(Originally appeared on Medium)
There has been a lot of debate on social media about a study recently published (Schoenfeld et al., 2018) that appears to show a dose-response relationship between training volume (defined as number of sets performed) and muscle hypertrophy (measured as muscle thickness by ultrasound). From this study and their previous meta-analysis, the authors conclude that:
(…) we show that increases in muscle hypertrophy follow a dose-response relationship, with increasingly greater gains achieved with higher training volumes.Thus, those seeking to maximize muscular growth need to allot a greater amount of weekly time to achieve this goal.
This, in layman terms, means that they suggest that for maximizing hypertrophy, a high volume routine is needed.
There has been some criticism of the study by me and others. The two major issues for me are:
- The acute effect of training on muscle thickness (MT) values.
- The design of the study.
Minor issues include:
- How sets are counted.
- No baseline data reporting.
- No body composition data.
- Measurements not blinded and performed by the first author.
Below, by analyzing the study’s data and interpreting it in light of the available evidence, I will show that the study conclusion is not as straight-forward as some people think.
The acute effect of training on muscle thickness (MT) values.
(See last updates at the bottom of the article)
This paper, similar to others on the field, depends entirely on MT measurements for assessing muscle hypertrophy. I was thus surprised to see that the effect of different training variables (intensity, volume, rest intervals, etc.) on the acute MT increase after a training session has not been systematically tested.
The methods section states:
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. This is consistent with research showing that acute increases in MT return to baseline within 48 hours following a RT session (19).
Reference 19 is “Time course for arm and chest muscle thickness changes following bench press training” (Ogasawara et al., 2012).
One would expect that this reference contains the experimental evidence that supports that swelling from the kind of training performed in the study (multi-set training) already subsides after 48–72h. Surprisingly, this appears to be the supporting evidence:
Pilot data from our laboratory suggest that the acute increase in MTH (~12%) following bench press returns to pre-exercise levels within 24 h and is maintained for up to 48 h after the session.
In this study, the authors tested MT responses on the chest and triceps after bench press in untrained subjects. Because the paper doesn’t show any details on what the training was for the pilot, I asked one of the authors:
So the 48h figure comes from measuring the acute effect of 1 set of bench press at 75% of 1RM. In his opinion, further sets won’t promote more swelling, only the duration of the swelling.
Upon inspection, Schoenfeld and co. have used the same reference and sentences in their papers to support this, dating back to the first controlled trial on the subject he published (2014); the same reference has been used throughout his career:
In an effort to help ensure that swelling in the muscles from training did not obscure results, images were obtained 48–72 hours before commencement of the study and after the final training session. This is consistent with research showing that acute increases in MT return to baseline within 48 hours after a resistance training session (33).
But is there any data backing up this assumption?
One key aspect is that any supporting evidence must ideally include studies using trained subjects and performing similar exercise types.
After my initial inquiry in Lyle McDonald’s Facebook group, Peter Bond found this study that showed that in trained men, vastus lateralis (quad) thickness increased significantly after 9 sets at 10RM (5 sets of leg press and 4 sets of squats in the Smith). This increase was maintained 24 and 48 h after the session. This study was published in 2011, 1 year before Ogasawara et al., 2012. So it was available by 2014 .
I’ve plotted the difference in vastus lateralis (VL) MT between both groups below:
While the difference was short of reaching statistical significance (p = 0.052), there is a clear difference in both training interventions at 72h compared to baseline (2 times higher for HV compared to HI). Remember that this is data from all participants (due to the cross-over design).
Here is another study that compared different chest exercises (bench press on the Smith machine, barbell or dumbbell), again on trained subjects. They performed 8 sets at 10RM with 2 minute rests. Subjects reported usually doing 8–10 sets of chest per training session (important for later). The MT values of the elbow extensors at different time points is shown below:
While the differences were not statistically significant, the data shows that:
- The barbell chest press promoted the longer lasting increase in MT compared to baseline, which was maintained after 96h (3.8%). MT was still increased at 48h (4.3%) and 72h (2.3%) post-session.
