Saint-Georges-de-Mons, France
Saint-Georges-de-Mons, France

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Theurel J.,Aix - Marseille University | Theurel J.,University of Burgundy | Crepin M.,Aix - Marseille University | Foissac M.,Oxylane Research | Temprado J.J.,Aix - Marseille University
Scandinavian Journal of Medicine and Science in Sports | Year: 2012

The present study aimed to test the influence of the pedalling technique on the occurrence of muscular fatigue and on the energetic demand during prolonged constant-load cycling exercise. Subjects performed two prolonged (45min) cycling sessions at constant intensity (75% of maximal aerobic power). In a random order, participants cycled either with their preferred technique (PT) during one session or were helped by a visual force-feedback to modify their pedalling pattern during the other one (FB). Index of pedalling effectiveness was significantly (P<0.05) improved during FB (41.4±5.5%); compared with PT (36.6±4.1%). Prolonged cycling induced a significant reduction of maximal power output, which was greater after PT (-15±9%) than after FB (-7±12%). During steady-state FB, vastus lateralis muscle activity was significantly (P<0.05) reduced, whereas biceps femoris muscles activities increased compared with PT. Gross efficiency (GE) did not significantly differ between the two sessions, except during the first 15min of exercise (FB: 19.0±1.9% vs PT: 20.2±1.9%). Although changes in muscular coordination pattern with feedback did not seem to influence GE, it could be mainly responsible for the reduction of muscle fatigue after prolonged cycling. © 2011 John Wiley & Sons A/S.

Goislard De Monsabert B.,Aix - Marseille University | Rossi J.,Aix - Marseille University | Rossi J.,Oxylane Research | Berton E.,Aix - Marseille University | Vigouroux L.,Aix - Marseille University
Medicine and Science in Sports and Exercise | Year: 2012

PURPOSE: The aim of this study was to estimate muscle and joint forces during a power grip task. Considering the actual lack of quantification of such internal variables, this information would be essential for sports sciences, medicine, and ergonomics. This study also contributed to the advancement of scientific knowledge concerning hand control during power grip. METHODS: A specially designed apparatus combining both an instrumented handle and a pressure map was used to record the forces at the hand/handle interface during maximal exertions. Data were processed such that the forces exerted on 25 hand anatomical areas were determined. Joint angles of the five fingers and the wrist were also computed from synchronized kinematic measurements. These processed data were used as input of a hand/wrist biomechanical model, which includes 23 degrees of freedom and 42 muscles to estimate muscle and joint forces. RESULTS: Greater forces were applied on the distal phalanges of the long fingers compared with the middle and the proximal ones. Concomitantly, high solicitations were observed for FDP muscles. A large cocontraction level of extensor muscles was also estimated by the model and confirmed previously reported activities and injuries of extensor muscles related to the power grip. Quantifying hand internal loadings also resulted in new insights into the thumb and the wrist biomechanics. Output muscle tension ratios were all in smaller ranges than the ones reported in the literature. CONCLUSIONS: Including wrist and finger interactions in this hand model provided new quantification of muscle load sharing, cocontraction level, and biomechanics of the hand. Such information could complete future investigations concerning handle ergonomics or pathomechanisms of hand musculoskeletal disorders. Copyright © 2012 by the American College of Sports Medicine.

Chambon N.,Aix - Marseille University | Chambon N.,Oxylane Research | Delattre N.,Oxylane Research | Gueguen N.,Oxylane Research | And 2 more authors.
European Journal of Applied Physiology | Year: 2015

Methods: Twelve healthy male subjects ran with three shoes of different drops (0, 4, 8 mm) and barefoot on a treadmill and overground. Vertical ground reaction force (vGRF) (transient peak and loading rate) and lower limb kinematics (foot, ankle and knee joint flexion angles) were observed.Purpose: Minimalist running shoes are designed to induce a foot strike made more with the forepart of the foot. The main changes made on minimalist shoe consist in decreasing the height difference between fore and rear parts of the sole (drop). Barefoot and shod running have been widely compared on overground or treadmill these last years, but the key characteristic effects of minimalist shoes have been yet little studied. The purpose of this study is to find whether the shoe drop has the same effect regardless of the task: overground or treadmill running.Results: Opposite footwear effects on loading rate between the tasks were observed. Barefoot running induced higher loading rates during overground running than the highest drop condition, while it was the opposite during treadmill running. Ankle plantar flexion and knee flexion angles at touchdown were higher during treadmill than overground running for all conditions, except for barefoot which did not show any difference between the tasks.Conclusions: Shoe drop appears to be a key parameter influencing running pattern, but its effects on vGRF differ depending on the task (treadmill vs. overground running) and must be considered with caution. Unlike shod conditions, kinematics of barefoot condition was not altered by treadmill running explaining opposite conclusions between the tasks. © 2014, Springer-Verlag Berlin Heidelberg.

