Do isolation exercises respond well with high reps eg 20reps with perfect form. And compound lifts low reps eg 5 reps with high weight.
So for example. Legs. Start off with high rep low weight calves. Then high rep low weight quad extensions then 5reps squats high weight low reps
Is this a good approach?
Also, the bigger the muscle the higher the weight and lower the reps. Vice Versa?
No reason to use only one approach. Do some training cycles one way and some another
Totally agree with @T3hPwnisher on switching it up. For some added context, there are some isolation movements I would just never do heavy/ low-rep because I’d lose feel or I feel it’s unsafe.
Leg extensions, for example, I wouldn’t do heavy - I think it becomes all knee. I can still find ways to do effective low reps, though. This morning, for example, I put a weight on there and did 10 reps (pretty close to failure), then I just did a bunch of mini-sets with 5 seconds in between. Light enough I can use all muscle, but I still got the fatigue high enough that I could use low reps effectively.
On the other hand, I have effectively used both heavy weight and high reps for some isolation movements - take DB side raises or rear raises, grab heavy ones, and then just rep out partials with some momentum until your shoulders go numb. These are a great change, too.
On the compound side, check out some of @T3hPwnisher’s videos here for examples of what some high-rep sets can do!