I m 40, male, sit at a desk all day. I usually exercise 3 times a wk. 45 minuts cardio with my heart at around 145-160 bpm. Then sit ups, 250 pounds crunch, 50 reps. I then move to the lower back extensions 250 pounds 30-50 reps. I have lower back pain in what feels like my tail bone , shaking legs, arms etc. This is after 3 to 4 days off from exercise (just testing things out to fingure out what is going on). I actually feel my best after the exercise and for a day or two after. Wake up in the morning regardless of any exercise and my lower back hurts like no tomorrw. ANy thought on this? Head aches come and go with sharp pains in my head and then they stop, at time I can get a little dizzy. Around 3:30 in the afternoon I am whipped and very tired.