What happens inside a tennis players body after the energy is in his muscles?

Once energy is stored in a tennis player's muscles, it is converted into mechanical energy through muscle contractions during play. This process primarily relies on adenosine triphosphate (ATP) for immediate energy. As the match progresses, the body utilizes anaerobic and aerobic energy systems to sustain performance, leading to lactic acid buildup in anaerobic conditions, which can cause fatigue. Additionally, the cardiovascular and respiratory systems work to deliver oxygen and nutrients to the muscles while removing waste products.