
So you went to the gym or for a jog yesterday and now have to crawl up the stairs, it鈥檚 agony to stand or sit, or your arms are so sore you can鈥檛 brush your teeth. Congratulations, you have #majorDOMS 鈥 a badge of honour used in the weights room to indicate that you have pumped some serious iron. But what, or who, is major Doms? And is pain a good thing when it comes to building muscle?

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If your muscles ache directly after exercise, it鈥檚 known as acute muscle soreness. This is thought to be caused by a combination of three things: muscle fatigue, the accumulation of acidic waste products 鈥 chiefly hydrogen ions 鈥 from the chemical reactions involved in using your muscles, and a build-up of the fluid sent to remove these waste products.
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The aching should ease after a bit of rest. 鈥淚f you are in a lot of pain straight afterwards, it鈥檚 more likely you鈥檝e damaged the muscle. It could be indicative of a strain, which might take more like seven days to heal,鈥 says of Loughborough University, UK.
But if the muscle ache kicks in 24 to 72 hours after your bout of exercise, you have delayed onset muscle soreness 鈥 or DOMS to your Instagram followers. Your muscles contract by pegging together fibres called actin and myosin. Every time a muscle lengthens, these fibres experience significant load. As they tire through continued exercise, the fibres struggle to resist that load and individual actin and myosin pairs are ripped apart, causing microtears in the muscle.
鈥淲hen this microdamage occurs, recovery and repair processes kick in,鈥 says Furlong. 鈥淭he stiff feeling is the inflammation caused by the chemicals rushing to the area to heal it.鈥 These include , which are attracted by chemicals released by the injured muscles, and engulf damaged cells. Once these are removed, muscle regeneration can begin.
As the muscles are repaired, they are adapted to resist the exertion that tore them 鈥 increasing the size of the fibres and building up strength in the muscle, says Furlong.
These microtears need a few days to recover, she says, but there鈥檚 nothing stopping you from working on a different muscle group while you wait. And as you crawl up to bed, take comfort in the fact that these little tears are how muscles grow.
This article appeared in print under the headline 鈥淲hy are my muscles aching?鈥