Try doing a good warmup before any kind of training. When I start my work out, I am already sweating heavily after @ a 15 minute warm up. Also focus on the type of workout you are doing that day. For example, if you are doing sprints, do some light jogging, major muscle movements like squats, followed by about 5 sprints starting with 2 at 25% max speed, 2 at 50% max speed, and then 1 or 2 at 75-80% max speed. Then go do the sprint workout. If your muscle are super tight, do some stretching on your rest days, not after or before your workout. Stretching should be a separate program and done at another time instead of right before or right after your workout. Thats just begging for an injury.
A good warm up is the cross-fit warmup, guaranteed to warm you up.