Research pick: “Resistance training volume enhances muscle hypertrophy but not strength in trained men”

For this research pick I’ll briefly address a study which recently came out by Schoenfeld and colleagues. The study evaluated the effects of training volume on muscle hypertrophy and strength [1]. Schoenfeld et al. have published a meta-analysis earlier in which they showed there was a dose-response relationship between training volume and increases in muscle mass [2]. Their results showed a trend that 10+ sets weekly per muscle were better than 5-9 sets and 5-9 sets were better than <5 sets. A dose-response. It wasn't possible with the data to see if there was a relationship beyond 10+ sets per week. This randomized-controlled trial was set to figure that out. First I'll discuss the study set-up, followed by the results. And then I'll give my 2 cents on it.

Study set-up

The participants in this study were resistance-trained subjects. This is a strength of the study, since untrained folks respond differently than trained ones. Basically, untrained folks respond to EVERYTHING quite well. The inclusion criteria note that the participants had to lift weights consistently for at least a year and 3 times per week. The strength 1-RMs at baseline indeed reflect a trained population (although, as usual, lower body was lacking compared to upper body. The mean bench press 1-RM was close to the squat 1-RM…).

The number of participants was good too. They did a power analysis up-front to detect a fairly small effect size, and they determined that 36 participants would be enough. In order to account for drop-outs, they recruited 45 participants in total. Unfortunately they had a tiny bit more drop-outs than expected, leaving them with 34 participants instead of the 36 they aimed for. Drop-outs were reported in the paper, and it did not seem it lead to differences between the groups. As such, there appears no attrition bias was introduced to the study and it was adequately powered.

They randomized the participants to three groups. One group doing 1 set per exercise per training session (1SET), one group doing 3 sets per exercise per training session (3SET) and one group doing 5 sets per exercise per training session (5SET). This lead to a weekly training volume per muscle group of 6 and 9 sets for the 1SET group, 18 and 27 sets for the 3SET group and 30 and 45 sets for the 5SET group in the upper and lower limbs, respectively. As such, the 3SET and the 5SET group would allow to see if going beyond the 10+ sets weekly per muscle would lead to more muscle hypertrophy and strength gains. (They also tested muscle endurance, but I don’t care.)

So how did they measure muscle hypertrophy and strength gains? Were the methods appropriate? Certainly! For strength-testing they tested the 1-RM squat for lower body strength and 1-RM bench press for upper body strength. This is perfectly fine to test someones strength, in fact, I rather see this than shit on dynamometers. And muscle hypertrophy? They used ultrasound to measure muscle thickness. This is quite a fine method to assess this and has some advantages over methods measuring total body lean body mass. It measures muscle specifically, it can be performed relatively quickly, and it has a high precision and reliability when used by an experienced technician. However, there is definitely a bit of leeway in this. This paper reports the following figures:

The standard error of the measurement (SEM) for elbow flexor, elbow extensor, mid-thigh and lateral thigh MT was 0.70, 0.83, and 1.09, and 0.34 mms, respectively.

When did they perform these measurements? Here it is:

In an effort to ensure that swelling in the muscles from training did not obscure results, images were obtained 48-72 hours before commencement of the study, as well as after the final RT session

They acknowledge the fact that muscle swelling, caused by the previous workout(s), can influence results. To counteract this, they delay measurements with 48-72 hours. I’ll get back to this, as I think it’s an important factor to consider when interpreting the results.

Moving on to the statistics: they used a frequentist and a Bayesian approach. For the frequentist approach they applied a baseline-adjusted ANCOVA on the change scores. This is perfectly okay and they factored in correction for the family-wise error rate (basically when you measure more things you need to correct for that, else you’ll just increase your chances of a type I error). I can’t comment on the Bayesian approach at all, because I know way too little about it. I’ll put some faith in their statistician (James Krieger) for this. So the statistics are a-ok.

James Krieger torturing the study data. A practice also known as “Kriegering”, resulting in “Kriegered” data.

The study results: muscle hypertrophy following a dose-response relationship

I’m gonna skip over the results on muscle strength a bit quick. In a nutshell; they didn’t find any significant differences between the groups. As such, it appears only a relatively low threshold of volume needs to be reached for strength. (The 1SET group only trained for ~39 minutes a week!). Nevertheless, keep in the back of your head that they employed 8-12 reps per set. This is not necessarily generalizable to someone doing 1 set per muscle group per training session with say, 2 reps vs. someone doing 5 sets per muscle group with the same amount of reps.

Anyways, the good stuff is in the muscle thickness measurements aka. dem gains. I’ve listed them in the table below (values are mean + SD):

Outcome Group Pre Post Change
Biceps thickness (mm) 1SET 42.6 (4.3) 43.3 (5.1) 0.7 (2.0)
3SET 44.6 (5.9) 46.7 (5.8) 2.1 (1.6)
5SET 42.6 (4.3) 43.3 (5.1) 2.9 (1.7)
Triceps thickness (mm) 1SET 47.2 (4.5) 47.7 (4.6) 0.6 (2.0)
3SET 48.4 (6.2) 49.8 (6.3) 1.4 (3.1)
5SET 47.1 (3.5) 49.7 (4.9) 2.6 (2.3)
Rectus femoris thickness (mm) 1SET 59.7 (6.7) 61.7 (5.5) 2.0 (2.6)
3SET 57.9 (8.1) 61.0 (8.7) 3.0 (3.1)
5SET 54.4 (3.4) 61.2 (4.5) 6.8 (3.6)
Vastus lateralis thickness (mm) 1SET 57.5 (6.0) 60.4 (6.3) 2.9 (1.9)
3SET 57.9 (8.0) 62.5 (7.0) 4.6 (2.3)
5SET 52.4 (6.2) 59.6 (5.8) 7.2 (3.0)

So if you take a quick look at the change column, you indeed see a dose-response relationship. The higher the volume, the bigger the change. However, the frequentist approach found none of this to be statistically significant. The Bayesian approach only found weak evidence for it, or better said, not worth more than a bare mention.

