You conduct an experiment on twenty 18-year-old female subjects to see how various intensities of exercise influence heart rate. Which of the following is/are considered an independent variable?

age of subjects

gender of subjects

more than one of these

intensity of exercise

heart rate

"Heart rate" is considered as a independent variable.

Explanation:

The rise in cardiac output at concentrations up to 50-60% of a individual's extreme heart rate is attributable to surge in heart rate and stroke volume. As the strength of exercise surpasses 60% of a individual's determined heart rate the rise in cardiac output is exclusively attributable to rise in heart rate. All through exercise, heart rate can increase intensely, from a latent rate of 60–80 beats per minute to a extreme rate of around 200 for a young adult. While you are running, blood flow is abstracted toward tissues that need it most. For example, muscles in the arteries in your legs relax to allow more blood flow.