Thomas D. O’Brien, Neil D. Reeves, Vasilios Baltzopoulos, David A. Jones and Constantinos N. Maganaris
Justin M. Stanek, Todd A. McLoda, Val J. Csiszer and A.J. Hansen
Selected muscles in the kinetic chain may help explain the body’s ability to avert injury during unexpected perturbation.
To determine the activation of the ipsilateral rectus femoris (RF), gluteus maximus (MA), gluteus medius (ME), and contralateral external obliques (EO) during normal and perturbed gait.
Single-factor, repeated measures.
University research laboratory.
32 physically active, college-age subjects.
Subjects walked a total of 20 trials the length of a 6.1-m custom runway capable of releasing either side into 30° of unexpected inversion. During 5 trials, the platform released into inversion.
Main Outcome Measures:
Average, peak, and time to peak EMG were analyzed across the 4 muscles, and comparisons were made between the walking trials and perturbed trials.
Significantly higher average and peak muscle activity were noted for the perturbed condition for RF, MA, and EO. Time to peak muscle activity was faster during the perturbed condition for the EO.
Rapid contractions of selected postural muscles in the kinetic chain help explain the body’s reaction to unexpected perturbation.
Robert U. Newton, William J. Kraemer, Keijo Häkkinen, Brendan J. Humphries and Aron J. Murphy
The aim of this study was to investigate the kinematics, kinetics, and neural activation of the traditional bench press movement performed explosively and the explosive bench throw in which the barbell was projected from the hands. Seventeen male subjects completed three trials with a bar weight of 45% of the subject's previously determined 1RM. Performance was significantly higher during the throw movement compared to the press for average velocity, peak velocity, average force, average power, and peak power. Average muscle activity during the concentric phase for pectoralis major, anterior deltoid, triceps brachii, and biceps brachii was higher for the throw condition. It was concluded that performing traditional press movements rapidly with light loads does not create ideal loading conditions for the neuromuscular system with regard to explosive strength production, especially in the final stages of the movement, because ballistic weight loading conditions where the resistance was accelerated throughout the movement resulted in a greater velocity of movement, force output, and EMG activity.
Raffy Dotan, Cameron Mitchell, Rotem Cohen, Panagiota Klentrou, David Gabriel and Bareket Falk
Children differ from adults in many muscular performance attributes such as size-normalized strength and power, endurance, fatigability and the recovery from exhaustive exercise, to name just a few. Metabolic attributes, such as glycolytic capacity, substrate utilization, and VO2 kinetics also differ markedly between children and adults. Various factors, such as dimensionality, intramuscular synchronization, agonist-antagonist coactivation, level of volitional activation, or muscle composition, can explain some, but not all of the observed differences. It is hypothesized that, compared with adults, children are substantially less capable of recruiting or fully employing their higher-threshold, type-II motor units. The review presents and evaluates the wealth of information and possible alternative factors in explaining the observations. Although conclusive evidence is still lacking, only this hypothesis of differential motor-unit activation in children and adults, appears capable of accounting for all observed child—adult differences, whether on its own or in conjunction with other factors.
Mikko Virmavirta and Paavo V. Komi
Electromyographic (EMG) activities of gluteus maximus (GL), vastus later-alis (VL), vastus medialis (VM), tibialis anterior (TA), and gastrocnemius (GA) were measured telemetrically from four world-class athletes during the entire ski jumping performance. Integrated electromyographic activities (IEMG) were calculated from the different phases of jump. TA and GA showed alternate activation during the curve, suggesting that maintenance of the inrun position is a process requiring continuous active control. VL and VM were observed to contribute mostly to the entire takeoff phase whereas GL became strongly active within the last 4 meters of the takeoff. GA was slightly but continuously active during the inrun and showed only a small increase during takeoff. The quick lifting of the skis, as evidenced by the activation of TA, does not seem to allow effective use of GA at the end of the takeoff. Strong continuous activity of the knee extensors and TA dominated the midflight phase whereas the activation of GL and GA increased toward the end of the flight.
Federico Quinzi, Valentina Camomilla, Alberto Di Mario, Francesco Felici and Paola Sbriccoli
Training in martial arts is commonly performed by repeating a technical action continuously for a given number of times. This study aimed to investigate if the repetition of the task alters the proper technical execution, limiting the training efficacy for the technical evaluation during competition. This aim was pursued analyzing lower-limb kinematics and muscle activation during repeated roundhouse kicks.
Six junior karate practitioners performed continuously 20 repetitions of the kick. Hip and knee kinematics and sEMG of vastus lateralis, biceps (BF), and rectus femoris were recorded. For each repetition, hip abduction–adduction and flexion–extension and knee flexion–extension peak angular displacements and velocities, agonist and antagonist muscle activation were computed. Moreover, to monitor for the presence of myoelectric fatigue, if any, the median frequency of the sEMG was computed. All variables were normalized with respect to their individual maximum observed during the sequence of kicks. Linear regressions were fitted to each normalized parameter to test its relationship with the repetition number.
Linear-regression analysis showed that, during the sequence, the athletes modified their technique: Knee flexion, BF median frequency, hip abduction, knee-extension angular velocity, and BF antagonist activation significantly decreased. Conversely, hip flexion increased significantly.
Since karate combat competitions require proper technical execution, training protocols combining severe fatigue and technical actions should be carefully proposed because of technique adaptations. Moreover, trainers and karate masters should consider including specific strength exercises for the BF and more generally for knee flexors.
Momoko Yamagata, Ali Falaki and Mark L. Latash
-dependent noise in muscle activation levels (cf. Harris & Wolpert, 1998 ; Jones, Henry, Raasch, Hitt, & Bunn, 2012 ; Valero-Cuevas, Venkadesan, & Todorov, 2009 ) and facilitation of transmission of perturbations along the body axis, also potentially contributing to postural destabilization. In this study, we
Daniel Gilfeather, Grant Norte, Christopher D. Ingersoll and Neal R. Glaviano
ratio between the volitional muscle contraction and muscle activation elicited by an exogenous electrical stimulus. 13 SIBT is the application of an electrical stimulation during a maximal voluntary isometric contraction (MVIC) that, in theory, activates the remaining motor units that the patient was
Esther Casas, Arturo Justes and Carlos Calvo
a longer period of time. Conclusion Using developmental positions on the basis of ontogenesis of human motor locomotion elicits the right muscular coactivation of antagonist muscular pairs; especially it promotes higher muscle activation of phasic muscles. Adding facilitators did not change the