Many people think that running will make them 'stronger' to some degree this is true. There is an anaerobic component to running that will increase your overall leg strength ... so why when you're injured do you need to do strength exercises?
Running is thousands of, hopefully little steps. It is aerobic exercise that repeats lots of submaximal contractions progressively over time this can lead to tissue breakdown because we 'overload' certain structures. We just do too much for what the tissue can cope with. It is usually muscle and tendon that becomes overloaded first with most running injuries.
Injuries create pain and when we're in pain the injured tissue and surrounding tissues 'switch off' ie they become underactive - this is called pain inhibition. In order to improve your injury we need to 'switch these tissues back on'.
Whilst running is thousands of little steps, best current evidence suggests heavier (high load, low rep) rehab 'strength' based exercise adapt soft tissue more quickly and allow it to cope with higher forces more quickly than high rep, low load rehab exercises. Despite having injured soft tissue, if exercises are prescribed correctly they shouldnt hurt and wont further harm the injured tissue and will help you return to pre-injury activity sooner!
Craig Ellis
Running Physio
Body Fit Physiotherapy