Mechanomyogram and electromyogram responses of upper limb during sustained isometric fatigue with varying shoulder and elbow postures

To investigate the behavior of mechanomyogram (MMG) and electromyogram (EMG) signals in the time and frequency domains during sustained isometric contraction, MMG and surface EMG were obtained simultaneously from four muscles: upper trapezius (TP), anterior deltoid (DL), biceps brachii (BB), and brachioradialis (BR) of 10 healthy male subjects. Experimental conditions consisted of 27 combinations of 9 postures [3 shoulder angles (SA): 0 degree, 30 degrees, 60 degrees and 3 elbow angles (EA): 120 degrees, 90 degrees, 60 degrees] and 3 contraction levels: 20%, 40%, and 60% of maximum voluntary contraction (MVC). Subjective evaluations of fatigue were also assessed using the Borg scale at intervals of 60, 30, and 10 sec at 20%, 40%, and 60% MVC tests, respectively. The mean power frequency (MPF) and root mean square (RMS) of both signals were calculated. The current study found clear and significant relationships among physiological and psychological parameters on the one hand and SA and EA on the other. EA's effect on MVC was found to be significant. SA had a highly significant effect on both endurance time and Borg scale. In all experimental conditions, significant correlations were found between the changes in MPF and RMS of EMG in BB with SA and EA (or muscle length). In all four muscles, MMG frequency content was two or three times lower than EMG frequency content. During sustained isometric contraction, the EMG signal showed the well-known shift to lower frequencies (a continuous decrease from onset to completion of the contraction). In contrast, the MMG spectra did not show any shift, although its form changed (generally remaining about constant). Throughout the contraction, increased RMS of EMG was found for all tests, whereas in the MMG signal, a significant progressive increase in RMS was observed only at 20% MVC in all four muscles. This supports the hypothesis that the RMS amplitude of the MMG signal produced during contraction is highly correlated with force production. Possible explanations for this behavioral difference between the MMG and EMG signals are discussed.     

EMG responses resulting from transient and steady-state dynamic isometric loading of the human biceps can be distinguished.

In order to determine if differences in human muscle EMG response to steady-state (STD) dynamic load and transient (TRN) load could be detected, two distinct sinusoidal loads having identical amplitude and frequency were applied to the forearm, which was held in a fixed posture. The first condition used application of a constant amplitude, constant frequency, STD sinusoid, and the second condition used application of a single sinusoid of identical amplitude and frequency as the STD load. Time-domain parameters of Half-Mass, Dispersion Moments, Asymmetry Moments, Peak Ratio (ratio of cycle peak RMS EMG to cycle mean RMS EMG) and Time-to-Peak Ratio (ratio of cycle time to reach peak RMS EMG to cycle time duration) were used to quantify responses in the time domain. A single frequency-domain parameter, Dispersion Moments, was used to quantify responses in the frequency domain. Individual ANOVA's of the time domain parameter results revealed that p = 0.689 for Dispersion Moments, p = 0.111 for Half-Mass, p = 0.007 for Asymmetry Moments, p = 0.001 for Peak Ratio, and p = 0.001 for Time-to-Peak Ratio. The time-domain MANOVA and frequency-domain ANOVA revealed that EMG responses resulting from STD and TRN applied loads were statistically different in the time domain (p = 0.001), but not in the frequency domain (p = 0.810). Thus, use of Asymmetry Moments, Peak Ratio, and Time-to-Peak Ratio parameters can distinguish EMG responses to STD and TRN loads.     

Correlation of PP and PR intervals in premature low birth weight infants.

