The acute effect of a high intensity interval, strength set or total workout is a decline in fitness. We become fatigued. Key to making progress is therefore at least partly in recovery. Although recovery sounds very passive, it requires an active approach. Let’s have a look at what the best recovery strategy is: relaxing on the couch or low intensity exercise.
Active recovery or Passive recovery
The aim of recovery is to relax after a training set or session, so you can get ready for the next one. Passive recovery between high intensity sets is probably what your automatic pilot would do. You stop running, sit on the bench or even lay down. You can also passively recover between workout days, which simply means doing no training. Active recovery within a training session is when you keep moving at a low intensity. For instance, jogging or low intensity cycling. You can also do active recovery between workout days, which could be a short low intensity bike ride or some flexibility exercises without weights.
Recovery within a training session
We will start looking at recovery between intervals or strength sets within a training session. First think of your personal preference. What do you do to recover as fast as possible during your workout? Are you the typical sit down and check your smartphone fitness member or the high cadence low intensity cyclist?
On to the facts. After a hard set, lactate accumulates in your body and H+ will decrease your pH. Proper recovery should clear the lactate and increase pH back to normal. Science tells us that active recovery (AR) is without a doubt better in doing so than passive recovery (PR). You will see better results of AR on lactate clearance in almost all studies. Whether it is measured in swimming or during a bench press workout. This means you can start the next interval with lower lactate levels when doing AR vs PR.
But does this also mean you perform better in your second set after AR vs PR? Not really… You will not have more power in the second bench press set, you will not have more power in the second 20 minute cycling test and kickboxers will not perform better after AR vs PR. When recovery time is lower than 60 seconds, AR can even decrease the performance of intervals within a training session when comparing to PR. This negative relationship disappears when recovery time is above 100 seconds.
When lactate clearance goes faster in AR but performance is not per se better, then there are obviously other mechanisms playing a role here as well. Some studies say active recovery impairs restorage of muscle energy (glycogen). In other words, staying active will leave you with less energy at the start of the next interval or set. Psychological processes could also play a role.
Recovery between workout days
Recovery between workout days is about making sure you are not fatigued of the previous training session in your next training session. Again, ask yourself the question: do you ever do a “training session” to enhance recovery or do you prefer an evening as a couch potato?
There is not a lot of research that dives into this subject. My personal guess is that it works quite the same as recovery within a training session. I’m sure AR will again clean up some side products of a previous hard training session like lactate. This could give you a sense of freshness. AR also adds up to your endurance training hours since this works accumulative.
Just like in recovery within a training session, I do not expect you to perform much better on the second workout day when you did AR vs PR. If you do your AR too intense though, it will definitely have a negative effect on performance. That is because you will be less recovered for the next training session, which as a result will be less well executed.
Practical conclusion
At the end it does not matter what the studies about some subjects say, it matters how well you react on both recovery strategies. Try it yourself! Start varying in AR intensities up to – let’s say – 70% of your max heart rate or without weights in case of strength training. See how you feel and react and maybe even measure how well you recover with tools like heart rate variability! 
Would you like to read more about recovery? Check all recovery content!
Founder of Molab, Human Movement Scientist and Freelance Content Marketer.