My back had been feeling beat-up since deadlifts until yesterday, when it felt better. Was driving home from work looking forward to a killer squat session when all of a sudden my back injured itself just from shifting slightly in the driver seat. Nixed my barbell squat plan and did:

Single leg extensions

290 x 15, 15

Super-set with single leg curls

290 x 15, 25

Belt squats

380 x 8, 10, 10

Belt squats are lifesavers. So glad I set-up a way to do them.

Also, get a load of this. When I was training Muay Thai 5 years ago, I wrote in my training log "I'm saving up to get a Winning FG 5000 headpiece. Comes out to $340 on Rakuten". I'm going to start sparring in boxing and that headgear is now over $650. Should have pulled the trigger back then!