We examined the developmental change by which autonomic neural activity associated respiration modulates spontaneous firing rate of sinus (SA) node and atrioventricular (AV) conduction in premature infants born with low birth weight (LBWI). The purpose of this study was to clarify whether variation of PR is correlated with that of PP or those are independent in LBWI with immature autonomic nervous system. We investigated, therefore, whether there are spontaneous functional differences in the innervation of SA and AV nodes. Further, we evaluated the maturation of autonomic nervous system progressing in the period, on the day of birth (Day 0) to approximately one month after the birth (Month 1). This study was performed in thirteen LBWI during deep sleep. EEG, EOG, ECG, respiratory waves were digitized on line, spontaneous firing cycle of SA node (PP), and AV nodal conduction time (PR) that were recorded on Day 0 and Month 1. Then, the data were analyzed as follows: 1) correlations among the means and standard deviations (SD) of PP, PR and RR, 2) variance evaluation of PP and PR intervals by Lorenz plot analysis method, 3) correlation analysis among PP, PR and RR intervals by linear regression method and 4) frequency analysis for PP and PR intervals by high-speed Fourier transform method (FFT) and determination of frequency density. The PP interval decreased as growing in the period. Contrary PR interval increased. In LBWI, the automatic nervous activities including parasympathetic nerve activity for spontaneous firing cycle of SA node and ventricular excitation cycle on Month 1 were higher than Day 0. It was assumed that the vagal nerve activity for the AV conduction was enhanced. However, there was no significant change in linear regression slope for the spontaneous firing cycle of SA node and the AV conduction time. Postnatal LF/HF changes for PP and PR obtained by frequency analysis, were opposite. Therefore, it was suggested that the maturity of autonomic nervous system progresses in the period, Day 0 to approximately Month 1, but the variations in PP and PR are independent each other.     

Relationship Between Time- and Frequency-Domain Analyses of Angular Head Movements in the Squirrel Monkey

We used the three-dimensional magnetic search-coil recording technique to study the range of active angular head movements made by squirrel monkeys. There were two goals in this study: (1) to determine the range of angular velocities and accelerations as well as the bandwidth and other frequency characteristics of active head movements and (2) to compare analyses of transients of velocity and acceleration that are studied by residual analysis, Fourier transform, and wavelet transform of the head velocity signal.The residual analysis showed that the shape and duration of the transients affected the bandwidth. During the time after the head had begun to accelerate, the frequency content of the head movement extended into the range of 6 to 12 Hz. When considering all three planes of rotation, approximately 75% of the transients had peak acceleration between 2,000 and 10,000 deg/s² and a peak velocity of 50 to 400 deg/s. A peak acceleration of >10,000 deg/s² was recorded in 10% of the transients.These findings indicate that active head movements in squirrel monkeys cover a higher range of frequencies, accelerations, and velocities than have typically been used in previous eye-movement and neuronal studies of the reflexes that control gaze. We further conclude that the choice of a method for analyzing transient, time-varying biological signals is dependent on the desired information. Residual analysis provides detailed resolution in the time domain, but estimation of the frequency content of the signal is dependent on the portions selected for analysis and the choice of filters. Fourier transform provides a representation of the power spectrum in the frequency domain but without any inherent temporal resolution. We show that the wavelet transform, a novel method as applied to the signal analysis goals of this study, is the most useful technique for relating time- and frequency-domain information during a continuous signal.     

Postural-induced phase shift of respiratory sinus arrhythmia and blood pressure variations: insight from respiratory-phase domain analysis

The purpose of this study is to evaluate the multiple effects of respiration on cardiovascular variability in different postures, by analyzing respiratory sinus arrhythmia (RSA) and respiratory-related blood pressure (BP) variations for systolic BP (SBP), diastolic BP (DBP), and pulse pressure (PP) in the respiratory-phase domain. The measurements were conducted for 420 s on healthy humans in the sitting and standing positions, while the subjects were continuously monitored for heart rate and BP variability and instantaneous lung volume. The waveforms of RSA and respiratory-related BP variations were extracted as a function of the respiratory phase. In the standing position, the waveforms of the BP variations for SBP, DBP, and PP show their maxima at around the end of expiration (pi rad) and the minima at around the end of inspiration (2 pi rad), while the waveform of RSA is delayed by approximately 0.35 pi rad compared with the BP waveforms. On the other hand, in the sitting position, the phase of the DBP waveform (1.69 pi rad) greatly and significantly (P < 0.01) differs from that in the standing position (1.20 pi rad). Also, the phase of PP is delayed and that of RSA is advanced in the sitting position (P < 0.01). In particular, the phase shift of the DBP waveform is sufficiently large to alter whole hemodynamic fluctuations, affecting the amplitudes of SBP and PP variations. We conclude that the postural change associated with an altered autonomic balance affects not only the amplitude of RSA, but also the phases of RSA and BP variations in a complicated manner, and the respiratory-phase domain analysis used in this study is useful for elucidating the dynamic mechanisms of RSA.     

