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Ankle and foot injuries are common among athletes and physically active individuals. The most common residual disability, ankle sprain, is characterized by instability along with postural sway. If the supporting structures around a joint become lax, posture stability and balance are also affected. Previous studies have examined muscle stiffness and elasticity and postural sway separately; however, the relationship between these factors is yet unknown. It is well known that the levels of sex hormones, especially estrogen, change in women over the phase of the menstrual cycle. Therefore, this study examined the relationship between the mechanical properties of tissue and balance activity using a non-invasive digital palpation device to determine if they undergo any changes over the menstrual cycle in young women.

Sixteen young women with regular menstrual cycles completed the study. Tone, stiffness, and elasticity of the ankle muscles (lateral gastrocnemius, peroneus longus, and tibialis anterior) were measured using a non-invasive digital palpation device.

Postural sway was recorded while the participants performed balance tasks during ovulation and menstruation.

Significantly greater posture sway characteristics and ankle muscle elasticity were found during ovulation than during menstruation; lower tone and stiffness of the ankle muscles were observed at ovulation (p < 0.05). Additionally, weak-to-strong relationships between ankle muscle mechanical properties and postural sway characteristics were found (p < 0.05).

These results suggest the effect of estrogen on human connective tissues. We therefore postulate that estrogen increases joint and muscle laxity and affects posture stability according to the phase of the menstrual cycle.

Keywords: ankle muscles; dynamic stiffness; menstrual cycle; muscle elasticity; postural sway

Sexual hormones such as estradiol and progesterone and even testosterone concentration in either blood or saliva should be measured to confirm the sexual hormone changes during the menstrual cycle. In addition, muscle tone, stiffness, and elasticity were measured only once in the relaxed position. In a previous study (Vain et al. 2015), researchers assessed these mechanical variables on subjects with them standing and in the relaxed position, which can show more precise correlations between variables. Finally, it would be useful to stabilize limb temperature to see the effect of body and shell temperature and estrogen independently. Therefore, we recommend that women should be aware of these changes of muscle tone, mechanical properties, and its relation to postural sway throughout the menstrual cycle to prevent risk of lower extremity injuries during sports activities.