Supersets are the use of two successive exercises, targeting opposing body parts, performed in an alternating fashion. Normally, the muscles targeted by supersets are agonist-antagonist pairs, or muscles that work in opposition to one another, such as the biceps and triceps. Superset workouts are often used to overcome workout stagnation, or to boost psychological drive. Physiologically, superset training delivers increased blood flow to the target area, and has been shown to increase both muscle fiber recruitment and natural growth hormone production.
Generally, a superset workout will target a specific area while retaining the normal routine for the rest of the body. In this way, the risk of over-training is reduced and energy is reserved for the target body parts. For a biceps-triceps split, for example, a typical superset workout might include alternating biceps curls and triceps extensions for three to five sets, followed by a brief rest, before moving on to another body part. This accelerated focus is generally continued for two to four weeks, at which point the superset routine can be shifted to a different target area, such as the hamstrings and quadriceps.
One benefit of supersets is that they allow the body to channel increased blood flow to the target area in an efficient way. If the biceps and triceps are being worked together, there is little re-routing of blood flow required for both muscles to remain adequately oxygenated. Despite this, however, the intensity of superset training is such that there will still be some oxygen deficit within the muscle. Typically, oxygen deficit during exercise leads to lactic acid accumulation.
Lactic acid is the by-product of anaerobic metabolism, a process by which muscle tissue is able to release energy under low oxygen conditions. The burning or stinging sensation experienced during an intense workout is caused by the accumulation of lactic acid. Besides causing pain in the muscle, lactic acid has been shown to have another important action within the exercising body — growth hormone stimulation.
As an added benefit, training using supersets has been shown both to raise the resting metabolic rate and also to shift substrate oxidation for hours after the workout is over. This means that, not only is the body burning more energy, but an increased percentage of that energy is coming from the body's fat stores. Overall, it can be inferred that carefully implemented supersets have the potential to build more muscle and burn more fat than the same exercises performed in a straight set routine.