Loud noises, gritting your teeth and screwing up your face … Does it actually help you go on for longer?

(We’re talking about whilst lifting weights of course!)

“I used to fake it all the time to impress people, but it became so much of a habit I was still doing it when on my own.”

Says JD Gyms Liverpool PT, Dave Hogan.

We asked Dave to tell us more about the science behind how our muscles work and if the grunting will aid performance.

“Muscles are made of muscle fibres. The central nervous system decides how many are needed and then fires them into action. Each muscle fibre executes at 100% or not at all. We use as many muscle fibres as needed to complete a task. The rest are ready, but aren’t being used.”


A Kettlebell weighs 1kg. Your central nervous system fires 1 muscle fibre into 100% action.
Another weighs 10kg. Your central nervous system fires 10 fibres into action.

If you’re told a 1KG Kettlebell weighs 50KG. Your central nervous system would fire 50 fibres into action. The Kettlebell would almost end up through the ceiling.
If you’re told a 5KG Kettlebell weighs 1KG. Your central nervous system would fire 1 fibre into action. Initially, you wouldn’t be able to lift it, but you would adapt and fire an excess of muscle fibres and powerfully lift that 5KG.

“As you work out, your fibres will fatigue or burn out. Your central nervous system looks for ‘spare’ or ‘ready’ muscle fibres to complete further reps, but you’ll only fire up as many fibres as needed to lift the weight.  At this point, you growl, clench, and make funny noises as it is hard work. But the grunts aren’t challenging your muscles any more, because as one muscle fibre drops out and other is ready to replace it. Until we hit failure due to lack of energy, or mentality. The noises are simply psychological to help us get through it mentally.”  Says Dave.

For more information on weight lifting or any other forms of training, contact Dave or any of the PTs in your branch of JD Gyms