Motor strategies and adiabatic invariants: The case of rhythmic motion in parabolic flights.

The role of gravity in human motor control is at the same time obvious and difficult to isolate. It can be assessed by performing experiments in variable gravity. We propose that adiabatic invariant theory may be used to reveal nearly conserved quantities in human voluntary rhythmic motion, an individual being seen as a complex time-dependent dynamical system with bounded motion in phase space. We study an explicit realization of our proposal: An experiment in which we asked participants to perform ∞- shaped motion of their right arm during a parabolic flight, either at self-selected pace or at a metronome's given pace. Gravity varied between 0 and 1.8 g during a parabola. We compute the adiabatic invariants in the participant's frontal plane assuming a separable dynamics. It appears that the adiabatic invariant in vertical direction increases linearly with g, in agreement with our model. Differences between the free and metronome-driven conditions show that participants' adaptation to variable gravity is maximal without constraint. Furthermore, motion in the participant's transverse plane induces trajectories that may be linked to higher-derivative dynamics. Our results show that adiabatic invariants are relevant quantities to show the changes in motor strategy in time-dependent environments.

Adiabatic invariants drive rhythmic human motion in variable gravity.

Voluntary human movements are stereotyped. When modeled in the framework of classical mechanics they are expected to minimize cost functions that may include energy, a natural candidate from a physiological point of view also. In time-changing environments, however, energy is no longer conserved-regardless of frictional energy dissipation-and it is therefore not the preferred candidate for any cost function able to describe the subsequent changes in motor strategies. Adiabatic invariants are known to be relevant observables in such systems, although they still need to be investigated in human motor control. We fill this gap and show that the theory of adiabatic invariants provides an accurate description of how human participants modify a voluntary, rhythmic, one-dimensional motion of the forearm in response to variable gravity (from 1 to 3g). Our findings suggest that adiabatic invariants may reveal generic hidden constraints ruling human motion in time-changing gravity.

Contribución al estudio de los efectos sistémicos neurovegetativos del masaje terapéutico mediante el análisis espectral de la variabilidad de la frecuencia cardiaca / Contribution to the study of autonomic systemic effects of therapeutic massage by power spectral analysis of heart rate variability

Objetivo. Analizar las modificaciones que el masaje terapéutico produce en la actividad neurovegetativa sistémica del organismo a través del estudio de la modificación de la actividad autónoma cardiaca. Material y método. Estudio comparativo sobre 15 mujeres de la variabilidad de la frecuencia cardiaca (VFC) (intervalo R-R) obtenida mediante fotopletismografía durante 2 sesiones de 20 minutos de duración: control y masaje. Dicha VFC fue medida en 4 ocasiones diferentes sobre duraciones de 5 minutos cada una. La sesión de masaje consistió en effleurage superficial y presiones deslizadas de gran amplitud. Además, las participantes debían cumplimentar inmediatamente después de la sesión de control y de la de masaje el cuestionario de la escala visual analógica (EVA) de bienestar. Resultados. Para comparar los resultados obtenidos se ha utilizado el t-test pareado de Student y se ha empleado el coeficiente de correlación de Pearson para cuantificar la fuerza de la relación existente entre distintos tiempos en cada uno de los parámetros. Se observa un aumento estadísticamente significativo de la VFC (potencia total) y también un aumento de la actividad parasimpática en la sesión de masaje durante los 5 últimos minutos del mismo (respecto a valores basales), superior a la sesión control. Esta respuesta, sin embargo, tiende a disminuir 5 minutos después de la interrupción del mismo. Finalmente, la puntuación de la EVA de bienestar aumentó significativamente después del masaje, pero su ganancia no se correlaciona con la evolución de las variables fisiológicas. Conclusiones. El masaje aplicado sobre sujetos sanos tiene efecto sobre el sistema neurovegetativo (AU)

