What physiological change is typically enhanced by regular training?

Regular training typically enhances cardio-respiratory endurance, which refers to the ability of the heart and lungs to supply oxygen to the muscles during sustained physical activity. This improvement occurs as the body adapts to the stress of exercise through various physiological changes, such as increased stroke volume, improved oxygen uptake, and more efficient blood circulation. Over time, with consistent training, individuals experience better overall cardiovascular health, increased aerobic capacity, and enhanced performance in endurance activities.

The other options indicate physiological changes that do not correlate with the benefits of regular training. Increased fatigue can occur from overtraining or insufficient recovery, muscle stiffness may result from inactivity or improper warm-up, and reduced strength is typically not a goal of regular training, as most training methodologies aim to maintain or improve strength levels.