From Kyoshi David Baker Midtown Karate Dojo NYC
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Balance opposing muscles

Each joint has opposing muscle groups and if you exercise one muscle group
(on one side of the joint) a lot, you must also exercise the opposing set of
muscles (on the other side of the same joint).

If you do a lot of pushups and punches (triceps), do some bicep curls
(biceps) to balance.

If you do a lot of kneebends and many repetitions of kata, emphasizing a low
squat (quadriceps), then do kicks and maybe some walking or jogging
(hamstrings) to balance.

If you do a lot of sit-ups and ab work (abdominals), then do some back
exercises or yoga (back muscles) to balance.

Otherwise, pain may develop in the joint, or just above or below the joint in
the tendons and ligaments if one set gets so strong that it overpowers the
weaker set and starts to pull at the joint.

If you experience pain near the joint, first make sure that you are doing the
technique properly (e.g., that the forward foot is perfectly straight forward
in zenkutsudachi so that you aren't torquing the forward knee).

Then exercise the opposing muscle group. (Hamstrings if the pain is just
above the front of the knee; biceps if the pain is directly above the outside
of the elbow; and back muscles if the pain is in the lower back), to relieve
the pain.

We're always seeking balance in life and that includes our muscles.