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Is Regional Hypertrophy Predictable? • Stronger by Science

Notice: This text was the MASS Analysis Evaluate cowl story for January 2023 and is a overview of a latest paper by Albarello et al. If you’d like extra content material like this, subscribe to MASS.

Key Factors 

  1. The current research (1) measured acute EMG and muscle swelling (thickness and cross-sectional space, assessed through ultrasound) responses within the higher and mid chest after flat and incline benching. 
  2. A earlier research (2) reported larger longitudinal higher chest hypertrophy and related mid chest hypertrophy when evaluating incline to flat benching.
  3. EMG responses differed in a predictable method within the current research, with incline bench inflicting increased higher chest exercise and flat bench inflicting increased mid chest exercise. Nonetheless, muscle swelling outcomes differed from the EMG outcomes, and likewise did not comport with the longitudinal hypertrophy knowledge from the prior research.   

Regional hypertrophy is the well-established phenomena (demonstrated right hereright here, and right here) the place non-uniform development happens in a muscle or muscle group. For instance, in case your biceps grew extra close to the elbow in response to coaching than they did close to the shoulder, that will be an instance of regional hypertrophy. In one other instance, Greg beforehand reviewed a research by Chavez and colleagues wherein a gaggle of untrained males performing incline bench press solely, flat bench press solely, or a combination of each, skilled completely different hypertrophy patterns within the higher and mid pecs (2). Apparently, there have been no vital variations between teams, besides that the incline bench press solely group had a considerably larger (and fairly substantial) enhance of their higher chest thickness (i.e., the clavicular head of the pectoralis main) in comparison with the opposite two teams. To my information, that is the one research inspecting longitudinal regional pec hypertrophy variations between teams performing completely different urgent workout routines; nevertheless, there are a good variety of research acute responses (corresponding to EMG) that you just would possibly suppose would offer some indication of what regional hypertrophy responses you’d get long run (34). The current research (1) in an fascinating instance, because the individuals carried out flat and incline bench press periods whereas the researchers examined their higher chest and mid chest (i.e., the sternal head of the pectoralis main) EMG exercise, and ultrasound-derived muscle swelling (i.e., acute muscle thickness and cross-sectional space modifications) following coaching. This design permits us to check these two acute proxy measures to see how they comport with each other, however we will additionally see if both acute measure traces up with the one present research on longitudinal hypertrophy following incline and flat bench urgent (2). As one would possibly count on, EMG exercise was larger for the higher than the mid chest throughout incline bench press and the other was noticed throughout flat bench, and these variations have been vital between workout routines. Nonetheless, as I’ll talk about on this article, the normalization procedures used within the current research make it troublesome to conclude a lot from these findings. Muscle swelling elevated to a larger extent within the higher than the mid chest following the incline bench, and the other sample was noticed following the flat bench. Nonetheless, when evaluating absolute muscle swelling between workout routines, the one vital distinction was that mid chest swelling was larger following flat bench than incline bench, however notably, higher chest swelling was related after each bench press variations. Due to this fact, acute muscle swelling didn’t observe the sample of longitudinal regional hypertrophy noticed within the one present coaching research (2). On this overview I’ll talk about the detailed findings of the present research and the way they inform our capacity (or lack thereof) to foretell regional hypertrophy in response to particular train variations.

Goal and Hypotheses


The aim of this research was to find out if there are variations in floor EMG throughout, and muscle thickness and cross-sectional space after the incline and flat bench press in particular areas of the pectoralis main. Additional, this research aimed to make clear whether or not “the muscle area of the pectoralis main with the best sEMG [surface EMG] amplitude throughout train corresponds to the one with the best acute variations in cross-sectional space and/or muscle thickness.”


The authors hypothesized “that the pectoralis main head with the best sEMG amplitude throughout train would be the one with the best acute variations in muscle structure [i.e., muscle thickness and cross-sectional area].” 