- Both free weight exercises promoted a greater acute increase in MT compared to the same exercise performed in the Smith machine.
So we have data, relatively old and new that suggest that the effect of a high volume routine on MT persists at least up to 72h. This is likely why, other studies, wait 3–5 days for MT measurements (probably also because they were performed on untrained subjects, although the relevance of this after 6-8 weeks of training should be not so significant).
Both Schoenfeld and Krieger have answered to this criticism. While Schoenfeld suggests that because of the repeated bout effect (RBE), swelling does not confound results, Krieger argues that because he found (with a new analysis of the data) a correlation between the change in training volume load (reps x weight) and VL MT, then swelling cannot be responsible for the increases in MT.
Let’s address first Schoenfeld’s claim that on the RBE and muscle damage. He is conflating swelling or an acute increase in MT with muscle damage, which is not what is being argued. Second, both of the above studies have shown that after a typical resistance exercise session there is still an acute increase in MT in experienced, trained subjects. So any protection conferred by the RBE on acute swelling (indicated by an increase in MT) would be already present. Furthermore, there is evidence of cross-exercise RBE; that is, one exercise can promote protection against damage from a different exercise performed by the same muscle. However, this still assumes that all acute MT increase or swelling is due to muscle damage. Interestingly, Schoenfeld himself, reviewing exercise-induced muscle damage (2012), notes that:
“Although these effects are attenuated with regimented exercise via the repeated bout effect, significant swelling nevertheless persists even in trained subjects with increases in muscle girth seen 48 hours postworkout (71)”
Since then, as shown above, this has been observed repeatedly.
On the other hand, the argument by Krieger is only partially correct because one hypothesis (longer-lasting acute muscle swelling on higher volumes) is not incompatible with the other (higher volumes induce more hypertrophy). As I will elaborate next, the results are likely a combination of both major issues (swelling and design).
There is one very recent study that Krieger also mentions in order to show that higher volumes do not increase swelling as measured by MT (Haun et al., 2018):
“The paper by Huan (sic) and colleagues , a chronic training study, measured muscle thickness a mere 24 hours after training, yet there was no evidence of swelling according to the ultrasound data In fact, the muscle thickness changes in the Huan paper were quite small, despite ramping the volume up to over 30 weekly sets, which would refute any notion of swelling.”
Haun et al. 2018 randomized three groups (consuming whey, graded whey or maltodextrin) to perform a training protocol with a graded increase in volume, until 32 sets (at 60% 1RM) per week were reached, over 6 weeks. A detailed discussion of the paper is beyond the scope of this post, but with regards to MT values, there were no major differences between groups. With all groups combined, VL MT increased by 2.2%, and bicep brachii MT by 2.3% when measured at 24 hours.
However, despite also performing a very high number of sets, one cannot use these values to extrapolate that in Schoenfeld et al. acute swelling was also minimal, because:
- Training was at 60% 1RM, and as I understand from the methods, not to failure. They were essentially training with very submaximal loads and with average repetitions in reserve (RIR) of 4.45 by the last week. Basically, what some would consider “junk volume”.
- The only exercise for legs was squats, whereas in Schoenfeld et al, there were three different quad exercises, including one isolation exercise (leg extension, see below).
- The only exercise that targeted biceps indirectly was lat pulldowns, whereas in Schoenfeld et al., subjects performed pulldowns and rows.
- Subjects in Schoenfeld et al. performed ~30% more sets (45 sets) than those in Haun et al. (32 sets).
It is possible that the acute increase in MT in Schoenfeld et al. is also very small as that in Haun et al.; however, given the different protocols, and taking into account the studies mentioned above, it is very likely that acute swelling (small or big) might very well still be present after 48–72h.
