Assessment Of Changes In Muscle Glycogen Content Across The Menstrual Cycle

Abstract

Muscle glycogen content (MGC) has the potential to impact exercise performance and has implications for timing of exercise testing & prescription. Previously difficult to assess, MGC can now be estimated non-invasively using ultrasound imaging. PURPOSE: The aim of this study was to compare changes in muscle glycogen scores across the menstrual cycle using ultrasound imaging. METHODS: Twenty-eight subjects (10 male; 18 female) ages 18-30 (24.0 ± 2.78) participated in this study. Subjects were divided into Control (CON; 10 male), Non-Contraceptive (NC; 8 Female), and Oral-Contraceptive (OC; 10 Female) groups. Measurements at 22, 56, & 73% of the thigh were taken on the vastus medialis, vastus lateralis, & rectus femoris of the dominant leg using ultrasound. Subjects were measured at the follicular, ovulatory & luteal phases of the menstrual cycle. Using ImageJ, muscle pixelation values were determined by capturing a 25 x 8 mm section of the muscle directly below the superficial aponeurosis. The mean of three images from each site were taken and adjusted for gain setting to calculate a total leg MGC score. A higher pixelation value corresponds to a lower MGC score and vice versa. A repeated-measures ANOVA (group X time) with post-hoc comparisons was performed to assess differences across groups and visits. RESULTS: No significant differences in MGC were observed between visits or groups (all p>.05). The CON (0.96 ± 0.21, 0.82 ± 0.10; 0.86 ± 0.23) and the OC (1.05 ± 0.17; 0.94 ± 0.17; 1.01 ± 0.18) groups showed a tendency to increase MGC during the ovulatory visit but for the NC group (0.97 ± 0.15; 1.05 ± 0.27; 0.91 ± 0.15) to decrease (Figure 1). CONCLUSIONS: While there were no significant effects found, there was a trend for the MGC of the CON and the OC groups to increase during the ovulatory visit but for the NC to decrease. Further research is needed to fully understand the implications of these changes during the menstrual cycle and how it relates to exercise performance.