Objective: The purpose of this study was to examine acute changes in muscle thickness (MTH) and echo-intensity (EI), following four sets of biceps curls, when it is known that the change in MTH is due entirely to swelling.
Approach: Forty-nine resistance-trained men and women participated in this study. Individuals in the experimental group (n = 23) visited the lab on two separate occasions. During the first visit, paperwork and one repetition maximum (1RM) strength were measured. During the second visit (3-5 d after visit 1), individuals performed four sets of biceps curls to failure using 70% of their 1RM. MTH and EI measurements were taken before and immediately following exercise using B-mode ultrasound. The ultrasound probe was equipped with a level to minimize the influence of probe tilt on the EI measurement. A time-matched control group (n = 26) was included to account for measurement error for both MTH and EI. Results are presented as means (95% CI).
Main results: For MTH there was a group (Experimental versus Control) by time (Pre-Post) interaction (p < 0.001). MTH increased in the experimental group (mean value change = 0.44 (0.33-0.54) cm), but not in the control group (mean value change = -0.015 (-0.03-0.01) cm). For EI, there was no group by time interaction (p =.074). In addition, there were no main effects for group (p = 0.254) or time (p = 0.314). The mean difference in the change in EI between groups was -2.99 (-6.25-3.03) arbitrary units.
Significance: EI cannot be used to detect exercise induced changes in muscle thickness.