Filingeri D.,Loughborough University | Redortier B.,Oxylane Research | Hodder S.,Loughborough University | Havenith G.,Loughborough University
Skin Research and Technology | Year: 2015

Background/purpose: In the absence of humidity receptors in human skin, the perception of skin wetness is considered a somatosensory experience resulting from the integration of temperature (particularly cold) and mechanical inputs. However, limited data are available on the role of the temperature sense. Methods: Wet and dry stimuli at 4°C and 8°C above local skin temperature were applied on the back of seven participants (age 21 ± 2 years) while skin temperature and conductance, thermal and wetness perceptions were recorded. Results: Resting local skin temperature was always increased by the application of the stimuli (+0.5-+1.4°C). No effect of stimulus wetness was found on wetness perceptions (P > 0.05). The threshold (point '-2 slightly wet' on the wetness scale) to identify a clearly perceived wetness was never reached during any stimulations and participants did not perceive that some of the stimuli were wet. Overall, warm temperature stimuli suppressed the perception of skin wetness. Conclusion: We conclude that it is not the contact of the skin with moisture per se, but rather the integration of particular sensory inputs (amongst which coldness seems dominant) which drives the perception of skin wetness during the initial contact with a wet surface. © 2014 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.

Casanova R.,Aix - Marseille University | Borg O.,Aix - Marseille University | Borg O.,Oxylane Research | Bootsma R.J.,Aix - Marseille University
Journal of Sports Sciences | Year: 2015

Abstract: Using plain white and chequered footballs, we evaluated observers’ sensitivity to rotation direction and the effects of ball texture on interceptive behaviour. Experiment 1 demonstrated that the maximal distance at which observers (n = 8) could perceive the direction of ball rotation decreased when rotation frequency increased from 5 to 11 Hz. Detection threshold distances were nevertheless always larger for the chequered (decreasing from 47 to 28 m) than for the white (decreasing from 15 to 11 m) ball. In Experiment 2, participants (n = 7) moved laterally along a goal line to intercept the two balls launched with or without ±4.3 Hz sidespin from a 30-m distance. The chequered ball gave rise to shorter movement initiation times when trajectories curved outward (±6 m arrival positions) or did not curve (±2 m arrival positions). Inward curving trajectories, arriving at the same ±2 m distances from the participants as the non-curving trajectories, evoked initial movements in the wrong direction for both ball types, but the amplitude and duration of these reversal movements were attenuated for the chequered ball. We conclude that the early detection of rotation permitted by the chequered ball allowed modulation of interception behaviour without changing its qualitative characteristics. © 2015 Taylor & Francis.

Ouzzahra Y.,Loughborough University | Havenith G.,Loughborough University | Redortier B.,Oxylane Research
Journal of Thermal Biology | Year: 2012

Although several studies have compared thermal sensitivity between body segments, little is known on regional variations within body segments. Furthermore, the effects of exercise on the thermal sensation resulting from a cold stimulus remain unclear. The current experiment therefore aimed to explore inter- and intra-segmental differences in thermal sensitivity to cold, at rest and during light exercise. Fourteen male participants (22.3±3.1 years; 181.6±6.2cm; 73.7±10.3kg) were tested at rest and whilst cycling at 30% VO 2max. Sixteen body sites (front torso=6; back=6; arms=4) were stimulated in a balanced order, using a 20°C thermal probe (25cm 2) applied onto the skin. Thermal sensations resulting from the stimuli were assessed using an 11-point cold sensation scale (0=not cold; 10=extremely cold). Variations were found within body segments, particularly at the abdomen and mid-back where the lateral regions were significantly more sensitive than the medial areas. Furthermore, thermal sensations were significantly colder at rest compared to exercise in 12 of the 16 body sites tested. Neural and hormonal factors were considered as potential mechanisms behind this reduction in thermal sensitivity. Interestingly, the distribution of cold sensations was more homogenous during exercise. The present data provides evidence that thermal sensitivity to cold varies within body segments, and it is significantly reduced in most areas during exercise. © 2012 Elsevier Ltd.

Rossi J.,Aix - Marseille University | Rossi J.,Oxylane Research | Vigouroux L.,Aix - Marseille University | Barla C.,Oxylane Research | Berton E.,Aix - Marseille University
Scandinavian Journal of Medicine and Science in Sports | Year: 2014

The effects of tennis racket grip size on the forces exerted by muscles affecting lateral epicondylalgia (LE) were assessed in this study. Grip forces and joint moments applied on the wrist were quantified under three different handle size conditions, with and without induced muscle fatigue for intermediate and advanced players. The obtained experimental results were then used as input data of a biomechanical model of the hand. This simulation aimed to quantify the impact of grip strength modulation obtained in the experiment on the wrist extensor muscle forces. Our results show that there is an optimal grip diameter size defined as the handle inducing a reduced grip force during the stroke, in both fatigued and non-fatigued sessions. The results of the simulation suggested that extensor muscles were highly employed during forehand strokes, which confirms that the mechanical overuse of extensor tendons is a potential risk factor for tennis elbow occurrence. The handle grip size appeared to be a significant factor to reduce this extensor tendon loading. This suggests that grip size should be taken into account by players and designers in order to reduce the mechanical risk factors of overuse injury occurrence. © 2014 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.

