I was having some pretty severe knee pain so I decided to start running sprints on leg days instead. I haven't run full speed in probably over a year and pulled a hammy on the first night
Just going too hard, too soon.
That was the Saturday before last and I feel about 90%. I figure I'll give it another few days before I try it out again and be sure to ease into this time.
I really can't wait though. For the 20 or so minutes of sprints that I did, I remembered how much I love running. HATE long distance- love the short stuff.