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Early resistance training-induced increases in muscle cross-sectional area are concomitant with edema-induced muscle swelling

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It has been proposed that skeletal muscle shows signs of resistance training (RT)-induced muscle hypertrophy much earlier (i.e., ~3–4 weeks of RT) than previously thought. We determined if early increases in whole muscle cross-sectional area (CSA) during a period of RT were concomitant with edematous muscle swelling and thus not completely attributable to hypertrophy.


We analyzed vastus lateralis muscle ultrasound CSA images and their respective echo intensities (CSA-USecho) at the beginning (T1), in the 3rd week of RT (T2) and at the end (T3) of a 10-week RT period in ten untrained young men. Functional parameters [training volume (TV = load × reps × sets) and maximal voluntary contraction (MVC)] and muscle damage markers (myoglobin and interleukin-6) were also assessed.


Muscle CSA increased significantly at T2 (~2.7 %) and T3 (~10.4 %) versus T1. Similarly, CSA-USecho increased at T2 (~17.2 %) and T3 (~13.7 %). However, when CSA-USecho was normalized to the increase in muscle CSA, only T2 showed a significantly higher USecho versus T1. Additionally, TV increased at T2 and T3 versus T1, but MVC increased only at T3. Myoglobin and Interleukin-6 were elevated at T2 versus T1, and myoglobin was also higher at T2 versus T3.


We propose that early RT-induced increases in muscle CSA in untrained young individuals are not purely hypertrophy, since there is concomitant edema-induced muscle swelling, probably due to muscle damage, which may account for a large proportion of the increase. Therefore, muscle CSA increases (particularly early in an RT program) should not be labeled as hypertrophy without some concomitant measure of muscle edema/damage.

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Analysis of variance


Arbitrary units


Cross-sectional area

CSA-USecho :

Cross-sectional area echo-intensity


Effect size






Maximum voluntary isometric contraction torque


Muscle protein synthesis


Magnetic resonance imaging


Resistance training


Standard deviations


Total training volume

USecho :

Ultrasound echo-intensity


Vastus lateralis


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We would like to acknowledge all the participants of this study. This work was supported by São Paulo Research Foundation (FAPESP) Grants #2012/24499-1, #2014/19594-0 and #2013/21218-4. CU and HR are supported by the National Council for Scientific and Technological Development (CNPq) Grant (#304205/2011-7 and #307023/2014-1, respectively). Portions of this work were also supported by a Grant from the Natural Science and Engineering Research Council (NSERC) of Canada to SMP.

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Correspondence to Felipe Damas.

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All procedures performed herein were in accordance with the ethical standards of the institutional and national research committee and with the 1964 Helsinki Declaration and its later amendments or comparable ethical standards.

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Communicated by Anni Vanhatalo.

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Damas, F., Phillips, S.M., Lixandrão, M.E. et al. Early resistance training-induced increases in muscle cross-sectional area are concomitant with edema-induced muscle swelling. Eur J Appl Physiol 116, 49–56 (2016).

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