Force production and spatial arm coordination profile in arm crawl swimming in a fixed position

This study analyzed the relationship between mechanical force production and spatial arm position of the swimming movement for each side of the swimmer. Eight internationally recognized male swimmers performed fix positioned arm only swimming with a dynamometer synchronized with underwater cameras. The upper arm positions (α in side, β in frontal view) and the elbow angles (γ in 3D) were determined at the moment where the force production reached the peak (Fmax) and the maximal values of rate of force development (RFDmax). RFDmax and α values showed significant differences between the sides (P<0.05). To show the motion integration structure of the performance, Multiple Regression Analysis (MRA) was employed separately for both sides. For the criterion variable, the impulse of force (ImpF50%) was calculated. The defined parameters as the mechanical and spatial predictor system were used for the model. The results of the MRA showed that the predictor system yielded the model structure of the variables that explain the criterion variables for ImpF50% by the dominant (P=0.007) and by the nondominant side (P=0.001), respectively. The alternate contribution of the variables to the models can objectively express the performance difference between the two sides of the swimmer.     

Wireless Tri-Axial Trunk Accelerometry Detects Deviations in Dynamic Center of Mass Motion Due to Running-Induced Fatigue

Small wireless trunk accelerometers have become a popular approach to unobtrusively quantify human locomotion and provide insights into both gait rehabilitation and sports performance. However, limited evidence exists as to which trunk accelerometry measures are suitable for the purpose of detecting movement compensations while running, and specifically in response to fatigue. The aim of this study was therefore to detect deviations in the dynamic center of mass (CoM) motion due to running-induced fatigue using tri-axial trunk accelerometry. Twenty runners aged 18–25 years completed an indoor treadmill running protocol to volitional exhaustion at speeds equivalent to their 3.2 km time trial performance. The following dependent measures were extracted from tri-axial trunk accelerations of 20 running steps before and after the treadmill fatigue protocol: the tri-axial ratio of acceleration root mean square (RMS) to the resultant vector RMS, step and stride regularity (autocorrelation procedure), and sample entropy. Running-induced fatigue increased mediolateral and anteroposterior ratios of acceleration RMS (p < .05), decreased the anteroposterior step regularity (p < .05), and increased the anteroposterior sample entropy (p < .05) of trunk accelerometry patterns. Our findings indicate that treadmill running-induced fatigue might reveal itself in a greater contribution of variability in horizontal plane trunk accelerations, with anteroposterior trunk accelerations that are less regular from step-to-step and are less predictable. It appears that trunk accelerometry parameters can be used to detect deviations in dynamic CoM motion induced by treadmill running fatigue, yet it is unknown how robust or generalizable these parameters are to outdoor running environments.     

Criterion validation of surface EMG variables as fatigue indicators using peak torque: a study of repetitive maximum isokinetic knee extensions.

A number of studies have been published that have used variables of the electromyogram (EMG) power spectrum during dynamic exercise. Despite these studies there is a shortage of studies of the validity of surface EMG registrations during repetitive dynamic contractions with respect to fatigue. The aim of this study was to investigate if the surface EMG variables mean frequency (MNF [Hz]) and the signal amplitude (RMS [microV]) are valid indicators of muscular fatigue (defined as "any exercise-induced reduction in the capacity to generate force or power output") during maximum repeated isokinetic knee extensions (i.e. criterion validity using peak torque). Twenty-one healthy volunteers performed 100 isokinetic knee extensions at 90 degrees s(-1). EMG signals were recorded from the vastus lateralis, the rectus femoris and the vastus medialis of the right thigh by surface electrodes. MNF and RMS of the EMG together with peak torque (PT [Nm]) were determined for each contraction. MNF showed consequently higher correlation coefficients with PT than RMS did. Positive correlations generally existed between MNF and PT. The majority of the subjects had positive correlations between RMS and PT (i.e. decreases both in PT and in RMS).In conclusion, at the individual level MNF generally - in contrast to RMS - showed good criterion validity with respect to biomechanical fatigue during dynamic maximum contractions.     

