Thomas D. O’Brien, Neil D. Reeves, Vasilios Baltzopoulos, David A. Jones and Constantinos N. Maganaris
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.
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.
Benjamin Henry, Todd McLoda, Carrie L. Docherty and John Schrader
Peroneal reaction to sudden inversion has been determined to be too slow to overcome the joint motion. A focused plyometric training program may decrease the muscle's reaction time.
To determine the effect of a 6-wk plyometric training program on peroneus longus reaction time.
University research laboratory.
48 healthy volunteers (age 20.0 ± 1.2 y, height 176.1 ± 16.9 cm, weight 74.5 ± 27.9 kg) from a large Midwestern university. Subjects were randomly assigned to either a training group or a control group.
Independent variables were group at 2 levels (training and no training) and time at 2 levels (pretest and posttest). The dependent variable was peroneal latency measured with surface electromyography. A custom-made trapdoor device capable of inverting the ankle to 30° was also used. Latency data were obtained from the time the trapdoor dropped until the peroneus longus muscle activated. Peroneal latency was measured before and after the 6-wk training period. The no-training group was instructed to maintain current activities. The training group performed a 6-wk plyometric protocol 3 times weekly. Data were examined with a repeated-measures ANOVA with 1 within-subject factor (time at 2 levels) and 1 between-subjects factor (group at 2 levels). A priori alpha level was set at P < .05.
Main Outcome Measures:
Pretest and posttest latency measurements (ms) were recorded for the peroneus longus muscle.
The study found no significant group-by-time interaction (F 1,46 = 0.03, P = .87). In addition, there was no difference between the pretest and posttest values (pretest = 61.76 ± 14.81 ms, posttest = 59.24 ± 12.28 ms; P = .18) and no difference between the training and no-training groups (training group = 59.10 ± 12.18 ms, no-training group = 61.79 ± 15.18 ms; P = .43).
Although latency measurements were consistent with previous studies, the plyometric training program did not cause significant change in the peroneus longus reaction time.
Devon Long, Raffy Dotan, Brynlynn Pitt, Brandon McKinlay, Thomas D. O’Brien, Craig Tokuno and Bareket Falk
The electromyographic threshold (EMGTh) is thought to reflect increased high-threshold/type-II motor-unit (MU) recruitment and was shown higher in boys than in men. Women differ from men in muscular function.
Establish whether females’ EMGTh and girls–women differences are different than males’.
Nineteen women (22.9 ± 3.3yrs) and 20 girls (10.3 ± 1.1yrs) had surface EMG recorded from the right and left vastus lateralis muscles during ramped cycle-ergometry to exhaustion. EMG root-mean-squares were averaged per pedal revolution. EMGTh was determined as the least residual sum of squares for any two regression-line data divisions, if the trace rose ≥ 3SD above its regression line. EMGTh was expressed as % final power-output (%Pmax) and %VO2pk power (%PVO2pk).
EMGTh was detected in 13 (68%) of women, but only 9 (45%) of girls (p < .005) and tended to be higher in the girls (%Pmax= 88.6 ± 7.0 vs. 83.0 ± 6.9%, p = .080; %PVO2pk= (101.6 ± 17.6 vs. 90.6 ± 7.8%, p = .063). When EMGTh was undetected it was assumed to occur at 100%Pmax or beyond. Consequently, EMGTh values turned significantly higher in girls than in women (94.8 ± 7.4 vs. 88.4 ± 9.9%Pmax, p = .026; and 103.2 ± 11.7 vs. 95.2 ± 9.9%PVO2pk, p = .028).
During progressive exercise, girls appear to rely less on higher-threshold/type-II MUs than do women, suggesting differential muscle activation strategy.
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