Topics and Strategies


13 injury-free, resistance-trained males (28.79 ± 4.46 years previous; 174.64 ± 5.60cm tall; weighing 79.43 ± 8.99kg) participated on this research. Contributors wanted to have at the least one yr of resistance coaching expertise, not be usually performing different types of bodily exercise, and have a 1RM flat bench of at the least their body weight. 

Examine Design

The individuals attended 4 lab periods. The primary two have been 1RM periods and the final two have been experimental coaching periods. Particularly, the primary session was a familiarization which included ultrasound measurements and a 1RM evaluation the place the individuals examined each the flat and 45° diploma incline bench press with half-hour relaxation between the 2. The second session was a repeat of the primary session that was carried out for reliability functions. I imagine the train order of the 1RM check days was randomized, as train order was randomized within the coaching periods, however this was not explicitly clear. The third session occurred 72 hours after the second 1RM testing session, and consisted of 4 units of the flat or incline bench press (the train that was carried out on every day was randomly decided) to failure with 60% of 1RM, throughout which pec EMG exercise was recorded, and after which muscle swelling was captured. The fourth and ultimate experimental session occurred 96 hours after the third session (the extra day was supplied to permit for muscle harm restoration), and was a repeat of session three with the bench variation that had not but been carried out. The individuals rested at the least three minutes between these 4 units on each days. Contributors have been requested to keep away from any strenuous exercise through the research. 


Electrodes have been positioned on the clavicular and sternal head of the pectoralis main as proven right here. EMG knowledge have been reported as the basis imply sq. (RMS) of exercise through the concentric part of every rep inside every set. Primarily, the RMS tells you the typical energy of {the electrical} sign from the muscle over the time interval sampled. These RMS values for every head of the pec have been normalized inside every train individually to the best RMS worth noticed for the particular pectoral head throughout every set. Which means, the typical EMG values for every pec area have been scaled to their very own peak inside every train. Sadly, this presents a considerable limitation which prevents significant comparisons between muscle areas inside, and between workout routines. In the event you’re , the specifics of what the EMG findings on this research can let you know I talk about within the Criticisms and Statistical Musings part. 

Ultrasound-Derived Muscle Swelling

Adjustments in muscle thickness and cross-sectional space (which I seek advice from collectively as modifications in “muscle swelling” on this article) have been derived from panoramic ultrasound photographs guided by a customized made help to extend probe stability and standardize probe placement as proven right here. The share change in cross-sectional space and muscle thickness was calculated by evaluating the typical thickness and cross-sectional space values from earlier than to after every coaching session. The identical technician analyzed all the photographs. 



The authors ensured an correct relative load choice by recruiting skilled individuals with expertise within the bench press, by having a familiarization session, and by repeating their 1RM exams twice to make sure reliability. Likewise, they took ultrasound measurements on every 1RM testing day to make sure muscle thickness and cross-sectional space reliability. They reported their reliability statistics, which aren’t value discussing intimately on this overview. However, in abstract, reliability was fairly good, indicating that we will trust within the reported values. 


As proven in Determine 1, inside every train there was a major distinction reported in sternal and clavicular head EMG exercise. The authors reported that flat bench press produced extra exercise (~30 %; p < 0.001) within the sternal than the clavicular head in each set, whereas the incline bench press produced extra exercise (~34%; p < 0.001) within the clavicular than the sternal head in each set. Whereas these findings are intuitive, as a result of normalization procedures, we truly can’t make inferences about relative excitation between the pectoral areas. 

Likewise, the authors reported that the flat bench produced considerably extra sternal exercise than the incline bench press (~35%, p < 0.001), whereas the incline bench press produced considerably extra clavicular exercise than the flat bench press (~28%; p < 0.001). Nonetheless, as soon as once more, these between-exercise muscle exercise comparisons also needs to be interpreted with warning, if made in any respect (see the Criticisms part). 

