eccentric slider (d = -1.09, 90% CI = -0.20 to -1.97), isometric strength at 0/0 (d = -1.06, 90% CI = -0.18 to -1.93) and 45/45 (d = -0.88, 90% CI = -0.02 to -1.74) and peak RFD at 45/45 (d = -0.88, 90% CI = -0.02 to -1.74).

Conclusions: The novel apparatus provides a reliable measure of isometric knee flexor strength, peak RFD and force impulse during an eccentric slider, with deficits seen in previously injured hamstrings for these measures.

Authors accepted manuscript. As per [https://www.jospt.org/page/authors/editorialPolicies?code=jospt-site] the editorial policies (03/2018) of the Journal of Orthopaedic & Sports Physical Therapy, this can only be accessed by current ACU staff and students.