Genetics play a significant role in determining fitness levels by influencing physical traits such as muscle fiber composition, metabolism, and response to training. Some individuals may naturally have a higher proportion of fast-twitch fibers, making them better suited for explosive activities, while others may excel in endurance sports due to a higher percentage of slow-twitch fibers. Genetic predispositions can affect how efficiently individuals gain strength, lose weight, or recover from exercise, underscoring the need for personalized training approaches.