Surviving 60 years of less than sedentary life has taught me at least one thing... It is much easier for the young buck to recover from minor overexertion than I.
Case in point...
I have been introducing my grand kids to the joys of equestrian interaction. They have responded with enthusiasm and some bit of patience (as has my older Appy gelding).
This last week, Daniel (the gelding) showed some consternation at the grand children's mixed cues, and quit on them. After the children left I decided not to let Daniel think he was getting away with something, and to reinforce the correct cues, took the kids saddle off and climbed up bareback. Daniel responded well and after about 20 minutes of light exercise I put him away.
Next morning my lower back is really tight. Bareback riding requires balance to source from thighs, pelvis, and hips... can be stressful on the lower back if you are not regularly riding this way.
Went to the driving range anyway, and took three times as long to limber back up and swing with a bit of comfort.
Moral - We ain't near as elastic and resilient as we used to be. Deal with it. Try not to overexert any muscle group... our muscle mass is not building it's fading. Work every day on stretching and flexibility.
Don't give up... adapt!