Muscle Swelling

As proven in Determine 2, muscle swelling responses differed between pectoral areas within-exercise, and between workout routines. After flat benching, the individuals’ sternal head elevated in thickness considerably greater than their clavicular head (~11.06%; p < 0.005) and this sample held true for cross-sectional space (~5.42%; p < 0.005). Conversely, after incline benching, the individuals’ clavicular head cross-sectional space elevated considerably greater than their sternal head (~10.81%; p < 0.001), and though this sample roughly held true for muscle thickness, it was not vital (~6.83%; p = 0.08). Notably, nevertheless, the one between-exercise variations in muscle swelling have been that the flat bench press produced considerably larger will increase in muscle thickness (~3-fold; p < 0.001) and cross-sectional space (~17.89%; p < 0.001) within the sternal head in comparison with the incline bench press. Additional, the will increase in clavicular pec muscle swelling weren’t considerably completely different between incline and flat bench (p = 0.842-0.992), and actually, appeared fairly related visually.  

Criticisms and Statistical Musings

As I’ve talked about earlier on this article, the EMG knowledge from this research don’t enable many helpful inferences to be made. Initially after I wrote this text, I believed solely the between-exercise knowledge was topic to this limitation, however Greg fortunately (however sadly) caught that it additionally utilized to the within-exercise knowledge. To grasp this limitation, we have to talk about normalization. Normalization is the method by which you scale uncooked EMG knowledge into extra usable info. However, which uncooked EMG knowledge you select to be scaled and what you scale it to, is essential. Notably, on this research, the authors used the typical EMG exercise for every pec area throughout every set for every train, and normalized it to the best EMG exercise produced by that identical pec area, inside that very same set. This offers you the ratio of the typical EMG exercise of every pec area to its personal peak EMG, throughout every set of every train. So, if a pec area reached a peak that truly was equal to its theoretical max excitability (which we wouldn’t know), and stayed at 90% of that peak worth on common throughout every set, its worth could be 90% (out of 100%). Nonetheless, if the pec area reached a peak that truly was equal to solely half of its theoretical max excitability (which once more, we wouldn’t know), and stayed at 90% of that peak worth on common, its worth would additionally be 90%. Which means, all these values actually inform us are how near the best EMG exercise (which can or could not have been very excessive relative to the muscle’s most capability) recorded in every set was the typical EMG exercise in every set. In the event you’re questioning “okay, so what does that inform me?” Sadly, the reply will not be very a lot. In the event you needed to know the relative variations in muscle-specific EMG exercise inside and between the 2 lifts, EMG exercise would should be normalized to a theoretical muscle-specific most worth, like a most voluntary isometric contraction (MVIC). An MVIC is precisely what it appears like, an isometric contraction achieved with most effort utilizing a joint angle that ought to present a muscle-specific theoretical maximal EMG excitation worth which may then be used as a reference throughout workout routines (as I mentioned right here in additional element within the “limitations of EMG” part). Because the authors didn’t use this method, you possibly can’t truly make any inferences about relative EMG exercise between pec areas, inside or between workout routines. With all that stated, it’s value mentioning that normalizing knowledge to an MVIC introduces different limitations. There are assumptions as as to if MVIC performances symbolize true maximums, which additionally lengthen to the workout routines they’re in contrast towards. Joint angle variations between workout routines acutely alter muscle morphology and place, subsequently impacting EMG sign energy and acquisition. As well as, not all muscle mass have the identical recruitment sample. Some observe a superficial to deep sample, whereas others deep to superficial, which may understandably impression floor EMG (5). Due to this fact, comparisons between completely different workout routines which prepare the identical muscle, even when primarily based on MVICs, might not be legitimate representations of relative sign strengths, and subsequently of anticipated longitudinal hypertrophy variations (6).

