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Introduction: The significant sex disparity in sports-related knee injuries may be due to underlying differences in motor control. Although the development of sex-specific movement patterns is likely multifactorial, this study specifically focuses on the potential modulatory role of sex hormones. Purpose: This study aimed to investigate the muscle stretch reflex (MSR) across the menstrual cycle. We hypothesized that the MSR would fluctuate throughout the menstrual cycle and that the lowest response would correspond with peak concentrations of estrogen. Methods: Nineteen healthy women age 18-35 yr participated in this study: 8 eumenorrheic women and 11 women taking oral contraceptives. Serum estradiol and progesterone concentrations, anterior knee laxity (AKL), and the MSR response of the quadriceps muscles were measured three times during the menstrual cycle. Results: The MSR response of the rectus femoris (RF) varied significantly across the menstrual cycle in both groups. Specifically, the RF MSR response was 2.4 times lower during the periovulatory phase when compared with the luteal phase (P = 0.007). The same trend was seen in the vastus medialis, but this did not reach statistical significance (P = 0.070). The MSR response of the vastus lateralis did not change significantly across the menstrual cycle (P = 0.494). A mixed model comparison did not show an association between endogenous concentrations of estradiol and progesterone, exposure to hormonal contraceptives or AKL, and the MSR response for any muscle. Conclusions: Our results demonstrate that the RF MSR response varies throughout the menstrual cycle with the lowest response around the time of ovulation. Additional research is needed to clarify the exact relationship between sex hormones, AKL, and MSR response and to determine the specific origin of the change along the monosynaptic reflex arc. [ABSTRACT FROM AUTHOR]

The article presents a study on the effect of sex differences in anterior knee laxity (AKL) towards the knee joint biomechanics during weight acceptance. According to the article, serious knee trauma, such as anterior cruciate ligament (ACL) injury, occurs when the knee converts from non-weight-bearing (NWB) to weight-bearing (WB) during sudden deceleration or change-of-direction with the knee relatively extended. It is said that females have higher risk of suffering ACL injury and are reported to have greater AKL values than males, with these differences being more pronounced at certain times of their menstrual cycle. It also mentions that AKL is a measure of the displacement of the tibia relative to the femur in response to an anterior-directed load applied to the tibia.

The article presents a study which examines the association of anterior knee laxity (AKL), general joint laxity (GJL), and genu recurvatum (GR) to sagittal plane energetics during a drop jump task in males and females. The study involves 50 males and 68 females who were assessed for AKL, GJL, and GR and were equipped with instruments to get biomechanical and neuromuscular data on their dominant limb during a 45-centimeter drop jump as first landing phase. The result shows that the joint laxity in males has little effect on knee energetics, although an important relationship was seen between greater GJL and reduced ankle stiffness. It concludes that females with lower GR and greater GJL and AKL showed a landing technique that amplified work absorption and stiffness on the knee.

The article examines one study which investigates whether fatigue-induced landing biomechanics have been governed by a centrally fatiguing mechanism. It is believed that fatigue does contribute directly to anterior cruciate ligament (ACL) injury through high risk biomechanics. For investigation purposes, 20 female athletes associated with the National Collegiate Athletic Association (NCAA) were asked to perform single-leg squats and randomly ordered landings for them to feel fatigue. After data analysis, it was revealed that there do exist a central fatigue that must be controlled effectively in order to successfully counter the debilitative impact of fatigue on ACL injury risk.