Bench Press Study: The Higher the Weight, the Less of it Will be Lifted by Your Pecs - What are the Implications?

Lighter weight = relatively larger contribution of the pecs ≠ greater gains
In their latest paper in the Journal of Strength & Conditioning Research, Henryk Król, and Artur Golas (2017) write about an experiment they designed to identify the "prime movers" during the bench press - an interesting and methodologically complex experiment that can tell us one or two things about the effects of increasing the weight you bench gradually from the standard 12-rep (70%-1RM) to the maximal 1-rep (100%-1RM) load and how it affects the activity of your chest (pectoralis major), front delts (anterior deltoids), triceps (triceps brachii) and even your lats (latissimus dorsi) during different phases of the movement.
Learn all about training your chest/pectoralis muscle at the SuppVersity

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By combining IEMG and camera techniques in a multimodular measuring system SMART, the scientists were also able to record the muscle activity and track the exact path of the barbell in the twenty healthy, male recreational weight trainers with at least 1 year of lifting experience (the mean +/- SD = 3.3 +/- 1.6 years) who were recruited for their study.
Figure 1: As you can see in the relative difference between pectoralis and anterior deltoid activity (negative value = anterior deltoids do the main work) the magic happens during the early phase of the
In the measuring session, the participants performed consecutive sets of a single repetition of bench pressing with an increasing load (about 70, 80, 90, and 100% of their 1 repetition maximum - 1RM).
Relative increase in load (%) = increase of EMG activity of pecs, delts, triceps and lats compared to lifting only the 12-RM (70% of 1RM).
Previous studies showed: More weight = more activity -- While this is right, these previous studies did not do the same complex measurement of how the load spreads across the pectoralis, deltoid and triceps muscle. If you look at the absolute values, this is still the case... I've plotted that for you in the figure to the left. If you scrutinize the data you will see that the relative change in load with an increase in weight on the pectoralis during when you go from 70% of the 1RM to 80% is 13% during the descending phase and 1% during the ascending phase. For the triceps, however, it's 29% and 22% - that's a difference of 16% and 21%, respectively; and if you ramp the weight up from 70% to 100% of the 1RM the difference increases to 62% and 82%.

In other words: If you go from your 12RM (that's ~70% of your 1RM) the relative load on the pecs on the descending and ascending phase of the bench press increases 62% and 82% less, respectively, than the load on your triceps.
As you can see in Figure 1, the relative contribution of pectoralis and deltoid muscle at the beginning of the movement reverses with increasing weights. Let's look at an example: At a weight equal to your 12RM (70% of the 1RM max), the pectoralis is still doing most of the work (3-6% more than the delts), with increasing weights, however, the anterior deltoid will take over. Eventually, at 100% of the 1RM, its normalized EMG activity will be 14-26% higher than those of the pectoralis.
Figure 2: Phase structure of the movement. Internal structure (averaged and normalized IEMG of shoulder muscle activity) of the descent phase (left string of figures) and ascent phase (right string of figures) during the flat bench press when attempting loads at 70% of the 1RM (top) and 100% of the 1RM (bottom | Król. 2017).
As you can conclude based on the absolute activity levels in Figure 2, the anterior deltoid muscles are yet not the only muscle group to help the pectoralis as the light increases. Especially during the middle segment of the ascending phase (25-75%) of the movement, it is the triceps that fills the gap between what your chest muscle can actually press and the weight you've loaded onto the bar.
"EMG Study Can Tell Us Something About Using Dumbbells, Barbells and Machines During Chest & Triceps Workouts"- The dumbbell bench press is a pec-stretcher. Doesn't it already look like maximal pectoralis major activity? I've discussed this and related questions in an October 2016 article about a study from Brazil.
So, does that mean that you should always bench with light weight? It's not that simple, no. It's true that the main message of Król's study is that the load on the pectoralis increases much less with increasing weights. So much less, in fact, that during the ascending phase (Figure 2, right, bottom) the activity of all three supporting muscles, i.e. delts, triceps, and lats, will be higher than that of the pectoralis muscle. On the other hand, though, the absolute EMG activity the scientists measured for the pectoralis major, the large chest muscle, will still increase (see Figure in the light box) - linearly up to 90% of the 1RM, a weight with which you should be able to perform ~3-4 reps and thus the lowest number of reps of which it appears to make sense to use them as the rep-goal in your regular workouts (Yes, you can train by doing only 1-RM max efforts, but does that make sense for the average gymrat?).

To cut my long elaborations short: If you are aware of the caveat that increasing the weight will reduce the ability of the bench press to isolate the chest muscle, you are free to increase the weight to 90% of the 1RM and train with 3-4 reps and will still see a higher muscle activity in the pecs than you'd do with 70% and 12 reps. Whether that's conducive to your goals, however, is a totally different question, one that you are most likely to answer affirmatively if your goal is to build strength and/or to doing full body workouts with only a limited number exercises | Comment!
  • Król, Henryk, and Artur Golas. "Effect Of Barbell Weight On The Structure Of The Flat Bench Press." The Journal of Strength & Conditioning Research (2017).
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