New protocols to assess trunk muscle strength and endurance

Laburpena

Due to the important contribution of the trunk musculature to many sports and daily life activities, diverse field and laboratory protocols have been developed to assess trunk muscle strength and endurance in sport, fitness, clinical and research settings. Nevertheless, the isokinetic dynamometry protocols have rarely been used to evaluate trunk muscle endurance. In addition, field tests that measure rotation trunk muscle endurance in the horizontal plane are lacking. The main purposes of this doctoral thesis were: a) to develop new protocols to assess trunk muscle performance in healthy and physically active populations; and b) to analyze the most important characteristics of these protocols in order to facilitate their adequate use. The 3 studies included in this doctoral thesis provide 2 new reliable protocols to assess trunk muscle performance: 1) an isokinetic trunk flexion–extension protocol to simultaneously assess trunk muscle strength and endurance; and 2) a timed field test to measure trunk flexion-rotation endurance (flexion-rotation trunk test [FRT test]). Based on the good reliability results obtained for all isokinetic strength variables in the first study, any of them could be used to assess trunk muscle strength. However, regarding the isokinetic endurance variables, endurance ratio and modified endurance ratio showed the best reliability results, mainly in the extension direction, and overall in males. As no learning effect was found in the isokinetic protocol, only 1 session seems enough to assess trunk muscle strength and endurance in males and females. In the second study, the FRT test showed high reliability values in males and females, which improved with test practice. Significant increases in FRT test scores across testing sessions indicated the need for performing at least 3 trials of practice to make learning effect negligible. In this study, males showed higher FRT test scores than females, as well as a higher learning effect, especially in the first 2 testing sessions. In the third study, an electromyographic and kinematic analysis of the FRT test was performed. The results of this study showed the main role of the abdominal muscles (mainly rectus abdominis) in the execution of the FRT test and the effect of test execution on abdominal muscle fatigue. On the other hand, although each trunk flexion-rotation repetition involved an average 8–14º hip flexion, the rectus femoris activation was low and it showed no muscle fatigue after test execution. Based on these results, the FRT test is a valid field protocol to assess abdominal muscle endurance in trunk flexion-rotation exertions.