I had a month off after injuring my knee and discovered tonight I have lost very little of my fitness. I easily did a 30 min run and could have run longer. I was running a bit slower as wanted to protect my knee a bit longer, but still kept a good pace and an acceleration at the end proved to me I am still fit enough for 5k which will be my next goal as I have been missing my park runs! So anyone out there worrying you will lose fitness I am proof you probably won't !!