Ahlem Arfaoui

Visualizations of the flow around a swimmer in turbulent regime

Graphical abstract

Infrared Thermography in Sports Activity

The origin of infrared thermography comes in 1800 when William Herschel discovered thermal radiation, the invisible light later called infrared, but only in the mid-sixties infrared thermography became a technique of temperature cartography. He proved that this radiation, called infrared, followed the same law as visible light. Later, this phenomenon was connected with the laws of Planck and Stefan. The first detectors for this type of radiation, based on the principle of the thermocouple and thermopile called, were developed around 1830. In 1970, the first cameras appeared for commercial. The first models were made up of a technology-based pyroelectric tube with an optical IR instead of the classical elements. Today, these concepts have been improved with new technologies in electronics and computing. Infrared acquisition systems can arrive at very high frame rates. The major argument is whether infrared thermography can determine thermal variations to enable sufficient quantitative analyses. The creation of computerized systems using complex statistical data analysis, which ensure high quality results, and the enhancement of thermal sensitivity have increased the development of technology of infrared thermography.

Influence of a postural change of the swimmer's head in hydrodynamic performances using 3D CFD

This study deals with recent researches undertaken by the authors in the field of hydrodynamics of human swimming. The aim of this numerical study was to investigate the flow around the entire swimmers body. The results presented in this article focus on the combination of a 3D computational fluid dynamics code and the use of the k–ω turbulence model, in the range of Reynolds numbers representative of a swimming level varying from national to international competition. Emphasis is placed on the influence of a postural change of the swimmers head in hydrodynamic performances, which is directly related to the reduction of overall drag. These results confirm and complete those, less accurate, of a preliminary 2D study recently published by the authors and allow the authors to optimise the swimmers head position in underwater swimming.

Relationship between the gross efficiency and muscular skin temperature of lower limb in cycling: a preliminary study

In cycling, the gross efficiency (GE, %), defined as the ratio of the power output to the metabolic power (total energy expended according to the time), is one of the main determinants of the performance (Ettema et al. 2009; Jobson et al. 2012). In the literature, the average GE values reported vary from10% to 25% (Faria et al. 2005). In this range, close to 75–90% of metabolic energy is not converted to mechanical energy, but is used to maintain metabolic equilibrium (from adenosine triphosphate hydrolysis) and released as heat. Tomaintain the central temperature close to 37.58C, this produced energy must be dissipated using a thermoregulation process. Infrared thermography measurements can be used to analyse this thermoregulation process and understand the way one part of the energy dissipates (Arfaoui et al. 2012). The aim of this studywas to analyse the relationships that may exist between the GE and the muscular skin temperature of the lower limb in cycling.

Relationships between facial temperature changes, end-exercise affect and during-exercise changes in affect: A preliminary study

Abstract The present study was performed as an evaluation of the relationships between changes in facial temperature and self-reported pleasure–displeasure during an acute aerobic exercise bout. Ninety-two students performed a 10-minute long session of cycle ergometry at 80–85% of age-predicted maximal heart rate. Using infrared thermography and a single-item measure of pleasure–displeasure (the Feeling Scale, FS), facial temperature and the FS score were sampled at the beginning (Min1:00) and at the end of the exercise session (Min9:00). Statistical analyses revealed that cheek (but not forehead) temperature was higher at the end of the exercise bout compared to Min1:00 (it increased by about 5%). Change in cheek temperature was negatively related to end-exercise affect (β = −0.28, P < 0.001) and to during-exercise affective changes (β = −0.35, P < 0.001). No significant relationship with forehead temperature was found. Some of the possible reasons for this differential effect as well as theoretical and practical implications of our findings are discussed.

Effect of whole body vibration in energy expenditure and perceived exertion during intense squat exercise

PURPOSE The purpose of this study was to investigate the effect of whole body vibration in oxygen uptake during intense squatting exercise with an added weight and whole body vibration compared with the same exercise without vibration. METHODS Nine male sub- jects performed three trials of dynamic squatting with an additional load of 50% of their body weight during 3 min. One trial without vibration, one trial with the frequency of 40 Hz and amplitude of 2 mm and one trial with the frequency of 40 Hz and amplitude of 4 mm. RESULTS The results showed no difference between the three experimental trials in relative and absolute oxygen uptake. However, the metabolic power and energy expended in whole body vibration (2 mm) were significantly different from exercise without vibration. The data analysis also showed a significant difference in rating of perceived exertion with whole body vibration (4 mm) compared with the exercise without vibration. Results showed that the addition of vibration stimulus has an increase in the energy expenditure particularly with 40 Hz and 2 mm amplitude, suggesting that the high metabolic power during heavy resistance training could be increased by the addition of vibration stimulation. CONCLUSIONS Involuntary contractions generated by the vibration can be used by coaches to increase the intensity of heavy resistance training or to increase the energy expended during the workouts if the goal is a decrease of body mass.

