I have found that I did not have weak quads but that my abs were not doing enough work and this was placing more stress on my left quad initially which became injured and placed more stress on my right quad subsequently.
The injury was occurring from my teeth. I have realised, from consultation with a qualified physiotherapist and wearing a mouth guard, that I tend to bite or grind my teeth throughout the day and hold my breath. This closes my airways. Over a long period of time this has negative effects on my abs as my lungs are not expanding to their potential and in turn not keeping my abs activated. My abdominal muscles, particularly on my right side due to there being more internal organs on that side of the body, were shuting off.
Wearing the mouthguard, and undertaking daily short exercises to work my abs particularly the left side of my body, has reactivated my left lower abs and my left glute muscles. This has reduced the workload on my quads, because my glutes and abs are doing more of the work, and has returned myself to the condition I was in before