The only cure for skin burn is slow healing, although skin creams can help. Heart fatigue is caused by pushing too hard for your fitness level. The symptoms are a pounding heart, gasping for breath, lack of energy on hills, a feeling of internal stress, and becoming flush with heat. This problem is more likely to occur after traveling beyond the normal distance and is most likely to show up when climbing a hill. The cure is to stop, cool down, take a break, and give the heart a chance to recover.
Prevention can come from cycling at a slower pace or by training up to a higher fitness level.
Muscle exhaustion is caused by burning up the energy stored in the muscles, sometimes called the bonk. If heart fatigue comes mostly from pushing too hard, this problem occurs mainly from pushing too far. Symptoms are difficulty in pedaling, a desire to coast, and sometimes cramping. The effects of muscle exhaustion can last more than one day. Take a break, ingest sugars, travel at a slower pace, and train up.