Introduction Identification of the seat features that could improve driving experience is a main issue for automotive companies. Objective Long duration real driving sessions were performed to assess the effect of three seats (soft-S-1, firm-S-2 and suspended-S-3) on perceived discomfort and neuromuscular fatigue (NMF). Materials & methods For each seat, the muscular activity of bilateral Trapezius Descendens (TD), Erector Spinae (ES) and Multifidus (MF) muscles of twenty-one participants was recorded during real driving sessions of 3-hours each lasting approximately 3 hours and following the same itinerary. During each driving session, participants were also regularly asked to self-evaluate their level of whole-body and local discomfort. In addition, an endurance static test (EST) was performed before (ESTpre) and after (ESTpost) each driving session to assess the seat effect on physical capacity. Results Whole-body discomfort increased with driving time for all seats, but this increase became significant latter for S-3. The highest scores of local discomfort occurred for neck and lower back. Contrary to S-1 and S-2, the duration of ESTpost was not significantly lower compared to ESTpre with the S-3. Interestingly, muscular activity of S-1 remained stable throughout the driving task which could be attributed to sustained muscular contraction, while muscular recruitment adjustments occurred for S-2 and S-3 from 1H00 of driving. This muscular compensation concerns mostly the right side for S-2 and S-3 but with different profiles. On the left side, the muscular adjustments concern only the MF with S-2 and the ES with S-3. Conclusion Overall, our results demonstrated that S-3 could be considered as the most suitable seat to delay discomfort and NMF appearance.

Prolonged driving under real conditions can entail discomfort linked to driving posture, seat design features, and road properties like whole-body vibrations (WBV). This study evaluated the effect of three different seats (S-1 = soft; S-2 = firm; S-3 = soft with suspension system) on driver's sitting behavior and perceived discomfort on different road types in real driving conditions. Twenty-one participants drove the same 195 km itinerary alternating highway, city, country, and mountain segments. Throughout the driving sessions, Contact Pressure (CP), Contact Surface (CS), Seat Pressure Distribution Percentage (SPD%) and Repositioning Movements (RM) were recorded via two pressure mats installed on seat cushion and backrest. Moreover every 20 minutes, participants rated their whole-body and local discomfort. While the same increase in whole-body discomfort with driving time was observed for all three seats, S-3 limited local perceived discomfort, especially in buttocks, thighs, neck, and upper back. The pressure profiles of the three seats were similar for CP, CS and RM on the backrest but differed on the seat cushion. The soft seats (S-1 & S-3) showed better pressure distribution, with lower SPD% than the firm seat (S-2). All three showed highest CP and CS under the thighs. Road type also affected both CP and CS of all three seats, with significant differences appearing between early city, highway and country segments. In the light of these results, automotive manufacturers could enhance seat design for reduced driver discomfort by combining a soft seat cushion to reduce pressure peaks, a firm backrest to support the trunk, and a suspension system to minimize vibrations.

Osteoarthritis (OA) is a common degenerative disease whose early management includes promising mechanical treatments. New treatments are initially validated using an animal model in which OA is induced. The MMT (mechanical induction) and MIA (chemical induction) models of OA induction are widespread, but their use to generate early OA is poorly documented. We analyzed and compared early-stage knee OA-induction via these two methods in 16 rats divided into two groups. After 4 weeks of induction, the knees were sampled and studied using both histology (Toluidine Blue and Sirius Red) and surface topology, an innovative technique for characterizing osteoarthritic cartilage. The Mankin-modified score confirms that the two OA-induction models evolved at the same speed. At this early stage, the two models can be differentiated morphologically, although no significant differences were revealed by either cellularity or birefringence analysis. However, the topological analysis generated two forms of quantitative data, the deformation ratio and the cohesion index, that differentiated between the two groups. Thus, the early-stage OA induced by these two models is revealed to differ. The patterns of cartilage damage induced point to MMT as the better choice to assess mechanical approaches to clinical OA treatment.

