Adam C. Stewart
The idea that Regional Hypertrophy is normal and can be manipulated with exercise selection is now well established. However, the question remains, can we predict the results of longitudinal regional Hypertrophy with acute measures such as EMG and muscle swelling?
Note: This article was the cover of MASS Research Review for January 2023 and is a review of a recent article by Albarello et al. If you want more content like this, subscribe to MASS.
Regional hypertrophy is the established phenomenon (shown here, here and here) in which uneven growth occurs in a muscle or muscle group. For example, if your biceps have increased closer to the elbow in response to exercise than near the shoulder, this would be an example of Regional hypertrophy. In another example, Greg previously reviewed a study by Chavez and his colleagues in which a group of untrained men who only did the inclined bench press, the flat bench press or a mixture of both had different hypertrophy patterns in the upper and middle pectoral muscles (2). Interestingly, there were no significant differences between the groups, except that the Inclined Bench Press group only had a significantly larger (and quite significant) increase in its upper chest thickness (i.e. the clavicular head of the pectoralis major) compared to the other two groups. To my knowledge, this is the only study that examines the longitudinal regional differences in Pec hypertrophy between groups performing various pressing exercises; however, there are many studies looking at acute responses (such as EMG) that you think could give an indication of the regional hypertrophy responses that you would get in the long term (3, 4). The present study (1) in an interesting example, when the participants performed flat and inclined presses while the researchers studied their EMG activity in the upper chest and the middle part of the chest (that is, the sternal head of the pectoralis major) and the muscle swelling derived from ultrasound (that is, the sternal head of the pectoralis major) and the – ie This design allows us to compare these two acute Proxy measures to see how they behave with each other, but we can also see if one of the acute measures corresponds to the existing study on longitudinal hypertrophy after an oblique and flat bench press (2). As expected, EMG activity was greater in the inclined bench press for the upper chest than for the middle chest, and the reverse was observed in the flat bench, and these differences were significant between the exercises. However, as I will discuss in this article, the standardization procedures used in the present study make it difficult to conclude these results. The muscle swelling increased more strongly in the upper part of the chest than in the middle part after the inclined bench, and the opposite pattern was observed after the flat bench.
However, when comparing the absolute muscle swelling between the exercises, the only significant difference was that the swelling of the middle chest after a flat bench was greater than an inclined bench, but in particular, the swelling of the upper chest after both bench presses was similar variations. Therefore, the acute muscle swelling did not follow the pattern of longitudinal regional hypertrophy observed in the only existing training study (2). In this review, I will discuss the detailed results of the current study and how they affect our ability (or lack thereof) to predict Regional Hypertrophy in response to specific variations in exercise.
Objective and assumptions
Objective
The purpose of this study was to determine if there were differences in the surface EMG during and muscle thickness and cross section after the oblique and flat bench press in certain regions of the pectoralis major. In addition, this study aimed to clarify whether “the pectoralis major muscle region with the highest sEMG [surface EMG] amplitude during exercise corresponds to that with the greatest acute variations in cross-section and/or muscle thickness.”
Hypothesis
The authors hypothesized that “the major pectoral head with the greatest sEMG Amplitude during exercise will be the one with the greatest acute variations in muscle architecture [i.e. muscle thickness and cross section].”
Themes and methods
Topics
Thirteen resistance-trained men without issue (28.79 ± 4.46 years old; 174.64 ± 5.60 cm tall; 79.43 ± 8.99 kg) participated in this study. Participants had to have at least one year of experience in bodybuilding, not regularly practice other forms of body activity and have a 1RM flat bench with at least their body weight.
