Abstract
PURPOSE: This study evaluated the effects of eccentric resistance training on hamstring muscles properties in women using oral contraceptives (OC) and naturally menstruating women. METHODS: Before and after the training intervention, we measured maximal isometric and eccentric moment of the knee flexor muscles, thickness and shear wave velocity (SWV) of the biceps femoris long head (BFlh), semitendinosus (ST) and semimembranosus (SM) muscles, and BFlh fascicle length using ultrasonography and dynamometry. RESULTS: The 12-week training intervention resulted in a modest but statistically significant increase in resting BFlh fascicle length (~2% on average, p = 0.005) across both groups, with no observed effect of OC use on any variable. The muscle strength and thickness increased comparably in both groups, with an average increase of ~20% in isometric knee flexor moment and 14% in eccentric knee flexor moment (p < 0.001 for both tests). ST muscle thickness increased by ~4% on average (p = 0.016), while no main effect of training was observed for SM and BFlh thickness. The shear modulus of the SM muscle decreased by 9% (p = 0.021) for the combined groups. However, it remained unchanged in the BFlh and ST muscles, and OC use did not influence these measurements either. CONCLUSION: These findings suggest that eccentric training induces similar adaptations in women regardless of OC use. Furthermore, fascicle lengthening was not attributable to changes in muscle shear modulus under the present conditions.