Which of the following is an effect of engaging in physical activity?

Engaging in physical activity leads to a multitude of positive effects on both physical and mental health, and one of the most notable outcomes is the improvement in physical fitness. When individuals participate in regular exercise, they enhance various components of physical fitness, including cardiovascular endurance, muscular strength, flexibility, and body composition. This improvement is a result of the physiological adaptations that occur in response to the demands of physical activity, such as increased heart efficiency, improved oxygen uptake, and enhanced muscle function.

The other options do not align with the benefits of regular physical activity. Decreased energy levels, a heightened stress response, and an increased risk of mental illness are typically associated with a lack of physical activity or sedentary lifestyles, rather than regular engagement in exercise. In fact, consistent physical activity is known to boost energy levels, reduce stress through the release of endorphins, and lower the risk of mental health issues by promoting better mood and overall mental well-being. Therefore, the improvement in physical fitness stands out as a key positive effect of engaging in physical activity.