Temporal effects of acute static stretching on neuromechanics of the muscle-tendon-unit

Performance of human movement is primarily depending (a) on the mechanical-morphological properties of the involved structure (bones, tendons, muscle, etc.) and (b) on the activation dynamics from the nervous system. Several chronic processes like aging, chronic use, disuse, training, etc. are able to alter the involved structures and/or the activation dynamics and as consequence the performance of human movement. Specifically when it comes to stretching, little is known about its temporal and dose-dependent effect on performance, mechanical-morphological porperties of the muscle-tendon unit and neuromuscular parameters. Although there is an abundance of different studies which examined different stretching methods under different conditions, there still is a lack of a structured study that thoroughly examines I. How long should a stretching intervention last to have an effect on (a) performance (b) mechanical and morphological properties of the muscle or tendon structure, and (c) neuromuscular parameters? II. How long will an effect on (a) performance (b) mechanical and morphological properties of the muscle or tendon structure, and (c) neuromuscular parameters last? In the literature it has been criticized that most studies which analyzed effects of stretching used stretching times clearly beyond stretching times typically performed in sports practice and therapy. Specifically there is a lack of studies with stretch interventions below 30 s. Furthermore, few studies have examined mechanical, morphological, and neurological properties which could all be responsible for changes in performance. Therefore, we will be the first to conduct an experimental study during which we will thoroughly examine the effect of short (15s) to long (5 min) static stretching interventions on structure, excitability, and performance. Furthermore, we will thoroughly examine how long such effects last. In this project expertise from three departments is joined together. While the Institute of Sports Science from the University of Graz will provide its knowledge of performance and mechanical and morphological properties of the muscle and tendon structure, the Center for Medical Physics and Biomedical Engineering of the Medical University of Vienna and the Department for Physiology of the Medical University Graz will provide their knowledge on the peripheral and central nervous system, respectively. It is expected that the project will reveal different and time-dependent effects of static stretching on performance, mechanical and morphological properties, and neuromuscular parameters. The results could help to develop more specific and exact programs of static stretching in sports and therapy.

Temporal effects of acute static stretching on neuromechanics of the muscle-tendon-unit and performance of human movement depend primarily (a) on the mechanical-morphological properties of the involved structure (tendons, muscles, etc.) and (b) on the activation dynamics from the nervous system. Specifically when it comes to stretching, little is known about its temporal and dose-dependent effect on performance, mechanical-morphological properties of the muscle-tendon unit, and neuromuscular parameters. Although there is an abundance of different studies that examined different stretching methods under different conditions, this was the first that analysed: 1. How long should a stretching intervention last to have an effect on (a) performance (b) mechanical and morphological properties of the muscle or tendon structure, and (c) neuromuscular parameters? 2. How long will an effect on (a) performance (b) mechanical and morphological properties of the muscle or tendon structure, and (c) neuromuscular parameters last? Within several sub-studies we could show that the effects of static stretching on performance, and mechanical-morphological properties is timed-dependent. Flexibility was increased already following one minute of stretching and lasted for at least 40 minutes. This can be partly explained following long stretching durations (3/5 min) by alterations in the muscle structure which, however, recovered within 10 minutes. Contrariwise, tendon structure was not affected by static stretching up to five minutes. Maximum force decreased only following five minutes of stretching.Only minor neuromuscular changes could be observed following static stretching and these were independent of stretching duration (1-5 min). Specifically, the central nervous system (on brain and spinal level) was affected only for seconds. However, the peripheral nervous system in the muscle was inhibited for several minutes already following one minute of stretching. Subsequent muscle contractions restored normal conditions. The findings of the current study allow a goal-oriented application of static stretching to induce alterations of the flexibility, mechano-morphological properties of the muscle and the nervous system in sports and therapy.