The effect of leg muscle activation state and localized muscle fatigue on tibial response during impact

The purpose of this research was to examine the effects of voluntarily manipulating muscle activation and localized muscle fatigue on tibial response parameters, including peak tibial acceleration, time to peak tibial acceleration, and the acceleration slope, measured at the knee during unshod heel impacts. A human pendulum delivered consistent impacts to 15 female and 15 male subjects. The tibialis anterior and lateral gastrocnemius were examined using electromyography, thus allowing voluntary contraction to various activation states (baseline, 15%, 30%, 45%, and 60% of the maximum activation state) and assessing localized muscle fatigue. A skin-mounted uniaxial accelerometer, preloaded medial to the tibial tuberosity, allowed tibial response parameter determination. There were significant decreases in peak acceleration during tibialis anterior fatigue, compared to baseline and all other activation states. In females, increased time to peak acceleration and decreased acceleration slope occurred during fatigue compared to 30% and 45%, and compared to 15% through 60% of the maximum activation state, respectively. Slight peak acceleration and acceleration slope increases, and decreased time to peak acceleration as activation state increased during tibialis anterior testing, were noted. When examining the lateral gastrocnemius, the time to peak acceleration was significantly higher across gender in the middle activation states than at the baseline and fatigue states. The acceleration slope decreased at all activation states above baseline in females, and decreased at 60% of the maximum activation state in males compared to the baseline and fatigue states. Findings agree with localized muscle fatigue literature, suggesting that with fatigue there is decreased impact transmission, which may protect the leg. The relative effects of leg stiffness and ankle angle on tibial response need to be verified.     

Lumbar muscles recruitment during resistance exercise for upper limbs

The aim of this study was to evaluate the EMG activity of lumbar multifidus (MU), longissimus thoracis (LT) and iliocostalis (IC) muscles during an upper limb resistance exercise (biceps curl). Ten healthy males performed maximal voluntary isometric contraction (MVC) of the trunk extensors, after this, the biceps curl exercise was executed at 25%, 30%, 35% and 40% one repetition maximum during 1 min, with 10 min rest between them. EMG root mean square (RMS) and median frequency (MFreq) were calculated for each lifting and lowering of the bar during the exercise bouts, to calculate slopes and intercepts. The results showed increases in the RMS and decreases in the MFreq slopes. RMS slopes were no different between muscles, indicating similar fatigue process along the exercise irrespective of the load level. MU and LT presented higher RMS irrespective of the load level, which can be related to the specific function during the standing position. On the other hand, IC and MU presented higher MFreq intercepts compared to LT, demonstrating possible differences in the muscle fiber conduction velocity of these muscles. These findings suggest that trunk muscles are differently activate during upper limb exercises, and the fatigue process affects the lumbar muscles similarly.     

Acoustic accelerometry reveals diel activity patterns in premigratory Port Jackson sharks

Distinguishing the factors that influence activity within a species advances understanding of their behavior and ecology. Continuous observation in the marine environment is not feasible but biotelemetry devices provide an opportunity for detailed analysis of movements and activity patterns. This study investigated the detail that calibration of accelerometers measuring root mean square (RMS) acceleration with video footage can add to understanding the activity patterns of male and female Port Jackson sharks (Heterodontus portusjacksoni) in a captive environment. Linear regression was used to relate RMS acceleration output to time‐matched behavior captured on video to quantify diel activity patterns. To validate captive data, diel patterns from captive sharks were compared with diel movement data from free‐ranging sharks using passive acoustic tracking. The RMS acceleration data showed captive sharks exhibited nocturnal diel patterns peaking during the late evening before midnight and decreasing before sunrise. Correlation analysis revealed that captive animals displayed similar activity patterns to free‐ranging sharks. The timing of wild shark departures for migration in the late breeding season corresponded with elevated diel activity at night within the captive individuals, suggesting a form of migratory restlessness in captivity. By directly relating RMS acceleration output to activity level, we show that sex, time of day, and sex‐specific seasonal behavior all influenced activity levels. This study contributes to a growing body of evidence that RMS acceleration data are a promising method to determine activity patterns of cryptic marine animals and can provide more detailed information when validated in captivity.     

