Abstract

Following resistance training, muscles swell due to a combination of damage, an increased demand for oxygen, and buildup of substrates. Cross-Sectional Area (CSA), thickness, and Echo Intensity (EI) are measurements that have been used to monitor muscle damage and recovery. Due to the variety in responses to resistance training, the aim of this study was to examine the time course changes in muscle size and EI of the elbow flexors and knee extensors following an acute bout of resistance training and determine the potential differences in response between males and females. Twenty Males (71.00±2.07cm, 74.11±9.37kg, Age 19.85±0.41) and 20 females (63.35±2.99cm, 60.62±8.92kg, Age 20.00±0.72) had panoramic ultrasound images taken of the largest circumference of the Bicep Bracii (BB), Vastus Medialis Oblique (VMO) and Vastus Lateralis (VL) and were used to determine CSA, muscle thickness and EI. Participants performed four sets to failure at 70% on a bicep curl and leg extension machine with a 90 second rest between sets. Ultrasounds were done pre and post exercise, 24 and 48-hours post. Males and females had similar responses over time (P=0.17-0.96) for each variable. Post exercise values for CSA, thickness, and EI (P<0.001) where all large but returned to baseline values by 24hrs. Males had large muscle size (P<0.001), and lower EI values (P<0.001) of the knee extensors but not of the elbow flexors (P=0.769). This study demonstrated that immediately following resistance training, muscle size and EI were significantly larger for both males and females and returned to baseline in 24hrs. Males and females exhibited similar patterns; however, males had larger knee extensor and elbow flexors muscles and lower EI values of the knee extensors on average than females.

Keywords:Fatigue; Muscle swelling; Muscle quality; Ultrasound imaging