What are the most productive strength training exercises?

Squats with a weight bar. Total Legs, glutes and abs.
Lunges with Dumbells. Legs, abs, glutes and posture.
Any exercises that concentrate on your back. Back and Obliques.
Incline leg raises. Lower and mid abs.

The most important thing to remember is to use free weights. They strengthen multiple muscles at once, and help keep everything in balance. Balance is vital if you want to avoid further injury. Do squats, and over time do it slower and slower for strength. Running speed relies more on fibres for short bursts though (people who can leg press huge weights aren’t necessarily good runners), so there is nothing better than actually getting out there and running. Sprint for 100m bursts, then jog 100m, then sprint again.

i’m not so sure about the legs, but as for your stomach try doing the typical sit up. Do a set of ten sit ups very, VERY slowly. Do that three times every day

Lots of great advice above. It’s so hard to give specifics because everyone seems to have their own magic formula. Really it’s whatever motivates you and keeps you moving.

In general, the most productive exercises involve more than one set of joints (sometimes called compound exercises). So squats are a great example, you’re bending your knees, hips, and to some extent your ankles. The happy side effect if that most of those exercises will improve your core strength and balance as @FireMadeFlesh mentioned. Form is important with these so you don’t hurt yourself, I’ve had great luck googling ”<exercise here> form video” before trying something new.

As for specific tips (and again everyone is different, but maybe some things to try). I really like doing relatively light weight and high reps for the goals you’re describing. So I’ll set a weight and until I can do 20+ reps on my last set with that weight I won’t increase it. I also like to set a tempo where the part where I’m moving with the weight is slow (say 3 counts) and the part against it is faster (say 1 count). So for example, on squats, down slow in 3 counts then burst up fast in 1 count. I just feel like this gives you the best of both worlds working on balance and control going down, and the speed you’re looking to develop going up.

Also, you may be more flexible than I am, but I’ve always felt stretching to increase my flexibility (different than warming up), helped me run better. I’m pretty inflexible to start though so your mileage may vary.

Good luck getting back into it, and I’m sorry to hear you were hurt. Are you training for something specific goal/distance wise?

Thanks for all the advice so far. This is great.

@funkdaddy, I’d like to run a hilly, gnarly half-marathon in early November, but I am worried if I set too ambitious a goal this tendinitis will never go away. That’s the distance I’d like to get back up to within the next few months, and possibly try for a full sometime late next year, but only if I can get my pace up to something reasonable. I don’t ever want to be running for 5 hours.

I’ve never found better workouts than those designed at crossfit.com. Too difficult to do as prescribed, so you’ll need to scale them back for a long time. However, I was able to improve every aspect of fitness faster than anything I’ve ever done.