29 research outputs found
Regular changes in foot strike pattern during prolonged downhill running do not influence neuromuscular, energetics, or biomechanical parameters
No full textResearch has suggested that a high variability in foot strike pattern during downhill running is associated with lower neuromuscular fatigue of the plantar flexors (PF). Given the popularity of trail running, we designed an intervention study to investigate whether a strategy with regular changes in foot strike pattern during downhill running could reduce the extent of fatigue on neuromuscular, energetics and biomechanical parameters as well as increase an uphill time- to-exhaustion trial (TTE) performance. Fourteen experienced trail runners completed two interventional conditions (separated by 15 days) in a pseudo-randomized and counter-balanced order that consisted of 2.5-h of treadmill graded running with (switch condition) or without (control condition) a change between fore- and rear-foot strike pattern every 30 s during the downhill sections. Pre and Post, neuromuscular tests were performed to assess PF central and peripheral fatigue. Energy cost of running was assessed using an indirect calorimetry system and biomechanical gait parameters were acquired with an instrumented treadmill. TTE was performed after both the graded running conditions. There were not significant condition × time interactions (P ≥ 0.085) for any of the variables considered, and TTE was not different between the two conditions (P = 0.755). A deliberate strategy to alternate between foot strike patterns did not reduce the extent of fatigue during prolonged graded running. We suggest that it is not the ability to switch between foot strike patterns that minimises fatigue; rather the ability to adapt foot strike pattern to the terrain and therefore a better running technique
Pompée, les Italiens et le Sénat (de 62 à 49 av. J.-C.)
No full textThis paper attempts to show that Pompey, in order to face the opposition of many senators after his return fromthe East in 62 B. C., decided to encourage the incorporation of members of the Italian elite in the Roman Senate. Those senators, who do not belong to the roman aristocracy, allowed Pompey to obtain a durable support at the Curia during the last decade before the Civil Wars.Horvais Charles-Alban. Pompée, les Italiens et le Sénat (de 62 à 49 av. J.-C.). In: Vita Latina, N°195-196, 2017. pp. 5-21
Step Length and Grade Effects on Energy Absorption and Impact Attenuation in Running
No full textWe sought to examine the effect of step length manipulation on energy absorption and impact attenuation during graded running. Nineteen runners (10F, 9M) ran on an instrumented treadmill at three step lengths (preferred and ±10% preferred) at each of five grades (0°, ±5°, and ±10°) while 3D motion data were captured. Speed was held constant at 3.3 m/s and step length was manipulated by syncing cadence to a metronome. Manipulating step length altered energy absorption (p≤0.002) and impact attenuation (p<0.0001) across all grades. Energy absorption at the knee joint was most responsive to step length manipulations [∆ range (±10%SL- PrefSL)=0.076-0.126 J/kg, p<0.0001], followed by the ankle (∆ range=0.026-0.100 J/kg, p=0.001) and hip (∆ range=0.008-0.018 J/kg, p<0.006). Shortening step length reduced knee joint energy absorption at all grades with the smallest effect observed during uphill running (∆≥- 0.053 J/kg), while large reductions occurred during level (∆=-0.096 J/kg) and downhill running (∆≥-0.108 J/kg). Increasing step length resulted in greater knee joint energy absorption (p≤0.037) across all grades of running. Impact attenuation was greatest at long step lengths (∆=2.708) and lowest at short step lengths (∆=-2.061), compared to preferred. Overall, Step length influenced the energy absorption and impact attenuation characteristics of the lower extremity during level and graded running. Adopting a shorter step length may be a useful intervention to reduce knee joint loading, particularly during downhill or level running. Elongating step length placed a greater demand on the lower extremity joints, which may expedite the development of neuromuscular fatigue
Effects of Foot-Strike Pattern on Neuromuscular Function During a Prolonged Graded Run
