Excessive cardio can negatively impact muscle mass by promoting muscle catabolism if not balanced with proper nutrition and resistance training. When engaging in prolonged aerobic exercise, the body may start to break down muscle tissue for energy, particularly if calorie intake is insufficient. This can lead to a reduction in strength and overall metabolism. To mitigate this effect, practitioners should incorporate strength training and ensure adequate protein consumption to support muscle maintenance during high-volume cardio regimens, fostering a balanced approach to fitness.