Quad strain/tear - what exercises can I do?

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Hello all!

I have been working out pretty intensely for a few months now and for a while i have been getting quite bad pain in my left quad after i go running... i usually try to just ignore this but now I just want it to go away! It hurts when i initially start walking but then subsides a bit and i can usually bear the pain. It hurts when I start running too quite a lot so now i think I need to rest till it gets better because I am fed up but from my internet research apparently this can take 3 weeks?!

There is no way I can not do any exercise for three weeks so can anyone recommend stuff I can do to keep fit in the mean time whilst resting?

Weight machines? swimming? yoga? cross trainer? any other suggestions or thoughts on the matter?

Thank you all advice appreciated.