There are five ways that we are currently using at Results Fitness to do metabolic interval training with our clients:
1) Fixed work, fixed recovery (based on time)
e.g. 30s on, 60s off
2) Fixed work, variable recovery (HR)
e.g. 30s work, recover based on HR
3) Variable work, variable recovery (HR)
e.g. Work until HR = X, recover until HR=Y regardless of how long each interval takes
4) Fixed work, progressive recovery
e.g. rounds 1-10 30s on, 60s off. Rounds 11-20: 30s on, 75s off etc
5) Regressive work, fixed recovery
e.g. rounds 1-10 30s on, 60s off. Rounds 11-20: 25s on, 60s off etc
The idea follows the principle Chris Frankel taught us that you have to ask if recovery is based on by design (ie you’ve planned the work period to end) or by default (the work period has to end due to fatigue).
These different variations will give you five different types of workout when you do your metabolic work. Pick one form and follow it for 2-3 weeks before trying another one, and note the differences in your results.