EFFECT OF POSTURAL DIFFERENCES ON THE ACTIVATION OF INTRINSIC FOOT MUSCLES DURING RAMP-UP TOE FLEXION IN YOUNG MEN

M. Komiya¹, N. Maeda¹, S. Tsutsumi¹, H. Ishihara¹, R. Mizuta¹, S. Arima¹, K. Kaneda¹, Y. Urabe¹

¹Hiroshima University, Department of Sport Rehabilitation, Graduate of Biomedical and Health Sciences, Hiroshima, Japan

Background: Intrinsic foot muscles (IFMs) exercises are used in clinical and sports practice to improve jump and balance performance. Force generation during toe flexion is greater in the standing posture than in the sitting posture; nonetheless, the mechanism underlying the activation of IFMs during force generation and whether there exists a difference between these two postures still remain unclear.

Purpose: This study aimed to compare the activation patterns of IFMs in the ramp-up task between the sitting and standing postures using high-density surface electromyography (SEMG) in order to provide useful information for the spatial and temporal aspects of exercise decisions regarding IFMs.

Methods: Seventeen men (Age; 24.8±3.0 y.o., Body mass index; 21.4±1.9 kg/m²) participated in this study. Each participant performed a force ramp-up toe flexion task from 0 to 80% of the maximal toe flexor strength (MTFS) in sitting and standing postures. High-density SEMG signals from the right IFMs were recorded using an electrode grid consisted of 64 electrodes. The grid was attached to the heel and toe fat pads with the columns along the longitudinal axis of the foot. There signals are obtained during the task were determined by calculating the root mean square (RMS). Additionally, modified entropy and coefficient of variation (CoV) were calculated at 20–80% MTFS for each 10% MTFS. The %RMS value was calculated by dividing the RMS value at each intensity by the RMS of the MTFS used in the task calculation. IFMs activity (%MVC) and TFS (%MTFS) during the ramp-up task were analyzed using two-way [Posture×TFS level] repeated-measures analysis of variance. Post-hoc analyses were performed using the paired t-test between the postures for each TFS level. The modified entropy and CoV of RMS were analyzed using the Bonferroni post hoc test for the Friedman test among the TFS levels for each group. The significance level was set at 0.05.

Results: The RMS between the two postures indicated an interaction effect (p<0.01). Post-hoc analyses revealed that intrinsic foot muscle activity during the ramp-up task was significantly higher in the standing posture than in the sitting posture at 60% MTFS (54.6±19.3 vs 67.5±15.9% maximal voluntary contraction (MVC), p=0.03), 70% MTFS (63.3±18.7 vs 78.1±12.9% MVC, p=0.01), and 80% MTFS (66.9±20.3 vs 81.8±14.1% MVC, p=0.02). In the standing posture, the modified entropy at 80% MTFS was lower than that at 20% MTFS (p=0.03), and the CoV at 80% MTFS was higher than that at 20% MTFS (p=0.03).

Conclusions: These results indicated that posture selection is important for high-intensity exercises of the IFMs, such as resistance training. Thus, improving performance related to toe flexor strength might be more effective when conducted under adequate weight-bearing situations, such as in the standing posture.

Implications: The IFMs training aimed at improving balance ability in the elderly and performance in athletes related to muscle strength might be more effective when conducted under adequate weight-bearing conditions such as the standing posture.

Funding acknowledgements: We have no funding acknowledgement in this study.

Keywords:
Intrinsic foot muscles
Surface electromyography
Toe flexor strength

Topics:
Sport & sports injuries
Musculoskeletal: lower limb

Did this work require ethics approval? Yes

Institution: Graduate School of Biomedical and Health Sciences, Hiroshima University

Committee: Hiroshima University Committee

Ethics number: E-2090