Background: The abdominal muscles are vital in providing core stability for proper function in most activities. There is a correlation between side asymmetry of theses muscles and dysfunction. Thus, the purpose of this study was to evaluate and compare trunk muscle morphology and trunk rotational strength between sprinters, a symmetrical sport and sprint hurdlers, an asymmetrical sport. Methods: Twenty-one trained collegiate sprinters and sprint hurdlers were recruited for the study (12 M, 9 F), average age (years) 20.2   1.5, height (cm) 176.9   9.1, and weight (kg) 70.6   9.8. Using real-time ultrasound, panoramic images of the internal oblique (IO) and external oblique (EO) were obtained at rest and contracted in a seated position for both right and left sides of the trunk. Results: Average trunk rotation strength to the right was greater among all participants, p < 0.001. The IO had greater thickness changes than EO for all participants. The IO side asymmetry was significantly different between groups p < 0.01. Conclusion: Sprinters, although involved in a seemingly symmetrical sport, exhibit asymmetrical trunk morphology and rotational strength, while hurdlers, involved in a unilaterally demanding sport, exhibit the expected asymmetry in muscle morphology and trunk rotational strength.

Objective: The purpose of this study was to determine inter-rater and intra-rater reliability of synchronous ultrasound imaging and electromyography measures of lumbopelvic-hip muscle activity performed by a novice and an experienced investigator in healthy individuals. Electromyography (EMG) has served as the gold standard for quantification of onset of muscle activation; however, ultrasound imaging can visualize muscle activity when collected simultaneously. Methods: A novice and experienced investigator collected a series of 3 ultrasound images at rest and 3 M-mode clips during contraction of each muscle while EMG electrodes collected muscle activity. Muscles collected included: external oblique, erector spinae, rectus abdominis, gluteus maximus, and gluteus medius. Participants were asked to return 48-72 hours for a second session. After all muscles were collected, muscle thickness was measured from the US images and latency based on onset of activity from EMG was processed and averaged. Results: Moderate inter-rater reliability (ICC2,k=.5-.7) was found for most thickness, modulated thickness, and latency variables between the experienced and novice raters, however rectus abdominis had poor reliability compared to the other muscles assessed. Intra-rater reliability between sessions 1 and 2 for the novice rater revealed moderate reliability (ICC2,k=.5-.7) in the abdominal muscles (external oblique, erector spinae, contracted rectus abdominis) and poor reliability in the gluteal muscles. Conclusions: Modulated thickness values had the strongest reliability for inter- and intra-rater reliability, when thickness measures were divided by body weight in kilograms before analysis. Subcutaneous tissue, notably abdominal adipose, and its role on participant positioning should receive added attention during training and instruction of novice investigators during M-mode acquisition and timing of contraction with EMG synchronization.