Influence of ankle loading on the relationship between temporal pressure and motor coordination during a whole-body paired task.

We investigated whether ankle loading modifies the relationship between temporal pressure and motor coordination during a whole-body paired task. Eight young healthy adults standing in an erect posture performed multiple series of simultaneous rapid leg flexions paired with ipsilateral index finger extensions. They repeated the task ten times in three load conditions: unloaded, loaded (where additional 5-kg inertia was attached to the ankles), and post-loaded (immediately following the loaded condition). These conditions were conducted in two blocks of temporal pressure: self-initiated (SI) versus reaction time (RT). When participants were unloaded, the results showed that index finger extension preceded swing heel-off in RT, and conversely in SI. By contrast, when the participants were loaded, swing heel-off preceded index finger extension in both SI and RT, showing that loading modified the relationship between temporal pressure and movement synchronization in RT only. However, loading did not induce any increase in the error of synchronization. Furthermore, in both the unloaded and loaded conditions, the duration of "anticipatory postural adjustments" (APA) was shorter when the temporal pressure was increased. Interestingly, the shorter APA duration was compensated by an increase in APA amplitude. Thus, loading did not modify the relationship between temporal pressure and anticipatory postural dynamics. Post-loaded and unloaded conditions produced the same results. These results show that the central nervous system optimally adapts the relationship between temporal pressure and motor coordination to transitory changes in the mechanical properties of the lower limbs, here due to ankle loading.

Influence of experience on postural control: effect of expertise in gymnastics.

The authors investigated how expertise in motor skills that require fine postural control, such as gymnastics, influences postural regulation. Gymnasts and nongymnasts performed a postural stabilization task after anterior-posterior destabilization while looking at a target in front of them. The authors recorded and analyzed the center of pressure and the ankle, knee, and hip displacements. Gymnasts were able to react rapidly after destabilization to decrease their center of pressure and the angular movements. Moreover, they used their knees to stabilize posture, whereas the nongymnasts used their hips. These findings suggest that specific postural experience modifies the ability to coordinate and regulate posture. The authors discuss these results from an ecological perspective.

A new methodology providing evidence of two distinct processes in the production of hand/foot simultaneous responses.

To get simultaneous responses of the hand and the foot, it is mandatory to compensate for the longer peripheral motor conduction delay of the foot. According to the reactive-projective model [Paillard, J. (1948). Quelques données psychophysiologiques relatives au déclenchement de la commande motrice (Some psychophysiological data in relation to the releasing of the motor commands). Année Psychologique, 28-47; Paillard, J. (1990). Réactif et prédictif: deux modes de gestion du geste de la motricité. In V. Nougier, & J. Blanchi (Eds.), Pratiques sportives et modélisation du geste (Sport activity and gesture modeling) (pp. 13-56). Grenoble: Université Joseph-Fourier.] no compensation occurs in a reaction time situation; the hand responds before the foot, which indicates a single motor command released for both effectors. However, in a self-initiated condition, the foot tends to precede the hand suggesting that two distinct motor commands are issued, with the foot command first. Fully self-initiated movements are not usual. It is more usual to prepare a response in anticipation of the time occurrence of a stimulus (e.g., a musician following a conductor, synchronized swimmers emerging together with the music). Therefore, we developed a methodology to test whether the model holds in an anticipation coincidence task. In Experiment 1, the participants were asked to initiate a synchronized hand/foot response when the continuous visual stimulus (constant speed) reaches a target. The results fitted the model. In Experiment 2, anticipation coincidence tasks were performed in three conditions: using the foot (1) or the hand (2) alone, and using the hand and the foot simultaneously (3). Following a constant stimulus protocol, short tones were randomly produced, prior the stimulus, to indicate the participants to inhibit their response. As expected, the frequencies of correct inhibition in each preset period followed a sigmoid curve. The command release is assumed to occur at the biserial point (50% of inhibition). The results confirmed that the motor command of the foot is released sooner than the command of the hand. The hand/foot delay is lower in the simultaneous condition, because the command of the hand is released 40 ms earlier; while the foot command is 10 ms earlier. These data confirm and extend the projective-reactive model to a new category of coordination behavior.

Postural Preparation to Stepping: Coupled Center of Pressure Shifts in the Anterior-Posterior and Medio-Lateral Directions.

We explored changes in the postural preparation to stepping introduced by modifications of the initial coordinates of the center of pressure (COP). We hypothesized that the postural adjustments in the anterior-posterior direction would persist across all initial COP manipulations while the adjustments in the medio-lateral direction would be highly sensitive to the initial COP coordinate. Healthy subjects stood on a force plate, shifted the body weight to one of the initial conditions that spanned the range of COP coordinates in both directions, and initiated a single step or started to walk. No major changes were observed between the stepping and walking conditions. Changes in the initial COP coordinate in the medio-lateral direction led to scaling of the magnitude of the COP shift in that direction prior to stepping accompanied by a nearly proportional change in the COP shift in the anterior-posterior direction. Changes in the initial COP coordinate in the anterior-posterior direction led to scaling of the magnitude of the COP shift in that direction prior to stepping without consistent changes in the COP shift in the medio-lateral direction. We interpret the results as reflecting a neural organization using a small set of referent body configurations for the postural adjustments.