In conclusion, even in trained subjects (which are adapted to resistance exercise), an acute -albeit small- increase in MT is observed after a resistance exercise session. This appears to be likely in addition to any protection by the RBE. However, there is no data that I am aware of that compares the dose-dependent effect of volume (as number of sets) on acute muscle swelling, specially before or after a 8 weeks of the same training. It is likely, based on our current knowledge, that a higher volume would promote an acute increase in MT of longer duration. This does not mean that in Schoenfeld et al., the MT values in the high volume group are only due to temporary swelling; rather, that the results can be confounded by the time in which the values were taken and maybe increase the magnitude of the apparent response as compared to lower volumes. This could inflate the observed increase in MT values and thus, affect the interpretation of the data.
The design of the study
The study compared three groups performing either 1 set (1-SET), 3 sets (3-SET) or 5 sets (5-SET) of the same exercises, three times per week (full body routine). The characteristics of the training protocol were:
- Seven exercises per session: flat barbell bench press, barbell military press, wide grip lateral pulldown, seated cable row, barbell back squat, machine leg press, and unilateral machine leg extension.
- Each set was performed for 8–12 repetitions to momentary concentric failure, with 90 seconds rest between sets.
“The load was adjusted for each exercise as needed on successive sets to ensure that subjects achieved momentary failure in the target repetition range. Thus, if a subject completed more than 12 repetitions to momentary failure in a given set, the load was increased based on the supervising researcher‟s assessment of what would be required to reach momentary failure in the desired loading range; if less than 8 repetitions were accomplished, the load was similarly decreased.”
Probably one of the most important characteristics of the training used was the short rest between sets. According to the author, this was due to practical limitations of using a very high volume routine with longer rest periods as it would take a long time to complete (which begs the question, if its of limited pratical value then why such design?).
Schoenfeld himself has shown that longer rest periods between sets (~3 minutes) appears to be better for muscle hypertrophy and strength than short periods (~1 minute). Short inter-set rests (1 minute) seem to blunt resistance exercise-induced myofibrillar muscle protein synthesis (MPS) (up to 4h after the session) and anabolic intracellular signalling, compared to longer (5 minutes) rests when training at 75% of 1RM. However, there appears to be no effect of short (30 seconds) or long (2.5 minutes) rest periods when training with low loads (40% 1RM) in untrained subjects. If the same is observed for trained subjects, the apparent discrepancy might be explained by the fact that short rests do not allow for enough recovery between heavy sets, so either the load/weight (if the repetitions are held constant) or the number of repetitions (if the weight is held constant) has to be reduced. In either case, the stimulus for muscle growth (load) is reduced.
Taking this into consideration, by design, the training program would favor the 5-SET condition for the simple reason that you can compensate less effective sets with more work than on lower volume conditions. In other words, when performing a suboptimal training program, you might need more sets to compensate.
Exercise selection, how sets are counted and comparison with Ostrowski et al. 1997
Another important point is the exercise selection. MT values were measured, in addition to quadriceps muscles, for the biceps and triceps. However, there were no “direct” exercises targeting the triceps or biceps; triceps were hit by the pushing movements and biceps by the pulling movements. Because of this reason (and likely because their involvement in these exercises might increase as the number of sets increase due to fatigue) more work is needed to see any effect. This agrees with the fact that the group performing 1 set saw virtually no growth in both biceps and triceps: they were effectively doing no work for either muscle.
This fact is related to another common criticism: the way in which sets were counted. According to their previous meta-analysis, the authors counted as “1 set” those exercises in which biceps and triceps were hit, but not as a direct exercise (ie. pushing movements as a tricep exercise, pulling movements as a bicep exercise). Whereas I personally (and most) don’t “count” these compound movements as an exercise for biceps or triceps, some people count them as half a set. Thus, using this more logical criteria, the 5-SET group performed 15 sets for triceps and biceps, whereas the 3-SET performed 9 sets and the 1-SET, 3 sets.
