The purpose of this master's thesis was to investigate the effect of shin inclination during the Nordic hamstring exercise on: a) peak knee flexor torque, b) muscle activation of the knee flexors, c) the knee joint angle at which the peak torque is developed, and d) the knee joint angle at which the peak muscle activation occurs. We focused on three variations of the Nordic hamstring exercise: variation with a positive shin inclination (knees positioned higher than the ankles), a horizontal shin inclination, and a negative shin inclination (knees positioned lower than the ankles). The study included 15 participants with an average of 7,5 years of strength training experience. Their average age was 25,3 years, height 1,81 m, and body mass 94,7 kg. Measurements were conducted using a device, specifically designed for the Nordic hamstring exercise, which allowed for the adjustment of shin inclination and measurement of knee flexor torque. The knee angle was measured using an electronic goniometer, and muscle activation was recorded with electromyographic electrodes placed on the gastrocnemius, biceps femoris, semimembranosus, and gluteus maximus muscles. We performed a one-way repeated measures analysis of variance and found significant differences in the peak knee flexor torque and angle of peak knee flexor torque between the Nordic hamstring exercise variations. The highest knee flexor torque was measured in the variation with a positive shin incline (position where knees were higher than ankles) at 19,3 Nm/kg at a knee flexion angle of 25,72°. In the variation where the shin incline was horizontal, the peak knee flexor torque was measured at 1,89 Nm/kg at a knee flexion angle of 57,92°. In the variation with negative shin incline, peak knee flexor torque was measured at 1,74 Nm/kg at a knee flexion angle of 75,48°. We found no significant differences (p > 0,05) in peak muscle activation, whereas the knee flexion angle of peak muscle activation significantly differed between all of the measured muscles (p < 0,05). Based on our findings, we conclude, that the Nordic hamstring exercise with a positive shin inclination (knees placed above the ankles) is more applicable in practice, because it enables for a higher peak knee flexor torque at a lower knee flexion angle. Based on our findings, we conclude that the variation of the Nordic exercise with a positive shin angle is more effective for practical use, as it allows for the development of greater knee flexor torque at a more extended knee position. This aligns with the loads and activation of the knee flexor muscles during sprinting and the mechanisms of hamstring injury occurrence.
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