Instrumented assessments of quiet-stance postural control typically involve recording and analyzing of body sway signal, most often the center of pressure movement. It has been recently suggested that transient characteristics of body sway may offer additional information regarding postural control. In this study, we explored the relationship between whole-trial estimates of body sway and corresponding transient behavior indexes, as well as the effects of leg preference. A total of 705 healthy young athletes performed 30 s single-leg body sway trials for (...) both legs. It was found that the transient characteristics of the body sway are in negligible or weak correlation with the corresponding variables, averaged across the whole trial. All CoP variables showed transient characteristics, reflected in statistically significant decrease or increase throughout the trial. The preferred leg showed smaller body sway; however, the effect sizes were very small. Moreover, differences between the legs were also noted in terms of transient characteristics of body sway. In particular, the preferred leg showed earlier reduction in anterior–posterior body sway and larger reduction in medial–lateral body sway. Further studies should focus on examining the clinical utility of indexes of transient behavior of body sway, for instance, their sensitivity to aging-related changes and risk of falling. (shrink)

Brief submaximal actions are important for wide range of functional movements. Until now, rate of force development and relaxation scaling factor have been used for neuromuscular assessment using 100–120 isometric pulses which requires a high level of attention from the participant and may be influenced by physiological and/or psychological fatigue. All previous studies have been conducted on a smaller number of participants which calls into question the eligibility of some of the outcome measures reported to date. Our aims were: to (...) find the smallest number of rapid isometric force pulses at different force amplitudes is still valid and reliable for RFD-SF slope and RFR-SF slope calculation, to introduce a new outcome measure – theoretical peak of rate of force development/relaxation and to investigate differences and associations between kRFD–SF and kRFR–SF. A cross-sectional study was conducted on a group of young healthy participants; 40 in the reliability study and 336 in the comparison/association study. We investigated the smallest number of rapid isometric pulses for knee extensors that still provides excellent reliability of the calculated kRFD–SF and kRFR–SF. Our results showed excellent reliability of the reduced protocol when 36 pulses were used for the calculations of kRFD–SF and kRFR–SF. We confirmed the negligibility of the y-intercepts and confirmed the reliability of the newly introduced TPRFD and TPRFR. Large negative associations were found between kRFD–SF and kRFR–SF, while comparison of the absolute values showed a significantly higher kRFD–SF compared to kRFR–SF. The advantage of the reduced protocol is the shorter assessment time and the reduction of possible influence of fatigue. In addition, the introduction of TPRFD and TPRFR as an outcome measure provides valuable information about the participant’s maximal theoretical RFD/RFR capacity. This can be useful for the assessment of maximal capacity in people with various impairments or pain problems. (shrink)

Prolonged trunk flexion is known to affect passive and active stabilization of the trunk. Previous studies have evaluated changes in spinal range of motion, muscle activity and reflex behavior induced by prolonged trunk flexion, whereas the effect on sitting postural control is vastly underexplored. In this study, we compared the effects of supported and unsupported intermittent trunk flexion on center of pressure motion during sitting on an unstable seat. Participants were exposed to 1-h intermittent trunk flexion and CoP root mean (...) square distance, velocity and frequency before and after the exposure were assessed. Contrary to our hypothesis, there were no main effects of exposure, no main effects of condition, and no interaction between exposure and condition. Our results indicate that prolonged intermittent flexion does not induce any changes in CoP motion during a seated balance task, regardless of the presence of a trunk support during prolonged intermittent flexion. This suggests a successful compensation of decreased passive stiffness by increased reflex activity. (shrink)