Which of the following would NOT help increase cardio fitness?

Walking slowly for long periods is less effective for increasing cardio fitness compared to the other options because it typically does not raise the heart rate to a level that significantly improves cardiovascular conditioning. For cardio fitness to improve, activities need to engage the cardiovascular system at a moderate to high intensity for sustained periods.

While walking does have health benefits and can contribute to overall physical activity levels, the intensity of slow walking may not be sufficient to provide the cardio fitness improvements that more elevated activities, such as running, high-intensity interval training, or cycling at a moderate pace, can offer. These alternative activities involve higher intensity efforts that challenge the heart and lungs, leading to improved endurance and aerobic capacity.