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The present study aimed to compare various entropy measures to assess the dynamics and complexity of center of pressure (COP) displacements. Perturbing balance tests are often used in healthy subjects to imitate either pathological conditions or to test the sensitivity of postural analysis techniques. Eleven healthy adult subjects were asked to stand in normal stance in three experimental conditions while the visuo-kinesthetic input was altered. COP displacement was recorded using a force plate. Three entropy measures [Sample Entropy (SE), Multi-Scale Entropy (MSE), and Multivariate Multi Scale Entropy (MMSE)] describing COP regularity at different scales were compared to traditional measures of COP variability. The analyses of the COP trajectories revealed that suppression of vision produced minor changes in COP displacement and in the COP characteristics. The comparison with the reference analysis showed that the entropy measures analysis techniques are more sensitive in the incremented time series compared to the classical parameters and entropy measures of original time series. Non-linear methods appear to be an additional valuable tool for analysis of the dynamics of posture especially when applied on incremental time series.

Several studies have investigated the influence of perceiving colors on affective outcomes and/or performance. However, the effects of seeing colors on self-selected behaviors have received little attention from physiologists and psychologists. Therefore, the present study aimed at examining whether exposure to green and red environments could influence affective judgments, perception of effort, heart rate, and gait speeds when walking and running at a self-selected pace. Participants were randomly assigned to one of the three experimental conditions: Green, red, or white (neutral) environment. The experimental task consisted in a 20-min trial of either walking (Study 1) or running (Study 2) at the most comfortable speed on a treadmill surrounded by three large HD TV screens displaying specific properties of the studied colors. Study 1 revealed that walking in a green environment induced a significant reduction in heart rate values as compared to the red and white conditions although no differences in gait speed were found. This corroborates the calming and relaxing effect of green on the human organism. Study 2 showed that running in a green environment was associated with an increased level of perceived exertion at similar speeds (compared to other color conditions), while exposure to red induced a significant decrease in the level of tension. In both studies, the preferred gait speed was not affected by the colored environment which is discussed in relation to the energy-conservation principle. Furthermore, both studies showed that performing a 20-min walk or run at preferred pace presented beneficial mood changes. Implications of the effects of self-selected exercise under colored environments on human functioning are addressed in the discussion.

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This study investigated how novices learn an energy demanding and biomechanically constrained task like racewalking. The first aim was to examine if movement reorganizes according to some fundamental strategies, proceeding in different stages (Newell, 1985). The second aim was to investigate the link between movement reorganization, metabolic efficiency and perceived exertion. Seven participants undertook seven racewalking learning sessions on a motorized treadmill, with increased velocity as the experiment progressed, in order to reach a goal performance speed of 10 kmh(-1). Peripheral/central perceived exertion ratings, kinematic and metabolic data were collected during the 1st, 4th, 6th and 7th session. Repeated-measures (Learning Session×Speed) ANOVAs on kinematic data showed a proximal-to-distal directional trend in movement reorganization, with significant practice-related changes in pattern coordination and decreased variability. Early movement reorganization occurred at the 1st session ("coordination stage") and progressed until the 4th session ("control stage") to reach a plateau. In contrast, metabolic efficiency and peripheral perceived exertion continued optimizing until the last session, probably occurring in concurrence with the control stage. Peripheral perceived exertion presented the highest correlation with the global movement reorganization variables suggesting that it could play a key role in guiding movement reorganization in the learning process, improving efficiency as a result.