Which of these is a long-term adaptation to regular exercise?

Regular exercise leads to several physiological changes in the body over time, and a decreased resting heart rate is one of the significant long-term adaptations. When an individual engages in consistent cardiovascular exercise, the heart becomes more efficient due to several factors, including increased stroke volume (the amount of blood pumped per heartbeat) and better cardiovascular health overall. As a result of these adaptations, the heart doesn't need to work as hard to maintain circulation when the body is at rest, thus leading to a lower resting heart rate.

In contrast, the other options do not reflect long-term adaptations. An increased heart rate during exercise is a normal response to the physical demands being placed on the body and does not indicate a long-term adaptation. Increased muscle soreness is typically a short-term response to new or intense exercise, often associated with delayed onset muscle soreness (DOMS), rather than an adaptation. Immediate energy release from ATP is a process that occurs in the muscle cells during activity and is an acute response rather than a change that occurs with long-term training.