STUDY DESIGN: Reliability and case-control injury study. UBACKGROUND: Knee flexor strength is a key variable when dealing with hamstring strain injury (HSI), and methodologies of objective measurement of strength are often limited to single exercises. UOBJECTIVES: To establish test-retest reliability of a novel apparatus to measure knee flexor strength during various hamstring exercises, and to investigate whether the measure can detect between-leg differences in male participants with and without history of unilateral HSI. UMETHODS: Twenty male participants without and 10 male participants with previous unilateral HSI participated. Isometric knee flexor strength and peak rate of force development (RFD) at 0°/0°, 45°/45°, and 90°/90° 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, and typical error as a coefficient of variation were calculated for all measures. The magnitudes of between-leg differences within each group were calculated using estimates of effect sizes, reported as Cohen’s d and 90% confidence interval (CI). URESULTS: Moderate to high test-retest reliability was observed for isometric knee flexor strength (ICC = 0.87-0.92) and peak RFD (ICC = 0.88-0.95) across 3 positions and for mean force impulse during the eccentric slider (ICC = 0.83-0.90). In those with prior HSI, large deficits were observed 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, –1.97), isometric strength at 0°/0° (d = –1.06; 90% CI: –0.18, –1.93) and 45°/45° (d = –0.88; 90% CI: –0.02, –1.74), and peak RFD at 45°/45° (d = –0.88; 90% CI: –0.02, –1.74). UCONCLUSION: 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.