The kidneys are located just behind the lower
ribsRib cage pain and not in the lower back.Pain in the kidney region is due to stretch of the kidney capsule by stone, fluid etc.
The feeling of tightness after exercise may be
muscularBecker's muscular dystrophy
Duchenne muscular dystrophy
Muscular dystrophy
Muscular dystrophy - resources rather than related to the kidney. However if this is persistent you should see a physican who can examine you to decide whether further investigation is warranted.
This answer is not intended and does not substitute for medical advice- the information is for patient education only.
Follow-up with a physician is advisable