A comparison of isotonic and elastic resistance exercise on trapezius muscle balance in overhead athletes

Abstract

The scaption exercise (elevation of the arm in the scapular plane) is often performed in shoulder rehabilitation and preventive exercise programs. Three studies were performed to better understand the activation characteristics of the upper trapezius (UT) and lower trapezius (LT) muscles during scaption. The purpose of these studies was to 1) quantify and compare trapezius muscle activation ratios and onset of activation in normal subjects, 2) compare the findings from normal subjects with overhead athletes, and 3) compare the activation ratios and onset of the trapezius with 2 modes of resistance (elastic and isotonic) in overhead athletes. Methods. Healthy college-aged subjects performed scaption to 90⁰ with (W) and without (UW) standardized resistance. The average activation of the UT and LT was determined with surface electromyography (EMG) over 30⁰ increments in concentric and eccentric directions. The UT:LT ratio was then determined for each interval and condition, as well as the average onset of activation. Statistical analysis using repeated measures and t-tests were used to determine significant differences. Results. The UT:LT ratios of both W and UW conditions demonstrated a u-shaped curve over 90⁰. The UW condition consistently demonstrated significantly higher UT:LT ratios ranging from 1.5 to 4.5, while the W ranged from 0.9 to 2.4. There was no significant difference in activation ratios between athletes and non-athletes, or between elastic and isotonic resistance. The UT demonstrated earlier activation than the LT in the UW condition. The LT reduced its latency with the addition of resistance, reversing the firing order in overhead athletes. Isotonic resistance provided slightly faster activation of the LT compared to elastic resistance. Conclusion. These 3 studies suggest that overhead athletes demonstrate the same UT:LT ratios as non-athletes over 90⁰ during scaption with and without resistance. Adding resistance to the scaption exercise significantly reduces the UT:LT ratio and reverses the firing order, activating the LT significantly earlier than the UT. Both elastic and isotonic resistances demonstrate similar activation ratios in overhead athletes, although isotonic resistance activates the LT faster than elastic resistance. Using these results, clinicians may improve their clinical decision-making in prescribing scaption exercises.