The Edema Illusion: Distinguishing Swelling from Real Growth

Higher training volume is often associated with greater hypertrophy. But, when measures of muscle size increase after a period of high volume sessions, is that true structural growth, or simply transient swelling? This distinction has practical and research implications, particularly when muscle size is assessed within days of training. This new study compared 7, 14, and 21-set lower-body sessions in resistance-trained men to determine whether higher per-session volume meaningfully alters muscle swelling, edema, performance recovery, or perceptual fatigue.

Overview

• What did they test? Thirteen resistance-trained men completed three randomized, counterbalanced lower-body sessions consisting of 7, 14, or 21 total sets (squat, leg press, knee extension). Sessions were separated by 7 days. Immediately after each session and at 24, 48, and 72 hour post-session timepoints, muscle thickness and echo-intensity (as a proxy for edema) of the proximal and distal anterior thigh were assessed using ultrasound. They also measured 10RM volume load performance, perceived recovery status, and ratings of perceived exertion.
• What did they find? Higher session volumes (14 and 21 sets) resulted in greater accumulated volume load and higher session RPE compared to 7 sets. The 21-set condition also produced lower perceived recovery at 24 and 48 hours. Muscle thickness and echo-intensity increased immediately post-session but returned to baseline within 24 hours across all conditions. No between-condition differences were observed for muscle thickness, echo-intensity, or 10RM volume load recovery. Notably, 10RM volume load performance was not impaired and was greater than baseline at 24, 48, and 72 hours following each session.
• What does it mean for you? In resistance-trained men, increasing per-session volume from 7 to 21 sets elevates perceptual fatigue but does not produce sustained increases in muscle thickness or echo-intensity beyond 24 hours. Acute post-session increases in muscle thickness resolved to baseline levels within 24 hours across all conditions. Within the limits of ultrasound measurement error, these findings suggest that assessing muscle size ≥24 hours after training is unlikely to be meaningfully confounded by residual swelling under similar conditions.

What’s the Problem?

Resistance training volume is widely considered a primary driver of hypertrophy, with evidence suggesting a graded dose–response relationship, albeit one that appears logarithmic and subject to diminishing returns at higher volumes 1 2. However, interpreting hypertrophy research is complicated by the fact that acute resistance exercise induces transient increases in muscle size due to fluid shifts (“muscle swelling”) and, in some cases, edema associated with exercise-induced muscle damage (EIMD) 3.

Because many longitudinal studies assess muscle size within 24–48 hours of the final training session, residual swelling or edema may artificially inflate hypertrophy estimates. While transient swelling typically resolves quickly, edema related to EIMD can persist longer. Despite the widespread discussion of training volume, limited data exist on whether very high per-session volumes meaningfully alter the time course of acute swelling or edema in resistance-trained individuals. This is the research gap that Alvarez et al. sought to address with this new study.

Purpose

The purpose of this study was to examine whether three different per-session resistance training volumes (7, 14, and 21 sets) differentially affect acute markers of muscle swelling, EIMD, performance, and perceptual responses in resistance-trained men.

Hypothesis

The authors hypothesized that higher sessional RT volume would elicit more pronounced acute responses in muscle swelling (i.e., immediately post exercise) with no transient effects associated with EIMD in trained individuals.