Advancing age is associated with progressive reductions in skeletal muscle mass, strength, and functional capacity, a condition often referred to as sarcopenia. Concurrently, aging populations are increasingly susceptible to insulin resistance, a key factor in the development of metabolic disorders. The primary aim of this study was to examine how age-related declines in skeletal muscle structure and function influence insulin resistance in adults, as measured by the Homeostasis Model Assessment of Insulin Resistance (HOMA IR). This descriptive quantitative study recruited a diverse adult sample representing both sexes and a range of physical activity levels. Skeletal muscle mass, regional distribution, and functional performance (handgrip strength and sit-to-stand test) were assessed alongside fasting glucose and insulin levels to calculate HOMA IR. Correlation analyses were conducted to explore the relationships between muscle variables and insulin resistance, enabling a comprehensive evaluation of both structural and functional predictors of metabolic health. The findings demonstrated significant inverse relationships between total and regional muscle mass, functional performance measures, and insulin resistance. Lower limb muscle mass and functional capacity emerged as particularly strong predictors of HOMA IR, emphasizing the metabolic relevance of both muscle quantity and quality. These results underscore the importance of preserving skeletal muscle through targeted interventions, including resistance training and functional exercises, to mitigate age-related insulin resistance and support long-term metabolic health.