Three-dimensional CFD analysis of the hand and forearm in swimming

The purpose of this study was to analyze the hydrodynamic characteristics of a realistic model of an elite swimmer hand/forearm using three-dimensional computational fluid dynamics techniques. A three-dimensional domain was designed to simulate the fluid flow around a swimmer hand and forearm model in different orientations (0°, 45°, and 90° for the three axes Ox, Oy and Oz). The hand/forearm model was obtained through computerized tomography scans. Steady-state analyses were performed using the commercial code Fluent. The drag coefficient presented higher values than the lift coefficient for all model orientations. The drag coefficient of the hand/forearm model increased with the angle of attack, with the maximum value of the force coefficient corresponding to an angle of attack of 90°. The drag coefficient obtained the highest value at an orientation of the hand plane in which the model was directly perpendicular to the direction of the flow. An important contribution of the lift coefficient was observed at an angle of attack of 45°, which could have an important role in the overall propulsive force production of the hand and forearm in swimming phases, when the angle of attack is near 45°.     

A comparison of the effects of agonist and antagonist muscle fatigue on performance of rapid movements

The aim of this study was to investigate the effects of agonist and antagonist muscle fatigue on the performance of rapid, self-terminating movements. Six subjects performed rapid, consecutive elbow flexion and extension movements between two targets prior to and after fatiguing either the elbow flexor or elbow extensor muscles. The experiments demonstrated consistent results. Agonist muscle fatigue was associated with a decrease in peak velocity and peak deceleration, while a decrease in peak acceleration was particularly prominent. Antagonist muscle fatigue, however, was associated with a decrease in peak deceleration, while a decrease in both the peak velocity and peak acceleration was modest and, in some tests, non-significant. The relative acceleration time (i.e. acceleration time as a proportion of the total movement time) increased when agonists were fatigued, but decreased when antagonists were fatigued. Taken together, these results emphasize the mechanical roles of the agonist and antagonist muscles; namely, the fatigue of each muscle group particularly affected the movement phase in which that group accelerated a limb, while changes of the movement kinematics pattern provided more time for action of the fatigued muscles. In addition, the results presented suggest that agonist muscle fatigue affects movement velocity more than antagonist muscle fatigue, even in movements that demonstrate prominently both mechanical and myoelectric activity of the antagonist muscles, such as rapid, self-terminating movements. Accepted: 11 February 1997     

Relationship between neuromuscular fatigue and spasticity in chronic stroke patients: A pilot study

IntroductionThe aim of this study was to assess the effects of neuromuscular fatigue on stretch reflex-related torque and electromyographic activity of spastic knee extensor muscles in hemiplegic patients. The second aim was to characterize the time course of quadriceps muscle fatigue during repetitive concentric contractions.MethodsEighteen patients performed passive, isometric and concentric isokinetic evaluations before and after a fatigue protocol using an isokinetic dynamometer. Voluntary strength and spasticity were evaluated following the simultaneous recording of torque and electromyographic activity of rectus femoris (RF), vastus lateralis (VL) and biceps femoris (BF).ResultsIsometric knee extension torque and the root mean square (RMS) value of VL decreased in the fatigued state. During the fatigue protocol, the normalized peak torque decreased whereas the RMS of RF and BF increased between the first five and last five contractions. There was a linear decrease in the neuromuscular efficiency-repetitions relationships for RF and VL. The peak resistive torque and the normalized RMS of RF and VL during passive stretching movements were not modified by the fatigue protocol for any stretch velocity.DiscussionThis study showed that localized quadriceps muscle fatigue caused a decrease in voluntary strength which did not modify spasticity intensity. Changes in the distribution of muscle fiber type, with a greater number of slow fibers on the paretic side, may explain why the stretch reflex was not affected by fatigue.     

