Running continues to be a very popular sport acivity. However, in recent years an increase in the amount and intensity of training is often associated with overuse injuries. Pain related movements tend to decrease joint coordination variability as a kind of protective mechanism. Modern motor learning theories consider movement variability as an essential factor for technique improvement. According to Bernstein (1967), movement results from forces generated directly by muscle activities and reactive phenomena such as gravitation, inertia or forces stored in muscle-tendon units. Changes in reactive phenomena during running require different neuromuscular impulses for an optimal movement outcome. Whereas the inherent variability on a macroscopic level decreases as performance increases, the microscopic movement variability behaves the opposite, it increases following a U-shaped function (Stöggl et al, 2010). In order to achieve the ability to adapt to such changes, reactive phenomena should be increased in the training process. The application of external goal oriented perturbations, so-called motor constraints, might enable an increase of functional variability within the running movement pattern, and this might lead to more flexible, and to external perturbations, more adaptable movement patterns (Hamill et al, 2012). Examples of such motor constraints are obstacles, unstable running shoes or elastic tubes applied to the lower extremities. In recent years, our working group investigated various studies that examined the effect of goal-oriented external perturbations created by elastic tubes attached to the hip and ankles on running pattern variability. In most of the studies, 3D-kinematics and muscle activities (EMG) were analysed. We reviewed the acute short-term effects, as well as the long-term adaptations after a 7-week training intervention. The results showed major acute effects on EMG, on kinematics, and on joint coordination variability, due to the constraints. However, after the intervention, variability of the tube running situation returned to normal for most parameters. No transfer effects to normal running were observed. The constraint serves to acutely increase variability; however, a long-term effect might require different constraint variations.
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