Filingeri D.,Loughborough University | Fournet D.,Oxylane Research | Hodder S.,Loughborough University | Havenith G.,Loughborough University
Journal of Neurophysiology | Year: 2014

Although the ability to sense skin wetness and humidity is critical for behavioral and autonomic adaptations, humans are not provided with specific skin receptors for sensing wetness. It has been proposed that we “learn” to perceive the wetness experienced when the skin is in contact with a wet surface or when sweat is produced through a multisensory integration of thermal and tactile inputs generated by the interaction between skin and moisture. However, the individual roles of thermal and tactile cues and how these are integrated peripherally and centrally by our nervous system is still poorly understood. Here we tested the hypothesis that the central integration of coldness and mechanosensation, as subserved by peripheral A-nerve afferents, might be the primary neural process underpinning human wetness sensitivity. During a quantitative sensory test, we found that individuals perceived warm-wet and neutral-wet stimuli as significantly less wet than cold-wet stimuli, although these were characterized by the same moisture content. Also, when cutaneous cold and tactile sensitivity was diminished by a selective reduction in the activity of A-nerve afferents, wetness perception was significantly reduced. Based on a concept of perceptual learning and Bayesian perceptual inference, we developed the first neurophysiological model of cutaneous wetness sensitivity centered on the multisensory integration of cold-sensitive and mechanosensitive skin afferents. Our results provide evidence for the existence of a specific information processing model that underpins the neural representation of a typical wet stimulus. These findings contribute to explaining how humans sense warm, neutral, and cold skin wetness. © 2014 the American Physiological Society.

Filingeri D.,Loughborough University | Fournet D.,Oxylane Research | Hodder S.,Loughborough University | Havenith G.,Loughborough University
Journal of Applied Physiology | Year: 2014

Sensing skin wetness is linked to inputs arising from cutaneous cold-sensitive afferents. As thermosensitivity to cold varies significantly across the torso, we investigated whether similar regional differences in wetness perception exist. We also investigated the regional differences in thermal pleasantness and whether these sensory patterns are influenced by ambient temperature. Sixteen males (20 ± 2 yr) underwent a quantitative sensory test under thermoneutral [air temperature (Tair) = 22°C; relative humidity (RH) = 50%] and warm conditions (Tair = 33°C; RH = 50%). Twelve regions of the torso were stimulated with a dry thermal probe (25 cm2) with a temperature of 15°C below local skin temperature (Tsk). Variations in Tsk, thermal, wetness, and pleasantness sensations were recorded. As a result of the same cold-dry stimulus, the skin-cooling response varied significantly by location (P = 0.003). The lateral chest showed the greatest cooling (-5 ± 0.4°C), whereas the lower back showed the smallest (-1.9 ± 0.4°C). Thermal sensations varied significantly by location and independently from regional variations in skin cooling with colder sensations reported on the lateral abdomen and lower back. Similarly, the frequency of perceived skin wetness was significantly greater on the lateral and lower back as opposed to the medial chest. Overall wetness perception was slightly higher under warm conditions. Significantly more unpleasant sensations were recorded when the lateral abdomen and lateral and lower back were stimulated. We conclude that humans present regional differences in skin wetness perception across the torso, with a pattern similar to the regional differences in thermosensitivity to cold. These findings indicate the presence of a heterogeneous distribution of cold-sensitive thermoafferent information. Copyright © 2014 the American Physiological Society.

Chambon N.,Aix - Marseille University | Chambon N.,Oxylane Research | Delattre N.,Oxylane Research | Gueguen N.,Oxylane Research | And 2 more authors.
Gait and Posture | Year: 2014

Many studies have highlighted differences in foot strike pattern comparing habitually shod runners who ran barefoot and with running shoes. Barefoot running results in a flatter foot landing and in a decreased vertical ground reaction force compared to shod running. The aim of this study was to investigate one possible parameter influencing running pattern: the midsole thickness. Fifteen participants ran overground at 3.3ms-1 barefoot and with five shoes of different midsole thickness (0mm, 2mm, 4mm, 8mm, 16mm) with no difference of height between rearfoot and forefoot. Impact magnitude was evaluated using transient peak of vertical ground reaction force, loading rate, tibial acceleration peak and rate. Hip, knee and ankle flexion angles were computed at touch-down and during stance phase (range of motion and maximum values). External net joint moments and stiffness for hip, knee and ankle joints were also observed as well as global leg stiffness. No significant effect of midsole thickness was observed on ground reaction force and tibial acceleration. However, the contact time increased with midsole thickness. Barefoot running compared to shod running induced ankle in plantar flexion at touch-down, higher ankle dorsiflexion and lower knee flexion during stance phase. These adjustments are suspected to explain the absence of difference on ground reaction force and tibial acceleration. This study showed that the presence of very thin footwear upper and sole was sufficient to significantly influence the running pattern. © 2014 Elsevier B.V.

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