A Novel Device Using the Nordic Hamstring Exercise to Assess Eccentric Knee Flexor Strength: A Reliability and Retrospective Injury Study

STUDY DESIGN: Reliability and case-control injury study. OBJECTIVES: To determine if a novel device designed to measure eccentric knee flexor strength via the Nordic hamstring exercise displays acceptable test-retest reliability; to determine normative values for eccentric knee flexor strength derived from the device in individuals without a history of hamstring strain injury (HSI); and to determine if the device can detect weakness in elite athletes with a previous history of unilateral HSI. BACKGROUND: HSI and reinjury are the most common cause of lost playing time in a number of sports. Eccentric knee flexor weakness is a major modifiable risk factor for future HSI. However, at present, there is a lack of easily accessible equipment to assess eccentric knee flexor strength. METHODS: Thirty recreationally active males without a history of HSI completed the Nordic hamstring exercise on the device on 2 separate occasions. Intraclass correlation coefficients, typical error, typical error as a coefficient of variation, and minimal detectable change at a 95% confidence level were calculated. Normative strength data were determined using the most reliable measurement. An additional 20 elite athletes with a unilateral history of HSI within the previous 12 months performed the Nordic hamstring exercise on the device to determine if residual eccentric muscle weakness existed in-the previously injured limb. RESULTS: The device displayed high to moderate reliability (intraclass correlation coefficient = 0.83-0.90; typical error, 21.7-27.5 N; typical error as a coefficient of variation, 5.8%-8.5%; minimal detectable change at a 95% confidence level, 60.1-76.2 N). Mean +/- SD normative eccentric flexor strength in the uninjured group was 344.7 +/- 61.1 N for the left and 361.2 +/- 65.1 N for the right side. The previously injured limb was 15% weaker than the contralateral uninjured limb (mean difference, 50.3 N; 95% confidence interval: 25.7, 74.9; P<.01), 15% weaker than the normative left limb (mean difference, 50.0 N; 95% confidence interval: 1,4, 98.5; P =.04), and 18% weaker than the normative right limb (mean difference, 66.5 N; 95% confidence interval: 18.0, 115.1; P<.01). CONCLUSION: The experimental device offers a reliable method to measure eccentric knee flexor strength and strength asymmetry and to detect residual weakness in previously injured elite athletes.