Abstract
Abstract: Although side-to-side asymmetry of the shoulder rotators calculated by independent peak torque (IPT) has been used for interpretation of injury risks in athletes, it may not measure strength through the entire range of motion (ROM) tested. The aim of this study was to compare side-to-side asymmetry of the shoulder rotators between independent peak torque (IPT) and ten-degree angle specific torque (AST). Twenty healthy adult males (24.65 ± 2.4 years) performed concentric and eccentric internal rotation (IR) and external rotation (ER) of the preferred and non-preferr ed arms on an isokinetic dynamometer at 60°/s through 150° of total ROM. The total ROM was divided into 14 ten-degree angles of the physiological ROM from −90° of ER to 60° of IR. Concentric and eccentric IR IPT (10.5% ± 8.7% and 12.1% ± 7.2%) and ER IPT (13.6% ± 9.8% and 8.7% ± 5.6%) were significantly less than AST at several angles ( p < 0.05). IPT might lead to erroneous interpretations of side-to-side asymmetry in the shoulder rotators and does not represent the entire ROM tested. This information could be us ed to prescribe strength exercises to enhance overhead performance and reduce risk of shoulder injuries.
Highlights
The shoulder rotator muscles are important for coordinated performance of overhead activities, such as pitching in baseball, swinging a racket in tennis or pushing against the water in swimming [1,2,3].Forceful and repetitive actions in overhead sports have been associated with an increased susceptibility of shoulder rotator injuries [3,4], strength differences between external and internal rotator muscles [1,3,4,5], and side-to-side differences between upper-limbs [2,5]
We have previously demonstrated that shoulder independent peak torque (IPT) dynamic control ratios are significantly different than angle specific torque (AST) at several angles when calculated by 10° intervals over a 150° total range of motion (ROM) [1]
We found that eccentric external rotation (ER) AST at 50°, which represents the last deceleration angle at the end of the ROM, had the greatest difference and magnitude of change across all angles when compared to IPT
Summary
The shoulder rotator muscles are important for coordinated performance of overhead activities, such as pitching in baseball, swinging a racket in tennis or pushing against the water in swimming [1,2,3].Forceful and repetitive actions in overhead sports have been associated with an increased susceptibility of shoulder rotator injuries [3,4], strength differences between external (antagonists) and internal rotator (agonists) muscles [1,3,4,5], and side-to-side differences between upper-limbs [2,5]. Typical shoulder strength asymmetry has been reported as an upper-limb dominance of 5%–10% measured by independent peak torque (IPT) in nonathletic and recreational-level athletes [5] These IPT measurements fail to reproduce the functionality of muscles during sporting activities, because torque is not calculated through the entire range of motion (ROM), or at corresponding angles [1,6,7]. IPT evaluations may be more sensitive to assess muscle strength balance changes after strength rehabilitation programs [10], AST analysis has been shown to be a more appropriate tool to precisely locate potential muscle imbalances present at specific joint angles [1,6,7]. This information may be used for the prescription of strength exercises of the weak angles
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