Association between dominant and non-dominant limb concentric quadriceps strength and low skeletal muscle mass index in community-dwelling older adults: a cross-sectional study

Background Sarcopenia is common in older adults and predicts adverse outcomes. Contemporary consensus definitions use low muscle strength as the entry point for case-finding, but confirmation requires demonstration of low muscle mass, typically quantified by dual-energy X-ray absorptiometry (DXA) or bioelectrical impedance analysis (BIA), which are not universally accessible. Quadriceps strength is functionally central to lower-limb health and can be objectively measured by concentric dynamometry. However, previous concentric studies in sarcopenia have typically assessed a single, usually dominant, limb, and the relative contribution of the dominant and non-dominant limbs to the association with muscle mass has not been examined. We therefore compared concentric knee muscle performance between the dominant and non-dominant limbs and examined the association of dominant and non-dominant limb quadriceps strength with low skeletal muscle mass index (low SMI) in community-dwelling older adults. Methods In this cross-sectional study, community-dwelling adults aged ≥ 60 years underwent concentric knee strength testing at an angular velocity of 60°/s. Peak torque, total work, and average power of the quadriceps and hamstrings were measured bilaterally, and the hamstring-to-quadriceps (H: Q) ratio was calculated. Leg dominance was self-reported, and right- and left-side values were reassigned to the dominant and non-dominant limbs. Participants were classified as normal SMI or low SMI using sex-specific Asian Working Group for Sarcopenia (AWGS) 2019 criteria. Paired t-tests compared dominant and non-dominant limb variables; age- and sex-adjusted binary logistic regression, receiver operating characteristic (ROC) curve analysis with DeLong comparison, and a mixed-design (limb SMI group) analysis evaluated the contribution of each limb to low SMI. Results A total of 171 participants were included in the analysis (139 normal SMI, 32 low SMI; mean age 69.88 ± 7.97 years). Dominant limb quadriceps peak torque, total work, and average power were significantly greater than the corresponding non-dominant limb values (all p ≤ 0.004), whereas hamstring variables showed no significant between-limb differences. In adjusted models, higher quadriceps peak torque, total work, and average power of the dominant limb were associated with lower odds of low SMI (odds ratios [ORs] 0.968, 0.993, and 0.958; all p ≤ 0.010); in the non-dominant limb, total work and average power were significantly associated (ORs 0.994 and 0.966; p = 0.049 and 0.030), whereas peak torque was not (OR 0.976; p = 0.058). The limb × SMI group interaction was not significant for any quadriceps variable (all p > 0.10). Area-under-the-curve (AUC) values were similar for the dominant (0.63–0.64) and non-dominant limbs (0.60–0.64; all DeLong p ≥ 0.34), and all remained below 0.70. Conclusions Lower quadriceps strength in both the dominant and non-dominant limbs was associated with low SMI, and neither limb contributed disproportionately to this association or showed superior discriminative ability. These findings indicate a bilateral reduction in knee-extensor strength that is independent of limb dominance; given the modest discrimination, quadriceps concentric strength should complement, rather than replace, established muscle mass assessment.