Author(s): BRUSCO, C.M., CARBONARO, M., MARTINO, G., LAURETANI, F., PORCELLI, S., BOTTER, A., FRANCHI, M., Institution: UNIVERSITÀ DEGLI STUDI DI PADOVA, Country: ITALY, Abstract-ID: 2520

INTRODUCTION:
The capacity of a muscle to produce force to move the human body is significantly affected by the aging process. Alongside the decline in neuromuscular function, structural changes in muscle architecture and in the morphology of the contractile and non-contractile tissues also occur with aging, which might in turn affect force capacity [1,2]. Namely, when contracted, pennate muscles change in fascicle length and angle [3], hence the absolute decrease in fascicle length and fascicle pennation angle with age [4] might also impact relative fascicle behave during contraction. In addition, aging muscles present greater muscle stiffness. As intramuscular connective tissue has a key role in maintaining the structural integrity of the muscle, these alterations might also impact how connective tissue and muscle stiffness will influence muscle shape changes during contraction [5]. In this study we analyzed age differences in fascicle behavior during ramped isometric knee extension.
METHODS:
In this preliminary analyses of an ongoing study, data of five (E) elderly (76 ±4 years) and five young (Y) adults (26±2 years) were analysed. Ultrasound imaging of the vastus lateralis (VL) was recorded during isometric ramp contractions up to 30% and 50% of the maximum voluntary contraction (MVC) with slow force increase (2% MVC/s). The probe was placed longitudinally and the recording was synchronized to the force trace. Changes in fascicle behaviour (fascicle length- Lf, fascicle angle- FA, and muscle thickness- MT) were compared from the beginning of the force contractions to 10, 20 and 30% of MVC.
RESULTS:
Paired sample t-tests did not reveal significant differences between E and Y were observed for Lf, FA and MT at any time point (p>0.05). In the E group, significant decrease in muscle thickness was observed between the beginning of the contraction to 10 (p=0.02), 20 (p=0.01) and 30% (p<0.01) of MVC, whereas no significant differences were detected in Lf and FA. In the Y group, no significant differences were detected in Lf, FA and MT from the beginning of the contraction to the different time points.
CONCLUSION:
Although preliminary, the change in muscle morphology, as described by the decrease in muscle thickness with increased contraction levels observed in the elderly, might indicate alterations of the contractile and non-contractile tissue interfering in muscle behaviour.

References
1. Imrani L et al. (2022) J Gerontol A Biol Sci Med Sci
2. Fede C et al. (2022) Int J Mol Sci
3. Eng CM. et al. (2018) Integr Comp Biol.
4. Narici MV et al. (2021) J Cachexia. Sarcopenia Muscle
5. Holt NC et al. (2016) J Exp Biol