Many guys and gals in the gym isolate muscles to develop particular muscle groups, is this necessary and appropriate for everyone?
Most of the time joint isolation is NOT necessary because for many people their muscles will respond in the manner they desire through compound movements (pressing and pulling).
However for some individuals who have hit a “plateau” and through nutritional and compound movement adjustments they simply cannot grow, perhaps isolating a joint will help increase the LOAD placed on a particular muscle.
Caveat: it depends on your goals! If your goal is to lose fat, stay healthy and live long…you do not have to isolate joints! (even most bodybuilders do not have to) Only individuals who have a priority #1 goal of growing a particular muscle group AND have tried other options (nutrition, varying exercises, angles, loads etc) to no avail may have to consider isolating a joint.
Personally I try to keep joint isolation to a minimum. The more muscles that can help stabilize a movement the better. My training consists of 90% pushing and pulling for all of my muscle groups. Only my calves and upper chest are isolated each week for the above reasons.