Before we go on I have no access to weights etc. I want to gain some strength but my main focus needs to be endurance (military pft).
Up to now I've just been working out three times a week, intervals and sprints twice a week, and a longer run not more than 5k. Usually MWF. I also do bodyweight pyramids; push-ups and sit-ups in pyramid form before the runs.
How do I incorporate strength training into this? One thing in particular I'd like to do is strengthen my core and back; it's been injured in the past but I want to try my best to prevent anything like that happening again.
Any programming suggestions?