Arthroplasty is a surgical procedure to restore the function of the joint of patient suffering from knee osteoarthritis. However, postoperative functional deficits are reported even after a rehabilitation program. In order to determine the origin of functional deficits of patient suffering from knee osteoarthritis and total knee arthroplasty, we developed a rodent model including a chemically-induced-osteoarthritis and designed a knee prosthesis (Ti6Al4V/PEEK) biomechanically and anatomically adapted to rat knee joint. Dynamic Weight-Bearing, gait kinematics, H-reflex from vastus medialis muscle and activities from metabosensitive III and IV afferent fibers in femoral nerve were assessed at 1 and 3 months post-surgery. Results indicate that knee osteoarthritis altered considerably the responses of afferent fibers to their known activators (i.e., lactic acid and potassium chloride) and consequently their ability to modulate the spinal sensorimotor loop, although, paradoxically, motor deficits seemed relatively light. On the contrary, results indicate that, after the total knee arthroplasty, the afferent responses and the sensorimotor function were slightly altered but that motor deficits were more severe. We conclude that neural changes attested by the recovery of the metabosensitive afferent activity and the sensorimotor loop were induced when a total knee replacement was performed and that these changes may disrupt or delay the locomotor recovery.

Prolonged driving could induce neuromuscular fatigue and discomfort since drivers have little opportunity to adjust their position. However, better car seat design could play a major role in limiting these effects. This study compared the effect of two different seats (S - soft and F - firm) on neuromuscular fatigue and driver's perceived discomfort during prolonged driving, also assessing the effect of different road types on neuromuscular activity. Twenty participants performed two 3-h driving sessions, one for each seat, on a static simulator. Every 20 min, participants self-evaluated their level of whole-body and individual body-area discomfort. Surface electromyography (sEMG) was recorded for eight muscles including Trapezius descendens (TD), Erector spinae longissimus (ESL), Multifidus (MF), Vastus lateralis (VL) and Tibialis anterior (TA) throughout the driving sessions. Moreover, an endurance static test (EST) was performed prior to and after each driving session. Whole-body discomfort increased with time with both seats, but no difference in discomfort scores was observed between seats throughout the driving sessions. The highest discomfort scores were for neck and lower back areas with both seats. Neuromuscular fatigue was revealed by a shorter endurance time in post-driving EST for both seats. EMG recordings showed different neuromuscular fatigue profiles for the two seats, with earlier onset of fatigue for S. Despite the lack of difference in perceived discomfort level, the two seats have different impacts: the softness of S induces greater activity of the lower back muscles, while F offers greater support for the lower back.

Surface treatments are considered as a good alternative to increase biocompatibility and the lifetime of Ti-based alloys used for implants in the human body. The present research reports the comparison of bare and modified Ti6Al4V substrates on hydrophilicity and corrosion resistance properties in body fluid environment at 37 °C. Several surface treatments were conducted separately to obtain either a porous oxide layer using nanostructuration (N) in ethylene glycol containing fluoride solution, or bulk oxide thin films through heat treatment at 450 °C for 3 h (HT), or electrochemical oxidation at 1 V for 3 h (EO), as well as combined treatments (N-HT and N-EO). In-situ X-ray diffraction and ex-situ transmission electron microscopy have shown that heat treatment gave first rise to the formation of a 30 nm thick amorphous layer which crystallized in rutile around 620 °C. Electrochemical oxidations gave rise to a 10 nm thick amorphous film on the top of the surface (EO) or below the amorphous nanotube layer (N-EO). Dual treated samples presented similar results with a more stable behavior for N-EO. Finally, for both corrosion and hydrophilicity points of view, the new combined treatment to get a total amorphous N-EO sample seems to be the best and even better than the partially crystallized N-HT sample.

Despite the worldwide high prevalence of total joint arthroplasty (TJA), life expectancy of prosthesis remains limited by mechanical and chemical constraint which promote wear debris production, surrounding tissues damage and finally prosthesis loosening. Such results could be amplified by neuro-myoelectrostimulation (NMES; widely used to reduce neuromuscular deficits observed following TJA surgery). It was previously described in an in vivo experiment that interactions between NMES and Ti6Al4V implant are deleterious for both implant and surrounding muscles. The purpose of the present study was to compare the biocompatibility of four common orthopedic biomaterials, two metallic (Ti6Al4V, CrCo) and two nonmetallic (PEEK, Al2 O3 ) alloys, fixed on rat tibial crest in which the surrounding muscles were electrostimulated. Muscle cell death rate was not found significantly increased, with or without electrical stimulation for nonmetallic implants. Contrary to Ti6Al4V alloy, the CrCo implant did not induce destruction of the surrounding muscle. However, cell viability decreased for both metallic alloys when NMES was applied but within a greater significant extent for Ti6Al4V implant. Otherwise, when NMES was applied, implant-to-bone adhesion significantly decreased for Ti6Al4V while no significant difference was found for PEEK, Al2 O3 , and CrCo. Statistical analyses reveal also a lesser adhesion strength for Ti6Al4V compared with CrCo when NMES was applied. Selecting the most suitable material in term of biocompatibility remains a major concern and non-metallic materials seems to be more appropriated in regard to electrical currents used for post TJA care. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 106B: 1156-1164, 2018.

