Author(s): PARRELLA, M., BORZUOLA, R.1, SICILIANO, F.P.1, ARVANITIDIS, M.2, NUCCIO, S.1, FALLA, D.2, PIACENTINI, M.F.1, MACALUSO, A.1, Institution: UNIVERSITÀ DEGLI STUDI DI ROMA , Country: ITALY, Abstract-ID: 2300

INTRODUCTION:
Fatigue resistance of the trunk extensor muscles is associated with mobility in older adults (1). However, the neuromuscular mechanisms associated with age-related changes in fatigue resistance of these muscles are unclear. When muscle fatigue occurs, changes in the spatial distribution of motor unit activity within a muscle or muscle group play a significant role in modulating motor output (2). This study aims to examine how ageing affects the spatial distribution of lumbar erector spinae (ES) activity during a fatiguing task. Preliminary findings are reported here and will be updated at the time of the congress.
METHODS:
Fourteen volunteers, 7 older (O, age: 66±1) and 7 young (Y, age: 25±2), performed an isometric trunk extension at 30% of their maximal voluntary isometric force until failure. High-density surface electromyography signals were recorded using a 13x5 grid of electrodes placed over the lumbar ES. Mean power spectral frequency (MNF) was computed across the entire grid, and the x- and y-coordinates of the centre of gravity (CoG) of the root mean square (RMS) map were measured for the medial-lateral and cranial-caudal direction, respectively. Force steadiness was quantified using the coefficient of variation of force (CVf). A two-way mixed ANOVA was used to detect differences in MNF, CoG coordinates and the CVf over time (5 epochs of equal duration) and between groups. The Wilcoxon test was performed to compare endurance time between groups.
RESULTS:
Endurance time did not differ between groups (Y: 85.80±48.60s; O: 81.00±39.60s) (p=0.90). MNF significantly decreased from the beginning to the end of the fatiguing task in both Y (p<0.01) and O (p<0.01). There was a significant time*group interaction for the x-coordinate of the CoG (p<0.01), indicating a shift of the CoG in the lateral direction in O, while the opposite was observed in Y, particularly for the last two epochs. A trend was observed for the y-coordinate (p=0.08) with O exhibiting a more caudal position of the CoG compared to Y. Lastly, CVf significantly increased at the end of the fatiguing task in both Y (p=0.01) and O (p=0.01).
CONCLUSION:
Preliminary observations show comparable trunk extension endurance in older and young subjects together with a comparable decrease in MNF and an increase in CVf during the sustained task. However, the spatial distribution of ES activity differed between groups, suggesting a different motor control strategy to counteract fatigue of the ES with ageing. Likely, a different load sharing within the ES muscle occurs. However, this does not affect endurance time.
REFERENCES
1) Habenicht et al., Journal of neuroengineering and rehabilitation, 2020
2) Farina et al., Journal of electromyography and kinesiology, 2008