I’ve one ultimate notice, unrelated to EMG, which is a protection towards potential criticisms relatively than a criticism of this text. Some might moderately disagree with how I’ve positioned differential hypertrophy within the higher and mid chest on account of train choice as “regional hypertrophy.” Whereas the clavicular and sternal heads of the pecs are each a part of the pectoralis main, and never thought of separate muscle mass, they’re innervated by completely different motor nerves (7). Thus, they arguably perform extra like separate muscle mass than areas of the identical muscle. In a previous period, say a decade in the past, when the “evidence-based” neighborhood was typically skeptical of the idea of regional hypertrophy, you would possibly hear somebody level this out and declare a differential hypertrophy response within the higher versus mid chest was subsequently not proof of regional hypertrophy. Nonetheless, at this level, with extra consciousness of the numerous research displaying the prevalence of regional hypertrophy, I didn’t suppose it was a distinction value quibbling over. For completeness I needed to acknowledge this nuanced level, however from a bodybuilding perspective, it’s immaterial, because it’s merely helpful to know what workout routines may be more practical for rising the higher and mid chest.


It will be good to have the ability to predict which workout routines reliably produce particular regional hypertrophy in particular muscle mass. As a aggressive bodybuilder and a coach of physique athletes, I would like that to be our actuality. Sadly, we simply aren’t there but. Moreso, we want extra knowledge to find out which acute proxy measures would possibly be capable of predict hypertrophy long run, however we even have to simply accept that there’ll all the time be inherent limitations to such predictions.

To start out, let’s summarize the place we’re with predicting regional hypertrophy primarily based upon train choice. As I discussed within the Strategies and Criticisms sections, the EMG knowledge on this research sadly can’t inform us very a lot. Regardless of this, it’s nonetheless an essential reminder relating to the challenges and complexities of predicting long run diversifications from acute measurements which every have their very own distinctive limitations. Notably, whereas EMG exercise is beneficial in different methods, it’s restricted in its capacity to check the hypertrophy stimuli between workout routines (56). Alternatively, I can’t consider any cause why you possibly can’t make legitimate muscle swelling comparisons between workout routines. Apparently, the muscle swelling findings counsel that flat bench press is an throughout higher train than incline for each higher and mid chest growth (if we assume muscle swelling is indicative of the stimulus). Particularly, the flat bench produced larger will increase within the thickness and cross-sectional space of the mid chest in comparison with incline, and related will increase within the higher chest. However what does acute muscle swelling actually inform us? Effectively, a rationale to make use of it as a proxy measure for hypertrophy may be that will increase in swelling might point out elevated blood stream, edema, and metabolic exercise (which may be skilled as a larger pump) in a given area, probably on account of work being carried out by these particular muscle fibers. Certainly, there are some (albeit not robust) relationships between acute modifications in muscle dimension and longitudinal hypertrophy (8). 

So, if we take the muscle swelling outcomes at face worth, we’d conclude that flat bench press is an general superior chest builder in comparison with incline, because it higher stimulates the mid chest and offers an identical stimulus to the higher chest. Additional, we’d conclude that the anecdotal experiences of lifters that incline is a greater higher chest developer are subsequently incorrect. This could possibly be true. Anecdotal experiences may be confounded by a whole lot of elements, and moreover, particular person variations may be amplified by loud or distinguished voices and unduly affect what turns into “collective knowledge.” For instance, think about {that a} distinguished bodybuilder with a robust affect in the neighborhood did truly get extra higher pec hypertrophy from incline in comparison with flat bench on account of their particular person biomechanics, after which reported their expertise as if it was the norm, when in truth, most individuals wouldn’t reply the identical approach. One of these factor occurs, nevertheless, we don’t must make this shaky, speculative comparability between a proxy measure and anecdotal proof. Slightly, we will make a barely much less shaky and speculative comparability (however simply barely) between the current research with present knowledge on hypertrophy.