Plantar fasciitis is a cause of chronic pain under the heel and bottom of the foot. One of the treatments to reduce pain consists of using plantar orthoses to address specific imbalances during foot placement or gait. The aim of the present study was to determine if reduction of pain with a treatment based on plantar orthoses is related to changes in reflexes and muscle activity of the muscles of the lower limbs. Ten patients (51.0±3.5 years, 76.0±2.38 kg, 171.9±1.8 cm, 3 women and 7 men) with plantar fasciitis for less than 1 year were followed up during nine weeks. Soleus M, H, and V waves recorded at rest and during voluntary contraction and Root Mean Square-Electromyogram from four leg muscles recorded during walking and static position were analyzed in patients before and 3, 6, and 9 weeks after wearing orthoses. Pain level and gait and posture parameters were also analyzed. Results were compared to five healthy participants exhibiting no pain (30.6±2.1 years, 60.0±3.5 kg, 167.0±3.4 cm, 3 women and 2 men). Results indicated that pain was significantly reduced after 3 weeks. Hmax/Mmax and Hsup/Msup ratios were significantly higher and MHmax/Mmax and MHsup/Msup were significantly lower in healthy participants compared to patients with plantar fasciitis. No difference in the V/Msup ratio was found between groups. Furthermore, all other measured locomotor, stabilometric, and electromyographic parameters remained unchanged throughout the entire protocol. The reduction of pain is not related to change in neural activity suggesting that, after 9 weeks of wearing plantar orthoses, patients are not yet cured and return to physical activity should be delayed.

Nowadays, salt consumption appears to be drastically above the recommended level in industrialized countries. The health consequences of this overconsumption are heavy since high-salt intake induces cardiovascular disease, kidney dysfunction, and stroke. Moreover, harmful interaction may also occur with orthopaedic devices because overconsumption of salt reinforces the corrosive aspect of biological tissues and favors bone resorption process. In the present study, we aimed to assess the in vivo effect of three weeks of a high-salt diet, associated (or not) with two weeks of the neuro-myoelectrostimulation (NMES) rehabilitation program on the biocompatibility of four biomaterials used in the manufacture of arthroplasty implants. Thus, two non-metallic (PEEK and Al2O3) and two metallic (Ti6Al4V and CrCo) compounds were implanted in the rat tibial crest, and the implant-to-bone adhesion and cell viability of two surrounded muscles, the Flexor Digitorum (FD) and Tibialis Anterior (TA), were assessed at the end of the experiment. Results indicated lower adhesion strength for the PEEK implant compared to other biomaterials. An effect of NMES and a high-salt diet was only identified for Al2O3 and Ti6Al4V implants, respectively. Moreover, compared to a normal diet, a high-salt diet induced a higher number of dead cells on both muscles for all biomaterials, which was further increased for PEEK, Al2O3, and CrCo materials with NMES application. Finally, except for Ti6Al4V, NMES induced a higher number of dead cells in the directly stimulated muscle (FD) compared to the indirectly stimulated one (TA). This in vivo experiment highlights the potential harmful effect of a high-salt diet for people who have undergone arthroplasty, and a rehabilitation program based on NMES.

Knee pain is one of the most common lower leg complaints. It is often treated with plantar orthoses to provide cushioning and correct locomotion, imbalances of the foot, and postural deficits. However, the published scientific data are poor concerning the mechanisms involved in pain reduction after wearing foot orthoses, and, to the best of our knowledge, no trial has investigated the mid-term effectiveness. The aim of the present study was to evaluate the effectiveness of foot orthoses according to sound biomechanical principles in the treatment of knee pain. Attention was mainly focused on changes in the central control strategies. Fifteen subjects were included in the protocol. The patients with knee pain were compared with healthy participants (control group) exhibiting no knee pain. In the patients with knee pain, pain perception, dynamic analysis of the gait, stabilometry, the soleus Hoffmann reflex at rest and during voluntary contraction, and V-wave were measured before and 3, 6, and 9 weeks after wearing orthoses. In the control group (n = 5), the same parameters were recorded at 0, 3, 6, and 9 weeks, but the subjects had not worn orthoses. In the patient group (n = 10), the results indicated that pain had significantly decreased from the third week onward, although the parameters of gait and stabilometry remained unchanged. From the sixth week, the soleus Hoffmann reflex during voluntary contraction wave was significantly reduced, suggesting an increase in motoneuronal presynaptic inhibition by non-nociceptive afferents. The V-wave amplitude increased throughout the 9 weeks of the experiment, suggesting a progressive increase in corticospinal and/or extrapyramidal descending pathway inputs, probably due to pain reduction. In the control group, no change was observed throughout the experimental sessions. Our data indicated that foot orthoses relieved patients’ knee pain and reduced the descending motor inhibition. Changes in spinal modulation could contribute to a better quality of life. However, this treatment failed to change the altered gait, despite changes in spinal and supraspinal modulation.

