Associations Among Eccentric Hamstrings Strength, Hamstrings Stiffness, and Jump-Landing Biomechanics

Context: Anterior cruciate ligament (ACL) injury risk can be assessed from landing biomechanics. Greater hamstrings stiffness is associated with a landing-biomechanics profile consistent with less ACL loading but is difficult to assess in the clinical setting. Eccentric hamstrings strength can be easily evaluated by clinicians and may provide a surrogate measure for hamstrings stiffness. Objective: To examine associations among eccentric hamstrings strength, hamstrings stiffness, and landing biomechanics linked to ACL injury risk. Design: Cross-sectional study. Setting: Research laboratory. Patients or Other Participants: A total of 34 uninjured, physically active participants (22 women, 12 men; age = 20.2 +/- 1.6 years, height = 171.5 +/- 9.7 cm, mass = 67.1 +/- 12.7 kg). Intervention(s): We collected eccentric hamstrings strength, active hamstrings stiffness, and double- and single-legged landing biomechanics during a single session. Main Outcome Measure(s): Bivariate associations were conducted between eccentric hamstrings strength and hamstrings stiffness, vertical ground reaction force, internal kneeextension moment, internal knee-varus moment, anterior tibial shear force, knee sagittal-plane angle at initial ground contact, peak knee-flexion angle, knee frontal-plane angle at initial ground contact, peak knee-valgus angle, and knee-flexion displacement using Pearson product moment correlations or Spearman rank-order correlations. Results: We observed no association between hamstrings stiffness and eccentric hamstrings strength (r= 0.029, P= .44). We also found no association between hamstrings stiffness and landing biomechanics. However, greater peak eccentric strength was associated with less vertical ground reaction force in both the double-legged (r= -0.331, P= .03) and single-legged (r= -0.418, P= .01) landing conditions and with less internal kneevarus moment in the single-legged landing condition (r= -0.326, P= .04). Conclusions: Eccentric hamstrings strength was associated with less vertical ground reaction force during both landing tasks and less internal knee-varus moment during the single-legged landing but was not an acceptable clinical estimate of active hamstrings stiffness.