Journal of Sport and Health Science最新文献

Background: While Nordic hamstring exercise (NHE) training has been shown to reduce hamstring strains, the muscle-specific adaptations to NHE across the 4 hamstrings remain unclear. This study investigates architectural and microstructural adaptations of the biceps femoris short head (BFsh), biceps femoris long head (BFlh), semitendinosus (ST), and semimembranosus (SM) in response to an NHE intervention.

Methods: Eleven subjects completed 9 weeks of supervised NHE training followed by 3 weeks of detraining. Magnetic resonance imaging was performed at pre-training, post-training, and detraining to assess architectural (volume, fiber tract length, and fiber tract angle) and microstructural (axial (AD), mean (MD), radial (RD) diffusivities, and fractional anisotropy (FA)) parameters of the 4 hamstrings.

Results: NHE training induced significant but non-uniform hamstring muscle hypertrophy (BFsh: 22%, BFlh: 9%, ST: 26%, SM: 6%) and fiber tract length increase (BFsh: 11%, BFlh: 7%, ST: 18%, SM: 10%). AD (5%), MD (4%), and RD (5%) showed significant increases, but fiber tract angle and FA remained unchanged. After detraining, only ST showed a significant reduction (8%) in volume, which remained higher than the pre-training value. While fiber tract lengths returned to baseline, AD, MD, and RD remained higher than pre-training levels for all hamstrings.

Conclusion: The 9-week NHE training substantially increased hamstring muscle volume with greater hypertrophy in ST and BFsh. Hypertrophy was accompanied by increases in fiber tract lengths and cross-sections (increased RD). After 3 weeks of detraining, fiber tract length gains across all hamstrings declined, emphasizing the importance of sustained training to maintain all the protective adaptations.

Exercise is a therapeutic approach in cancer treatment, providing several benefits. Moreover, exercise is associated with a reduced risk for developing a range of cancers and for their recurrence, as well as with improving survival, even though the underlying mechanisms remain unclear. Preclinical and clinical evidence shows that the acute effects of a single exercise session can suppress the growth of various cancer cell lines in vitro. This suppression is potentially due to altered concentrations of hormones (e.g., insulin) and cytokines (e.g., tumor necrosis factor alpha and interleukin 6) after exercise. These factors, known to be involved in tumorigenesis, may explain why exercise is associated with reduced cancer incidence, recurrence, and mortality. However, the effects of short- (<8 weeks) and long-term (≥8 weeks) exercise programs on cancer cells have been reported with mixed results. Although more research is needed, it appears that interventions incorporating both exercise and diet seem to have greater inhibitory effects on cancer cell growth in both apparently healthy subjects as well as in cancer patients. Although speculative, these suppressive effects on cancer cells may be driven by changes in body weight and composition as well as by a reduction in low-grade inflammation often associated with sedentary behavior, low muscle mass, and excess fat mass in cancer patients. Taken together, such interventions could alter the systemic levels of suppressive circulating factors, leading to a less favorable environment for tumorigenesis. While regular exercise and a healthy diet may establish a more cancer-suppressive environment, each acute bout of exercise provides a further "dose" of anticancer medicine. Therefore, integrating regular exercise could potentially play a significant role in cancer management, highlighting the need for future investigations in this promising area of research.

Background: Deficits in quadriceps strength of the injured leg have been observed in patients following anterior cruciate ligament (ACL) reconstructions and may contribute to ACL re-injury risk. Single-leg forward hopping is a widely used task for assessing knee function in patients following ACL reconstructions as it has been shown not to be particularly challenging to the knee. This study aimed to quantify the effect of decreased quadriceps strength induced by a fatigue protocol on hopping performance and lower limb mechanics in single-leg forward, vertical, and backward hopping.

Methods: Thirty-four injury-free participants performed single-leg forward, vertical, and backward hopping on both legs pre- and post-fatigue, with 1 leg experiencing a fatigue protocol. Peak moments, power, and work of hip, knee, and ankle joints were quantified during the jumping phase. Hopping performance and bilateral asymmetries in performance were assessed.

Results: Single-leg backward hopping demonstrated the greatest knee moments, power, and work compared to forward and vertical hopping, regardless of leg and fatigue. Fatigue protocol resulted in significantly less knee moments, power, and work, and decreased performance of the fatigued leg among all tasks. Bilateral symmetries in hopping performance decreased in post-fatigue, with the greatest decrease in backward hopping.

Conclusion: The greater sensitivity of the backward hopping to detect quadriceps fatigue suggests it may act as a better or at least an additional metric to evaluate quadriceps strength deficits. The findings may contribute to the development of a clinically applicable and valid strength assessment to monitor the rehabilitation progress in patients following ACL reconstructions.