Validation of a new whole-body cryotherapy chamber based on forced convection

Whole-body cryotherapy (WBC) and partial-body cryotherapy (PBC) are two methods of cold exposure (from -110 to -195°C according to the manufacturers). However, temperature measurement in the cold chamber during a PBC exposure revealed temperatures ranging from -25 to -50°C next to the skin of the subjects (using isolating layer placed between the sensor and the skin). This discrepancy is due to the human body heat transfer. Moreover, on the surface of the body, an air layer called the boundary layer is created during the exposure and limits heat transfer from the body to the cabin air. Incorporating forced convection in a chamber with a participant inside could reduce this boundary layer. The aim of this study was to explore the use of a new WBC technology based on forced convection (frontal unilateral wind) through the measurement of skin temperature. Fifteen individuals performed a 3-min WBC exposure at -40°C with an average wind speed of 2.3ms-1. The subjects wore a headband, a surgical mask, underwear, gloves and slippers. The skin temperature of the participants was measured with a thermal camera just before exposure, just after exposure and at 1, 3, 5, 10, 15 and 20min after exposure. Mean skin temperature significantly dropped by 11°C just after exposure (p<0.001) and then significantly increased during the 20-min post exposure period (p<0.001). No critically low skin temperature was observed at the end of the cold exposure. This decrease was greater than the mean decreases in all the cryosauna devices with reported exposures between -140°C and -160°C and those in two other WBC devices with reported exposures between -60°C and -110°C. The use of this new technology provides the ability to reach decreases in skin temperature similar to other technologies. The new chamber is suitable and relevant for use as a WBC device.

Swimming drafting simulation using a k − ω turbulence model

It is now well known that swimming drafting leads to a reduction in energy spent to overcome drag forces (friction, wave and pressure) and enhances gains time in competitive swimming (Chatard et al. 1998; Vennell et al 2006; Bixler et al. 2007; Brisswalter and Hausswirth 2008). In underwater swimming, the flow past a swimmer induces a trailing adverse pressure gradient area in its near wake. Swimming drafting behind and close to another swimmer consequently leads to a reduction in pressure drag induced by the lead swimmer. To our knowledge, the only study in literature dealing with numerical analysis of drafting in swimming is the one of Silva et al. (2008) using computational fluid dynamics (CFD) in two-dimensional (2D) configuration and where the distance between swimmers varied in the range 0.5 , d , 8.0m. This study differs from this work as far as it focuses on a shorter distance between swimmers (0 ,d , 0.5m) in touch with the experimental conclusions by Chatard and Wilson (2003).

Heat and Mass Transfer in External Boundary Layer Flows Using Nanofluids

The application of additives to base liquids in the sole aim to increase the heat transfer coefficient is considered as an interesting mean for thermal systems. Nanofluids, prepared by dispersing nanometer-sized solid particles in a base-fluid (liquid), have been extensively studied for more than a decade due to the observation of an interesting increase in thermal conductivity compared to that of the base-fluid (Xuan & Roetzel, 2000; Xuan & Li, 2000). Initially, research works devoted to nanofluids were mainly focussed on the way to increase the thermal conductivity by modifying the particle volume fraction, the particle size/shape or the base-fluid (Murshed et al., 2005; Wang & Mujumdar, 2007). Using nanofluids strongly influences the boundary layer thickness by modifying the viscosity of the resulting mixture leading to variations in the mass transfer in the vicinity of walls in external boundary-layer flows. Then, research works on convective heat transfer, with nanofluids as working fluids, have been carried out in order to test their potential for applications related to industrial heat exchangers. It is now well known that in forced convection (Maiga et al. 2005) as well as in mixed convection, using nanofluids can produce a considerable enhancement of the heat transfer coefficient that increases with the increasing nanoparticle volume fraction. As concerns natural convection, the fewer results published in the literature (Khanafer et al. 2003; Polidori et al., 2007; Popa et al., 2010; Putra et al. 2003) lead to more mixed conclusions. For example, recent works by Polidori et al. (2007) and Popa et al. (2010) have led to numerical results showing that the use of Newtonian nanofluids for the purpose of heat transfer enhancement in natural convection was not obvious, as such enhancement is dependent not only on nanofluids effective thermal conductivities but on their viscosities as well. This means that an exact determination of the heat transfer parameters is not warranted as long as the question of the choice of an adequate and realistic effective viscosity model is not resolved (Polidori et al. 2007, Keblinski et al. 2008). It is worth mentioning that this viewpoint is also confirmed in a recent work (Ben Mansour et al., 2007) for forced convection, in which the authors indicated that the assessment of the heat transfer enhancement potential of a nanofluid is difficult and closely dependent on the way the nanofluid properties are modelled. Therefore, the aim of this paper is to present theoretical models fully describing the natural and forced convective heat and mass transfer regimes for nanofluids flowing in semi-infinite geometries, i.e. external boundary layer flows along

Effects of a new selective compression garment on thermoregulation and muscular oscillations during exercise

The market for compression clothing has developed considerably to manage the demand of athletes who are looking for optimum conditions to improve their performance and recovery (Doan et al. 2003; Bringard et al. 2006). Some studies are worked on the compression influences on physiology, biomechanics or thermoregulation. The effects on cardiovascular and thermoregulatory strain remain equivocal. For thermal regulation, many studies point out interests of compression garments in sport (Doan et al. 2003). Nielsen and Endrusick (1989) have shown that different knitwear structure influences the cutaneous temperature. Iker et al. (2016) studied the effects of an upper body compression garment on thermoregulatory responses during cycling in a laboratory. No differences are showed in thermoregulatory effects during exercise. Some research showed that by wearing compressive equipment, the muscle compression allows a better muscular support and significantly reduce muscular oscillations (Lussiana et al. 2015). The aim of the present study was to determine the effects of a new selective compression garment on thermoregulation and muscular oscillations with the aim of creating a new selective compression shorts.