Differentiating swelling and hypertrophy through indirect assessment of muscle damage in untrained men following repeated bouts of resistance exercise

Purpose To examine the swelling response and other markers of muscle damage throughout the early portions of a training program (Experiment 1). We also determined if a “swollen” muscle could swell further following additional exercise (Experiment 2). Methods Nine males performed four sets of biceps curls (or time-matched rest on control arm) at 70% of their one-repetition maximum three times over 8 days. Muscle thickness and torque were measured before and after exercise as well as on the days in between. Soreness was measured at the beginning of each day (Experiment 1). On the final day (Experiment 2), participants performed two bouts of exercise, followed by additional measures of muscle thickness. Results Following three bouts of exercise, muscle thickness was elevated over baseline (mean of visit 9 pre to visit 2 pre, 95% CI) at the 50% [0.21 (0.07, 0.34) cm], 60% [0.21 (0.02, 0.39) cm], and 70% [0.21 (0.06, 0.36) cm] sites. However, differences from a non-exercise control were only observed immediately following bouts of exercise (indicative of acute swelling). Torque was lower at every time point following the first bout of exercise and remained suppressed relative to pre at visit 9 [−6.1 (−11.7, −0.47 Nm] in the experimental arm. Experiment 2 found that a swollen muscle could not appreciably swell more. Conclusion Resting levels of muscle thickness do not appear to change beyond what occurs following the first naïve bout of exercise. Also, the acute swelling response may be used to differentiate swelling from muscle growth.