263 research outputs found
Colloque médico-technique autour des épreuves combinées, Saint-Etienne, 25 juin 2010 : (à l'occasion des championnats de France nationaux et jeunes)
No full textIntroduction et présentation du colloque / Pascal Edouard. Intérêt des relations force-vitesse dans l'approche de l'entraînement / Pierre Samozino. Mesure directe de la puissance lors du sprint en course à pied / Jean-Benoît Morin. Description et optimisation de la période d'affutage à partir de la modélisation / Luc Thomas. Les abandons en épreuves combinées : fréquence et causes / Pascal Edouard. Les lésions de l'insertion haute des ischio-jambiers / Jacques Pruvost. Suivi prospectif des blessures chez les internationaux d'épreuves combinées / Alain Kerspern et Pascal Edouard
Caracteristicas antropométricas y músculo-tendinosas relacionadas con el perfil fuerza-velocidad en acciones balísticas
No full textLa relación fuerza-velocidad de las capacidades intrínsecas musculares han sido objeto de estudio desde principios del siglo pasado. Con el fin de explicar el rendimiento neuromuscular, este constructo teórico ha sido estudiado desde el comportamiento de fibras musculares aisladas in vitro hasta en movimientos pluriarticulares durante diferentes gestos tanto cíclicos como acíclicos.
En la última década, el ya llamado "modelo de Samozino" trata de explicar mediante modelación matemática el comportamiento neuromuscular de los miembros inferiores en su conjunto durante las acciones explosivo-balísticas del salto y del sprint desde las menores variables mecánicas posibles, para dar explicación al comportamiento motor real y óptimo desde el concepto llamado "perfil fuerza-velocidad".
Este modelo biomecánico no corresponde directamente con las características fenotípicas de los miembros inferiores, pero representa el conjunto del funcionamiento neuromuscular de los miembros inferiores durante este tipo de acciones.
El objetivo de la presente tesis es determinar cómo algunas características fenotípicas podrían explicar la variabilidad del rendimiento en salto y en sprint medidas mediante la herramienta del perfil mecánico fuerza-velocidad.Terapia y Rehabilitació
Both Isometric and Dynamic Testing Are Essential for a Comprehensive Assessment of the Knee Extensors
No full textThe improvements of measurement tools and data analysis enhanced our possibilities to assess neuromuscular performance, but also created confusion regarding significance and practical applications of this available information. To simplify the strength assessment understanding, our purpose was to group force, velocity, and power metrics that could provide similar outcomes. We measured single-leg knee extensor strength under isometric and dynamic conditions on 64 young adults (33 men and 31 women). Subjects performed maximal and burst-like contractions under isometric conditions to assess maximal torque (MVT) and rate of torque development (RTD). Under dynamic conditions, a torque-velocity relationship was obtained from an incremental load test. Principal component analysis (PCA) was used to reduce the dimensionality of the data set and group variables. Principal component analysis identified 4 components: (a) "Maximal force" (composed by MVT, T0, RTD100, RTD150, Topt, Pmax), (b) "Explosiveness" (composed by RTD50, RTDpeak, RTD50N, RTD100N, RTD150N, RTDpeakN, time to peak torque, time to RTDpeak), (c) "Force at high velocity" (composed by V0 and Vopt), and (d) "Curvature" (C). When data were normalized by sex differences, "Explosiveness" resulted as the first component and Pmax was included in the "Force at high velocity" component. The present findings remark the importance of testing the explosiveness (i.e., early RTD and normalized RTD metrics) together with torque-velocity profiling, to have a more comprehensive assessment of neuromuscular qualities
Sex differences in the rate of torque development and torque–velocity relationship are due to maximal strength only
