A 2017 study by Król and Golaś had subjects perform bench press reps with loads ranging from 70% to 100% of 1RM. The researchers used EMG to estimate muscle activation throóghout the lift. The image above shows how pec, triceps, and anterior deltoid EMG changed between submaximal (70% of 1RM) and maximal loads.
Overall, it suggests that muscle activation doesn’t increase similarly for all prime movers as loads increase. Specifically, the pecs may already be near maximal activation with submaximal (70%) loads, whereas the anterior deltoids, and especially the triceps, experience larger increases in activation as loads get heavier.
Click to expand any of the corresponding figures for more info.
One potential implication from this information is that specifically training the triceps may give you a bit more top-end “kick” when you’re attempting maximal lifts. Another potential implication is that bench press training for pec hypertrophy may be best accomplished with somewhat lower loads. If pec activation is near-max from the first rep of a set, even with moderate loads, training heavier (say, in the 5-8 rep range) may simply be sacrificing the number of highly stimulating reps you can accomplish for your pecs over the course of a workout. However, it should be understood that both of these potential takeaways are speculative.
These studies were previously reviewed in more depth in 2017 issues of MASS research review. If you want to subscribe, you can find the plan that works best for you here. Subscribers get full access to our entire back catalog of study reviews.