Building brawn starts in your head.

That’s because your brain is the command centre for every movement your body makes. How, exactly, does your mind control your muscles? It’s complicated. But we’ve broken the process down into four steps, using your biceps as an example.

Step 1

When you’re ready to lift a weight, your brain identifies which and how many muscle fibres are needed. It then sends an electrical impulse down your spinal cord through a bundle of neurons, or nerve cells.

Step 2

This impulse exits your spinal cord at your lower neck, through a group of nerves known as the brachial plexus.

Step 3

To reach your biceps, the impulse then branches off to the musculocutaneous nerve. (If your spinal cord is a highway, think of this nerve as a side road.)

Step 4

When the impulse reaches the nerve ending, a neurotransmitter – in this case, acetylcholine – is released. This sets off a chain of biochemical reactions that cause your muscle fibres to contract.

The more you focus on the muscle you’re working, the more muscle fibres you activate. This mind-muscle connection was confirmed in a recent study from Denmark.

“The mind has a bigger influence on the body that we think,” says researcher Lars Anderson, Ph.D.

Here’s why your mental workload affects your physical workload: If your mind is busy thinking about deadlines, bills, or the long line for the benchpress, previous research has found that your brain won’t have all the resources it needs to send messages to your muscles. That means you may be churning out reps, but not getting as much out of your workout as you could be.

Next time you’re in the gym, think about the muscle working harder as you move it. Concentrate on the contraction of the body part as you lift and lower the weight, and how strong you feel while doing it.

This method works especially well with isolation exercises that zone in on just one muscle group, such as curls, lateral raises, and calf raises.