Biomechanical studies on the interrelation between trunk muscle strength and sports performance

In team sports such as football, ice hockey or basketball, athletes benefit from the body’s ability to tolerate high loads during start and stop movements, changes of direction, and tackles during competition. Likewise, in individual sports, such as track-and field or cross-country skiing, maximum performance is only possible with optimally trained and optimally controlled muscles. The strength of the abdominal and back muscles is widely considered crucial, as it is responsible for a high stability of the trunk during movement. The stability of the trunk is not only considered the basis of a high performance in specific sports discipline, but can also contribute to reduced back pain and risk of injuries to the lower extremities and, in general, to fewer overuse injuries. Therefore, a considerable amount of time in training is devoted in order to improve trunk strength in sports. A considerable number of tests, then, is typically applied in order to evaluate trunk muscle strength in athletes. But, surprisingly, the relevance and comparability of the measured values are poorly understood. Therefore, this study on some central aspects of the interrelation of trunk muscle strength and sports performance sets out to highlight the contribution made to the improvement of the athletes' performance in a wide range of sports and to the prevention of sports injuries. This thesis seeks to critically access the methodological presumptions which underlie and have guided the existing scholarship, and the experimental research, on the role of trunk muscles in sports. It will do so by using different methodological perspectives in its discussion and by making use of a set of new investigations and tests. In particular, the quantification of the activity of the trunk muscles in different movements will be discussed as well as measurements which try to determine the strength of the trunk muscles. Finally, this study aspires to contribute to a better overall understanding of the interrelation of trunk muscle strength and athletic performance on the one hand and to preventive training on the other hand. In four studies presented in this thesis, different methodological approaches are used to that end: electromyographic measurements for the determination and analysis of muscle activation as well as different methods of strength assessment for the differentiation of various strength qualities. The differentiation of the strength qualities allows the description of various aspects of trunk strength, such as maximum strength and strength endurance, which relate to essential athletic performance parameters such as sprint, change of direction or balance. The performance in the strength of the abdominal and back muscles is measured with laboratory and field methods in different movements. The findings are not only used to re-address the discussions on the comparability and reliability of different measuring methods but also seek to advance our understanding of the degree of activity of trunk muscles and the influence of trunk strength on basic performance parameters in sport. In the first study, a field test method which is frequently used in Switzerland (Bourbon test: prone plank, side plank, Sorensen test) is compared with a laboratory procedure (isometric trunk flexion, extension, lateral flexion, rotation test) in a group of high-level soccer players. This study aims to compare different assessment methods. No relevant correlation between the performance in the field test (time to failure) and the maximum isometric force measurements (Pearson's correlation: -.14< r