No full textPurpose: To study whether, during typical-level running, non-rear-foot strikers (non-RFS) or rear-foot strikers (RFS) presented a similar or different extent of neuromuscular fatigue after a prolonged graded run. Methods: Sixteen experienced male trail runners (8 non-RFS and 8 RFS) performed a 2.5-hour treadmill graded running exercise. Before and after exercise, neuromuscular tests were performed to assess neuromuscular fatigue of the plantar flexors. Biomechanical gait parameters were acquired with an instrumented treadmill, and electromyographic activity of the lower-limb muscles was collected as an index of muscle activation. Results: There were no significant time × foot strike interactions for neuromuscular (all P ≥ .742), muscle activation (all P ≥ .157), or biomechanical (all P ≥ .096) variables. Conclusions: A dominant level running foot-strike pattern did not directly affect the extent of neuromuscular fatigue during a prolonged graded run. This suggests that no ideal running foot-strike pattern exists to minimize neuromuscular fatigue during prolonged-duration races wherein cumulative uphill and downhill segments are high, such as in trail running
Individual physiological responses to changes in shoe bending stiffness: a cluster analysis study on 96 runners
No full textInternational audienceBackground Shoe longitudinal bending stiffness is known to influence running economy (RE). Recent studies showed divergent results ranging from 3% deterioration to 3% improvement in RE when bending stiffness increases. The variability of these results highlights inter-individual differences. Thus, our purpose was to study the runner-specific metabolic responses to changes in shoe bending stiffness. Methods After assessing their maximal oxygen consumption ( VO2 max) and aerobic speed (MAS) during a first visit, 96 het- erogeneous runners performed two treadmill 5 min runs at 75% VO2 max with two different prototypes of shoes on a second day. Prototypes differed only by their forefoot bending stiffness (17 N/mm vs. 10.4 N/mm). RE and stride kinematics were recorded during each trial. A clustering analysis was computed by comparing the measured RE and the technical measurement error of our gas exchange analyzer to identify functional groups of runners, i.e., responding similarly to footwear interventions. ANOVAs were then computed on biomechanical and morphological variables to compare the functional groups. Results Considering the whole sample (n = 96), there was no significant difference in RE between the two conditions. Cluster 1 (n = 29) improves RE in the stiffest condition (2.7 ± 2.1%). Cluster 2 (n = 26) impairs RE in the stiffest condition (2.7 ± 1.3%). Cluster 3 (n = 41) demonstrated no change in RE (0.28 ± 0.65%). Cluster 1 demonstrated 1.7 km•h -1 greater MAS compared to cluster 2 (p = 0.014). ConclusionThe present study highlights that the effect of shoe bending stiffness on RE is runner-specific. High-level runners took advantage of increased bending stiffness, whereas medium-level runners did not. Finally, this study emphasizes the importance of individual response examination to understand the effect of footwear on runner's performance.</div
Effects of footwear and fatigue on running economy and biomechanics in trail runners
No full textPurpose: This study aimed to examine the effects of footwear and neuromuscular fatigue induced by short distance trail running (TR) on running economy (RE) and biomechanics in well-trained and traditionally shod runners.
Methods: RE, vertical and leg stiffness (Kvert and Kleg), as well as foot strike angle were measured from two 5-min treadmill running stages performed at a speed of 2.5 (with 10% grade, uphill running) and 2.77 m·s-1 (level running) before and after an 18.4-km TR exercise (approximately 90% of maximal heart rate) in runners wearing minimalist shoes (MS), MS plus added mass (MSm), or traditional shoes (TS). Maximal voluntary contraction torque of knee extensors and perceived muscle pain were also evaluated before and after TR.
Results: Maximal voluntary contraction values decreased after TR in all footwear conditions (P < 0.001), indicating the occurrence of neuromuscular fatigue. In the nonfatigued condition, runners exhibited a better RE only during level running in MS and MSm (i.e., combined effects of shoe mass and midsole geometry), in association with significant decreases in foot strike angle (P < 0.05). However, no significant difference in RE was observed between shod conditions after TR during either uphill or level running. Decreases in both Kvert/Kleg and foot strike angle were more pronounced during running in MS and MSm (P < 0.05) compared with TS, whatever the period. Calf pain increased after TR when wearing MS and MSm compared with TS (P < 0.05).
