The Muscle Stretch Reflex throughout the Menstrual Cycle

Abstract

Introduction The significant sex-disparity in sports-related knee injuries may be due to underlying differences in motor control. While the development of sex-specific movement patterns is likely multi-factorial, this study specifically focuses on the potential modulatory role of sex hormones. Purpose 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 ages 18–35 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 RF varied significantly across the menstrual cycle in both groups. Specifically, the RF MSR response was 2.4 times lower during the peri-ovulatory phase when compared to the luteal phase (P = 0.007). The same trend was seen in the VM, but this did not reach statistical significance (P = 0.070). The MSR response of the VL 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 the MSR response and to determine the specific origin of the change along the monosynaptic reflex arc.

ACL Research Retreat VII: An Update on Anterior Cruciate Ligament Injury Risk Factor Identification, Screening, and Prevention

“…This idea is supported by studies that have demonstrated associations of normal physiologic variations in sex hormone concentrations across the menstrual cycle with substantial changes in markers of collagen metabolism and production, 191 kneejoint laxity, [130][131][132][133][134][135] muscle stiffness, 131 and the musclestretch reflex. 192 These biological changes may also have secondary neuromechanical consequences, as previously noted. 155,156,[158][159][160] Although results from prior epidemiologic studies have suggested that the risk of an ACL injury appears to be greater during the preovulatory phase of the menstrual cycle compared with the postovulatory phase, [193][194][195][196][197] our understanding of the underlying mechanism for this increased likelihood has not advanced.…”

Expression of sex steroid hormone receptors in human skeletal muscle during the menstrual cycle

“…The muscle stretch reflex and postural control seem to change over the menstrual cycle (Casey et al . ). Impaired postural control has been detected in the luteal phase when progesterone is high, but only in women with premenstrual symptoms (Fridén et al .…”

“…), while the muscle stretch reflex response seems to be lowest at this phase (Casey et al . ). Postural control has been reported to be impaired during the premenstrual phase (Darlington et al .…”

Fluctuations of state anxiety, spinal structure, and postural stabilityacross the menstrual cycle in active women

“…In some studies, increased levels of progesterone in the luteal phase were related to increased intensity of premenstrual complaints (anxiety, tension, irritability) (6,7), while in other studies decreased progesterone levels were found to be related to more pronounced negative mood changes (8,9). Moreover, the neuromusculoskeletal effects relating to muscle strength and stretch reflex (10), ligament laxity (11), biomechanical characteristics (12), and postural control (13,14) throughout the menstrual cycle have been investigated in the literature in order to determine the relationship between injury mechanisms in women and the differences between the sexes. Menarche itself was declared to be a risk factor in some sports and conditions (15).…”