What Happens In Muscle Fatigue When You Exercise?

What Happens In Muscle Fatigue When You Exercise? Is It Your Muscles That Are Tired or Your Brain?! Chiropractors in Bournemouth at the Charminster Chiropractic Clinic Look at Recent Research.

Have you noticed that when you start running or cycling in the new year, having made your new year resolution to get fitter,  you quickly become tired  – and that you just can’t keep going.

The usual idea is that there is a build up of lactic acid  in the muscles? Maybe you just done have enough muscle fibres? What IS happening to your body at that moment though?

Research in the Journal of Applied Physiology 2015 15 Oct 1;119(7):840-50 by Johnson, Sharpe, Williams and Hannah took eight men and got them to cycle fast to the limit of their tolerance for 4 minutes to the limit of their tolerance.

Then they made them to do the same but after they had performed cycling movements with only their arms for 8 minutes at the same power as when using their legs. Then they got them to do so a third time for 8 minutes without the arm cycling first.

They used EMG and electrical stimulation to measure how much fatigue was in the muscles themselves rather than the brain or spinal cord.

Findings showed that after 6 minutes rest their heart rates were still elevated from the exercise and also the levels of lactic acid were elevated. However, their legs felt perfectly fresh and not fatigued.

The interesting finding was that they reached exhaustion point 38% earlier when they had done the 8 minutes of arm cycling first. However when the leg muscles were tested for electrical activity, there was no explanation for why they had to give up …. they gave up when their legs were still less fatigued that in the leg only test.

In the third test they didn’t reach exhaustion even though when the muscles were tested, their fatigue was the same as in the testing done after they had first cycled with their arms.

They therefore concluded that it is not in fact muscle fatigue that makes you stop when you feel that you just can’t go any further, rather it is perceived effort that made them give up!

By using their arms in the activity, they felt they had done more exercise and should therefore feel tired and so they were tired already when they started to cycle with their legs and had to give up quicker. But this was only because they THOUGHT they were more tired having exercised their arms than if they hadn’t before they cycled.

So it is the SENSATION that you have made a big effort that affects your ability to do exercise, not the reality of the situation – your muscles COULD keep going if your BRAIN thought that they could!

Exercise is therefore potentially mediated by central fatigue in the brain and intolerable levels of sensory perception rather than a critical peripheral fatigue limit.

That tiredness could therefore be mind over matter – so listen to your body but don’t be fooled by your brain.