When examining injury rates in sports, in both men and women, it can be seen that a tearing of the anterior cruciate ligament (ACL) is one of the most common injuries.
However, although this injury is common in both genders, it is 2-8 times more likely to occur in women. Although there are obvious factors that could contribute to this increased injury rate, including biomechanical differences, anatomical differences, strength differences, as well as neuromuscular control differences. The effects that hormones such as estrogen and relaxin can have on joint laxity are often forgotten or overlooked.
This blog will serve to help gain a brief understanding of the menstrual cycle and the effects it can have on one’s joint laxity.
The menstrual cycle consists of multiple phases including the menstrual, follicular, ovulation, and luteal phases. These phases are typically on a cycle of 28 days, but can vary from person to person. The phases are as follows:
Menstrual (1-5 days)
This is the phase that is typically thought of as the period. This is when the uterus sheds its lining. Symptoms associated with this phase are bleeding, cramping, bloating, fatigue, and mood swings.
Follicular (1-13 days)
This phase overlaps with the menstrual phase. The body during this phase is preparing for ovulation, this means the pituitary gland releases follicle-stimulating hormone (FSH). Generally, during this phase energy levels will begin to rise and mood may improve.
Ovulatory (around day 14)
This stage allows for the dominant follicle from the previous stage to release a mature egg from the ovary and into the fallopian tube, where it may or may not be fertilised by sperm. Symptoms during this phase may include cervical mucus that is clear and stretchy, and some cramping or twinges in the lower abdomen.
Luteal (15- 28 days)
This phase that follows ovulation, secretes progesterone due to the ruptured follicle transforming into the corpus luteum. Progesterone helps thicken the uterine lining in preparation for a fertilised egg. If the egg is not fertilised, the corpus luteum degenerates causing estrogen and progesterone to drop. This triggers the start of menstruation if pregnancy does not occur.
The ACL is composed of fibroblasts and tightly bound collagen fibers. With more fibers comes greater strength, integrity, and ability to accept load. However, typically during days 1-14 days, or the preovulatory phase of the period, estradiol production can be found to be the highest. Laboratory studies suggest that an increase in estradiol results in a reduction in fibroblast and collagen synthesis. Additionally, relaxin, a hormone produced by the ovary and placenta contributes to the laxity of the pubic symphysis in pregnancy and childbirth, has also been been hypothesized to have an effect on joint laxity, specifically of the ACL, in non-pregnant women. Studies show that there are greater incidences of ligament damage, specifically the ACL, during the first 14 days, or pre-ovulatory phase of the period. Comparatively, these studies suggest that the lowest risk time in the menstrual cycle for these injuries are during the luteal phase, or days 15-28.
In conclusion, while factors such as biomechanics, anatomy, strength, and neuromuscular control play a significant role in female injuries, the influence of hormones on joint laxity, particularly during the menstrual cycle, should not be overlooked. Hormonal variations highlight the importance of considering the menstrual cycle when assessing injury risk and developing injury prevention strategies for female athletes. Understanding the interaction between hormones and joint stability is critical for optimising female training, recovery, and overall performance.
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