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Morin J.-B.,Jean Monnet University | Morin J.-B.,Laboratory of Exercise Physiology EA4338 | Samozino P.,Jean Monnet University | Samozino P.,Laboratory of Exercise Physiology EA4338 | And 5 more authors.
Journal of Biomechanics | Year: 2011

We investigated the changes in the technical ability of force application/orientation against the ground vs. the physical capability of total force production after a multiple-set repeated sprints series. Twelve male physical education students familiar with sprint running performed four sets of five 6-s sprints (24s of passive rest between sprints, 3min between sets). Sprints were performed from a standing start on an instrumented treadmill, allowing the computation of vertical (F V), net horizontal (F H) and total (F Tot) ground reaction forces for each step. Furthermore, the ratio of forces was calculated as RF=F HF Tot -1, and the index of force application technique (D RF) representing the decrement in RF with increase in speed was computed as the slope of the linear RF-speed relationship. Changes between pre- (first two sprints) and post-fatigue (last two sprints) were tested using paired t-tests. Performance decreased significantly (e.g. top speed decreased by 15.7±5.4%; P<0.001), and all the mechanical variables tested significantly changed. F H showed the largest decrease, compared to F V and F Tot. D RF significantly decreased (P<0.001, effect size=1.20), and the individual magnitudes of change of D RF were significantly more important than those of F Tot (19.2±20.9 vs. 5.81±5.76%, respectively; P<0.01). During a multiple-set repeated sprint series, both the total force production capability and the technical ability to apply force effectively against the ground are altered, the latter to a larger extent than the former. © 2011 Elsevier Ltd.

Morin J.-B.,Jean Monnet University | Morin J.-B.,Laboratory of Exercise Physiology EA4338 | Morin J.-B.,Laboratoire Of Physiologie Of Lexercice Ea4338 | Tomazin K.,Jean Monnet University | And 8 more authors.
European Journal of Applied Physiology | Year: 2012

We investigated the changes in constant velocity spring-mass behavior after high intensity sprint fatigue in order to better interpret the results recently reported after ultra-long distance (ULD) exercises. Our hypothesis was that after repeated sprints (RS), subjects may likely experience losses of force such as after ULD, but the necessity to modify their running pattern to attenuate the overall impact at each step (such as after ULD) may not be present. Eleven male subjects performed four sets of five 6-s sprints with 24-s recovery between sprints and 3 min between sets, on a sprint treadmill and on a bicycle ergometer. For each session, their running mechanics and spring-mass characteristics were measured at 10 and 20 km h -1 on an instrumented treadmill before and after RS. Two-way (period and velocity) ANOVAs showed that high-intensity fatigue did not induce any change in the constant velocity running pattern at low or high velocity, after both running and cycling RS, despite significant decreases (P<0.001) in maximal power (-27.1 ± 8.2% after running RS and -15.4 ± 11.5 % after cycling RS) and knee extensors maximal voluntary force (-18.8 ± 6.7 % after running RS and -15.0 ± 7.6 % after cycling RS). These results bring indirect support to the hypothesis put forward in recent ULD studies that the changes in running mechanics observed after ULD are likely not related to the decrease in strength capabilities, but rather to the necessity for subjects to adopt a protective running pattern. © Springer-Verlag 2011.

Giandolini M.,Jean Monnet University | Giandolini M.,Laboratory of Exercise Physiology EA4338 | Giandolini M.,Salomon SAS | Horvais N.,Salomon SAS | And 4 more authors.
European Journal of Applied Physiology | Year: 2013

Impact reduction has become a factor of interest in the prevention of running-related injuries such as stress fractures. Currently, the midfoot strike pattern (MFS) is thought as a potential way to decrease impact. The purpose was to test the effects of two long-term interventions aiming to reduce impact during running via a transition to an MFS: a foot strike retraining versus a low-drop/low-heel height footwear. Thirty rearfoot strikers were randomly assigned to two experimental groups (SHOES and TRAIN). SHOES progressively wore low-drop/low-heel height shoes and TRAIN progressively adopted an MFS, over a 3-month period with three 30-min running sessions per week. Measurement sessions (pre-training, 1, 2 and 3 months) were performed during which subjects were equipped with three accelerometers on the shin, heel and metatarsals, and ran for 15 min on an instrumented treadmill. Synchronized acceleration and vertical ground reaction force signals were recorded. Peak heel acceleration was significantly lower as compared to pre-training for SHOES (-33.5 ± 12.8 % at 2 months and -25.3 ± 18.8 % at 3 months, p < 0.001), and so was shock propagation velocity (-12.1 ± 9.3 %, p < 0.001 at 2 months and -11.3 ± 4.6 %, p < 0.05 at 3 months). No change was observed for TRAIN. Important inter-individual variations were noted in both groups and reported pains were mainly located at the shin and calf. Although it induced reversible pains, low-drop/low-heel height footwear seemed to be more effective than foot strike retraining to attenuate heel impact in the long term. © 2013 Springer-Verlag Berlin Heidelberg.

