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

Eur J Appl Physiol. 2016 Jan;116(1):49-56. doi: 10.1007/s00421-015-3243-4. Epub 2015 Aug 18.


Purpose: 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.

Methods: 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.

Result: 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.

Conclusion: 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.

Keywords: Echo intensity; Muscle damage; Muscle hypertrophy; Resistance exercise; Skeletal muscle; Ultrasound.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adaptation, Physiological / physiology
  • Adult
  • Edema / physiopathology*
  • Exercise / physiology*
  • Humans
  • Hypertrophy / physiopathology*
  • Male
  • Muscle Contraction / physiology*
  • Muscle, Skeletal / physiology*
  • Muscular Diseases / pathology
  • Muscular Diseases / physiopathology*
  • Quadriceps Muscle / physiology
  • Resistance Training / methods
  • Weight Lifting / physiology