Get PDFPurpose: This study aimed to analyse the sex differences in the rate of torque development (RTD) and torque-velocity parameters with and without normalisation for maximal voluntary torque (MVT). Methods: Right-leg knee extensors were tested in 64 healthy and active participants (31 F and 33 M). MVT and RTD were obtained under isometric conditions. Individual torque-velocity relationships were obtained using a curvilinear model on averaged torque and velocity over 80°-to-140° knee angle. Dynamic data were acquired through an incremental protocol on a leg extension machine, going from the lightest to the unmovable load despite maximal effort. Results: Independent samples t test revealed (p < 0.001) that males possess greater RTD measured at 50 ms (d = -1.2), 100ms (d = -2.1) and 150ms (d = -2.3), peak RTD (d = -1.3) and MVT (d = 2.1). When normalised by MVT, the sex differences in RTD disappeared. Curvilinear hyperbolic TV relationship well-fitted (R2 = 0.99). In FV parameters, maximal theoretical torque (d = -1.7), maximal power (Pmax) (d = -2.0), and torque at Pmax (d = -1.7) were greater in males (p < .05), while maximal theoretical velocity (V0) and velocity at Pmax did not differ. Conclusions: The sex differences in explosiveness (i.e., rapid isometric and dynamic force production) were mainly due to greater maximal strength in males than in females. These findings suggest that, in non-sedentary people, males do not present higher contraction velocity capacities, i.e. higher maximal velocity until which muscles can produce force, than females in knee extension
Bilateral deficit magnitude increases with velocity during a half-squat exercise
No full textMovement velocity has been viewed as one of the bilateral deficit (BLD) determinants. This research tested the velocity effect on BLD during a half-squat exercise. The role of muscle excitation in BLD was also assessed. BLD amplitude was assessed in 12 male soccer players while performing a half-squat exercise with incremental load. During the exercise’s pushing phase, the average force and velocity were measured in bilateral and unilateral conditions to provide the bilateral index (BI) at each interpolated velocity. The vastus lateralis and medialis excitation was assessed during the exercise by calculating the surface electromyography signal root mean square (sEMGRMS). The BI for sEMGRMS (sEMG BI) was calculated. The theoretical maximum force (F0) and velocity (v0) were also determined. F0 was +43
(28)% in bilateral compared with unilateral conditions (p < 0.001), whereas v0 was similar in both conditions (p = 0.386). The BI magnitude rose with the increase in velocity from −34 (7)% at 50%v0 to −70 (17)% at 90%v0 (p 0.03-<0.001), whereas no sEMG BI occurred (p: 0.07-0.991 in both muscles). The study reported velocity-dependent changes in the BLD amplitude, with the largest BLD amplitudes occurring at the highest velocities. This behaviour could provide useful information for setting specific contraction velocities to exploit/limit the BLD amplitude as a possible training stimulus
Lower Limb Force, Velocity, Power Capabilities during Leg Press and Squat Movements
No full textThe aim was to compare lower-limb power, force, and velocity capabilities between squat and leg press movements. Ten healthy sportsmen performed ballistic lower-limb push-offs against 5-to-12 different loads during both the squat and leg press. Individual linear force-velocity and polynomial power-velocity relationships were determined for both movements from push-off mean force and velocity measured continuously with a pressure sensor and linear encoder. Maximal power output, theoretical maximal force and velocity, force-velocity profile and optimal velocity were computed. During the squat, maximal power output (17.7±3.59 vs. 10.9±1.39 W·kg-1), theoretical maximal velocity (1.66±0.29 vs. 0.88±0.18 m·s-1), optimal velocity (0.839±0.144 vs. 0.465±0.107 m·s-1), and force-velocity profile (-27.2±8.5 vs. -64.3±29.5 N·s·m-1·kg-1) values were significantly higher than during the leg press (p=0.000, effect size=1.72-3.23), whereas theoretical maximal force values (43.1±8.6 vs. 51.9±14.0 N·kg-1, p=0.034, effect size=0.75) were significantly lower. The mechanical capabilities of the lower-limb extensors were different in the squat compared with the leg press with higher maximal power due to much higher velocity capabilities (e.g. ability to produce force at high velocities) even if moderately lower maximal force qualities
Leg Press vs. Smith Machine: Quadriceps Activation and Overall Perceived Effort Profiles