Giandolini M.,Jean Monnet University | Giandolini M.,Laboratory of Exercise Physiology EA4338 | Arnal P.J.,Jean Monnet University | Arnal P.J.,Laboratory of Exercise Physiology EA4338 | And 7 more authors.
European Journal of Applied Physiology | Year: 2013

Running-related stress fractures have been associated with the overall impact intensity, which has recently been described through the loading rate (LR). Our purpose was to evaluate the effects of four acute interventions with specific focus on LR: wearing racing shoes (RACE), increasing step frequency by 10 % (FREQ), adopting a midfoot strike pattern (MIDFOOT) and combining these three interventions (COMBI). Nine rearfoot-strike subjects performed five 5-min trials during which running kinetics, kinematics and spring-mass behavior were measured for ten consecutive steps on an instrumented treadmill. Electromyographic activity of gastrocnemius lateralis, tibialis anterior, biceps femoris and vastus lateralis muscles was quantified over different phases of the stride cycle. LR was significantly and similarly reduced in MIDFOOT (37.4 ± 7.20 BW s-1, -56.9 ± 50.0 %) and COMBI (36.8 ± 7.15 BW s-1, -55.6 ± 29.2 %) conditions compared to NORM (56.3 ± 11.5 BW s-1, both P < 0.001). RACE (51.1 ± 9.81 BW s-1) and FREQ (52.7 ± 11.0 BW s-1) conditions had no significant effects on LR. Running with a midfoot strike pattern resulted in a significant increase in gastrocnemius lateralis pre-activation (208 ± 97.4 %, P < 0.05) and in a significant decrease in tibialis anterior EMG activity (56.2 ± 15.5 %, P < 0.05) averaged over the entire stride cycle. The acute attenuation of foot-ground impact seems to be mostly related to the use of a midfoot strike pattern and to a higher pre-activation of the gastrocnemius lateralis. Further studies are needed to test these results in prolonged running exercises and in the long term. © 2012 Springer-Verlag.

Giandolini M.,Jean Monnet University | Giandolini M.,Laboratory of Exercise Physiology EA4338 | Giandolini M.,Salomon SAS | Giandolini M.,University of Savoy | And 14 more authors.
Journal of Biomechanics | Year: 2014

Identifying foot strike patterns in running is an important issue for sport clinicians, coaches and footwear industrials. Current methods allow the monitoring of either many steps in laboratory conditions or only a few steps in the field. Because measuring running biomechanics during actual practice is critical, our purpose is to validate a method aiming at identifying foot strike patterns during continuous field measurements. Based on heel and metatarsal accelerations, this method requires two uniaxial accelerometers. The time between heel and metatarsal acceleration peaks (THM) was compared to the foot strike angle in the sagittal plane (αfoot) obtained by 2D video analysis for various conditions of speed, slope, footwear, foot strike and state of fatigue. Acceleration and kinematic measurements were performed at 1000Hz and 120Hz, respectively, during 2-min treadmill running bouts. Significant correlations were observed between THM and αfoot for 14 out of 15 conditions. The overall correlation coefficient was r=0.916 (P<0.0001, n=288). The THM method is thus highly reliable for a wide range of speeds and slopes, and for all types of foot strike except for extreme forefoot strike during which the heel rarely or never strikes the ground, and for different footwears and states of fatigue. We proposed a classification based on THM: FFS<-5.49ms

Morin J.-B.,Jean Monnet University | Morin J.-B.,Laboratory of Exercise Physiology EA4338 | Morin J.-B.,Laboratoire Of Physiologie Of Lexercice Ea4338 | Bourdin M.,University of Lyon | And 6 more authors.
European Journal of Applied Physiology | Year: 2012

