What is a key characteristic of vigorous intensity exercise?

Vigorous intensity exercise is defined by the amount of effort it requires from the participant, making option B the correct choice. This level of exercise demands a higher heart rate and involves more strenuous activities compared to moderate intensity exercise. It typically brings into play activities such as running, swimming laps, or competitive sports, where individuals are pushing themselves significantly more.

Sustaining vigorous exercise for long periods without fatigue is generally not feasible for most people, as it often leads to quicker exhaustion. Options that imply gentle activities like light stretching and walking do not align with the vigorous intensity category, which necessitates pushing one's physical limits. Additionally, while some people at higher fitness levels may engage in vigorous exercise comfortably, it is not universally suitable for all fitness levels, as it can pose risks for those who are less conditioned or have certain health conditions. Thus, vigorous intensity exercise is specifically characterized by its higher energy and effort requirements compared to moderate intensity activities.