As I discussed within the introduction, Greg beforehand reviewed the one research I’m conscious of wherein the authors in contrast longitudinal modifications in regional hypertrophy between teams performing solely flat bench, incline bench, or a mix of the 2 (2). Sadly, their findings have been instantly opposite to what you’d count on primarily based on the muscle swelling knowledge within the current research, because the incline solely group skilled considerably larger higher pec hypertrophy than each of the opposite two teams, with no different variations between teams. Due to this fact, whereas the current acute knowledge signifies the flat bench is a hands-down higher train for pec growth in all areas in comparison with incline, the precise analysis on hypertrophy suggests the other. In case your response to this comparability is that we should always place extra religion within the precise longitudinal hypertrophy findings, in precept, I agree with you. Nonetheless, it’s value noting that we solely have this one research by Chavez (2) to go on, and, as Greg famous in his interpretation, the findings are slightly odd. Particularly, higher pec thickness elevated by greater than 62% within the incline urgent group, which is an exceptional enhance that stands out as an outlier in comparison with different research. The rationale for this huge diploma of hypertrophy reported by Chavez is unknown, however to be clear, neither I nor Greg are calling foul. As mentioned in Greg’s article, apart from the magnitude of change, the information don’t look “funky.” So this discovering could possibly be correct, however simply confounded by different elements which inflate its magnitude corresponding to muscle swelling (the measurement was taken inside 24-48 hours of the final coaching session), using untrained topics, poor measurement reliability, a mix of those elements or maybe different, unknown variables. Nonetheless, we want extra analysis to obviously decide the results of incline and flat bench press on regional pec hypertrophy. 

To provide you my private take, it doesn’t make sense to me that flat bench press is simply as efficient at inducing higher chest hypertrophy as incline bench and it additionally doesn’t make sense that incline bench is simply nearly as good as flat bench at inducing mid chest hypertrophy, and naturally, the 2 are mutually unique conclusions. This implies I’ve to query each the findings of Chavez and the relevance of the muscle swelling findings within the current research. This places me in a troublesome spot, as I truly suppose it’s cheap to invest that variations in acute muscle swelling may be grossly predictive of long run hypertrophy. Nonetheless, I feel there may be a believable clarification for why muscle swelling favored flat bench press. In the event you take a look at the inclusion standards, the individuals had a energy requirement for flat bench, however not incline. Thus, it’s doable that the skilled individuals have been extra skilled on flat bench press than incline, and simply couldn’t induce as a lot of a stimulus with the much less acquainted motion. Whereas this sounds believable, it’s admittedly not a rock strong clarification. In the event you take a look at the reliability knowledge for the 1RM exams, each workout routines have been equally dependable, and the individuals’ incline bench 1RM was ~85% of their flat bench press 1RM, which looks as if an affordable proportion. One other risk that Greg introduced up, is that it could possibly be associated to posture. Because you’re sitting extra upright with incline, that might simply promote higher venous drainage/much less blood pooling throughout train, leading to much less swelling on the time of measurement. Whereas doable, finally, I don’t have an excellent clarification for the (in my view) non-intuitive between-exercise muscle swelling variations, nevertheless it would possibly simply be that acute muscle swelling (and by proxy, your acute notion of a pump) simply aren’t that helpful as proxies for the hypertrophy stimulus. 

On that notice, I feel we merely want to check extra proxy measurements corresponding to T2 MRI (as mentioned right here), and maybe muscle oxygenation (as mentioned right here) along with EMG exercise (normalized in a different way) and muscle swelling, in addition to extra sensible measurements like “perceived pump” and subjective assessments of muscle soreness after coaching to see if and the way they affiliate with longitudinal modifications in regional hypertrophy. Nonetheless, even when we conduct such experiments, we’ve got to set real looking (i.e., low) expectations for these proxies’ predictive skills. As an example why, think about an skilled lifter who wants a given quantity of quantity and energy to keep up their muscle dimension. Then, think about that the lifter lowered their coaching to 1/tenth of that quantity for an prolonged time frame whereas sustaining excessive effort. Possible, they’d slowly begin getting smaller; nevertheless, in case you took a battery of measurements throughout and after considered one of their effortful, reduced-volume periods, you’d see loads of EMG exercise within the skilled muscle mass, elevated T2 MRI and muscle oxygenation in those self same muscle mass, the lifter would get a pump and get sore afterwards (in all probability greater than regular on account of a degradation of the repeated bout impact), they usually’d additionally expertise massive will increase in acute muscle swelling. Nonetheless, they’d nonetheless be getting smaller. My level is, there’s a lot that goes into the result of hypertrophy, and irrespective of how good a proxy is, it merely can’t seize all of the variables which affect it. 