There is only one other study that can be directly used for comparing the results of this study, namely, Ostrowski et al., 1997. Using the same rationale for counting the number of sets (half for pressing movements except close-grip bench press, one per direct triceps exercise), subjects in the high volume group in Ostrowski et al. performed 20 sets for triceps. It is importat to note that this comparison assumes that one set of a push compound movement that uses the triceps promotes the same stimulus as one set that directly targets the triceps, which seems to be unlikely. Accordingly, there is a plateau in the magnitude of change in Ostrowski at 10 sets: doubling the amount of volume did not induce any significant gains (0.1%). Therefore, a threshold appears to occur already at moderate volume (10 or 14 sets, depending on how you count) when performing direct tricep work. If you don’t perform any tricep work, then you have to perform much higher volumes to get any significant stimulus. As the number of sets increase and the primary muscles become more fatigued, the last sets might also provide a more direct work to both triceps and biceps. So this means that more volume is not inherently better for these muscle groups; rather, that under these circumstances, their involvement increases as the sets progress. Thus, more sets increase the work performed by the triceps in the 5-SET compared to the 3- and 1-SET groups.
Perhaps a more direct comparison would be that using the values for the quadriceps: in Schoenfeld et al., the 5-SET group performed 45 sets of direct leg training, whereas the high volume group in Ostrowski et al. performed 12 sets. Increases in MT (Schoenfeld) and CSA (Ostrowski) were 12–13% (depending on which quad site) and 13.1%, respectively. Thus, subjects in Schoenfeld et al had to perform almost 4 times more sets to promote a similar response as the subjects in Ostrowski et al. While the authors only mention that “the reason for this discrepancy remains unclear”, the answer might lie in the different training regimens.
The program used by Ostrowski et al. involved (all sets to failure):
- 12 reps/set for the first 4 weeks.
- 7 reps/set for weeks 5 to 7.
- 9 reps/set for the final 3 weeks.
- Rest was 3 minutes between sets.
(Interestingly, they mention that “the high volume group comprised the training for the active control group, since questionnaire responses had established that this volume was typically used by most subjects prior to the study”. Unfortunately, the usual training for the subjects in Schoenfeld et al., as well as the baseline characteristics per group, are unknown.)
As shown above, one of the main differences is that the number of repetitions were held constant, and there were three weeks in which repetitions were used with a greater load (used in the following discussion as the weight in the bar) (7 reps), than in the Schoenfeld et al. study, in which a repetition range was used. Therefore, for ~1/3rd of the study period, subjects trained with heavier weights. This further argues that the training program performed by subjects in Schoenfeld et al. was suboptimal, as implied by the design.
A more subjective, albeit real-world speculation, similarly supports the idea that subjects in Schoenfeld et al. were not training to “true” failure. Anyone who has trained to failure would agree that performing 5 sets of squats to “true” failure, with only 90 seconds rest in between would necessitate a big reduction in load after the first set (or to not reach true failure in those sets). On top of this, they also had to perform 5 sets of leg press and 5 sets of leg extension. This in addition to the other exercises, three times per week. It is very hard for me to believe that someone can endure such a training, to real failure, with 90 seconds rest and do it in ~68 minutes. If anything, it shows that such set up might be suboptimal as nearly 4 times of work is needed compared to elicit a similar hypertrophic response as the subjects in Ostrowski et al., which performed only 12 sets. Further, the difference in the quality of the sets (and training intervention) for each study is exemplified by the fact that 9 sets in the Schoenfeld study only increased rectus femoris (RF) MT by 3.3%, whereas 3 sets were sufficient in Ostrowski for inducing a 6.7% increase; 3 sets in Ostrowski et al. promoted a greater increase in RF MT than 27 sets in Schoenfeld et al. (5.3%)! All of this, of course, assuming that by the time MT was measured, acute swelling was already negligible.
Is training volume load the answer?
There is another variable that is not mentioned in either study: training volume load (reps x weight). I’m not sure why, given that some people argue that it is not necessarily the number of sets that define volume as the driver of hypertrophy, but the total volume load (or total workload). Thus, the number of sets, by increasing the training volume load, could then promote more hypertrophy than lower volume training.
