Red Threshold Intervals are similar to Green Threshold Intervals, but are done at a slightly higher intensity.
Focus on driving your heart rate up to the bottom of the red zone before you start the method, then hold it there. This should be right around the tipping point where you produce more energy anaerobically vs aerobically. The goal is to push back the anaerobic threshold, so you can produce more energy aerobically at high intensities.
Since this is such a high intensity method, you’ll need to take a longer active rest period to bring your heart rate back down into the blue zone before repeating the interval.
Goal: Increase the aerobic system’s ability to produce as much energy as possible without heavily relying on the fatigue-prone anaerobic system.
How: Thoroughly warm up and start from the bottom of your red zone. Go for 3-6 minutes at 100% max intensity while still maintaining good technique. Actively recover for 2-4 minutes down to the top of your blue zone. Repeat for 2-4 reps.
Exercises: Any cardiovascular exercise, particularly ones that are low impact, will work for this method.