Visual and postural control of an arbitrary posture: the handstand

The aim of this study was to increase our understanding of postural regulation by analysing an arbitrary posture - the handstand. We assessed the relative influence of peripheral vision and central visual anchoring on the postural balance of gymnasts in the inverted-stand posture. Displacements of the centre of pressure, the angles between the body segments, and the gymnast's height in the handstand were analysed. Postural regulation in the handstand appeared to be organized according to a system similar to that in erect posture, with three articular levels suggesting the existence of a typical organization of human posture. Moreover, both intra-modal (central and peripheral vision) and inter-modal sensory systems (vision and other balance systems) contributed to the postural regulation. The results are interpreted in terms of an ecological approach to posture in which postural regulation can be considered as an emergent phenomenon.     

Influence of a stressing constraint on stiffness and damping functions of a ski simulator's platform motion

The aim of this study was to assess the effect of stress on a previously acquired motor coordination. Following a longitudinal learning experiment, four participants performed oscillations on a ski simulator, either in normal or stressful conditions. The results showed that the amplitude of the oscillations decreased under stress, but no significant effect was seen regarding coordination, suggesting the strong resistance to stress of overlearned behaviour. Nevertheless, for one participant, a transient regression towards a former stage of learning was observed. This result was consistent with the regression hypothesis formulated by Fuchs (1962).     

A microfluidic device for on-chip agarose microbead generation with ultralow reagent consumption

Water-in-oil microdroplets offer microreactors for compartmentalized biochemical reactions with high throughput. Recently, the combination with a sol-gel switch ability, using agarose-in-oil microdroplets, has increased the range of possible applications, allowing for example the capture of amplicons in the gel phase for the preservation of monoclonality during a PCR reaction. Here, we report a new method for generating such agarose-in-oil microdroplets on a microfluidic device, with minimized inlet dead volume, on-chip cooling, and in situ monitoring of biochemical reactions within the gelified microbeads. We used a flow-focusing microchannel network and successfully generated agarose microdroplets at room temperature using the “push-pull” method. This method consists in pushing the oil continuous phase only, while suction is applied to the device outlet. The agarose phase present at the inlet is thus aspirated in the device, and segmented in microdroplets. The cooling system consists of two copper wires embedded in the microfluidic device. The transition from agarose microdroplets to microbeads provides additional stability and facilitated manipulation. We demonstrate the potential of this method by performing on-chip a temperature-triggered DNA isothermal amplification in agarose microbeads. Our device thus provides a new way to generate microbeads with high throughput and no dead volume for biochemical applications.     

Effect of swimming velocity on arm coordination in the front crawl: a dynamic analysis

We examined the preferred mode of arm coordination in 14 elite male front-crawl swimmers. Each swimmer performed eight successive swim trials in which target velocity increased from the swimmer's usual 3000-m velocity to his maximal velocity. Actual swim velocity, stroke rate, stroke length and the different arm stroke phases were then calculated from video analysis. Arm coordination was quantified by an index of coordination based on the lag time between the propulsive phases of each arm. The index expressed the three coordination modes in the front crawl: opposition, catch-up and superposition. First, in line with the dynamic approach to movement coordination, the index of coordination could be considered as an order parameter that qualitatively captured arm coordination. Second, two coordination modes were observed: a catch-up pattern (index of coordination?=??8.43%) consisting of a lag time between the propulsive phases of each arm, and a relative opposition pattern (index of coordination?=?0.89%) in which the propulsive phase of one arm ended when the propulsive phase of the other arm began. An abrupt change in the coordination pattern occurred at the critical velocity of 1.8?m?·?s^?1, which corresponded to the 100-m pace: the swimmers switched from catch-up to relative opposition. This change in coordination resulted in a reorganization of the arm phases: the duration of the entry and catch phase decreased, while the duration of the pull and push phases increased in relation to the whole stroke. Third, these changes were coupled to increased stroke rate and decreased stroke length, indicating that stroke rate, stroke length, the stroke rate/stroke length ratio, as well as velocity, could be considered as control parameters. The control parameters can be manipulated to facilitate the emergence of specific coordination modes, which is highly relevant to training and learning. By adjusting the control and order parameters within the context of a specific race distance, both coach and swimmer will be able to detect the best adapted pattern for a given race pace and follow how arm coordination changes over the course of training.     