Conclusions: These findings indicated specific alterations in RE and biomechanics over time during the MS and MSm conditions compared with the TS condition. Future studies are warranted to evaluate the relationship between RE and footwear with fatigue in experienced minimally shod runners
PHOTOCATALYTIC TEXTILES: DEGRADATION OF BODY ODORS FOR SPORTSWEARS
No full textInternational @ EAU+CRL:EPU:CGUInternational audienceNon
Biomechanics of Graded Running: Part I - Stride Parameters, External Forces, Muscle Activations
No full textBiomechanical alterations with graded running have only been partially quantified, and the potential interactions with running speed remain unclear. We measured spatiotemporal parameters, ground reaction forces and leg muscle activations (EMG) in nineteen adults (10F/9M) running on an instrumented treadmills at 2.50, 3.33 and 4.17 m·s-1 and 0, ±5o, and ±10o. Step frequency illustrated a significant speed × grade interaction (P < 0.001) and was highest (+3%) at the steepest grade (+10o) and fastest speed (4.17 m·s-1) when compared to level running (LR) at the same speed. Significant interaction was also observed for ground reaction forces (all P ≤ 0.047). Peak ground reaction forces in the normal direction increased with running speed during downhill running (DR) only (+9% at -10o and 4.17 m·s-1). Impulse in the normal direction decreased at fastest speed and steepest DR (-9%) and uphill running (UR) (-17%) grades. Average normal loading rate increased and decreased at fastest speed and steepest DR (+52%) and UR (- 28%) grades, respectively. Negative parallel impulse increased and decreased at fastest speed and steepest DR (+166%) and UR (-90%), respectively. Positive parallel impulse decreased and increased at fastest speed and steepest DR (-75%) and UR (+111%), respectively. EMG showed comparable u-shaped curves across the grades investigated, although only a change in vastus lateralis and tibilias anterior activity was detectable at the steepest grades and fastest speed. Overall, running grade and speed significantly influences spatiotemporal parameters, ground reaction forces, and muscle activations
DEGRADATION OF BODY ODORS AND BACTERIA BY PHOTOCATALYTIC INSOLES
No full textInternational @ EAU+CRL:EPU:CGUInternational audienceUnder the effect of physical activity human body activate the mechanism of thermoregulation by producing sweat. The incipient sweat is inherently odorless but moisture and warmth promotes the proliferation of microorganisms on the surface of the skin. In particular, sportswears and shoes are suited environments for the growth of several bacteria and fungus. These microorganisms are responsible for the degradation of the compounds present in sweat and on the skin surface, in malodorous molecules. To address this problem of odor associated with perspiration, it seems appropriate to confer to textiles a function against micro-organisms and odorant molecules. The way explored in this work is the use of photocatalysis [1] in order to inhibit the growth of bacteria and to directly destroy the malodorous compounds. During this project, various catalysts and impregnation methods of the textile with catalysts were investigated. Optimized the amount of catalyst was determined in term of adhesion and performances. Their photocatalytic activities were first evaluated in aqueous phase with their performances on the formic acid photocatalytic oxidation. Then, an experimental setup, including an electronic nose, was designed to evaluate the photocatalytic activity in gas phase. The performances of these materials have been studied under UV light on the degradation of isovaleric acid, a model smelly compound. The efficiency of these materials under UV-A lamp and LEDs centered at a wavelength of 365 nm were compared and the photonic flux optimized. Complemently, the adhesion of the catalyst is evaluated by mechanical tests such as leaching (ISO 6330) or abrasion tests (ISO 12947-2). In parallel, bacteriological tests on the strain S.epidermidis, responsible for foot malodor, was performed using the ISO 20743 standard with and without photocatalysis. The influence of the exposition time and UV-A irradiation flux were studied on the degradation of this bacteria. Photocatalytic textiles have clearly shown an ability to degrade isovaleric acid in air and formic acid in water with a rate increasing with the increase of the quantity of titania deposited on the textile. The optimal coverage of photocatalyst and degradation rate have been determined in each case. These textiles also present antimicrobial activity after a few time under UV-A light and no effect on these bacteria in darkness, that could be consider as a proof of undestroying cutaneous flora. Reference [1]S. Silver, L.T. Phung, G. Silver, Journal of Industrial Microbiology & Biotechnology, 33 (2006) 627-634
