First of all let’s answer the following question: “What interval method (set-rest and so on) is used for?” Stress (sets) repeated after breaks are used to get bigger influence on the training function.

There are two principles of multi set affect on training function:

• In the simplest case multi set impact is the aggregation of sets impacts. For example: if our purpose is micro injuries[^1] (main component of muscle strength and mass) and in each set we cause inj1, inj2, inj3 … micro injuries then the total affect of multi set approach is: inj1+inj2+inj3+… In this case there are no hard limits on rest duration. Rest can be from several minutes up to 20-30 min. (20-30 is the highest I’ve encountered, after executing several sets of an exercise in the beginning of the workout; it was repeated in the end of the workout). The only requirement from rest is that it should allow you to make the next set with required intensity.
• Multi set influence may have also higher than linear aggregation. Each set may increase the affect of the previous one. In similar to previous section’s notation: sets have s1, s2 … influence. Than the total affect is higher than s1+s2+… For instance: in case of short and intense stress, maximal oxygen consumption isn’t during stress but immediately afterwards (return of oxygen debt occurs). Reoccurring stress while oxygen consumption is still at high level will provide higher influence on the training function (thus, it can be used to improve our aerobic abilities). Reoccurring stress should be when ATP + CP were almost fully recovered. ATP + CP recovery time approximately equals to its consumption speed (after 60 sec set duration, 60 sec of rest needed to recover ATP). Therefore, in case we want to train max oxygen consumption rest between sets should be about duration of the sets.

What about short rests that’s recommended by many bodybuilders?

Short resting intervals that lead to “muscle burn” or in other words cause maximal oxidation of blood and muscles can be useful for our body as a resisting function against future inner PH level decreases. But, there is no direct link for muscle growth stimulation.

[^1]For more information see: muscle damage theory.