Not sure if it technically qualifies as strength training, but for your core, I find the best results are just you and the mat. Planks, leg raises, pushups, etc. Best if instructor lead though to push yourself. I do that in combination with the basic upper body weight lifting described in this thread.
"The first virtue in a soldier is endurance of fatigue; courage is only the second virtue."
- Napoleon Bonaparte
"The first virtue in a soldier is endurance of fatigue; courage is only the second virtue."
- Napoleon Bonaparte