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Biomedical subjects

A Boyadjian

Publications and source records attributed to A Boyadjian.

8 recordsLinked to original sources
PubMed2005

Motor cortex plasticity induced by extensive training revealed by transcranial magnetic stimulation in human.

This study examines the effect of high-level skilled behaviour on motor cortex representations of upper extremity muscles of ten sportswomen. We used transcranial magnetic stimulation to map proximal medial deltoid and distal extensor carpi radialis muscle representations on both hemispheres during low-level voluntary contraction. We compared cortical representation areas between two groups of subjects and between hemispheres within subjects. The first group comprised five elite volleyball attackers and the second group five runners. Four stimuli were delivered on multiple scalp sites (1.5 cm apart) to induce motor-evoked potentials recorded by surface EMG. Maps were described in terms of excitable scalp positions and of motor-evoked potentials. We observed differences in map areas between the two groups. Volleyball players had larger cortical representations of the proximal medial deltoid muscle than runners. Furthermore, the volleyball players had larger map areas for dominant muscles compared with non-dominant muscles. There was no difference, however, in map area for either muscle between the dominant and non-dominant arm in the runner group. Our results show that heavy training in a specific skill induces an expansion of proximal muscle representation in the contralateral primary motor cortex. This enlarged map area for proximal muscle is accompanied by an increase in the overlapping of proximal and distal muscle representations. This could reflect the fact that motor learning of co-ordinated movement involves a common control of both muscles. This reorganization supports the hypothesis of a cortical plasticity driven by activity.

Adult↗
PubMed2004

Effect of inertia on performance and fatigue pattern during repeated cycle sprints in males and females.

The effect of recovery duration on performance and fatigue pattern during short exercises was studied including and excluding the flywheel inertia. Subjects (11 males and 11 females) performed a force-velocity test to determine their optimal force (f (opt)). On the following day, subjects performed randomly 4 series of two 8-s sprints against f (opt), with 15 s (R (15)), 30 s (R (30)), 60 s (R (60)), and 120 s (R (120)) recovery between sprints. The cycle (Monark 824 E, Stockholm, Sweden) was equipped with an optical sensor to calculate the revolution velocity of the pedal. For each sprint, peak power (P (peak)), mechanical work (W) and time to reach P (peak) (t (Ppeak)) were calculated including (I) and excluding (NI) the acceleration of the flywheel. For a given sprint, P (peak) and W were greater and t (Ppeak) was lower in I compared to NI condition (p < 0.05). Differences averaged 13 % for P (peak), 20 % for W, 34 % for t (Ppeak), and remained constant between sprints 1 and 2. In sprint 2, P (peak) and W were significantly reduced compared to sprint 1 only after R (15) and R (30) in I and NI (p < 0.05), and no gender differences occurred. In each sprint, P (peak) and W were higher (p < 0.001) and t (Ppeak) was shorter (p < 0.05) in males than in females, and gender differences were the same including or excluding the flywheel inertia. In conclusion, values excluding inertia underestimated mechanical performance and consequently the total energy supply. However, the pattern of fatigue and gender differences in performance and fatigue remained unchanged whatever the condition (I or NI). This result may have practical implications when the flywheel inertia can not be taken into account in the calculation of mechanical work and power output.

Adult↗
PubMed2001

The effect of expertise in gymnastics on postural control.

The goal of this paper was (1) to investigate if gymnasts have a more stable standing posture than experts in other sports, and (2) to determine how much gymnasts are affected by the removal of vision in different postural tasks. Six expert gymnasts and six experts in other non-gymnastic sports were asked to maintain balance in three standing postures of increasing difficulty: bipedal, unipedal, and unipedal + unstable support (i.e. 7 cm thick foam surface). Each posture was tested successively with and without vision. Based on the displacement of the center of pressure (range and mean average speed), the results showed that when visual cues were available, postural sway increased with the difficulty of the task, but both groups had comparable performance in all the tasks. When vision was removed, although both groups demonstrated larger postural sway in the unipedal tasks, this effect was less accentuated for the gymnasts. We concluded that gymnasts are able to use the remaining sensory modalities to compensate for the lack of vision in unstable postures.

Adult↗
PubMed2001

[Developmental anomaly of the hyoid bone: an unusual cause of dysphagia].

We report the case of a hyoid syndrome caused by a developmental anomaly of the second branchial cleft, presenting at adult age by dysphagia without any abnormality detected at the barium swallow and at naso-pharyngeal endoscopy, first examinations to perform in case of dysphagia. The MRI findings of this anomaly showed a hyperintense well-limited vallecular mass syndrome. The diagnosis of hyoid bone anomaly was established at spiral CT with 3D reconstructions showing an incurvated and elongated lesser cornua causing persistant impingement on the lateral wall of the oropharynx. CT scan performed during Valsalva manoeuver showed the persistance of the compression during pharyngeal insufflation.

Adult↗
PubMed2000

Control of locomotion in expert gymnasts in the absence of vision.

The main aim of this study was to determine how gymnasts are affected by the removal of vision when executing simple moves. A secondary aim was to establish whether crucial sensory cues exist for blindfolded gymnasts. Eight expert gymnasts were asked to maintain a straight displacement during three types of blindfolded locomotion: walking, steering a wheelchair and verbally ordering a second person pushing their wheelchair. In the first two conditions, active displacement made proprioceptive cues available to update the body trajectory. In the last condition, however, proprioceptive cues were greatly reduced, since the gymnasts displaced passively. The performance of the gymnasts was compared to that of eight experts in other non-gymnastic sports (control group). The results showed that the participants veered in all conditions. However, except in the verbal condition, the gymnasts departed less from linearity than the controls. We conclude that: (1) even for a simple motor task, gymnasts' performance is altered by eliminating vision; (2) compared with other sportsmen and women, gymnasts are better able to deal with the absence of vision when proprioceptive cues are available. These findings suggest two possible explanations: (1) gymnasts are more able to 'pick up' crucial information and (2) a gymnast's proprioceptive system is more sensitive.

Adolescent↗
PubMed1999

Veering in human locomotion: the role of the effectors.

Without visual information, human subjects are not able to maintain displacement in a straight line. This tendency is called veering. The goal of this paper was to investigate the origin of veering in a population of subjects who were homotropic during walking (i.e. veering consistently in the same direction on repeated trials). Three types of locomotion were compared, each one required a specific set of effectors: (i) walking (LEG); (ii) propelling on a wheelchair (ARM) and (iii) verbally ordering a second person pushing the wheelchair (VERB). After 15 m displacement, all subjects (n = 8) exhibited large deviations from the initial direction (2.5 m in LEG, 3.2 m in ARM and 4 m in VERB). We also observed that all participants were homotropic in ARM, but only half of them continued to veer in the same direction than in LEG. By contrast in VERB, deviations occurred randomly. We concluded that systematic deviations occurring in two-limb displacements originate from a peripheral mechanism (slight different properties of the right and left limbs) rather than a central mechanism (systematic bias in the perceived body trajectory).

Adaptation, Physiological↗
PubMed1999

Timing in relay running.

Skillful performance in relay running requires that the athlete who is to take possession of the baton meets the baton carrier before reaching the end of the transmission zone while running at the highest speed possible. In the present study we examined the effects of variations in approach speed on the running behavior of the receiver. Kinematic analyses indicated that receivers regulated both the moment of initiation as well as the accelerative characteristics of their run. Contrary to the instructions given, baton carriers adapted their running speed as well to ensure a safe passage, making it difficult for the receiver to evaluate the appropriateness of their behavior.

Acceleration↗