Goal: To analyze the changes produced by therapeutic massage on systemic autonomic activity by analyzing the modification of cardiac autonomic activity. Material and methods: A comparative study was performed on 15 women on the variability of heart rate variability (HRV) (RR interval) obtained by photoplethysmography for 2 20-minute sessions: control and massage. HRV was measured at 4 different times for periods of 5 minutes each. The massage session consisted of effleurage massage and wide-ranging sliding pressure. In addition, the participants had to fill out the well-being visual analogue scale (Well Being VAS) questionnaire immediately after the control and massage session. Results: The paired Student’s t-test was used to compare the results obtained. Pearson correlation coefficient was used to quantify the relationship existing between the different times in each one of the parameters. A statistically significant increase was observed in HRV (total power) as well as an increase in parasympathetic activity in the massage session during the last 5 minutes (relative to baseline) compared to control session. However, this response tends to decrease 5 minutes after its interruption/timeout. Finally, the Well Being VAS score shows a significant increase after the massage. However, its gain is not correlated to the changes in the physiological variables. Conclusions: The massage applied on healthy subjects affects the autonomic nervous system (AU)

[Clinical and posturographic comparison of patients with recent total hip arthroplasty]. / Evolution comparée des tests cliniques et posturographiques lors de la rééducation des arthroplasties totales de hanche.

PURPOSE OF THE STUDY: To highlight the congruence of clinical and posturographic tests in patients undergoing hip arthroplasty. MATERIAL AND METHODS: Ten patients (six males and four females) were included in this study and tested when at admission and discharge from the rehabilitation department (12 and 27 days after surgery respectively). The patients were asked to stand undisturbed in the upright position, eyes closed on a system composed of two force platforms. Five successive 32s trials (sampled at 64 Hz) were conducted with rest intervals of similar duration between trials. The plantar center of pressure (CP), displacements, and resultant CP (CPRes) were then computed and analyzed in various ways. In parallel, various clinical tests, including muscular force, hip range of motion, walking speed, functional independence, pain, sensitivity, lateral reach, and get up and go aimed at evaluating global coordination. Correlations, using the non-parametric Spearman coefficient, were computed from the differences between clinical and posturographic parameters obtained at admission and discharge from the rehabilitation department. RESULTS: Certain statistically significant differences in postural behavior was observed both for clinical and posturographic tests between admission and discharge. Body weigh distribution over the two legs was largely asymmetric at onset and, though it declined, persisted at discharge. There was not difference for the mean positions of both the plantar CP and the resultant of the CP movements. On the contrary, it was noteworthy that the variances of CP displacements (data dispersion) were initially larger on the sound leg along the anteroposterior axis and that this compensatory feature disappeared at the end of the stay. At discharge, the variances computed from the sound and the prosthetic limb became equivalent. All the clinical tests demonstrated statistically significant improvements in results at discharge compared with admission. Several significant correlations involving clinical tests and mean positions along the anteroposterior axis, the degree of body weight asymmetry and variances along both the mediolateral and anteroposterior axes were found. DISCUSSION: These results enable a better understanding of strategies used by hip arthroplasty patients to keep balance. Even though their sensitivity was quite different, both clinical and posturographic measurements demonstrated their ability to assess recovery from surgery. These two evaluation techniques are complementary.

Energy cost, mechanical work, and efficiency of hemiparetic walking.

The energy cost of walking (C) in nine chronic hemiparetic patients was calculated by measuring the total mechanical work (Wtot) done by the muscles and the efficiency of this work production (eta). The energy cost was twice normal in slow walkers and 1.3 times greater in fast walkers. The increase in C was proportional to the increase in Wtot and eta was normal at around 20%, despite an increase in muscle tone and muscle co-contractions. This type of approach gives a greater understanding into how segmental impairments increase Wtot and C and contribute to a patient's disability.

Motion of the body centre of gravity as a summary indicator of the mechanics of human pathological gait.

Abnormal movements of the body segments due to lowest level gait disorders such as musculoskeletal disorders, peripheral neuropathies and radiculopathies or middle-level disorders such as hemiplegia, paraplegia and dystonia influence the motion of the centre of gravity (CG) during walking. The translation of the CG can be studied by the work done by muscles (WExt) with respect to the ground. The efficacy of gait's mechanism can be quantified by the energy transferred between gravitational potential and kinetic energies (recovery). WExt and recovery were investigated in lowest and middle-level gait disorders during level walking. No statistical significant difference was observed between patients with lowest-level gait disorders and normal subjects. However, WExt was increased for the patients with middle-level gait disorders and recovery decreased up to 20%. The measurement of changes in mechanical energy of the CG might be a summary indicator for the mechanics of pathological gait.