Modérateurs: Nutrimuscle-Conseils, Nutrimuscle-Diététique
par Plasma » 16 Fév 2010 19:11
par Criti » 16 Fév 2010 19:31
par Plasma » 16 Fév 2010 20:04
par Criti » 16 Fév 2010 20:34
par Plasma » 17 Fév 2010 11:46
Criti a écrit:Biomécanique
Lors de la prise d’impulsion, le pied est considéré comme point fixe. Le bassin est donc la partie mobile qui s’éloigne du sol, les gastrocnémiens agissent sur l’extension de la cheville et la partie basse du fémur.
Les ischios jambiers provoquent l’extension de la hanche et tire sur la partie haute du tibia.
La construction vectorielle de l’action de ces deux groupes musculaires montre que la résultante (somme vectorielle) amène un déplacement de l’articulation du genou vers l’arrière provoquant une extension. Comme nous pouvons le voir sur le schéma suivant, cette action est d’autant plus efficace si le genou est fléchi.
Source: http://www.choreos.fr/?p=347
et ça m'a permis de constater que la théorie proposée ne marche pas. Pour que l'articulation du genou s'ouvre, il faut que les gastro s'étirent.
par OLYBAR » 17 Fév 2010 12:31
par Blaze » 17 Fév 2010 12:59
par Blaze » 17 Fév 2010 13:19
World-class squatters know that the calves play a big role in squatting big: When you come up out of the hole, not only do you have extension at the hips and knees, but also at the ankles. The gastrocnemius--the upside-down heart-shaped muscle on the lower leg--is a major player here. Then there's the stabilization performed by the soleus throughout the entire exercise.
par Plasma » 17 Fév 2010 15:32
The purpose of this research was to determine the functions of the gluteus maximus, biceps femoris, semitendinosus, rectus femoris, vastus lateralis, soleus, gastrocnemius, and tibialis anterior muscles about their associated joints during full (deep-knee) squats. Muscle function was determined from joint kinematics, inverse dynamics, electromyography, and muscle length changes. The subjects were six experienced, male weight lifters. Analyses revealed that the prime movers during ascent were the monoarticular gluteus maximus and vasti muscles (as exemplified by vastus lateralis) and to a lesser extent the soleus muscles. The biarticular muscles functioned mainly as stabilizers of the ankle, knee, and hip joints by working eccentrically to control descent or transferring energy among the segments during ascent. During the ascent phase, the hip extensor moments of force produced the largest powers followed by the ankle plantar flexors and then the knee extensors. The hip and knee extensors provided the initial bursts of power during ascent with the ankle extensors and especially a second burst from the hip extensors adding power during the latter half of the ascent.
par Blaze » 17 Fév 2010 16:37
Purpose: Because a strong and stable knee is paramount to an athlete's or patient's success, an understanding of knee biomechanics while performing the squat is helpful to therapists, trainers, sports medicine physicians, researchers, coaches, and athletes who are interested in closed kinetic chain exercises, knee rehabilitation, and training for sport. The purpose of this review was to examine knee biomechanics during the dynamic squat exercise. Methods: Tibiofemoral shear and compressive forces, patellofemoral compressive force, knee muscle activity, and knee stability were reviewed and discussed relative to athletic performance, injury potential, and rehabilitation. Results: Low to moderate posterior shear forces, restrained primarily by the posterior cruciate ligament (PCL), were generated throughout the squat for all knee flexion angles. Low anterior shear forces, restrained primarily by the anterior cruciate ligament (ACL), were generated between 0 and 60° knee flexion. Patellofemoral compressive forces and tibiofemoral compressive and shear forces progressively increased as the knees flexed and decreased as the knees extended, reaching peak values near maximum knee flexion. Hence, training the squat in the functional range between 0 and 50° knee flexion may be appropriate for many knee rehabilitation patients, because knee forces were minimum in the functional range. Quadriceps, hamstrings, and gastrocnemius activity generally increased as knee flexion increased, which supports athletes with healthy knees performing the parallel squat (thighs parallel to ground at maximum knee flexion) between 0 and 100° knee flexion. Furthermore, it was demonstrated that the parallel squat was not injurious to the healthy knee. Conclusions: The squat was shown to be an effective exercise to employ during cruciate ligament or patellofemoral rehabilitation. For athletes with healthy knees, performing the parallel squat is recommended over the deep squat, because injury potential to the menisci and cruciate and collateral ligaments may increase with the deep squat. The squat does not compromise knee stability, and can enhance stability if performed correctly. Finally, the squat can be effective in developing hip, knee, and ankle musculature, because moderate to high quadriceps, hamstrings, and gastrocnemius activity were produced during the squat.
