Sex Differences In The Facial Expressions Of Effort During Exercise

Facial expressions quantification through surface electromyography (sEMG) have great potential in fatigue evaluation. Yet, this topic has not been widely studied, apparently due to a technological gap that does not allow convenient and accurate measurement during exercise. Recently, a new flexible multi-array electrode sensor was developed, allowing high-resolution and long-term recording. PURPOSE: To use facial electromyography for exploring gender differences in the “expression of effort” during both aerobic and anaerobic exercise. METHODS: 11 healthy (age 26 ± 5 y) subjects (6 females) performed an incremental cycling exercise test till exhaustion. A facial sticker, covering the forehead, zygomatic, buccal and labial regions by 16 embedded electrodes was used for continuous recording of sEMG. The root mean square (RMS) of the sEMG recorded from each electrode was calculated, and then averaged along the test. The RMS was then normalized to resting values. Paired T-tests were used to analyse differences in sEMG activity between exercise phases - high and low intensities (HI and LI, respectively). RESULTS: Overall, average RMS (obtained from all 16 electrodes) showed a stepwise increase with exercise intensity, reaching a maximal value of 2.4 ± 0.8, vs. 1.5 ± 0.4 for light intensity (p < 0.05). Compared with males, females presented a higher facial muscle activity in low intensity, yet lower activity in high intensity close to exhaustion. The non-frowning RMS was lower in females as compared to males at HI (2.1 ± 0.2 and 2.3 ± 0.4, respectively, p < 0.005) and higher in females at LI (1.6 ± 0.1 and 1.4 ± 0.1, respectively, p < 0.005). Similarly, the frowning RMS was higher in females as compared males at LI (1.7 ± 0.1 and 1.4 ± 0.1, respectively, p < 0.005), no significant difference found at HI. CONCLUSIONS: Facial muscles’ activity was differently expressed between males and females, and it is intensity dependent. The data allow us to further investigate the gender differences in facial muscles activation during exercise and understand "their story". The study was partially supported by a grant from Israel Defense Forces (IDF) Medical Corps and Directorate of Defense Research & Development, Israeli Ministry of Defense (IMOD DDR&D), and a grant from the Israel Science Foundation (ISF, 1355/17)