Delayed onset muscle soreness, known as DOMS.

It’s the muscle pain you feel 12-48 hours after your exercise session and is caused by microscopic tearing of the muscles fibres.
Some may inaccurately perceive this as having ‘hurt’ themselves. But it is actually a normal and necessary part of the training – and rebuilding process.
A muscle sprain or strain is an unintended, sudden and specific pain you feel during the activity and usually causes swelling or bruising. In contrast, DOMS is the intentional breaking down of muscles during a training session.
Whilst at rest the body rebuilds those muscles stronger than before, in order to tolerate exposure to that stimulus again. It is this repeated breaking down and rebuilding that achieves improvements.
Several factors determine the occurrence and severity of DOMS. If you are an exercise beginner, you are putting your body under new pressures and it will feel it. Similarly, even if you are a regular exerciser but try a new activity or make a big jump in intensity or duration, it will give your muscles a shock and you will probably get sore.
Certain exercises are also more likely to cause DOMS, such as the eccentric or lowering phase of a movement, especially when done super-slow and plyometric or very dynamic exercises. If you push your body to new limits you are likely to experience a healthy dose of DOMS. But how sore is too sore.
Ideally, your muscle pain should have peaked by 48 hours, with 24 and 72 hours (half way up and down the peak) being less. If you can still hardly walk down the stairs a week after your exercise session you may have over done it.
There has been too much break down and your body is struggling to repair and recover. Try some light aerobic activity, swimming and gentle stretching.
Have a massage and if necessary apply the RICE principle (rest, ice, compress, elevate). In future, ensure you warm up and cool down more thoroughly, be more gradual with your changes or increases and even book in with a personal trainer to check your techniques.
DOMS is helpful feedback that you have effectively challenged yourself in your training session, but you don’t want to be so sore that you miss your next 3 workouts.
By Rachel Livingstone Personal Trainer & Owner of The Health Hub www.healthhub.net.au