Although discrete auditory stimuli have been found useful for emergency braking, the role of continuous speed-related auditory feedback has not been investigated yet. This point may though be of importance in electric vehicles in which acoustic cues are drastically changed. The present study addressed this question through two experiments. In experiment 1, 12 usual drivers were exposed to naturalistic auditory feedback mimicking those issued from electric cars, while facing dynamic visual scenes in a 3D driving simulator. After being passively travelled up to a sustained constant speed, subjects had to stop their car in front of a traffic light that unexpectedly turned to red. Modifications of the speed related auditory feedback did not impact braking initiation and regulation. In experiment 2, synthesized auditory feedback based on the Shepard-Risset glissando was provided to a new sample of 15 usual drivers in the same task. Pitch variations of this acoustic stimulus, although not scaled to an absolute speed, were manipulated as a function of visual speed changes. Changing the mapping between pitch variations of the synthesized auditory feedback and visual speed changes induced adjustments on braking which depended on acceleration/deceleration feedback. These findings stressed the importance of the acoustic content and its dynamics for car speed control. (C) 2016 Elsevier Ltd. All rights reserved.

Aim of the study High-salt consumption has been widely described as a risk factor for cardiovascular, renal and bone functions. In the present study, the extent to which high-salt diet could influence Ti6Al4V implant surface characteristic, its adhesion to rat tibial crest, and could modify muscle cell viability of two surrounding muscles, was investigated in vivo. These parameters have also been assessed following a NMES (neuro-myoelectrostimulation) program similar to that currently used in human care following arthroplasty. Results After a three-week diet, a harmful effect on titanium implant surface and muscle cell viability was noted. This is probably due to salt corrosive effect on metal and then release of toxic substance around biologic tissue. Moreover, if the use of NMES with high-salt diet induced muscles damages, the latter were higher when implant was added. Unexpectedly, higher implant-to-bone adhesion was found for implanted animals receiving salt supplementation. Conclusion Our in vivo study highlights the potential dangerous effect of high-salt diet in arthroplasty based on titanium prosthesis. This effect appears to be more important when high-salt diet is combined with NMES.

PURPOSEThis study was designed to highlight the functional impairments and the neuromuscular adaptations following an anterior cruciate ligament (ACL) injury in rat.METHODSAnimals were randomized into five groups: control (n = 8), SHAM-1wk (n = 6), SHAM-5wk (n = 8), ACL-1wk (n = 8), and ACL-5wk (n = 8). Rats performed three behavioral tests (the ladder-climbing test, the dynamic weight-bearing distribution, and the dynamic function assessment during locomotion) before the surgery (PRE) and at day (D) 1 (D1), D2, D3, D5, D7, D14, D21, D28, and D35 after ACL transection. Electrophysiological recordings, including responses of muscle metabosensitive afferents to a combination of specific chemical activators, namely, lactic acid and potassium chloride, and the quadriceps motor reflex activity, were performed at D7 (ACL-1wk) and at D35 (SHAM and ACL-5wk).RESULTSBehavioral results indicated an alteration of both weight-bearing distribution over the four paws and fine motor skills (ladder-climbing test) for the injured animals. Maximal motor reflex amplitude was higher after ACL injury compared with the other groups. Moreover, the regulation of motor reflex induced by metabosensitive afferents was perturbed from the first week after ACL transection, without affecting the response of these muscle afferents to their specific stimuli.CONCLUSIONSThis study brings some new evidence about the motor dysfunctions and spinal adaptations after ACL rupture in rats. Such information might be needed for assessing, in our animal model, the effectiveness of the diverse functional rehabilitation strategies used in human clinic after knee injuries.

