The Muscle Ageing and Sarcopenia Study (MASS) Lifecourse has established a comprehensive database of muscle biopsies and functional assessments from 260 adults aged 18-85 in North East England. This deep-phenotyped cohort combines skeletal muscle tissue samples with detailed measurements of physical function, health status, and lifestyle factors across the entire adult lifespan. This resource represents a significant advancement in human muscle aging research infrastructure. Previous studies of muscle aging have relied heavily on animal models or small, narrowly-focused human biopsy studies that failed to capture the complexity of aging across decades. MASS addresses this critical gap by providing researchers with unprecedented access to human tissue samples paired with comprehensive phenotyping data spanning nearly seven decades of life. The study's broad age range and interdisciplinary approach could accelerate the translation of basic science discoveries into clinical interventions for sarcopenia and age-related muscle decline. However, as this is a preprint study from a single geographic region, the generalizability of findings to diverse populations remains to be established through peer review and replication. The observational design also limits causal inferences about muscle aging mechanisms.