Effects of Reduced Training Volume of Nordic Hamstring Exercise on Eccentric Knee Flexor Strength, and Fascicle Length and Stiffness of Biceps Femoris Long Head

This study investigated whether and how ultralow-volume Nordic hamstring exercise (NHE) training can maintain neuromuscular adaptations achieved through initial moderate-volume training. Specifically, we examined changes in eccentric knee flexor strength, fascicle length, and stiffness of the biceps femoris long head (BFlh) across different training volumes. Forty-five resistance-trained males were randomly assigned to three groups: low-volume, ultralow-volume, and control (n = 15 per group). Training groups performed standardized moderate-volume NHE training (48 repetitions/week) for 2 weeks, followed by low-volume (eight repetitions/week) or ultralow-volume (four repetitions/week) training for 8 weeks. Eccentric knee flexor strength, BFlh fascicle length, and BFlh stiffness assessed via shear wave elastography were measured at four time points: weeks 0 (baseline), 2, 6, and 10. In both training groups, eccentric knee flexor strength increased significantly during the initial 2 weeks and continued to increase through week 6 despite the reduction in training volume, with no further increases beyond week 6. BFlh fascicle length increased, and stiffness decreased significantly after 2 weeks of moderate-volume training, and these adaptations were maintained throughout the subsequent 8 weeks. No significant differences were found between the two training groups for any parameter. The control group showed no significant changes. These findings indicate that neuromuscular adaptations induced by 2 weeks of moderate-volume NHE training can be effectively maintained with as little as four repetitions per week of supramaximal NHE training, providing practical implications for in-season training programming.