Effects of apnea on motor and cardiac rhythms.

Usually, spontaneous rhythm of movements is studied through tasks involving an increase in heart rate (HR) such as physical exercises, locomotion or mental tasks. This experiment, instead, checks whether spontaneous rhythm is influenced by HR deceleration provoked by a voluntary apnea. The performances in a motor spontaneous tempo (MST) task performed for 3 min were compared to the same finger-tapping task performed in apnea. The results show a systematic adjustment period at the beginning of each trial in order to achieve a stable MST. More interestingly, HR and MST decreased simultaneously during apnea conditions and the finger-taps occur most frequently around the ventricular systole. Assuming that apnea increases arousal level, this parallelism between cardiac and motor rhythms is in contradiction with the sympathetic hypothesis that suggested that MST is mainly influenced by arousal.

Effect of arousal on internal clock speed in real action and mental imagery.

The possible implication of an internal clock as a mechanism accounting for the temporal homology between actual and mental walking is studied. To observe this phenomenon, stressful sound stimuli were used to increase arousal, which is known to activate the internal clock. Seventeen participants performed three tasks: (1) a time production task, used as a reference task reflecting the internal clock speed; (2) an actual walking task; and (3) a mental walking task, all three in two sound conditions (no noise and noise). The results showed a significant effect of arousal on time in each task. The effect of noise, increasing the arousal level, was greater in time production and mental imagery tasks than in real action. In addition, the percentages of change between the two sound conditions for actual and mental walking time were not statistically different. These findings are further evidence of the existence of a timing process common to actual and mental walking. The data are consistent with the implication of an internal clock in both actual and mental walking.

Relation between sport activity and mental rotation: comparison of three groups of subjects.

The aim was to observe the relation between sport activity and performance on a mental image-transformation task. A classical mental rotation task using abstract stimuli was administered to three groups: (a) gymnasts who used mental and physical rotations in their practice, (b) athletes whose activities required very little motor rotation, and (c) nonathletes. Both sport groups performed similarly and obtained significantly shorter response times than those of the nonathletes. We suggest that the regular practice of spatial activities, such as sports, could be related to the spatial capacities of the participants.

Physical exercise and time of day: influences on spontaneous motor tempo.

To identify whether spontaneous motor rhythm is influenced by external or internal events and whether this rhythm fluctuates across the day in parallel with heart rate diurnal variations, we simultaneously recorded heart rate and spontaneous motor rate before and after a pedaling task performed five times a day by 10 healthy human subjects. Each subject performed a Spontaneous Motor Tempo, i.e., a finger-tapping task, at a comfortable and spontaneous cadence. Pre- and postexercise Spontaneous Motor Tempo was measured as well as heart rate. There were diurnal variations in Spontaneous Motor Tempo. Both measures increased significantly after pedaling, suggesting that cardiac and spontaneous rhythms are influenced simultaneously after a moderate exercise. Also, finger-taps occurred most frequently around the initiation of the heart systole. These results suggest that a putative internal clock might regulate Spontaneous Motor Tempo and that cardiac rhythm might influence this tempo.

Relation between sport and spatial imagery: comparison of three groups of participants.

The literature suggests that sport may be considered a spatial activity and that engaging in spatial activities increases the capacity of an individual to implement mental imagery. Moreover, mental rotation calls upon motor processes that are heavily involved in sporting activities. For these reasons, the authors hypothesized that athletes ought to perform mental rotation tasks better than nonathletes. Also, athletes trained to react quickly to constantly changing environments should be faster at processing the information in a mental rotation task than athletes operating in more settled environments. The results of this study show that athletes performed the mental rotation task significantly faster than nonathletes. These results support the suggestion that there is a link between sport and the ability to perform mental image transformations; however, this ability may not be specific to the conditions in which the athlete performs.

Global stress response during a social stress test: impact of alexithymia and its subfactors.

