This work analyses surfers' postural control and their use of visual information in static (stable) and dynamic (unstable) postures according to their level of competition. Two groups of healthy surfers were investigated: a group of local level surfers (LOC) (n = 8) and a group of national/international level surfers (NIN) (n = 9). Posture was assessed by measuring the centre of foot pressure with a force platform for 50 s with stable support and for 25 s with unstable support (sagittal or frontal plane). The tests were completed with the eyes open (the subjects looked at a fixed level target at a distance of 2 m) and closed (they kept their gaze in a straight-ahead direction). Results showed that the contribution of vision in postural maintenance, with unstable support was less important in the NIN surfers than in the LOC surfers and that the NIN surfers had better postural control than the LOC surfers. Firstly, the results suggest that expert surfers could shift the sensorimotor dominance from vision to proprioception for postural maintenance. Secondly, there is a relationship between the postural ability and the competition level of surfers. These observations are likely to induce new prospects of training for surfers.

The aim of this study was to compare the effects of acute muscle fatigue of the ankle and knee musculature on postural control by immediate measures after performing fatiguing tasks (POST condition). One group of subjects (n = 8) performed a fatiguing task by voluntary contractions of the triceps surae (group TRI) and the other (n = 9) performed a fatiguing task by voluntary contractions of the quadriceps femoris (group QUA). Each muscle group was exercised until the loss of maximal voluntary contraction torque reached 50% (isokinetic dynamometer). Posture was assessed by measuring the centre of foot pressure (COP) with a force platform during a test of unipedal quiet standing posture with eyes closed. Initially (in PRE condition), the mean COP velocity was not significantly different between group TRI and group QUA. In POST condition, the mean COP velocity increased more in group QUA than in group TRI. The postural control was more impaired by knee muscle fatigue than by ankle muscle fatigue.

No abstract

Background: Demonstration is a widely used method in sports teaching and coaching, based on the assumption that it is more beneficial than verbal instructions or trial-anderror methods for skill acquisition. Although in teaching/coaching situations, the demonstration is usually carried out in front of the learners, in a research context, it is most often presented via a video. However, a direct comparison between these two types of model has rarely been undertaken in a motor context. Purpose: In this study, we aimed to compare the effectiveness of the observation of a live-and a video-model for the early acquisition of a complex judo movement. Research Design: Participants observed either a live-or a video-model executing the task. After observation, they practiced for three minutes taking five trials and then performed it for analysis. This procedure was repeated three times. The form and technique of each participant's execution were evaluated using a technical score. Main results: The results indicated a significant improvement in the task execution by the end of the practice session. However, this improvement occurred only for the video model group between the second and third block of practice. Conclusions: The video demonstration seems more effective than the live one for the early acquisition of a completely new complex coordination. This may be due to the simplification of the visual information in the former condition because of its twodimensionality. This simplification may allow the observer to identify the more key elements that would guide him/her for the subsequent performance of the task

No abstract