Author(s): ABENZA, Ó., GARCIA-RETORTILLO, S., BALAGUÉ, N., IVANOV, P., Institution: UNIVERSITAT DE BARCELONA, Country: SPAIN, Abstract-ID: 2149

INTRODUCTION:
Inter-muscular coordination measures how muscle groups synchronize their activation to move effectively and efficiently. A recent method has been developed to assess inter-muscular cross-frequency interactions through surface electromyogram (sEMG) (Garcia-Retortillo et al., 2023). The examination of spectral components within different frequency bands in sEMG signals can provide information about motor unit recruitment and fiber-type contributions to muscle activation.
Females exhibit greater muscle endurance due to their higher proportion of intermediate and Type I fibers compared to males, who typically present a higher proportion of Type II fast fibers. However, sex-related differences in the coordination of distinct fiber types across muscles have not yet been investigated. This study aimed to compare inter-muscular coordination during an endurance squat test performed until exhaustion in males and females.
METHODS:
Thirty-one sport science students (eleven males and twenty females) performed a bodyweight squat test until exhaustion. The squatting pace was controlled using a metronome (3:3 tempo; 3 sec. for eccentric and concentric phases, respectively). Simultaneous recordings of EMG signals from specific leg and back muscles were obtained during the squat test. The EMG recordings were initially decomposed into ten frequency bands [F1-F10], representing the activation of distinct muscle fiber types. Subsequently, inter-muscular coordination was quantified by pairwise coupling (cross-correlation C; amplitude-amplitude coupling) between the time series for all EMG spectral power frequency bands in each leg/back muscle.
RESULTS:
Overall, female adults exhibited higher coupling strength for all EMG frequency bands in leg and back muscles (CMEAN= 0.59, SD= 0.10) compared to male adults (CMEAN= 0.48, SD= 0.13; p < 0.05). Notably, these differences were more pronounced for intermediate [F4-F7] and high [F8-F10] EMG frequency bands, associated with the activation of type-II fast fibers (CMEAN= 0.48, SD=0.15 in males; CMEAN= 0.60, SD=0.12 in females), compared to the lowest frequency [F1-F3] EMG bands (CMEAN = 0.62, SD= 0.12 in males; CMEAN = 0.65, SD=0.11 in females).
CONCLUSION:
The uncovered higher degree of inter-muscular coordination in young female adults suggests greater neuromuscular efficiency during muscle endurance tasks, leading to a greater tolerance to fatigue. The increase in coordination among type-II fast fibers across muscles may serve as a compensatory mechanism to offset the reduced proportion of type-II fibers in females. This dynamic network approach to inter-muscular coordination has the potential to improve the understanding of sex-related differences during exercise.
REFERENCES:
1. Garcia-Retortillo, S., Romero-Gómez, C., & Ivanov, P. C. (2023). Network of muscle fibers activation facilitates inter-muscular coordination, adapts to fatigue and reflects muscle function. Communications Biology, 891(6). https://doi.org/10.1038/s42003-023-05204-3