However, there is evidence, in trained subjects (minimum of 2 years of training), that training with a higher load (“intensity”) leads to greater hypertrophy despite achieving a much lower training volume load (Mangine et al., 2015). In this study, subjects were randomized to two groups:
- 4 sets of 10–12 repetitions with ~70% of 1RM, with 1-min rest intervals (VOL)
- 4 sets of 3–5 repetitions with ~90% of 1RM, with 3-min rest intervals (INT)
Importantly, in this study, the authors standardized the groups with a pre-intervention training protocol, so all subjects started from the same position training-wise.
A big limitation of this study is that the VOL group used a 1 minute rest between sets, which has been shown to be suboptimal. Nevertheless, this study contradicts the thesis that volume (or volume load) is the primary driver of hypertrophy, as better hypertrophy results (by DXA-measured lean mass and ultrasound, albeit not all statistically significant) were observed for the group that performed the lower volume load:
Even if you argue that results are not different (due to lack of statistical significance), this still means that equal muscular gains can be achieved with approximately half the amount of total volume load when other training variables are manipulated. Interestingly, of all the muscles analyzed, the greatest difference was observed for the chest, which is not measured in any of the Schoenfeld studies that I am aware of.
Other study from Schoenfeld et al., which found that a higher intensity (as defined by higher percentages of 1RM) routine is worse than higher volume, lower intensity routine, used a load that is arguably too low in repetitions to promote sufficient hypertrophic adaptations (2–4 reps). Moreover, in this study, rest was equal in both conditions (2 minutes) and target repetitions fixed. As 2 minutes might be too short to recuperate from a ~3RM set to failure (compared to 8–12), and repetitions had to be kept at 2–4, subsequent sets after the first 3RM set would provide very little stimulus, as the weight would have to be reduced without an increase in repetitions. And again, as with the current study, biceps and triceps were measured as a proxy for overall muscle growth despite no direct exercises being performed for these muscles.
The other two recent studies
Very closely to the publication of Schoenfeld et al., 2018, two more studies addressing the effects of volume on muscle hypertrophy in trained subjects were published. One was the previously mentioned Haun et al., 2018. This study showed that with increasing volumes up to 32 sets per week, most of the gains were achieved at ~20 sets per week. As mentioned above, MT and CSA values increased only marginally, and lean body mass increases (assessed by DXA) at the higher volume portion of the study were largely driven by extracellular water accumulation (leaving only 200g of “gains” when increasing volume from 20 to 32 sets).
Of note, training was performed at 60% 1RM, with RIR of ~4 in the final week (so very far from failure). Total training volume load increased 3.2 times from week 1 to week 6. When comparing mid (3 weeks, 20 sets) to the final week (6 weeks, 32 sets), almost doubling the training volume load (1.64 times) produced 200g grams of lean body mass gains, as well as inconsistent differences in VL MT (+5%), biceps MT (-2.6%), but a 12.5% increase in average fiber CSA. Interestingly, for several of the outcomes, there was a regression from increasing sets from 10 per week to 20 per week.
It is important to mention that, similar to Schoenfeld et al., 2018, there was no direct bicep work in the training protocol. There was also no group performing a different training set up as the study wanted to address differences between supplementation regimens under very high volume conditions, so there is no training control.
Overall, these results show something similar to what Schoenfeld et al., 2018 suggests: if training with a suboptimal set up, more sets are needed to elicit any hypertrophic response, if any.
In this study, trained subjects performed either 9 (LOW), 18 (MID) or 27 (HIGH) sets of biceps exercises comprising one direct (seated supine biceps curl) and two compound (supine bent over row and supine grip pulldown) exercises. In contrast to Haun et al. and Schoenfeld et al., the compound movements involved more biceps work as they were performed with a supine grip. Using the counting rationale as previously, these would correspond to 6 sets for LOW, 12 sets for MID, and 15 sets for HIGH. However, supination in the compounds makes more reasonable to count these compounds as 1 set instead of half a set.
Training was performed at ~75% of 1RM, 2 RIR (close to failure), with a slower eccentric tempo than the other two studies (3 seconds) and resting for 3 minutes between sets. The big advantage of this study is that it trained the biceps directly and measured its response upon different volumes.
