When applying the physiological principle of overload to a cardio-respiratory workout what muscle should you target?

When applying the physiological principle of overload to a cardio-respiratory workout, the primary muscle to target is the heart. By increasing the intensity, duration, or frequency of cardiovascular exercise, you can enhance the heart's capacity to pump blood and improve overall cardiovascular endurance. Additionally, engaging muscles involved in respiration, like the diaphragm and intercostal muscles, can also benefit from overload to improve breathing efficiency during intense workouts.