Hi, I've just been out for my first run in 3 weeks after incurring a slight tear in my calf muscle. Just jogged 3 miles and it feels fine but, i'd totally lost my fitness (or so it felt). No energy and it was slow. The problem I have is...i have a 10k trail / fell run on Sunday. I'm doing 4 runs for charity this year so can't really not do it. What do you suggest - just rest it now and just jog around the course and finish or get out again / cross trainer / spinning class before the run to try and get some fitness back.   I'm new to running so unsure whether i'd actually feel any fitter if i done further training or i'd just get tired for Sunday.  

In all honestly you probably have not lost that much CV fitness in only 3 weeks probably just an off day anyway - some days you feel you can run forever and other days you just want to go home. Go for the Sunday trail with the intention of just finishing it in an easy run and see how it goes. I did a 10K race after 3 weeks off to injury was determined to at least give it a go and did a PB - races tend to lift performance so you may be surprised. Just go run and enjoy. The race experience is valuable in itself.