OBJECTIVES: Alexithymia is a personality trait characterized by difficulties in identifying, describing and communicating one's own emotions. Recent studies have associated specific effects of this trait and its subfactors with hypothalamo-pituitary-adrenal (HPA) axis markers during stress. The aim of this study was to analyze the association between alexithymia and its subfactors with HPA and sympatho-adrenal medullar (SAM) activity. Stress was induced experimentally using a public-speaking paradigm. Salivary cortisol, alpha-amylase (AA), chromogranin A (CgA) and heart rate (HR) were collected during the defined periods of baseline, stress, and recovery in 19 males and 24 female healthy university students. RESULTS: Subjects reacted to the stressor with a significant cortisol and SAM response. Subjects scoring high on alexithymia reacted significantly more intensely than low scorers in basal anticipatory as well as peak cortisol and area under the curve. Regression analyses revealed that the increased HPA activity was related to only one alexithymia subfactor, the difficulty in differentiating feelings and distinguishing them from bodily sensations and emotion arousal. CONCLUSION: Alexithymia and its subfactors were specifically related to cortisol responses. This research should be replicated with more subjects and should take into account more parameters reflecting sympathetic and/or parasympathetic activation, as well as HPA axis. Factors such as coping strategies and the perception of the situation as a challenge have also to be explored.

Age-related differences in motor coordination during simultaneous leg flexion and finger extension: influence of temporal pressure.

Although the effect of temporal pressure on spatio-temporal aspects of motor coordination and posture is well established in young adults, there is a clear lack of data on elderly subjects. This work examined the aging-related effects of temporal pressure on movement synchronization and dynamic stability. Sixteen young and eleven elderly subjects performed series of simultaneous rapid leg flexions in an erect posture paired with ipsilateral index-finger extensions, minimizing the difference between heel and finger movement onsets. This task was repeated ten times under two temporal conditions (self-initiated [SI] vs. reaction-time [RT]). Results showed that, first, temporal pressure modified movement synchronization; the finger extension preceded swing heel-off in RT, and inversely in SI. Synchronization error and associated standard deviation were significantly greater in elderly than in young adults in SI only, i.e. in the condition where proprioception is thought to be crucial for temporal coordination. Secondly, both groups developed a significantly shorter mediolateral (ML) anticipatory postural adjustment duration in RT (high temporal pressure) than in SI. In both groups, this shortening was compensated by an increase in the anticipatory peak of centre-of-gravity (CoG) acceleration towards the stance-leg so that ML dynamic stability at foot-off, quantified with the "extrapolated centre-of-mass", remained unchanged across temporal conditions. This increased CoG acceleration was associated with an increased anticipatory peak of ML centre-of-pressure shift towards the swing-leg in young adults only. This suggested that the ability to accelerate the CoG with the centre-of-pressure shift was degraded in elderly, probably due to weakness in the lower limb muscles. Dynamic stability at foot-off was also degraded in elderly, with a consequent increased risk of ML imbalance and falling. The present study provides new insights into the ability of elderly adults to deal with temporal pressure constraints in adapting whole-body coordination of postural and focal components of paired movement.

Postural and focal inhibition of voluntary movements prepared under various temporal constraints.

Large disturbances arising from the moving segments (focal movement) are commonly counteracted by anticipatory postural adjustments (APAs). The aim of this study was to investigate how APAs - focal movement coordination changes under temporal constraint. Ten subjects were instructed to perform an arm raising movement in the reactive (simple reaction time) and predictive (anticipation-coincidence) tasks. A stop paradigm was applied to reveal the coordination. On some unexpected trials, a stop signal indicated to inhibit the movement; it occurred randomly at different delays (SOA) relative to the go signal in the reactive task, and at different delays prior to the focal response initiation in the predictive task. Focal movement was measured using contact switch, accelerometer and EMG from the anterior deltoid. APAs were quantified using centre of pressure displacement and EMG from three postural muscles. The inhibition rates as a function of the SOA produce psychometric functions where the bi-serial points allow the moment of the motor "command release" to be estimated. Repeated measures ANOVAs showed that APAs and focal movement were closely timed in the reactive task but distinct in a predictive task. Data were discussed according to two different models of coordination: (1) hierarchical model where APAs and focal movement are the results of a single motor command; (2) parallel model implying two independent motor commands. The data clearly favor the parallel model when the temporal constraint is low. The stop paradigm appears as a promising technique to explore APAs - focal movement coordination.

Lecturing to 200 students and its effects on cytokine concentration and salivary markers of adrenal activation.

Stress not only activates the SAM system and the hypothalamic-pituitary-adrenal axes, but also the immune system. The aims of this study are to assess the physiological variations in saliva (cytokines, cortisol and alpha-amylase) and perceived stress in professors when they had to lecture to 200 students. A total of eight unstimulated saliva samples were collected from nine professors: four on a working day that included the lecture and four controls on a working day without a lecture. The professors also rated subjective stress on a seven-point scale 5 min before the lecture, immediately after the lecture and at the same times on the control day. The lecture elicited substantial increases in subjective stress ratings, with the values on the lecture day significantly higher than those on the control day. Lecturing resulted in significant increases in Tumor Necrosis Factor (TNF)-α, Interleukin (IL)-2 and IL-4 concentrations, but did not affect the IL-10 values. These changes appeared to be concomitant with changes in the concentrations of the stress markers, alpha-amylase and cortisol. The mechanisms by which psychosocial stress can induce cytokine changes and modify the activity of salivary alpha-amylase are not entirely understood, and further research is thus warranted.

