The world of sports and exercise physiology has been riddled with myths and assumptions, especially when it comes to gender differences. One of the most persistent beliefs is that the menstrual cycle significantly influences muscle adaptation to exercise. But how true is this statement? A recent study published in The Journal of Physiology has challenged this notion, revealing that the phases of the menstrual cycle do not affect muscle protein synthesis or myofibrillar proteolysis in response to resistance exercise.
Exploring the Myth: Hormones and Muscle Adaptation
Historically, premenopausal women have been excluded from exercise physiology research due to the belief that ovarian hormones in the menstrual cycle could alter metabolic and performance outcomes. This assumption has contributed to a gender bias in the exercise science literature. However, the evidence supporting this hypothesis is limited and often based on animal model studies that do not translate directly to humans.
It has been proposed that hormonal changes in the menstrual cycle influence protein catabolism, improving during the luteal phase compared to the follicular phase, possibly because progesterone counteracts the anabolic effect of estrogen. However, it is not clear whether this observation, based on amino acid oxidation in humans, is muscle specific. It is also suggested that muscle regeneration is greatest in the follicular phase, when estrogen is highest and progesterone lowest. Despite these speculations, few studies have examined how the phase of the menstrual cycle affects muscle anabolism. Variations in estrogen receptor RNA and protein content in muscle have also been observed during the menstrual cycle, although their relevance is still unclear.
How was the study conducted?
The study entitled “Menstrual cycle phase does not influence muscle protein synthesis or whole-body myofibrillar proteolysis in response to resistance exercise” investigated whether the phases of the menstrual cycle, characterized by fluctuations in estrogen andprogesteronelevels, affect muscle protein synthesis after resistance exercise. Twelve young, healthy women participated. Eligible candidates were between 18 and 30 years old, did not smoke or use tobacco products, and were in good health, according to a medical questionnaire. All participants reported having a regular menstrual cycle, verified by a tracking app, and had not used hormonal contraceptives in the six months prior to the study.
Key findings
The study found no differences in muscle protein synthesis or degradation across the menstrual cycle. Nor did it detect specific patterns in metabolites that might indicate variations according to cycle phase. This suggests that natural hormonal fluctuations do not affect the anabolic response of muscle to resistance exercise. These results are in agreement with those of Miller (2006), who also observed no influence of menstrual cycle phases on muscle protein synthesis at rest or after exercise. Previous studies used short-term isotope infusions to measure protein synthesis, which provides limited insight into long-term muscle growth. In contrast, this study used deuterated water to assess protein synthesis over five days, which provides a more complete picture of muscle adaptations.
Myofibrillar proteolysis was also analyzed using advanced methods and no significant differences were found between the phases of the cycle. These findings show no clear pattern of metabolic changes associated with menstrual phases, similar to previous studies using metabolomic approaches. Despite the belief that certain phases of the menstrual cycle might favor muscle anabolism, the study data do not support this idea. Considerable variability in hormone levels was observed among participants, underscoring the importance of directly measuring these hormones rather than assuming their concentrations.
This approach, involving direct assessments and advanced methods, found no evidence that one phase of the menstrual cycle is more anabolic than another. Although some studies suggest that follicular phase training may be more beneficial, the lack of rigorous methods in these papers limits their conclusions.
Final Considerations.
Understanding how hormones affect exercise physiology is crucial to developing effective and equitable training programs. This study underscores the need to reconsider gender-based assumptions in sports research and encourage the inclusion of women in future studies.
For sport professionals and students in the field, these findings offer a new perspective on coaching female athletes. Instead of adjusting training programs based on the menstrual cycle, it may be more beneficial to focus on other individual factors that affect performance and recovery.
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