Age-related muscle loss, known as sarcopenia, affects overall fitness levels by decreasing strength, balance, and functional mobility. As individuals age, the rate of muscle synthesis declines while the breakdown rate increases, leading to reduced muscle mass and quality. This results in diminished athletic performance, higher injury risks, and challenges in performing daily activities. Incorporating strength training and adequate protein intake can help mitigate these effects, preserving muscle function and overall fitness and promoting better quality of life as one ages.