Despite a much greater total volume load performed by the HIGH group, MT increased the most in the MID group, albeit the difference was not statistically significant between groups. However, the effect size was much larger for MID compared to the other groups. Thus, the “dose-response” was observed when going from 9 to 18 sets, which regressed when performing 27 sets.
The main limitation of this study is that participants were allowed to train outside of the study (but were not allowed to perform any exercise involving the elbow flexors). Moreover, the MID and HIGH trained two times per week versus only one in the LOW group, which means that both the volume (sets) and frequency was increased in the MID and HIGH groups.
Nevertheless, from the three recent studies, this is the only one in which bicep MT was assessed after performing a training protocol that included direct bicep work, thus evaluating directly the effect of volume on muscle growth.
There are several caveats to the interpretation that there is a graded dose-response of resistance training volume and muscle hypertrophy. When comparing studies, several conclusions arise:
- There might still be residual acute muscle swelling after a high volume routine at 48–72h, which could confound the results of measurements done in this time frame and the true magnitude of the response to high volume training protocols.
- Schoenfeld et al. always use a full body training program that does not include any direct exercise for biceps and triceps. However, these are the only upper body muscle groups measured and used as a proxy for upper body skeletal muscle hypertrophy. There is virtually no data that I am aware of measuring other upper body muscle groups and their relationship with training volume.
- Studies that include direct work for biceps or triceps show that there is a plateau in the apparent dose-response relationship between sets at a moderate intensity (as % of 1RM) and muscle growth between~10–20 sets. This cannot be extrapolated to other muscles.
- There is no consistent dose-response relationship between training volume load and muscle hypertrophy.
- The last Schoenfeld study has limited practical applicability (nearly all hypertrophy programs include exercises that train biceps and triceps directly) and shows that more work is needed when the routines utilized are suboptimal for muscle growth.
- Comparison of the changes observed in Ostrowski et al., 1997 and Schoenfeld et al., 2018 show that the latter used a very inefficient training protocol, which needs higher volumes to elicit a hypertrophic response.
- The above shows that the quality of the training protocol is more important than the quantity. When the latter is lower, the amount of sets needed is higher to get any response.
- Different training variables (tempo, time under tension, intensity/% of 1RM, etc.) could modify the volume-hypertrophy response.
In conclusion, based on the available evidence, a direct, dose-response relationship between volume and muscle hypertrophy is unwarranted. The number of sets required to elicit an optimal hypertrophic response depends on the characteristics of the training program; increasingly greater gains are not necessarily achieved with higher training volumes.
Edit 25/09/18: James Krieger wrote a response, partially, on the swelling issue brought up. As my position and data are pretty clear to me, I will only make the following points:
- I mention the potential residual swelling as a confounder, not as an exclusive explanation for the increased muscle thickness (MT) with higher volumes. In my entire article, I never say that the higher volume groups may “simply” have more edema. I just highlight that if your difference in magnitude is small to begin with, then any confounding issue becomes an important consideration. This is only one part of my interpretation of the study; the rest of the article details how the results can be explained in a manner better supported by all the evidence we have.
- He says that “ the three studies they cite are acute studies using protocols to which the subjects are not accustomed”. The two recent studies I have mentioned used a very typical training session. In Bartolomei et al., 2017, I the HI group underwent a protocol more likely to be different than anything a bodybuilder does (8 sets of 3 repetitions at 90% of 1RM); nevertheless, the acute increase in MT was much lower than with the more typical bodybuilding routine. Moreover, in Ferreira et al., 2017, subjects performed 8 sets of bench press. As I wrote, “Subjects reported usually doing 8–10 sets of chest per training session”. How is this a protocol for which the subjects were not accustomed?
- I didn’t mention Radaelli initially because it was done on untrained subjects. I would argue that after 6 months of training, they still wouldn’t be considered as trained, and I have limited my discussion using data on trained subjects.
