Final answer:
The man's sore muscles are likely caused by delayed onset muscle soreness (DOMS), which is a normal reaction to unfamiliar or intense physical activity and results from microscopic tears in the muscle fibers.
Step-by-step explanation:
The sore muscles experienced by the man the day after engaging in rigorous physical activity are likely due to delayed onset muscle soreness (DOMS).
When a person undertakes exercise, especially at a high intensity or when trying new activities, microscopic tears can occur in the muscle fibers. This is part of the reason someone may feel sore the following day. The sarcolemma and myofibrils in the muscle cells can be damaged after intense physical activity, leading to soreness. Muscles, however, repair this damage by adding new protein strands to muscle fibers, making them stronger and sometimes larger. This natural repair process is crucial for muscle growth. It is also worth noting that this soreness is a normal response to the stress of exercise and does not necessarily imply an injury.
Although DOMS is a common reaction to strenuous exercise, taking care to properly align joints during exercises, lifting appropriate loads, and allowing sufficient recovery time between workouts can mitigate the severity of DOMS and protect against overuse injuries.