To conclude, the current research is absolutely fascinating. It demonstrates distinctive EMG exercise within the higher and mid chest throughout flat and incline bench urgent and distinct regional-specific muscle swelling responses. Whereas these responses don’t comport with the present incline and flat bench longitudinal hypertrophy knowledge we’ve got, this space is ripe for additional analysis.   

Subsequent Steps

As I alluded to within the interpretation, there are two avenues for future analysis I’m inquisitive about. For one, we want further longitudinal analysis on hypertrophy following incline in comparison with flat bench press coaching to see if the observations of Chavez and colleagues (2) may be replicated. Moreover, we want longitudinal hypertrophy analysis that follows baseline proxy measures which may predict hypertrophy like T2 MRI, muscle oxygenation, and sensible measures of subjective soreness and pump high quality to see what relationships are strongest, and if they’re regionally correct. With this analysis performed we would be capable of probably make higher inferences about long run adaptation primarily based on acute research and presumably use sure proxies for coaching monitoring functions as properly. 

Software and Takeaways

  • We don’t but have good acute proxy measures to precisely predict hypertrophy broadly, not to mention in a area particular method. The current research demonstrates variations in muscle exercise throughout flat and incline bench coaching, and muscle swelling following flat and incline bench coaching within the higher and mid chest. Whereas intriguing, we want additional analysis to find out if these knowledge are cheap proxies for predicting long run adaptation.         

This text was the quilt story for the January 2023 situation of MASS Analysis Evaluate. In the event you’d wish to learn the complete, 126-page January situation (and dive into the MASS archives), you possibly can subscribe to MASS right here.

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  1. Albarello JCDS, Cabral HV, Leitão BFM, Halmenschlager GH, Lulic-Kuryllo T, Matta TTD. Non-uniform excitation of pectoralis main induced by modifications in bench press inclination results in uneven variations within the cross-sectional space measured by panoramic ultrasonography. J Electromyogr Kinesiol. 2022 Dec;67:102722. 
  2. Chaves SFN, Rocha-Júnior VA, Encarnação IGA, Martins-Costa HC, Freitas EDS, Coelho DB, et al. Results of Horizontal and Incline Bench Press on Neuromuscular Diversifications in Untrained Younger Males. Int J Exerc Sci. 2020 Aug 1;13(6):859-872.
  3. Rodríguez-Ridao D, Antequera-Vique JA, Martín-Fuentes I, Muyor JM. Impact of 5 Bench Inclinations on the Electromyographic Exercise of the Pectoralis Main, Anterior Deltoid, and Triceps Brachii through the Bench Press Train. Int J Environ Res Public Well being. 2020 Oct 8;17(19):7339.
  4. Trebs AA, Brandenburg JP, Pitney WA. An electromyography evaluation of three muscle mass surrounding the shoulder joint through the efficiency of a chest press train at a number of angles. J Power Cond Res. 2010 Jul;24(7):1925-30.
  5. Vigotsky AD, Halperin I, Lehman GJ, Trajano GS, Vieira TM. Deciphering Sign Amplitudes in Floor Electromyography Research in Sport and Rehabilitation Sciences. Entrance Physiol. 2018 Jan 4;8:985.
  6. Vigotsky AD, Halperin I, Trajano GS, Vieira TM. Eager for a Longitudinal Proxy: Acutely Measured Floor EMG Amplitude will not be a Validated Predictor of Muscle Hypertrophy. Sports activities Med. 2022 Feb;52(2):193-199.
  7. Haley CA, Zacchilli MA. Pectoralis main accidents: analysis and therapy. Clin Sports activities Med. 2014 Oct;33(4):739-56.
  8. Franchi MV, Longo S, Mallinson J, Quinlan JI, Taylor T, Greenhaff PL, et al. Muscle thickness correlates to muscle cross-sectional space within the evaluation of energy training-induced hypertrophy. Scand J Med Sci Sports activities. 2018 Mar;28(3):846-853.



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