- I counted 20 sets in Ostrowski et al. as a more logical, real-world counting strategy, not the strategy used by Schoenfeld and Krieger.
- We cannot know if the confounding by swelling would also be present in Ostrowski because there is absolutely no data regarding when the measurements were taken.
- Similarly, in McCall et al., biopsies were taken 1–5 days after the MRI measurements. However, there is no data on how many days after the last training session the MRI data was taken. Most importantly, interfiber space is measured ex vivo from stained and fixed biopsy samples, for which any information regarding in vivo hydration status cannot be determined (which should be obvious as we are talking about a histochemical analyses of muscle sections). What this research shows is that there is an accumulation of collagen and non-contractile protein concomitant with the increase in fiber size upon muscle hypertrophy. This reference is completely irrelevant for the edema/swelling discussion, and I am surprised it is being used. It appears that James is just looking for whatever study he can find to try to prove that there is no edema/swelling with high volumes, and is not actually reading the study or not understanding what he is reading.
Edit 26/09/18: Following up on James Krieger answers (you can see them in this Facebook post), I found something very interesting. Here is what James, after reading my comments above, had to say regarding edema/swelling (my highlight):
Brad Schoenfeld posted about a study by Damas et al. demonstrating the impact of the repeated bout effect on muscle damage. After the first training session (6 sets on quadriceps), there was a significant increase in muscle damage at 48 hours. This also coincided with an increase in soreness and a decline in MVC, both indirect markers of muscle damage. While edema was not assessed, it can be inferred that there would have been edema present. After 19 training sessions, there was no longer muscle damage at 48 hours after doing 6 sets. There was also no decline in MVC and no increase in soreness. Thus, it can be inferred that there would be no edema present.
(…) Thus, while edema cannot be ruled out without directly testing for it, and it also cannot be ruled out as a contributor (although not the sole reason for hypertrophy) that may reduce the magnitude of the differences between groups, it is unlikely that edema is a contributor over an 8-week training program due to the combination of data showing that 48-hour damage and edema vanish after several weeks of training (…)
I noted that I’ve tried to be careful enough to write “acute increase in MT”, and not “edema” because it is not clear to me that this increase is necessarily due to edema and/or muscle damage. It can very well be that you see an acute increase in MT due to temporal swelling produced by fluid shifts in the muscle (like intracellular volume expansion, or changes in the balance of osmolytes or electrolytes) and not necessarily by increased muscle damage.
Both Krieger and Schoenfeld like to use Damas et al., 2016 to show that after several weeks of training, muscle damage is greatly reduced, so any edema induced by muscle damage would be neglible due to the repeated-bout effect (RBE).
Big was my surprise upon finding that, upon reading the above cited paper, there is actually another paper published by Damas from the same subjects assessing edema. Here is what they found:
Untrained subjects followed a training routine consisting of 12 weekly sets of legs, at 9–12 repetitions to momentary failure. Measurements were taken 72 hours after the session at three time points: before starting (T1), after 3 weeks (T2) and at the last week (week 10, T3). By the way, all measurements were blinded.
Muscle hypertrophy was only observed at T3 (Figure 2a, CSA). However, from T1 to T2, there was an increase in muscle edema (Figure 2b, CSA-USecho) that was maintained at week 10 (T3). Because of the increase in CSA at T3, the ratio of edema to “true” muscle was lower than at T2. Importantly, as shown in the other paper, at T2 and T3, muscle damage (assessed by Z-band streaming and other markers of muscle damage) were greatly attenuated compared to T1. At T3, Z-band streaming was very low and lower than at T2; however, muscle edema was present to a similar degree. This means that, despite very low levels of muscle damage, after 10 weeks of 12 weekly sets of quad exercises, muscle edema can still be detected 72 hours after the last training session. Thus, it is reasonable to conclude that residual swelling (because of edema or otherwise, considering the other papers cited above) might be still present at 48–72 hours after performing 45 weekly sets of leg exercises. In theory, this should’ve been experimentally tested before doing any study trying to assess the effect of very high volumes on muscle hypertrophy.