It’s set in stone: first compound exercises, then isolation exercises. Seems logical, but this order of exercises is at the expense of the smaller muscle groups.
Compound exercises are the large, compound exercises that involve multiple muscle groups. There are the barbell row and pull-up for back and biceps, and the barbell bench press for chest, shoulders and triceps. There are good reasons to prioritize compounds in your training schedule. Most importantly, compound exercises disrupt homeostasis much more than isolation exercises. As a result, they cause more overload and therefore more muscle growth.
A logical training sequence is therefore row and/or pull-ups first and then biceps curls. This sequence ensures that your biceps can start fresh on the compounds, in which they function as an auxiliary muscle. But the reverse is also true: when you start training your biceps, they are already pre-tired by the compounds. As a result, you will be able to do fewer reps than if you were to start those sets fresh. And so your biceps don’t get an optimal stimulus.
Now the latter is not a disaster, because your biceps will grow, at most a little less quickly. But as you get more advanced, the risk of landing on a plateau increases. And from anecdotal evidence, it’s often the smaller muscle groups, especially the arms, that stop growing. There are many strength athletes who are satisfied with their back, but not with their biceps.
The solution? Train the smaller muscle group, for example the biceps, before the compound exercises. Yes, you will then be less strong in the compound because the auxiliary muscle, for example the biceps in rows, gives up prematurely. But your priority in this case is not your back, but your biceps. Your biceps get the maximum stimulus, while your back gets enough stimulus to at least maintain the muscle mass present.
Another solution is to train the smaller muscle group on a different day than the compound it is involved in. For example, biceps on the day you do push exercises. And if you really value the development of your biceps, you train them at the beginning of your training, if desired before the compounds. Those compounds will hardly be bothered by this, because the biceps only play a limited role in push exercises.
Mind you, this is not an argument against prioritizing compound exercises. As far as we are concerned, compounds form the basis of a training program, supplemented with isolation exercises. The message is that the muscles in your body do not all grow at the same rate. Over time, you will see that some muscle groups lag behind, which is why you need to give them extra attention. And that doesn’t even have to be by adding sets or inserting a specialization block; changing the order of exercises can be enough to trigger a new growth stimulus.