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Calisthenics
Lower backs are good candidates: lying flat on your front, tighten your glutens right up, toes forward (which takes the tension off your hams), hands by your head, tighten your core, left your legs then squeeze shoulders back and lift.
The order helps to get everything lined up and get your back working.
YMMV, of course, but doing this everyday is great for lower back health.
Deadlift and squats make my lower back quite sore at the moment, otherwise I'd be doing deadlift/squat/hip thrusters.
My main sport is Taekwondo, and have built up pretty strong abs, quads, hip flexors. Calisthenics/gymnastic strength type work has built up arms, chest, lats, but lower back seems to be a weak point at the moment.
I've done GTG for chinups/pullups to increase reps and strength endurance, so would be breaking up the swings into probably 4 sets of 50 reps spread throughout the day.
This would be on top of 6-8 hours of fairly intense TKD training, couple of bike rides/runs, and random bits of calisthenics dotted throughout the week.