Potential downsides to excessive exercise include increased risk of injury, fatigue, and negative effects on mental health. Overtraining can result in physical stress symptoms such as joint pain and muscle strain. It can also lead to diminished performance and burnout, which counteracts the benefits of regular exercise. Additionally, some individuals might develop an unhealthy obsession with fitness, leading to conditions like exercise addiction or eating disorders. It’s essential to find a balance in a fitness routine to ensure physical and emotional well-being, allowing for adequate rest and recovery.