Jernej Rosker

Effects of vertical center of mass redistribution on body sway parameters during quiet standing

Body sway is usually described by center of foot pressure (COP)-derived parameters. Their sensitivity to vertical center of mass (COM) redistribution below its natural position has not yet been examined during quiet stance tasks. We examined the effects of both lowering and raising the COM on the following body sway parameters: cumulative, medial-lateral and anterior-posterior COP average velocity, amplitude and frequency. For this purpose, 13 healthy male subjects performed a quiet stance balance task with feet positioned in parallel stance (PS) at hip width apart and with hands holding a stick across the rear part of the shoulders. Each subject carried out five different modifications of the PS task in a randomized order: no additional load, an additional load of 10 kg and 30 kg suspended from the waist at mid-lower leg height, and an additional load of 10 kg and 30 kg across the rear of the shoulders. The studied body sway parameters proved to be sensitive to these manipulations. Specifically, lowering and raising the COM was mirrored in a systematic decrease/increase of the velocity, amplitude, and frequency parameters, indicating a larger effect in the anterior-posterior direction. These results suggest that the elevation of the body COM from a lower to a higher position systematically decreases the postural control during quiet standing, and consequently, increases the intensity of the balancing task. Thus, this type of physical manipulation could provide the basis for a simple progression in functional resistance training for persons with compromised balance.

The effect of vision elimination during quiet stance tasks with different feet positions

Literature confirms the effects of vision and stance on body sway and indicates possible interactions between the two. However, no attempts have been made to systematically compare the effect of vision on the different types of stance which are frequently used in clinical and research practice. The biomechanical changes that occur after changing shape and size of the support surface suggest possible sensory re-weighting might take place. The purpose of this study was to assess the effect of vision on body sway in relation to different stance configurations and width. Thirty-eight volunteers performed four quiet stance configurations (parallel, semi-tandem, tandem and single leg), repeating them with open and closed eyes. Traditional parameters, recurrence quantification analysis and sample entropy were analyzed from the CoP trajectory signal. Traditional and recurrence quantification analysis parameters were affected by vision removal and stance type. Exceptions were frequency of oscillation, entropy and trapping time. The most prominent effect of vision elimination on traditional parameters was observed for narrower stances. A significant interaction effect between vision removal and stance type was present for most of the parameters observed (p<0.05). The interaction effect between medio-lateral and antero-posterior traditional parameters differed in linearity between stances. The results confirm the effect of vision removal on the body sway. However, for the medio-lateral traditional parameters, the effects did not increase linearly with the change in width and stance type. This suggests that removal of vision could be more effectively compensated by other sensory systems in semi-tandem stance, tandem and single legged stance.

Effect of 14 days of bed rest in older adults on parameters of the body sway and on the local ankle function.

This study explored the effects of a 14-day horizontal bed rest (BR) without countermeasures on postural sway, maximal voluntary torque and precision of voluntary torque matching. Sixteen subjects were tested before, immediately after and two weeks after BR. The increase in frequency and amplitude after BR was comparable for both sway subcomponents (rambling and trembling) in medial-lateral direction. But in anterior-posterior direction, rambling increased more in frequency (-7% vs. +31%, p < 0.05) while trembling increased more in amplitude (+35% vs. +84%, p < 0.05). The drop in maximal voluntary torque after BR was present for plantar flexion (p < 0.05) but not for dorsal flexion. After the BR, the subjects were less precise in the dorsal flexion torque matching task (p < 0.05). All the observed parameters, except the dorsal flexion torque matching error, returned back to the pre-BR values after the two weeks of re-conditioning. Results of this study indicate that body sway subcomponents responded differently to BR. Based on these findings, it was not possible to draw clear assumptions on the effects of neural and structural changes on body sway.

Kinaesthesia and Methods for its Assessment: Literature Review

Kinaesthesia and Methods for its Assessment: Literature Review In this review measurement techniques used for kinaesthetic sense assessment are presented. Kinaesthesia is an important part of human movement control and provides us with better understanding of specific movement system adaptations to fatigue, training and injury. Additionally, decreased kinaesthesia can be an injury predisposing factor, which stresses the necessity for its assessment in sports injury prevention programs. First, terminology and functional concept of kinaesthesia is presented in relation to other related concepts like proprioception and sensory-motor function. For better understanding, basic underlying neurological backgrounds are discussed in chapter two, encompassing peripheral sensory fields as well as the basics of the central processing. Additionally, factors affecting kinaesthesia and its adaptations to training are presented. Functional aspects are discussed, supporting the role of assessment of kinaesthesia in sports and rehabilitation. In the third chapter, a proposal for measuring methods classification is given. In the final chapter, different measuring protocols and their modifications are presented. Due to their usefulness in sports and injury prevention, methods for measuring sense of joint position, movement onset and active tracking are discussed in more detail. Possibilities and examples of their application to sports and sports injury rehabilitation settings are presented. Some basic guidelines are given of how to use these methods in training or for screening kinaesthesia.

Effects of Fourteen-Day Bed Rest on Trunk Stabilizing Functions in Aging Adults

Bed rest has been shown to have detrimental effects on structural and functional characteristics of the trunk muscles, possibly affecting trunk and spinal stability. This is especially important in populations such as aging adults with often altered trunk stabilizing functions. This study examined the effects of a fourteen-day bed rest on anticipatory postural adjustments and postural reflex responses of the abdominal wall and back muscles in sixteen adult men. Postural activation of trunk muscles was measured using voluntary quick arm movement and sudden arm loading paradigm. Measurements were conducted prior to the bed rest, immediately after, and fourteen days after the bed rest. Immediately after the bed rest, latencies of anticipatory postural adjustments showed significant shortening, especially for the obliquus internus and externus muscles. After a fourteen-day recuperation period, anticipatory postural adjustments reached a near to complete recovery. On the contrary, reactive response latencies increased from pre-bed-rest to both post-bed-rest measurement sessions. Results indicate an important effect of bed rest on stabilizing functions of the trunk muscles in elderly adults. Moreover, there proved to be a significant deterioration of postural reactive responses that outlasted the 14-day post-bed-rest rehabilitation.