Modulation of anticipatory postural adjustments in a complex task under different temporal constraints.

The aim of this experiment was to explore the behavioral effects of various temporal pressures on the anticipatory postural adjustments (APAs) in a complex task. Eighteen handball players performed a handball direct throw in three conditions of temporal pressure: (1) a reactive condition (RC), the throw was initiated as quickly as possible following a visual stimulus; (2) an anticipation-coincidence condition (AC), by synchronizing the impact of the ball with the passage of a visual mobile on a target; and (3) a self-initiated (SI) throw. The whole-body postural oscillation and the acceleration of the wrist were measured before and during the throwing action. Results showed that the delays between the onsets of the postural and focal activities were significantly different between RC and both the SI and the AC conditions. Movement time, time to peaks (negative and positive), are shorter in the RC, intermediate in the AC, and longer in the SI condition. Variability was significantly larger in AC in comparison with RC and SI. These results support the existence of different control modes triggered by the temporal pressure; they demonstrate that these control modes can be generalized to complex intentional movements such as the throwing skill and to an anticipation-coincidence situation.

Effects of regular training at the same time of day on diurnal fluctuations in muscular performance.

The aim of this study was to determine whether there is an effect of time of day on the adaptation to strength training at maximal effort. Fourteen participants took part in this experiment. Their peak anaerobic power (Wingate anaerobic test) and peak knee extension torque at six angular velocities (1.05, 2.10, 3.14, 4.19, 5.24 and 6.29 rad x s(-1)) were recorded in the morning (between 07:00 and 08:00 h) and in the evening (between 17:00 and 18:00 h) just before and 2 weeks after a 6 week course of regular training. Seven of them trained only in the morning and seven only in the evening. Multivariate analysis of variance revealed a significant group x pre-/post-training x time of day interaction effect for peak torque and peak anaerobic power. Before training, in both groups, peak torque and peak anaerobic power were significantly higher in the evening than in the morning. After training, there was no significant difference in peak torque and peak anaerobic power between the morning and the evening for the morning training group. In contrast, in the evening training group, peak torque and peak anaerobic power were higher in the evening than in the morning. As a result of training, both peak torque and peak anaerobic power increased from their initial values as expected. The morning training group improved their peak anaerobic power significantly in the morning and in the evening, the absolute increase being larger in the morning than in the evening. The evening training group did not improve their peak anaerobic power in the morning, whereas it improved significantly in the evening. Although peak torque was significantly improved by training in the morning and evening in both groups, the absolute increase was greater in the morning than in the evening in the morning training group, whereas the opposite was the case for the evening training group. These results suggest that training twice a week at a specific hour increases the peak torque and the peak anaerobic power specifically at this hour and demonstrates that there is a temporal specificity to strength training.

Effects of one night's sleep deprivation on anaerobic performance the following day.

The purpose of this study was to determine the effect of one night's sleep deprivation on anaerobic performance in the morning and afternoon of the following day. Thirteen healthy males were studied twice in a balanced, randomized design. The experiment consisted of two conditions 1 week apart. In the sleep deprivation condition (SDN) subjects remained awake overnight and in the control condition (reference night, RN) the same subjects slept at home, retiring between 2230 and 2330 hours, as decided individually, and rising at 0500 hours. In both conditions, activity, sleep and diet were monitored by actimetry and daily activity and dietary diaries. Physical performance testing was carried out at 0600 hours and at 1800 hours after the one night of sleep and the one night of sleep deprivation. At each test occasion, subjects were measured for maximal power ( P(max)), peak power ( P(peak)) and mean power ( P(mean)). Blood lactate concentrations were measured at rest, at the end of the force-velocity ( F- V) test, just before and just after the Wingate test and again 5 min later. Oral temperatures were measured every 2 h. In both conditions, the results showed a circadian rhythm in temperature. Analysis of variance revealed a significant (sleep x time of day of test) interaction effect on P(peak), P(mean) and P(max). These variables improved significantly from morning to afternoon after RN and SDN. The reference night was followed by a greater improvement than the SDN. Up to 24 h of waking, anaerobic power variables were not affected; however, they were impaired after 36 h without sleep. Analysis of variance revealed that blood lactate concentrations were unaffected by sleep loss, by time of day of testing or by the interaction of the two. In conclusion, sleep deprivation reduced the difference between morning and afternoon in anaerobic power variables. Anaerobic performances were unaffected after 24 h of wakefulness but were impaired after 36 h without sleep.