So, yesterday, as is my wont, I was humping a lovely gal, and this morning I have an extreme twinge in my lower back, which I call "hump back", or Quasimodo Syndrome.

If you wore a back brace, would it have any effect on your or her experience?  

Sometimes after a vigorous bedroom workout I get those annoying twinges too, and all to often while in the throes of passion, charley horses in places I didn't know I could get them.  Like you I work at staying fit, but how to work those muscles one uses when thrusting?  I've learned the hard way to avoid some things, like moving from being underneath to being on top or vice versa while still connected, and I never ever pick her up, even though I sure would like to.  Just being smarter about how we move during lovemaking is gonna almost always be the right answer.  Maybe talking to a personal trainer about how to target those areas of discomfort wouldn't be a bad idea either.

I’m 65, workout and stretch. After slipping on an icy sidewalk I developed sharp pain in my lower left back where the bones are close together. I had swelling around the bones. A friend from the gym suggested taking high potency serrapeptase by Doctor’s Best. My pain disappeared after 2-3 weeks. Some of my addition pains left as well. I found that Amazon had the best price for serrapeptase. There are also articles regarding serrapeptase.

Sounds like sciatica..it comes and goes..

because she likes to do that multiple times during the session, and I can feel the strain on my back when I do that.

I had that many years ago.   In fact, my exercise regimen was specifically designed to counter act the sciatica, and was and is quite successful against it.
This is just a pain localized right at the base of the spine (coccyx ?)  and lasts a few days, then goes away.

No. No side effects. It’s all natural. It reduces the swelling that presses against bone that causes the pinching and pain. It helps digest a certain protein that causes the swelling. Comes from the silk worm. You can google it for information. I was using ice packs, chiropractic, stretching and having someone pull my body. Nothing worked. It takes 2-3 weeks to work since it’s natural.

* Still not a doctor *

Just after you've been talking to Mikey.

For those of you taking blood thinners, be aware that serrapeptase may affect blood clotting.  Get your protime checked if you take serrapeptase.  

I have never answered.

with a money-back guarantee from a PHD Kinesiologist  that I trained with when I was a power lifter many years ago.  I still do  this short workout daily to keep back trouble away during fucking and golf, and you don't need a gym or any equipment!!

I'll be dead and buried.   8o)

plank exercises.

PLANK exercise.  What do YOU think? Lol

Keep feeding me.

I know it goes against the grain, but I'd rather knot. You might pine for more, but, after all, your bark is worse than your bite. I guess I'll leave you alone now so you can tend to the twig and berries on your own.

Maybe I'll balsam fir yew.  8o(

Prefers tongue in grove ...then screwing.

Do you do a bridge exercise? Bridge is good for lower back and glutes.

If so, then yes, I've added it to my routine.

^^^ This = Strengthen the core. Crunches for the abs, supermans for the back muscles, plus stretching. (Supermans are on stomach, raise legs and arms, alternate left arm, right leg, etc.)  
* Not a Doctor, but have had backpain since my 30s, managed by keeping muscles strong and flexible. Also insure all joints are moving by doing cats - on all fours. If two vertebrae 'stick together' the next ones have to move twice as much causing discomfort. If really 'stuck', a chiropractor can get them moving again.

Thanks for the heads-up.  I googled serrapeptase and found the side effects for those of us on clopidogrel and Eliquis are risky enough to contraindicate it's use. It can cause very easy bruising and bleeding.