My 2 cents

One issue is that these results on muscle thickness aren’t really in line with a previous study they cite, namely that of Ostrowski et al. [3]. Lyle McDonald aptly pointed this out in his article on this paper. The Ostrowski et al. study employed 1, 2 and 4 sets per exercise yielding 3, 6 or 12 sets per muscle group weekly. So that’s already a far lower volume than the 3SET and 5SET group in this study. Schoenfeld et al. cite that the highest volume group indeed showed a larger increase in triceps thickness compared to the lowest volume group. However, what they didn’t mention, was that the 2 set group in that study showed practically the exact same increase as the 4 set group. So apparently it plateaud there for this study, with already a way lower volume that Schoenfelds study. No explanation is provided for this. While not necessarily an issue of the validity of the study per se, it should be explained.

Something which is an actual issue with the internal validity of the paper, is the following:

The lead researcher, a trained ultrasound technician, performed all testing using a B-mode ultrasound imaging unit.

So Schoenfeld performed the testing, and he knew which subjects were in which group. With any measurement that is not 100% precise, there is the risk of observer bias. I’m not saying that this has influenced the results of this study, but the risk certainly was there. There is enough leeway in these measurements to introduce observer bias to the study and it should be considered a high risk for it, in line with the Cochrane Risk of Bias Tool.

Furthermore, while the groups were randomized, the method for randomization was not described. This leaves an unclear risk of selection bias, in line with the Cochrane Risk of Bias Tool. Additionally, both participants and personnel were not blinded from knowledge of which intervention a participant received. This introduces a high risk of performance bias, in line with the Cochrane Risk of Bias Tool.

Finally, the most important issue to me is when the measurements were taken. The issue here is twofold. One is that the measurements were taken 48 hours TO 72 hours after the final session. The paper does not note if the subjects were randomly measured within this timeframe, or that say, the 5SET group got measured 48 hours after, and the 3SET group got measured 72 hours after. Because I believe edema is certainly an issue still with these relatively brief periods of time between the training session and measurements. (And even beside that, you could get something analogous to the ‘batch effect’.) And this is actually the second issue I have with this. I do think muscle swelling played a role in said results. I do not think 48 hours is enough to let it subside fully. They cite a study which would support that 48 hours is enough for the swelling to subside [4], but I disagree with this one. This study reports:

Pilot data from our laboratory suggest that the acute increase in muscle thickness (~12%) following bench press returns to preexercise levels within 24 h and is maintained for up to 48 h after the session

The difference is that in this study they only performed 3 sets of 10 repetitions per session. That’s a wayyy lower volume than used in the study by Schoenfeld. And another study already demonstrated significant extracellular water retention after 24 hours with more sets [5], while this pilot data demonstrated the muscle thickness to return to preexercise levels within 24 hours. In fact, one study even demonstrated increased muscle swelling of the vastus lateralis 48 h post-training in strength-trained men [6]. To top it off, Schoenfeld himself wrote the following passage in his book “The Science and Development of Muscle Hypertrophy”:

(Reference 322 refers to [7])

So it could very well be that the results of Schoenfelds study can, at least partly, be attributed to more muscle swelling with higher volume.

Concluding. this study was actually performed well on many aspects, but I have serious doubts about the muscle swelling issue, and to a lesser extent I feel the observer bias in the ultrasound measurements should’ve been taken care of by blinding the technician (this issue isn’t addressed in the paper as being a threat to validity). Moreover, the conclusions made in the study are way too strong, since the statistics don’t support a dose-response relationship. It’s a trend at best and clearly more research would be needed. An extensive post on /r/weightroom on Reddit examines this.


  1. Schoenfeld, Brad J., et al. “Resistance Training Volume Enhances Muscle Hypertrophy.” Medicine & Science in Sports & Exercise (2018).
  2. Schoenfeld, Brad J., Dan Ogborn, and James W. Krieger. “Dose-response relationship between weekly resistance training volume and increases in muscle mass: A systematic review and meta-analysis.” Journal of sports sciences 35.11 (2017): 1073-1082.
  3. Ostrowski, Karl J., et al. “The effect of weight training volume on hormonal output and muscular size and function.” Journal of strength and Conditioning Research 11 (1997): 148-154.
  4. Ogasawara, Riki, et al. “Time course for arm and chest muscle thickness changes following bench press training.” Interventional Medicine and Applied Science 4.4 (2012): 217-220.
  5. Haun, Cody T., et al. “Effects of graded whey supplementation during extreme-volume resistance training.” Frontiers in Nutrition 5 (2018): 84.
  6. Ahtiainen, Juha P., et al. “Recovery after heavy resistance exercise and skeletal muscle androgen receptor and insulin-like growth factor-I isoform expression in strength trained men.” The Journal of Strength & Conditioning Research 25.3 (2011): 767-777.
  7. Howatson, Glyn, and Adi Milak. “Exercise-induced muscle damage following a bout of sport specific repeated sprints.” The Journal of Strength & Conditioning Research 23.8 (2009): 2419-2424.

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