The present review is focused on neural mechanisms responsible of group III and IV muscle afferent actions on central motor drive during physical exercise in both healthy and pathological populations. It seems that these mechanisms contribute to improve muscle performance by regulating the peripheral fatigue development and by avoiding excessive muscle impairments. Therefore, a great deal of attention is paid to their influences on motor unit activation during fatiguing exercise both in human and animal models. Recent evidence indicated that these afferents from a given active muscle could contribute to regulate the motor activity of the homonymous as well as surrounding skeletal muscles by acting at both spinal and supraspinal levels. In addition, given that the recovery of the sensory feedback plays a key role in the improvement of motor function following numerous neuromuscular traumas, the role of these afferents in preclinical and clinical situations is also explored in animal and human models. It is supposed that studying the motor and autonomic functions of group III and IV afferents might help healthcare professionals in the future to find appropriate treatments and rehabilitation programs.

BACKGROUNDHelicopter pilots are involved in a complex multitask activity, implying overuse of cognitive resources, which may result in piloting task impairment or in decision-making failure. Studies usually investigate this phenomenon in well-controlled, poorly ecological situations by focusing on the correlation between physiological values and either cognitive workload or emotional state. This study aimed at jointly exploring workload induced by a realistic simulated helicopter flight mission and emotional state, as well as physiological markers.METHODThe experiment took place in the helicopter full flight dynamic simulator. Six participants had to fly on two missions. Workload level, skin conductance, RMS-EMG, and emotional state were assessed.RESULTSJoint analysis of psychological and physiological parameters associated with workload estimation revealed particular dynamics in each of three profiles. 1) Expert pilots showed a slight increase of measured physiological parameters associated with the increase in difficulty level. Workload estimates never reached the highest level and the emotional state for this profile only referred to positive emotions with low emotional intensity. 2) Non-Expert pilots showed increasing physiological values as the perceived workload increased. However, their emotional state referred to either positive or negative emotions, with a greater variability in emotional intensity. 3) Intermediate pilots were similar to Expert pilots regarding emotional states and similar to Non-Expert pilots regarding physiological patterns.DISCUSSIONOverall, high interindividual variability of these results highlight the complex link between physiological and psychological parameters with workload, and question whether physiology alone could predict a pilot's inability to make the right decision at the right time.

Electrical currents have deleterious effects on biomedical metallic implants. However, following arthroplasty, neuro-myoelectrostimulation (NMES) is often used in patient rehabilitation. Such a rehabilitation technique could compromise patient recovery through deleterious effects on metallic alloys and biological tissues. The purpose of our study was to assess the effects of NMES on a Ti6Al4V implant placed in a rat tibial crest and the surrounding muscle tissues. This in vivo study allowed to bring to the fore the prosthesis behavior under mechanical and electromagnetic loads induced by NEMS stimulation. After 3 weeks, implant-to-bone adhesion significantly decreased in stimulated animals compared with nonstimulated animals. Surface mapping indicated titanium implant degradation after NMES. Furthermore, NMES alone did not induce muscle damage contrary to that found in implanted animals. The muscle damage rate was significantly higher in implanted and stimulated animals compared with implanted-only animals. It seems obvious that rehabilitation programs using the NMES technique could induce early deterioration of biomaterial employed for surgical implants. Clinicians should reconsider the use of NMES as a rehabilitation technique for patients with titanium prostheses. (c) 2014 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 103B: 1594-1601, 2015.

Despite growing interest over the decades, the question of estimating cognitive workload of operators involved in complex multitask operations, such as helicopter pilots, remains a key issue. One of the main difficulties facing workload inference models is that no single specific indicator of workload exists, so that multiple sources of information have to be inputted to the model. The question then arises as to the nature and the quantity of features to be used for increasing model performance. In this research, done in cooperation with Eurocopter, the effectiveness of physiological, psychological, and cognitive features for estimating helicopter pilots' workload was systematically investigated, using Bayesian networks (BNs). The study took place in two different contexts: a constrained laboratory situation with low ecological validity and a more realistic and challenging situation relying on virtual reality. The constrained conditions of the laboratory study allowed us for testing various combinations of entropy-based physiological, cognitive, and affect features as inputs of BN models. These three different kinds of features are shown to carry complementary information that can be used with advantage by the model. The results also suggest that increasing the number of physiological inputs improves the model performance. The second study aimed at challenging some of these conclusions in a more ecological context, by using the NH90 full-flight simulator of the Helisim company. The results emphasize the problem of accessing the ground truth, as well as the need for an efficient feature selection or extraction step prior to the classification step.