Influence of cognitive load on the dynamics of neurophysiological adjustments during fatiguing exercise.

We aimed to determine the neurophysiological mechanisms associated with reduced endurance performance during cognitive-motor dual task at different levels of cognitive load, compared to a motor task alone. Eighteen healthy men performed isometric quadriceps contractions at 15% of maximal voluntary contraction (blocks of 170 s interspaced by neuromuscular evaluations) until exhaustion. This task was performed on three separate days: (a) in the absence of concomitant cognitive task, (b) with concomitant 1-back task, and (c) with concomitant 2-back task. Autonomic nervous system activity, perceived exertion, and cognitive performance were continuously monitored. Peripheral and central determinants of neuromuscular function were assessed at rest, between each block, and at task failure using femoral nerve stimulation. Endurance time was shorter during 2-back (982 ± 545 s) and 1-back (1,128 ± 592 s) conditions, compared with control (1,306 ± 836 s). Voluntary activation level was lower in 2-back (87.1%; p < 0.001) and 1-back (88.6%; p = 0.04) conditions compared to control (91.2%) at isotime (100% of the shortest test duration). Sympathetic activity showed a greater increase in 2-back condition compared to control. Perceived muscular exertion was higher during 2-back than during control. Cognitive performance decreased similarly with time during both cognitive-motor dual task but was always lower during 2-back condition. Motor performance is reduced when adding a concomitant demanding memory task to a prolonged isometric exercise. This can be explained by the interaction of various psychological and neurophysiological factors including higher perceived exertion, greater perturbations of autonomic nervous system activity, and cerebral impairments leading to earlier onset of central fatigue.

Fast Regulation of Vertical Squat Jump during Push-Off in Skilled Jumpers.

The height of a maximum Vertical Squat Jump (VSJ) reflects the useful power produced by a jumper during the push-off phase. In turn this partly depends on the coordination of the jumper's segmental rotations at each instant. The physical system constituted by the jumper has been shown to be very sensitive to perturbations and furthermore the movement is realized in a very short time (ca. 300 ms), compared to the timing of known feedback loops. However, the dynamics of the segmental coordination and its efficiency in relation to energetics at each instant of the push-off phase still remained to be clarified. Their study was the main purpose of the present research. Eight young adult volunteers (males) performed maximal VSJ. They were skilled in jumping according to their sport activities (track and field or volleyball). A video analysis on the kinematics of the jump determined the influence of the jumpers' segments rotation on the vertical velocity and acceleration of the body mass center (MC). The efficiency in the production of useful power at the jumpers' MC level, by the rotation of the segments, was measured in consequence. The results showed a great variability in the segmental movements of the eight jumpers, but homogeneity in the overall evolution of these movements with three consecutive types of coordination in the second part of the push-off (lasting roughly 0.16 s). Further analyses gave insights on the regulation of the push-off, suggesting that very fast regulation(s) of the VSJ may be supported by: (a) the adaptation of the motor cerebral programming to the jumper's physical characteristics; (b) the control of the initial posture; and

Effect of action verbs on the performance of a complex movement.

The interaction between language and motor action has been approached by studying the effect of action verbs, kinaesthetic imagery and mental subtraction upon the performance of a complex movement, the squat vertical jump (SVJ). The time of flight gave the value of the height of the SVJ and was measured with an Optojump® and a Myotest® apparatuses. The results obtained by the effects of the cognitive stimuli showed a statistically significant improvement of the SVJ performance after either loudly or silently pronouncing, hearing or reading the verb saute (jump in French language). Action verbs specific for other motor actions (pince = pinch, lèche = lick) or non-specific (bouge = move) showed no or little effect. A meaningless verb for the French subjects (tiáo = jump in Chinese) showed no effect as did rêve (dream), tombe (fall) and stop. The verb gagne (win) improved significantly the SVJ height, as did its antonym perds (lose) suggesting a possible influence of affects in the subjects' performance. The effect of the specific action verb jump upon the heights of SVJ was similar to that obtained after kinaesthetic imagery and after mental subtraction of two digits numbers from three digits ones; possibly, in the latter, because of the intervention of language in calculus. It appears that the effects of the specific action verb jump did seem effective but not totally exclusive for the enhancement of the SVJ performance. The results imply an interaction among language and motor brain areas in the performance of a complex movement resulting in a clear specificity of the corresponding action verb. The effect upon performance may probably be influenced by the subjects' intention, increased attention and emotion produced by cognitive stimuli among which action verbs.

Motor performance may be improved by kinesthetic imagery, specific action verb production, and mental calculation.

Several results in the literature show that motor imagery, language production, mental calculation, and motor execution share the same or closely related brain motor cortical areas. The present study aimed at investigating the possible influence of specific action verb (AV) pronunciation and mental calculus upon motor performance compared with kinesthetic imagery (KI). Participants, novice in mental imagery, performed a vertical jump after a cognitive task (AV, silent AV, mental subtraction, meaningless verb, and KI). The results show that specific lower limbs AV, mental calculation, and KI improved the vertical jump in male, but not in female participants.