Author(s): ROMERO VALIA, L., GARCIA AGUIRRE, M., GUTIERREZ REGUERO, H., GARCIA ALBIN, D., BUENDÍA ROMERO, A., BALTASAR FERNANDEZ, I., ARA ROYO, I., GARCIA GARCIA, F.J., ALEGRE, L.M., ALCAZAR, J., Institution: UNIVERSITY OF CASTILLA-LA MANCHA, Country: SPAIN, Abstract-ID: 2030

INTRODUCTION:
The 5-repetition sit-to-stand (STS) muscle power test has emerged as a feasible and valid test to assess lower-limb muscle power in older adults. Skeletal muscle size is hypothesized to be one of the main determinants of muscle function during aging. The main goal of this study was to assess the relationship between regional vastus lateralis anatomical cross-sectional area (ACSA), muscle volume (MV) and allometric STS power in institutionalised older adults.
METHODS:
A cross-sectional study was conducted in thirty-one institutionalised older adults (13 men, 18 women; 81.9±8.9 years). Muscle ultrasound (GE Healthcare, Logiq F6, USA) was used to assess vastus lateralis ACSA at 35% (proximal), 50% (mid), and 65% (distal) of femur length, and vastus lateralis MV was calculated (Cornejo-Daza et al., 2024). All muscle size variables were normalised by body size (i.e. height squared, m²). Allometric STS power (W·m-²) was estimated from the 5-rep STS test using the equation proposed by Alcazar et al. (2018). Low allometric STS power was defined as <75.4 W·m-² in older men and <61.5 W·m-² in older women (Alcazar et al., 2021). In addition, specific STS power was calculated as the ratio of STS power and the different muscle size measures: mean ACSA, calculated as the average of regional ACSA values (W·cm-²) and MV (W·cm-³). Sex differences were examined using the Mann-Whitney U test. Unadjusted and age- and sex-adjusted linear regression models were performed to examine the association between allometric STS power and muscle size variables (SPSS v29.0)
RESULTS:
Low allometric STS power was observed in 54% of men and 44% of women. No differences between women and men were found in allometric STS power (81.5±32.1 vs 69.5±30.0 W·m-²; p=0.275), specific STS power (eg, 0.64±0.19 vs 0.68±0.32 W·cm-³; p>=0.258) or muscle size parameters (eg, MV=126.7±29.2 vs 102.8±14.3 cm-³·m-²; p>=0.062). Allometric STS power was initially associated with ACSA at 50% of femur length (std. ß=0.54; p=0.002) and MV (std. ß=0.43; p=0.017), but not with ACSA at 35% or 65% of femur length (std. ß<=0.37;p>=0.371). After adjusting for age and sex, no independent associations were found between any of the muscle size variables and allometric STS power (std. ß<=0.29;p>=0.068).
CONCLUSION:
In institutionalised older adults, vastus lateralis muscle size was not an independent predictor of STS muscle power, suggesting that factors beyond muscle quantity may influence muscle power production.

Funding: CB16/10/00456; CB16/10/00477; 2025-GRIN-38408; TEC 2022-007; SBPLY/19/180501/000312; PI031558; PI07/90637; PI07/90306; RD 06/0013; PI18/00972; SBPLY/23/180225/000155
References: Alcazar et al. J Cachexia Sarcopenia Muscle. 2021; 12(4): 921-932; Alcazar et al. Exp Gerontol. 2018; 112: 38-43; Cornejo-Daza et al. J Strength Cond Res. 2024; 38(3): 450-458.