Breaking down the research behind Cluster Training

Cluster training involves performing each set of an exercise in several clusters, with short intra-set rest periods in between clusters, as well as longer rest periods between sets.

Intra-set rest periods reduce the impact of fatigue, and this increases average bar speed over a set, just like velocity-based training.

But although cluster sets display higher mean velocity (as well as mean power) over the course of a set, they do not display higher mean force in a set compared to straight set training, at least when the same relative loads are used.

Cluster training can involve as little as one intra-set rest period. It can also involve an inter-repetition rest after every single rep.

Velocity-based training involves stopping a set several repetitions before reaching muscular failure. In normal training, the onset of fatigue during the set causes bar speeds to slow down. However, by stopping the set early, the average bar speed over the whole set can be maintained.

Avoiding losses in bar speed within a single set using velocity-based training seems to be beneficial for maximizing strength gains, particularly at high velocities. This effect may be partly mediated by differences in muscle fiber type adaptations, as greater retention of type IIX fibers has been noted.

Short-term studies show us that using short rests after every single rep can completely remove the effects of fatigue on bar speed. This could be valuable for athletes who compete in strength and power sports. In this way, it is just like velocity-based training.

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And while just a couple of intra-set rest periods can reduce the effects of fatigue on bar speed, it is better to use more frequent rests (every 2 reps) than less frequent ones (every 4 reps).

Interestingly, force production doesn’t seem affected by intra-set rests at all.

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Long-term studies on cluster training are slightly conflicting.

They all agree that cluster training is superior for improving power and velocity, which is in line with the idea of velocity-based training. However, while some also show a benefit for strength gains, others show the reverse.

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So how does this tie together?

Straight sets are likely superior for hypertrophy compared to cluster training, because of the closer proximity to muscular failure. But cluster training allows for higher average bar speeds, which makes them superior for power and velocity. This may happen either through the retention of more type IIX fiber area, or through other velocity-related adaptations. The impact on strength may be down to the individual.

So cluster training may be a great way of training when power is most important, such as in-season. It is perhaps less optimal when hypertrophy is key, such as in the off-season.