How is the intensity of cardio exercise primarily determined?

The intensity of cardio exercise is primarily determined by heart rate because heart rate measures how hard your heart is working during the activity. When engaging in cardiovascular exercise, as the intensity increases, so does the heart rate, reflecting greater exertion and oxygen consumption by the body. A higher heart rate indicates that the body is working at a more intense level, which is crucial for assessing the effectiveness of workouts in improving cardiovascular health and endurance.

While duration of the workout, type of exercise, and amount of calories burned can influence overall fitness and weight loss, they do not directly measure the intensity of the exercise itself. Duration affects total workload over time but does not inherently change the heart's response. Different types of exercise can have varying intensities, but the specific measure of intensity is best observed through heart rate. Calories burned provides a result of the workout's effectiveness but does not reflect the exercise's intensity during performance. Hence, heart rate remains the most precise gauge of exercise intensity.