Get PDFFirst aim was describing Smith machine squat and leg press exercise as nominal load, knee extensors activity, and rating of perceived exertion. Second aim was developing predictive equations to provide same muscular activation and same perceived exertion nominal loads during the two exercises. To do that, vastus lateralis and vastus medialis activation, as their summed surface electromyography signal integrals, and overall perceived exertions were measured at different nominal loads during Smith machine squat and leg press exercise in adult male athletes experienced in weight training. Correlation and multistep stepwise analyses were performed. Then, two different results-driven predictive equations to provide same electromyography signals and same perceived exertion nominal loads were developed. The same electromyography signal equation results were less accurate (i.e., less predictive) due to high inter-individual differences, whereas the same perceived exertion equation results were more accurate, because perceived exertion is more related to the Smith machine squat and leg press exercise overall level of exertion than to the two single muscles that were investigated. In conclusion, these two equations represented an initial attempt to provide athletes and coaches with a new tool to mutually convert equivalent nominal loads during Smith machine squat and leg press exercise over a training period
The Rate of Torque Development as a Determinant of the Torque-Velocity Relationship
Get PDFWe investigate the contribution of isometric rate of torque development (RTD) and maximal voluntary torque (MVT) to the dynamic force production capacities of knee extensors obtained from the torque-velocity (TV) relationship, that is, the theoretical maximal velocity (V0), torque (T0), and maximal power (Pmax). Single-leg knee extensors were tested in 64 young adults (31 females). RTD and root mean square (RMS) of electromyographic signals from the knee extensors were recorded during isometric and incremental load dynamic (nonisokinetic) contractions. In the dynamic test, torque and velocity were continuously measured and averaged over 80°-140° knee angles to determine individual TV relationships. TV relationships were well fitted by hyperbolic regression (r2 from 0.983 to 0.993). Stepwise linear regressions showed that the main determinant of V0 was normalized RTD50 (R2 = 0.145, p = 0.004); the main determinant of T0 was MVT (R2 = 0.760, p < 0.001); and the main determinant of Pmax was RTD150 (R2 = 0.612, p < 0.001). V0 (when obtained from averaged values over knee extension) is partially explained by rapid torque capacity (i.e., "explosive strength"). Therefore, the capacity to produce torque at high velocity partly depends on the capacity to rise quickly the torque in the early phase of the contraction, suggesting that some underlying determinants of RFD would also affect V0
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No full textAnalyse automatique de données radar de sprint, en vue d'extraire des valeurs caractéristiques du profil Puissance - Force - Vitesse des athlètes.Code python développé au Laboratoire Jean Kuntzmann (Caroline Bligny), en collaboration avec le FCG, et basé sur les travaux de recherche de Pierre Samozino
Methodological Considerations on the Relationship Between the 1,500-M Rowing Ergometer Performance and Vertical Jump in National-Level Adolescent Rowers
No full textInternational audienceThe purpose of this study was to investigate whether 3 different approaches for evaluating squat jump performance were correlated with rowing ergometer performance in elite adolescent rowers. Fourteen young male competitive rowers (15.3 ± 0.6 years), who took part in the French rowing national championships, performed a 1,500-m all-out rowing ergometer performance (P1500) and a squat jump (SJ) test. The performance in SJ was determined by calculating the jump height (HSJ in cm), a jump index (ISJ = HSJ·body mass·gravity, in J), and the mean power output (PSJ in W) from the Samozino et al.'s method. Furthermore, allometric modeling procedures were used to consider the importance of body mass (BM) in the relationships between P1500 and jump scores. P1500 was significantly correlated with HSJ (r2 = 0.29, p ≤ 0.05), ISJ (r2 = 0.72, p < 0.0001), and PSJ (r2 = 0.86, p < 0.0001). Furthermore, BM explained at least 96% of the relationships between SJ and rowing performances. However, the similarity between both allometric exponents for PSJ and P1500 (1.15 and 1.04, respectively) indicates that BM could influence jump and rowing ergometer performances at the same rate, and that PSJ could be the best correlate of P1500. Therefore, the calculation of power seems to be more relevant than HSJ and ISJ to (a) evaluate jump performance and (b) infer the capacity of adolescent rowers to perform 1,500-m all-out rowing ergometer performance, irrespective of their body mass. This could help coaches to improve their training program and potentially identify talented young rowers
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