A new index of flat breaststroke propulsion: A comparison of elite men and women

This study examined arm and leg coordination and propulsion during the flat breaststroke in nine elite male and eight elite female swimmers over three race paces (200?m, 100?m and 50?m). Coordination was expressed using four temporal gaps (T1, T2, T3, T4), which described the continuity between the propulsive phases of the limbs, as recorded on a video device (50 Hz). Glide duration was denoted T1, the time between the beginning of arm and leg recovery was denoted T2, the time between the end of arm and the leg recovery was denoted T3, and the time between 90° of flexion during arm recovery and 90° during leg recovery was denoted T4. Using these temporal gaps, four stroke phases (propulsion, glide, recovery and leg insweep) could be followed over a complete arm and leg stroke. The total duration of arm and leg propulsion was assessed by a new index of flat breaststroke propulsion (IFBP). Velocity, stroke rate and stroke length were also calculated for each pace. The elite swimmers showed short T2, T3 and T4; moreover, T1 decreased when the pace increased. Expertise in the flat breaststroke was thus characterized by synchronized arm and leg recoveries and increased continuity in the arm and leg propulsions with increasing velocity. Differences between the sexes in the spatio-temporal parameters were possibly due to anthropometric differences (the men were heavier, older and taller than the women) and different motor organization linked to arm and leg coordination (shorter T3, body glide and body recovery, and greater body propulsion and higher IFBP in the men). The men's propulsive actions showed greater continuity, particularly in the sprint. The best men adopted a superposition coordination and thus had the ability to overcome very great active drag. Temporal gap measurement and the IFBP are practical indicators of arm and leg coordination and propulsion that can be exploited by coaches and swimmers to increase the continuity between propulsive actions during the flat breaststroke.     

Engineering ethics at the Catholic University of Lille (France): Research and teaching in a European context

This paper relates to the development of non-technical education (and to ethics) in engineering curricula in Europe and particularly in France. Two projects being followed at the Centre de recherche en éthique de l'ingénieur (CREI) at the Catholic University of Lille (France) are discussed: the first is an engineering ethics course which has been running for 6 years in a state engineering school, where there is a strong emphasis on analysing the ethical issues of the students' first work experience. The second has to do with the writing of a European handbook on engineering ethics which gives us good insight into how engineering ethics as a discipline is shaped by the cultural background of those who develop it (dominant philosophical tradition, religious background, the way the engineering profession is organized and education). Two main approaches seem to be prevalent in Europe today: the first relates to professional ethics as discussed in the USA since the 1950s, the second relates to a new discipline that is developing in Europe, that of the ethics of technology.     

Kinematic analysis of butterfly turns of international and national swimmers

The aims of this study were (1) to evaluate the different turn phases of 200 m butterfly during competition in a 50 m pool, (2) to determine if wall contact times are related to swim speed and (3) to compare the turn variables of a European Champion with other swimmers. In the first part of the study, we assessed the turns of 22 swimmers ranked in three groups according to 200 m butterfly swim performance (fast group = 121.73+/-3.03 s, intermediate group = 126.25+/-0.55 s, slow group = 129.24+/-2.30 s). Two turn times were recorded: the first before the turn (i.e. the time it takes the swimmer's head to reach the wall from 7.5 m away) and the second after the turn (i.e. the time from the wall to the point at which the swimmer's head passes 7.5 m away). The third turn was performed significantly faster by the fast group than by the slow group, both before (P< 0.01) and after (P< 0.02) the turn. In the second part of the study, objectives (2) and (3) were evaluated among 15 swimmers based on a specific protocol. Three cameras (50 Hz) simultaneously recorded the turn; these were placed above the water 10 m before the wall, 5 m before and just above the wall. Longer contact times of the feet on the wall were associated with a faster push-off speed (P < 0. 02). The European Champion achieved an improved contact time while performing a rapid pull-out speed.     

Effect of expertise on butterfly stroke coordination

The aim of this study was to compare the arm-to-leg coordination in the butterfly stroke of three groups of male swimmers of varying skill (10 elite, 10 non-elite, and 10 young swimmers) at four race paces (400-m, 200-m, 100-m, and 50-m paces). Using qualitative video analysis and a hip velocity-video system (50 Hz), key events of the arm and leg movement cycles were defined and four-point estimates of relative phase were used to estimate the arm-to-leg coordination between the propulsive (pull and push of arms and downward movement of leg undulation) and non-propulsive phases (entry, catch, and recovery of arms and upward movement of leg undulation). With increasing race pace, the velocity, stroke rate, and synchronization between the arm and leg key points also increased, indicating that velocity and stroke rate may operate as control parameters. Finally, these changes led to greater continuity between the propulsive actions, which is favourable for improving the swim velocity, suggesting that coaches and swimmers should monitor arm-to-leg coordination.     

The effect of combined self- and expert-modelling on the performance of the double leg circle on the pommel horse

In this study, we investigated whether video modelling can enhance gymnasts' performance of the circle on a pommel horse. The procedure associated expert-modelling with self-modelling and quantitative performance analysis. Sixteen gymnasts were randomly assigned to one of two groups: (1) a modelling group, which received expert- and self-modelling, and performance feedback, or (2) a control group, which received no feedback. After five sessions of training, an analysis of variance with repeated measures indicated that the gains in the back, entry, front, and exit phases of the circle were greater for the modelling group than for the control group. During the training sessions, the gymnasts in the modelling group improved their body segmental alignment during the back phase more quickly than during the other phases. As predicted, although both groups performed the same number of circles (300 in 5 days, with 10 sequences of 6 circles), the modelling group improved their body segmental alignment more than the control group. It thus appears that immediate video modelling can help to correct complex sports movements such as the circle performed on the pommel horse. However, its effectiveness seemed to be dependent on the complexity of the phase.