Spine and trunk are important parts of the human kinetic chain. The spine represent the central axis of the skeletal system and is responsible for protecting the spinal cord. Stabile trunk on the other hand enables mobility of the limbs and is responsible for transferring forces between the limbs during movement. Key elements defining trunk stability are passive, active and controlling systems. Decreased trunk stability can have detrimental effects on athletes performance and can lead to injury. One of such factors causing decreased stability is a decrease in muscle performance resulting from a strenuous physical activity. In general these could be divided into (i) isolated loading of individual body parts such as during resistance training and (ii) general, whole body activities such as running. There are some reports in the literature, how local decrease in the ability to produce force affects trunk muscle responses during anticipatory postural adjustments and reflex responses. However, no such reports can be found on the effects of running interventions. Coaches and athletes need to be familiar with the effects of such activities on trunk function in order to be able to prepare safer and more effective training regimes. The purpose of this study was to analyse the effects of local strengthening exercises performed to exhaustion and 12-min middle-to-high intensity running on trunk stabilizing functions.
One hundred and one participants were divided in two groups. In the first group (51 participants, 20 women and 31 males, 1,78 ± 3,2 m; 73,5 ± 6,8 kg; 24,5 ± 2,2 years), the effects of 12-min middle-to-high intensity running were studied. In the second group (50 participants, 29 women and 21 males, 1,74 ± 2,9 m; 71,5 ± 5,9 kg; 24,7 ± 3,1 years), the effects of localized strengthening exercises on trunk stabilizing functions were studied. Before and after the intervention, following tests were performed; measures of anticipatory postural adjustments and reflex responses, balance during sitting on an unstable surface, trunk repositioning error and maximal voluntary contraction during trunk flexion and extension.
Local intervention has had an effect on the ability to develop maximal voluntary force in trunk extension and flexion, however no such changes were observed after running. No changes in integrated electromyogram during maximal voluntary contractions were observed. The trunk repositioning error also stayed unchanged following both interventions. Changes in the muscle activation latency during RR after running were observed in the obliquus externus, accompanied by changes in the latency average concurrent differences of trunk extensors. During anticipatory postural adjustments changes in latencies of the rectus abdominis were observed after running and of the obliquus externus after performing local strengthening exercises. No changes in the integrated electromyogram were observed after neither of the two interventions. No changes in the movement of the center of pressure during anticipatory postural adjustments and reflex responses were observed. However prominent changes were present for balance during sitting on unstable surface. Velocity and amplitude of the center of pressure movement in anterior-posterior and medial-lateral direction changed after performing a running protocol and all frequency parameters as well as medial-lateral velocity and amplitude after performing local strengthening exercises. Correlation analysis between the change-size for all parameters differed between the two groups.
The results of this study show, that the two interventions used cause intervention specific changes in the selected trunk stability indicators. After running, specific adaptations were observed, that could be caused by demands for coordinating pelvic and upper-body movement during running. On the other hand, local trunk muscle strengthening exercises cause earlier activation of the abdominal muscles, possibly indicating their compensatory role following fatigue of trunk musculature. In addition, running improved balance during sitting balance tasks, and local trunk strengthening exercises had the opposite effect.
Data from this study indicate, that strength training of the trunk muscles could have detrimental effects on trunk stability and spinal health. On the opposite, running proved to have some positive effects on trunk stability. These results land some important guidelines for preparing safer and more effective workouts.
|
