Abstract
Peak absolute eccentric knee-flexor force during the Nordic hamstring exercise (NHE) is associated with hamstring injury risk, but its assessment requires a device with a built-in load cell. This study investigated whether peak absolute eccentric knee-flexor force during the NHE can be estimated from break-point angle (BPA) measured using the Nordic Angle app in combination with body mass. Sixty-two male undergraduate and graduate students performed three maximal NHE trials. Peak absolute eccentric knee-flexor force was measured using a device with a built-in load cell, and BPA was assessed using the Nordic Angle app. Multiple linear regression analysis using the enter method identified predictors of peak absolute eccentric knee-flexor force. The resulting prediction equation was: peak absolute eccentric knee-flexor force (N) = 383.06 + 3.12 × body mass (kg) − 6.35 × BPA (°). The prediction model explained 77.9% of the variance in peak absolute eccentric knee-flexor force (R² = 0.779). Furthermore, internal validation using 10-fold cross-validation demonstrated a cross-validated R² of 0.758, an RMSE of 39.3 N, and an MAE of 28.2 N, indicating good generalizability and limited model overfitting. Bland–Altman analysis demonstrated a mean bias of −0.3 N, with 95% limits of agreement ranging from −74.5 to 73.9 N. However, these analyses were performed within the derivation dataset and do not represent independent validation. These findings suggest that peak absolute eccentric knee-flexor force during the NHE may be estimated using BPA obtained from the Nordic Angle app together with body mass. Independent validation is required before broader application.
