Grrrr. I achieved a PB in my back squat a few days ago - I lifted 60 kgs in a back squat, 5 times (with a 2 minute rest between each squat). Then went on to do what my PT cals "squat thrusters" - front squat and then push to overhead. Did one at 30kg, second one - back spasm! Had to stop & we went on to some HIIT stuff - it's better when I keep moving.
grrrr it's still sore 3 days later, although I managed to stagger gently through a Pilates class yesterday.
I realise that it's partly my own fault. I was lifting 75kg deadlifts in 3 sets of 3 on Friday, and then got keen and did 5 sets of 5 at 60kg on both Sunday and Monday.
My poor old back muscles are now teaching me:
Take a rest day, kids.
Now I wish I could sleep standing up. Lying down is painful.