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ISOMETRIC STRENGTH RATIOS DIFFER BETWEEN YOUTH BASEBALL PLAYERS WITH AND WITHOUT UPPER EXTREMITY PAIN

Abstract

BACKGROUND: Up to 73% of youth baseball players report upper extremity pain throughout a season. Throwing shoulder isometric (ISO) strength ratios differ between softball pitchers with and without upper extremity pain; however, it is unknown if this is true in youth baseball athletes. This paper aimed to investigate the difference in throwing shoulder and bilateral hip rotational ISO strength ratios (internal (IR) and external (ER)) between youth baseball players with and without upper extremity pain. METHODS: Forty-eight youth baseball players (13.5±2.1yr, 57.7±12.5kg, 165.0±12.1cm) completed a health history survey indicating whether they experienced upper extremity pain. Those who answered ‘yes’ were placed in the pain group. Those who answered ‘no’ were placed in a pain-free group. Throwing shoulder and bilateral hip IR and ER ISO strength were recorded using a handheld dynamometer. For hip rotation strength testing, participants were seated with knees flexed to 90° and legs hanging off the table. For shoulder rotation strength testing, participants were lying supine with their throwing shoulder abducted to 90° and elbow flexed to 90°. Participants were instructed to perform two three-second maximal effort IR and ER ISO contractions into the dynamometer. Data were averaged for analysis. A one-way analysis of variance (ANOVA) determined if hip and shoulder rotation strength ratios differed between groups. RESULTS: The one-way ANOVA revealed a significant difference based on pain-group membership (F1,45.6=5.23, p=.027) in stride hip ISO strength ratios, with those in pain having higher IR:ER ratios than those pain-free (1.34±0.33 vs. 1.11±0.36). No differences were present between groups in ISO strength ratios for the stance leg (F1,43.2=1.54, p=.22; pain = 1.00±0.15, pain-free = 0.99±0.19) or throwing shoulder (F1,43.8=2.16, p=.15; pain = 1.21±0.38, pain-free = 1.07±0.30). CONCLUSIONS: Youth baseball players with upper extremity pain have stride hip rotational ISO discrepancies, displaying an IR dominant ratio. Whereas those without upper extremity pain display a more balanced ISO ratio. Using stride hip ISO ratio as a screening test may assist clinicians in identifying players at risk of developing upper extremity pain in youth baseball. Additionally, an effort should be made in restoring imbalances in stride hip ISO strength, as it may be useful for reducing reported pain in this sample.

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