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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.

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.

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.

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.

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