Since biofeedback is and will be the foundation of training (Olympic athletes are doing it) in the future, preset protocols should be avoided. Sprint, bike, or do a movement until you feel or see your wattage or power output is dwindling (these numbers can be seen on a bike), then slow down and recover. Wait until your heart rate has dropped 30-40 BPM, then do it again. The time to stop is when your performance is really starting to suck. If you did sprints for 20 seconds before your performance dropped, and now at 5 seconds your performance drops, it's time to quit for the time being. Teaching your brain something is hard will make it hard and training your body that something is easy will become easier (neuroplasticity). Just look at gymnasts if you don't believe me. Look how easy they make movements. Even when they first started out, they relaxed without excessive tension and did what they could. When they kept getting worse, they stop for the day.