Mixing different aerobic and strength-building activities helps to prevent which of the following?

Mixing different aerobic and strength-building activities is effective in preventing overuse injuries. This approach of cross-training allows the body to engage different muscle groups and energy systems, reducing the repetitive stress that occurs when performing the same type of exercise repeatedly. Overuse injuries typically arise from excessive strain on specific muscles or joints, often due to the lack of variation in exercise routines. By integrating various activities, such as swimming, running, cycling, and strength training, the body can recover more effectively, and the risk of injury associated with continuous stress on particular areas is minimized.

In contrast, fatigue primarily relates to the body's energy levels and can occur even with varied workouts if not managed properly. Weight gain can result from various factors including diet and overall lifestyle, and muscle atrophy generally occurs due to inactivity or insufficient stimulus to the muscles, which might not be directly addressed by simply mixing workout types. Thus, the most direct benefit of diversifying exercise routines is in preventing overuse injuries.