Pinch strength and its variability: Novel insights into functional decline in sarcopenic obesity

Sarcopenic obesity (SO) represents a complex nutritional state associated with adverse health outcomes, especially in older adults. While grip strength has been extensively studied in relation to functional status, the role of pinch strength remains underexplored. This study aimed to investigate the associations between pinch strength parameters and different body composition phenotypes and to explore its potential role in the relationship between SO and functional status, including physical performance, cognitive function, and frailty.

This cross-sectional study included 954 community-dwelling older adults, categorized into four groups: healthy controls (HC), obesity only, sarcopenia only, and SO. We assessed body composition via bioelectrical impedance analysis, muscle strength (grip and pinch dynamometry), physical performance, cognitive function, and frailty. Sex-stratified correlation networks and mediation analyses were performed to elucidate relationships between body composition, muscle strength parameters, and functional status.

The SO and sarcopenia groups demonstrated significantly reduced pinch strength compared to the HC and obesity groups (e.g., women: 2.2 ± 0.8 kg in SO vs. 3.5 ± 1.1 kg in HC, P < 0.001), with higher pinch/grip ratios (0.20-0.25 vs. 0.15-0.20, P < 0.05). Notably, the SO groups exhibited significantly greater pinch strength variability (Coefficient of Variation) in both men and women (CV for women: 18.5% in SO vs. 12.1% in HC, P < 0.001), suggesting impaired neuromuscular control of fine motor function. The SO group exhibited the poorest functional performance. Mediation analyses suggested that pinch strength was a significant intermediary in the association between SO and cognitive impairment, and partially in the association with frailty in women ((indirect effect log-OR = -0.07, 95% CI [-0.12, -0.03] in women).

Pinch strength and its variability are strongly associated with SO and represent important markers of functional status. This finding identifies pinch strength as a potential clinically accessible biomarker for the early detection of functional decline in older adults with this double burden of malnutrition. The differential preservation of pinch versus grip strength and sex-specific potential pathways highlights the need for comprehensive hand function assessment in the nutritional and clinical evaluation of SO.