Agreement between isokinetic eccentric hamstring strength, Nordic hamstring strength and Nordic break-point angle in a sample of trained and healthy individuals

Different eccentric strength assessments are used to identifying the risk of hamstring injury in athletes. However, there is scarce information to determine the association between Nordic-based measurements and the gold standard measurement of eccentric hamstring strength in an isokinetic dynamometer. To investigate the relationship of different measures of eccentric hamstring strength (break-point angle and eccentric strength during Nordic exercise) with eccentric hamstring peak torque measured with an isokinetic dynamometer. Forty-six participants volunteered to participate in this study. Eccentric peak force in the Smart-Nordic System and break-point angle measured as trunk lowering at >20°/s and >150°/s2 during the Nordic exercise via high-frequency video-analysis were compared to eccentric hamstring peak torque in an isokinetic dynamometer set to produce knee extension at 30°/s. There was a moderate association between peak eccentric strength with the Smart-Nordic and isokinetic eccentric hamstring peak torque (r = -0.65, p < 0.001, 95%CI = [-0.76-(-0.50)]). The association between Nordic break-point angle measured at 20°/s (r = 0.49, p < 0.001, 95%CI = [0.30-0.64]) and at 150°/s2 (r = 0.52, p < 0.001, 95%CI = [0.33-0.66]) presented statistically significant but lower associations with isokinetic eccentric hamstring peak torque. All Nordic-based measurements presented acceptable associations with the gold standard isokinetic eccentric hamstring peak torque. However, peak eccentric force measured on the Smart-Nordic device had a better agreement with eccentric peak torque measured with an isokinetic dynamometer than the video-based measurements.Highlights Peak eccentric force measured on the isometric strain-gauges device had a better agreement with eccentric hamstring peak torque measured with an isokinetic dynamometer than the break-point angle.The Nordic-based measurements are an alternative cost-effective method to assess eccentric muscle strength and weakness when the access to isokinetic dynamometry is not feasible.Caution should be taken with certain variables such as participants body mass, hip position and movement speed when interpreting the results of Nordic-based measurements.