par Plasma » 18 Fév 2010 11:10
Blaze a écrit:ça reste controversé, puisque j'ai trouvé aussi ça sur le sujet :
Article : http://cat.inist.fr/?aModele=afficheN&cpsidt=909998
Blaze a écrit:Apparemment, son rôle dans le squat, se situe + au niveau de la cheville alors
la position fléchie des genoux relâche les gastrocnémiens qui s'attachent au-dessus de l'articulation du genou et en bas au tendon d'Achille ; dans cette position, ils ne participent donc que faiblement à l'extension du pied.
Cet exercice travaille l'ensemble des muscles ischio-jambiers ainsi que les gastrocnémiens et, en profondeur, le muscle poplité.
par Blaze » 18 Fév 2010 14:43
Donc, quand on fléchit les genoux pour faire les soléaires, ça désactive les gastros, mais quand on fléchit les genoux au squat, ça les activeraient ? C'est totalement illogique.
Six healthy participants performed 1 set of 8 repetitions (using a weight they could lift 8 times, i.e., 8RM, or 8 repetition maximum) for each of the free weight squat and Smith machine squat in a randomized order with a minimum of 3 days between sessions, while electromyographic (EMG) activity of the tibialis anterior, gastrocnemius, vastus medialis, vastus lateralis, biceps femoris, lumbar erector spinae, and rectus abdominus were simultaneously measured. Electromyographic activity was significantly higher by 34, 26, and 49 in the gastrocnemius, biceps femoris, and vastus medialis, respectively, during the free weight squat compared to the Smith machine squat (p < 0.05). There were no significant differences between free weight and Smith machine squat for any of the other muscles; however, the EMG averaged over all muscles during the free weight squat was 43% higher when compared to the Smith machine squat (p < 0.05). The free weight squat may be more beneficial than the Smith machine squat for individuals who are looking to strengthen plantar flexors, knee flexors, and knee extensors.
Researchers have shown that the use of eccentric single-limb squat exercises has a significant effect on performance8–,12,16; however, little was known about the exact biomechanics. In this study, we took biomechanical measurements and established that, as the decline angle of the single-limb squat increased, the knee-flexion moment increased, and the ankle-dorsiflexion moment decreased. We found, however, an increase in the EMG activity of the gastrocnemius at the 24° decline angle compared with the 16° decline angle, but we did not find a mechanical advantage about the knee between 16° and 24°.
Objectives of Second Study
1. Determine if hypergravity squats can produce foot forces similar to those measured while performing 10-repetition maximum (10-RM) squats under normal 1 Gz condition; and
2. Compare the integrated electromyography (iEMG) and goniometry of selected muscles and joints, respectively between hypergravity and 10-RM squats of similar foot forces.
Subjects completed (male = 8 subjects; females = 5 subjects) ten, 10-RM squats (97 12 kg) and 10 hypergravity squats (3.2 0.3 Gz; range of 3-3.75 Gz) under similar average total foot force conditions (104 percent 10-RM) in the same visit. Hypergravity squats were performed on a human-powered short-arm centrifuge. Foot forces were monitored using insole force sensors. Hip and knee flexion/extension, plantar/dorsi flexion, and EMG of the erector spinae, bicep femoris, rectus femoris and gastrocnemius were also monitored during the squats. There were no differences in average total foot forces, average duration per repetition, and iEMG and range of motion of the selected muscles and joints, respectively, between hypergravity and 10-RM squats except a 60 percent greater iEMG of the gastrocnemius muscles during hypergravity squats (P < 0.05). These results suggest that hypergravity squats are comparable to squats performed at 1 Gz and may represent an important countermeasure to microgravity. Collectively, we have performed a series of sequential studies that will culminate in two training studies.
4) The EMG results summarized that the co-contraction of the antagonists was observed markedly in the both lifting techniques; the tibialis anterior and the gastrocnemius in the ankle joint, the rectus femoris and the biceps femoris in the knee joint.