Sprint mechanics and field 100-m performances were tested in 13 subjects including 9 non-specialists, 3 French national-level sprinters and a world-class sprinter, to further study the mechanical factors associated with sprint performance. 6-s sprints performed on an instrumented treadmill allowed continuous recording of step kinematics, ground reaction forces (GRF), and belt velocity and computation of mechanical power output and linear force-velocity relationships. An index of the force application technique was computed as the slope of the linear relationship between the decrease in the ratio of horizontal-to-resultant GRF and the increase in velocity. Mechanical power output was positively correlated to mean 100-m speed (P<0.01), as was the theoretical maximal velocity production capability (P<0.011), whereas the theoretical maximal force production capability was not. The ability to apply the resultant force backward during acceleration was positively correlated to 100-m performance (rs[0.683; P<0.018), but the magnitude of resultant force was not (P = 0.16). Step frequency, contact and swing time were significantly correlated to acceleration and 100-m performance (positively for the former, negatively for the two latter, all P<0.05), whereas aerial time and step length were not (all P[0.21). Last, anthropometric data of body mass index and lowerlimb- to-height ratio showed no significant correlation with 100-m performance. We concluded that the main mechanical determinants of 100-m performance were (1) a "velocity-oriented" force-velocity profile, likely explained by (2) a higher ability to apply the resultant GRF vector with a forward orientation over the acceleration, and (3) a higher step frequency resulting from a shorter contact time. © Springer-Verlag 2012.

Grenier J.G.,Laboratory of Exercise Physiology EA4338 | Grenier J.G.,Safran Group | Peyrot N.,University of Reunion Island | Castells J.,Laboratory of Exercise Physiology EA4338 | And 4 more authors.
Medicine and Science in Sports and Exercise | Year: 2012

In the military context, soldiers carry equipments of total mass often exceeding 30%-40% of their body mass (BM) and complexly distributed around their body (backpack, weapons, electronics, protections, etc.), which represents severe load carrying conditions. Purpose: This study aimed to better understand the effects of load carriage on walking energetics and mechanics during military-type walking. Methods: Ten male infantrymen recently retired from the French Foreign Legion performed 3-min walking trials at a constant speed of 4 km•h on an instrumented treadmill, during which walking pattern spatiotemporal parameters, energy cost (CW), external mechanical work (Wext), and the work done by one leg against the other during the double-contact period (W int,dc) were specifically assessed. Three conditions were tested: (i) light sportswear (SP, reference condition considered as unloaded), (ii) battle equipment (BT, ∼22 kg, ∼27% of subjects' BM, corresponding to a military intermediate load), and (iii) road march equipment (RM, ∼38 kg, ∼46% of subjects' BM, corresponding to a military high load). Results: Repeated-measures ANOVA showed that military equipment carriage significantly (i) altered the spatiotemporal pattern of walking (all P < 0.01), (ii) increased absolute gross and net CW (P < 0.0001), and (iii) increased both absolute and mass-relative Wext (P < 0.01) and W int,dc (P < 0.0001) but did not alter the inverted pendulum recovery or locomotor efficiency. Conclusions: Military equipments carriage induced significant changes in walking mechanics and energetics, but these effects appeared not greater than those reported with loads carried around the waist and close to the center of mass. This result was not expected because the latter has been hypothesized to be the optimal method of load carriage from a metabolic standpoint. © 2012 by the American College of Sports Medicine.

Morin J.B.,Jean Monnet University | Morin J.B.,Laboratory of Exercise Physiology EA4338 | Samozino P.,Jean Monnet University | Samozino P.,Laboratory of Exercise Physiology EA4338 | And 6 more authors.
Journal of Biomechanics | Year: 2010

We tested the validity of an instrumented treadmill dynamometer for measuring maximal propulsive power during sprint running, and sought to verify whether this could be done over one single sprint, as shown during sprint cycling. The treadmill dynamometer modified towards sprint use (constant motor torque) allows vertical and horizontal forces to be measured at the same location as velocity, i.e. at the foot, which is novel compared to existing methods in which power is computed as the product of belt velocity and horizontal force measured by transducers placed in the tethering system. Twelve males performed 6. s sprints against default, high and low loads set from the motor torque necessary to overcome the friction due to subjects' weight on the belt (default load), and 20% higher and lower motor torque values. Horizontal ground reaction force, belt velocity, propulsive power and linear force-velocity relationships were compared between the default load condition and when taking all conditions together. Force and velocity traces and values were reproducible and consistent with the literature, and no significant difference was found between maximal power and force-velocity relationships obtained in the default load condition only vs. adding data from all conditions. The presented method allows one to measure maximal propulsive power and calculate linear force-velocity relationships from one single sprint data. The main novelties are that both force and velocity are measured at the same location, and that instantaneous values are averaged over one contact period, and not over a constant arbitrary time-window. © 2010 Elsevier Ltd.

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