Sore Back

[Jimmy]

I am having trouble with my back getting sore after workouts (Taekwondo & strength training). I have been strength training for almost a year. My goal is side splits

I had worked up to adductor pulldowns (25kg - 15rep sets of 3) isometrics 2-3 times a week, leg extensions (3 sets of 15 reps). Whole program was done 2-3 times a week. Then my back started getting sore. I revised my program because I had obviously not strengthened my back enough.

I started back at the beginning with only situps and squats (both with no weight). I worked up to 2 sets of 100 squats and 100 situps. Then went to back extensions (no weight 3 sets of 20). I worked up to 15kg weight in back extensions with the same no of reps and sets. My squats were 20kg 3sets of 30. Still 100 situps. Program was 2-3 times a week

I am currently doing 3 sets of 15 rep squats with 30 kg (reasonably easy). I am deadlifting 3 sets of 15 at 30 kg. 3 sets of 15 adductor flies at 16 kg and doing 100 situps. I then do Isometric side split stretches in 5 step horse stance. 3 sets. Program is 2-3 times a week

My back still gets sore. Is it a matter of going slower over 6 months or so and being more patient. Am I being unrealistic with my expectations? I think I should be feeling stronger by now. If I do any less I don't feel as if I am working out enough to have any gains and ultimately improve my flexibility. Some of my TKD workouts have been very light and I still have soreness in my back. To make things worse my flexibility hasn't seemed to improve or, if so, only slightly.

I am only small - 60kg, 160 cm and 45 yrs old.

Does anyone have any suggestions as I am getting frustrated.

cheers

Jimmy