The association between bowling performance and trunk muscle stability, strength-endurance and thickness in adolescent pace bowlers: a cross sectional study
Background The trunk is the centre of the kinetic chain, connecting upper and lower limbs and transferring energy during movement. Proximal stability serves as a base for quality movements distally. Trunk muscle stability and strength-endurance are associated with sporting performance. Asymmetrical sport-specific adaptation in the morphometry of the trunk muscles has been investigated and described in cricket pace bowlers, but not linked to or described in terms of the association with bowling performance. Aim The aim of this study is to investigate the association between bowling performance and trunk muscle stability, strength-endurance and thickness in adolescent pace bowlers. Method In this observational cross-sectional study, bowling performance, namely ball release speed and accuracy, was measured by means of a radar gun and accuracy target in the outdoor nets of the respective schools, where the 46 pace bowlers, aged 13-18 years old, were invited from. Trunk muscle stability was measured as the level passed on the Sahrmann Stability Scale and strength-endurance as the failing time in seconds according to the Bourbon Trunk Muscle Strength Test. Ultrasound imaging measured the thickness of external oblique, internal oblique, transversus abdominis and lumbar multifidus in millimetre. Spearman’s correlations were used to determine associations between individual variables and a multiple linear regression analysis calculated predictors of bowling performance, including independent variables such as age, height and weight. Statistical significance was set at p<0.05. Results No association was found between trunk muscle stability and ball release speed (r=0.278; p=0.061) or accuracy (r=0.026; p=0.866). Stability, however, accounted for a 60.7% variance in ball release speed (p=0.004), increasing ball release speed by 3.570 units per unit increase in stability. Strength-endurance of the trunk muscle chains did not correlate to ball release speed (r=-0.039-0.214; p=0.154-0.796) or accuracy (r=-0.062-0.131; p=0.385-0.801). A moderate and fair relationship was found between ball release speed and transversus abdominis (r=0.543; p=0.0001) at rest and contracted (r=0.440; p=0.002), respectively. Non-dominant transversus abdominis showed a fair relationship with height at rest (r=0.458, p=0.001) and a moderate correlation with weight (r=0.625, p<0.001). On the dominant side, transversus abdominis at rest, showed a moderate relationship to ball release speed (r=0.564; p<0.001), height (r=0.539; p<0.001) and weight (r=0.611; p<0.001). Thickness of bilateral transversus abdominis at rest had an R-square value of .67 and ball release speed increased with 5.133 units for each unit increase in the thickness of the non-dominant transversus abdominis and 4.677 for that on the dominant side. Accuracy did not correlate with any independent variable, but weight (R-square value .207) was found to increase accuracy by .766 units for each unit increase. Bowling performance was found to be predicted by age (R-square value 0.084). Conclusion A direct association between bowling performance and trunk muscle stability and strength-endurance was not found. Trunk muscle stability – as a suppressor variable – was found to be a predictor of ball release speed. Trunk muscle thickness accounted for the variance in ball release speed and weight for that of accuracy. These findings implicate that adolescent pace bowlers may be able to improve ball release speed by increasing trunk muscle stability and bilateral transversus abdominis thickness. However, future research is needed to confirm this statement.
A research report submitted to the Faculty of Health Sciences, University of the Witwatersrand Gauteng, May 2018
Trunk Muscle Stability