What is a muscle strain?
In short, it is the overstretching or tearing of muscle fibres. The majority of muscle strains occur for one of two reasons: either the muscle has been stretched beyond its capacity or it has beena forced to contract too strongly. The severity of injury can range from only a few muscle fibres that are damaged, and the muscle continues to function, through to complete tears where the muscle may be unable to function. 

How do I know if I have strained a muscle?
Symptoms include:

• Pain and tenderness in the muscle, especially after physical activity involving sudden stretches or forceful contractions
• Swelling / bruising of the muscle
• Cramp or spasm
• Decrease in muscle strength or in more severe cases a complete loss of muscle function

What do I do if I have strained or torn a muscle?
It is important following injury to have it assessed by a physiotherapist, as the severity of injury dictates prognosis and management.
Before you can get in to see a physio, there are some things you can do to speed up recovery.

Protect the injury – you do not want to aggravate the injury by doing too much too soon. However complete rest is also not advised as we require circulation to assist with healing.
Optimal Loading – gentle progressive loading of your injury can help promote healing and prevent delays in returning to normal function secondary to muscle atrophy or joint stiffness.
Ice – help to manage pain and swelling
Compression – help to manage swelling
Elevation – help to manage swelling 

It is important to note the healing stages of an acute injury.
Acute – initial stage of injury while pain and swelling is at its worst
Sub-acute – body transitions to repairing the injured tissue
Late – tissue matures but not yet strong enough to cope with increasing demand

We must respect the healing states of an injury, and treat accordingly to assure optimal outcomes.
A physiotherapist is able to provide guidance as to where you are along the continuum, and how to best manage your injury.