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Found in: osebi
Keywords: warm-up, stretch, performance, acute effects
Published: 15.10.2013; Views: 3189; Downloads: 83
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Abstract: The effects of healthy aging on postural sway and its rambling and trembling components were studied. Young and elderly subjects stood quietly for 1 min in different postures, and with eyes open and closed. We found that age-related changes in postural sway and its components were similar to those observed in young participants in challenging conditions. These changes may therefore be viewed as secondary to the increased subjective perception of the complexity of postural tasks. Contrary to our expectations, stronger effects of age were seen in characteristics of rambling, not trembling. The commonly accepted hypothesis that older persons rely on vision more was not supported by this study: we found no significant interaction effects of age and vision on any of the sway characteristics. It was concluded that the reported higher reliance on vision in older persons may be task-specific. The results are compatible with the ideas that much of the age-related changes in postural sway emerge at the level of exploring the limits of stability and using the drift-and-act strategy. Our results suggest that the dominant view on rambling and trembling as reflecting supraspinal and peripheral mechanisms, respectively, may be too simplistic
Found in: osebi
Keywords: postural control, aging, sway, rambling, trembling
Published: 15.10.2013; Views: 2616; Downloads: 75
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Abstract: We analysed the effects of task symmetry during bilateral accurate force production tasks performed by the two feet. In particular, we tested a hypothesis that bilateral deficit would lead to higher indices of synergies defined as co-varied adjustments in the two forces across trials that reduced total force variability. The subjects produced steady-state force followed by a quick force pulse into the target. The two feet could be acting both into plantar flexion and into dorsiflexion (symmetrical tasks), or in opposite directions (asymmetrical task). We used the framework of the uncontrolled manifold hypothesis to quantify two variance components, one of which did not change total force (VUCM), while the other did (VORT). Synergy indices during the asymmetrical task were higher than in either symmetrical task. The difference was due to higher VUCM (compared to the symmetrical plantar flexion task) or lower VORT (compared to the symmetrical dorsiflexion task). The synergy index showed a drop (anticipatory synergy adjustment, ASA) starting 100150 ms prior to the force pulse initiation. The ASA tended to be shorter and of a smaller magnitude for the asymmetrical task. This is the first demonstration of bilateral synergies during accurate force production by the legs. We conclude that bilateral deficit has no or weak effects on two-leg synergies. The results fit the earlier introduced scheme with two groups of neural variables defining average performance of a redundant system and patterns of co-variation among its elemental variables, respectively
Found in: osebi
Keywords: kinesiology, force, synergy, legs, bilateral deficit, symmetry
Published: 15.10.2013; Views: 3807; Downloads: 236
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Abstract: 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
Found in: osebi
Keywords: balance, Body sway, Sensory manipulation, vision
Published: 15.10.2013; Views: 2831; Downloads: 140
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Abstract: Aim of this study was to investigate the effects of two different types of strength training programs on static balance in elderly subjects. Subjects older than 65 years of age were enrolled and assigned to control group (CG, n =19), electrical stimulation group (ES, n = 27) or leg press group (LP, n = 28). Subjects in both the training groups were exposed to training (2-3x/week) for a period of 9 weeks. In the ES group the subjects received neuromuscular electrical stimulation of the anterior thigh muscles. In the LP group the subjects performed strength training on a computer-controlled leg press machine. Before and after the training period, static balance of the subject was tested using a quiet stance task. Average velocity, amplitude and frequency of the center-of-pressure (CoP) were calculated from the acquired force plate signal. The data was statistically tested with analysis of (co)variance and t-tests. The three groups of subjects showed statistically significant differences (p < 0.05) regarding the pre-training vs. post-training changes in CoP velocity, amplitude and frequency. The differences were more pronounced for CoP velocity and amplitude, while they were less evident in case of mean frequency. The mean improvements were higher in the LP group than in the ES group. Our results provide supportive evidence to the existence of the strength-balance relationship. Additionally, results indicate the role of recruiting central processes and activation of functional kinetic chains for the better end effect
Found in: osebi
Keywords: balance, aging, falls, strength, training
Published: 15.10.2013; Views: 2662; Downloads: 233
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