Final answer:
The accumulation of lactic acid is the main factor causing recovery resistance after sprints due to anaerobic metabolism generating excess lactic acid, which lowers intracellular pH and leads to muscle fatigue.
Step-by-step explanation:
The primary factor contributing to recovery resistance after sprints on a flat surface is C) Accumulation of lactic acid. When you sprint, your muscles engage in anaerobic metabolism due to the high demand for energy over a short period, which leads to the production of lactic acid as a byproduct. This buildup of lactic acid can result in decreased pH within the muscle cells, affecting enzyme and protein activity and leading to muscle fatigue. Moreover, the exhaustion of energy reserves also contributes, as ATP is a crucial energy source for muscle contractions, and high-intensity activities like sprints deplete ATP much faster than longer, endurance-focused activities such as marathons. During recovery, the body must clear the lactic acid and replenish ATP, which is why adequate rest and proper nutrition are necessary post-exercise to facilitate quick recovery.