When looking at muscle function, people often look at one joint, consider the muscles that act on that joint, and identify the muscles that perform opposite actions as antagonists to one another. In some cases, this is a suitable explanation. However, some muscles cross more than one joint. The word used to describe muscles that cross two joints is biarticulate (bi =2, articulation = a joint, biarticulate = 2-joint). These 2-joint muscles create synergy in muscle groups that are often thought of as antagonistic. Watch the video below.

In the video, I talked about the need for balance in the muscle groups, which is a legitimate conclusion. But what I should have pointed out more clearly is that muscles are designed for synergy, and they should be trained in synergy. How is this done? It’s quite simple. Synergy occurs when multiple joints are flexing together or extending together. This occurs naturally during all task-oriented movements. Running, jumping, cutting, pushing, pulling, picking things up, throwing, squatting, lunging… all these movements feature muscle synergy. Consider the vertical jump example in the video. The hamstrings and glutes extend the hips. By doing so, they assist the rectus femoris in performing knee extension. The rectus femoris and the other three quadriceps extend the knee. By doing so, they assist the hamstrings in hip extension and assist the gastruc in performing ankle extension. The hamstrings and rectus femoris form a synergistic loop that simultaneously extends the hips and knees or flexes the hips and knees. The glutes, quads, and gastruc form a synergistic chain that simultaneously extends the hips, knee, and ankles. The muscles work in synergy during task-oriented movements. So we do not need to overthink exercise selection or seek out fancy training. Keeping things simple is best.

On the other hand, some less functional movements interrupt muscle synergy. In a glute bridge or hip thrust the knees are held in flexion while the hips extend. In a Nordic hamstring curl, the hips are held in extension while the knees are flexed. These movements cut the quads out of the synergistic loop and chain. These exercises may provide a strong stimulus to one particular muscle group. But looking at the big picture, these exercises break up muscle synergy and train a different intermuscular coordination than task-oriented movements.

Why is this is important to recognize? There are a thousand ways to work a muscle. But in training for performance, we have to develop strength that carries over to sport. Achieving that is not a matter of just working the right muscles. It requires neurological transfer. Training movements outside the sport need to feature similar large scale coordination to movements within the sport. This is why single-joint machine exercises are not effective for sports performance. They can target the right muscles, but there is no neurological transfer. While exercises like the barbell hip thrust and the Nordic hamstring curl do not isolate as much as a machine, the same principle still applies.

People have long known that developing a muscle group in isolation is not useful for improving sports performance. Biarticulate muscles and synergy give us insight as to why.