High resolution electrocardiography in healthy dogs: time domain parameters and comparison of the non-stationary (Wigner distribution) versus standard stationary frequency domain analysis methods

Fractionated heart activation can be detected as late potentials from surface recordings of signal-averaged electrocardiograms (SA ECG) which are considered as a marker of sustained ventricular tachycardia. For animal studies, reference values in time and frequency domain analyses are essentially missing. In the present study, we have established reference values in SA ECG time domain analysis and time-frequency representation of heart activation in healthy dogs. A group of 25 healthy mongrel dogs (body weight 12-15 kg) was investigated. Wigner distribution and our modification of Fast Fourier transform (FFT), gliding window FFT, was applied in SA ECG frequency domain analysis. Reference values in time domain SA ECG were established. Time and voltage criteria were adapted to short duration of heart cycle and fast voltage decrement of the QRS complex in dogs. Wigner distribution and gliding window FFT were applied in order to describe mean heart activation in the frequency domain. Contribution of higher frequencies (30-80 Hz) was detected by both frequency analysis methods in the second third of ventricular activation in healthy animals. Presented results could offer a basis for further experimental arrhythmologic studies.     

Test-retest reliability of EMG and peak torque during repetitive maximum concentric knee extensions.

The aim of this study was to investigate the reliability of peak torque and surface electromyography (EMG) variable's root mean square (RMS) and mean frequency (MNF) during an endurance test consisting of repetitive maximum concentric knee extensions. Muscle fatigue has been quantified in several ways, and in isokinetic testing it is based on a set of repetitive contractions. To assess test-retest reliability, two sets of 100 dynamic maximum concentric knee extensions were performed using an isokinetic dynamometer. The two series were separated by 7-8 days. The subjects relaxed during the passive flexion phase. Twenty (10 men and 10 women) clinically healthy subjects volunteered.Peak torque and EMG from rectus femoris, vastus medialis, vastus lateralis and biceps femoris were recorded. RMS and MNF were calculated from the EMG signal. The reliability was calculated with intraclass correlation coefficient ICC (1.1) and standard error of measurements (SEM). The reliability of peak torque was good (ICC=0.93) and SEM showed low values. ICC was good for absolute RMS of rectus femoris (ICC>/=0.80), vastus medialis (ICC>/=0.88) and vastus lateralis (ICC>/=0.82) and MNF of rectus femoris (ICC>/=0.82) and vastus medialis (ICC>/=0.83). Peak torque, and MNF and RMS of rectus femoris and vastus medialis are reliable variables obtained from an isokinetic endurance test of the knee extensors.     

Muscle Activity Adaptations to Spinal Tissue Creep in the Presence of Muscle Fatigue

Aim

The aim of this study was to identify adaptations in muscle activity distribution to spinal tissue creep in presence of muscle fatigue.

Methods

Twenty-three healthy participants performed a fatigue task before and after 30 minutes of passive spinal tissue deformation in flexion. Right and left erector spinae activity was recorded using large-arrays surface electromyography (EMG). To characterize muscle activity distribution, dispersion was used. During the fatigue task, EMG amplitude root mean square (RMS), median frequency and dispersion in x- and y-axis were compared before and after spinal creep.

Results

Important fatigue-related changes in EMG median frequency were observed during muscle fatigue. Median frequency values showed a significant main creep effect, with lower median frequency values on the left side under the creep condition (p≤0.0001). A significant main creep effect on RMS values was also observed as RMS values were higher after creep deformation on the right side (p = 0.014); a similar tendency, although not significant, was observed on the left side (p = 0.06). A significant creep effects for x-axis dispersion values was observed, with higher dispersion values following the deformation protocol on the left side (p≤0.001). Regarding y-axis dispersion values, a significant creep x fatigue interaction effect was observed on the left side (p = 0.016); a similar tendency, although not significant, was observed on the right side (p = 0.08).

Conclusion

Combined muscle fatigue and creep deformation of spinal tissues led to changes in muscle activity amplitude, frequency domain and distribution.     

Short-term in-season ballistic training improves power,muscle volume and throwing velocity in junior handball players. A randomized control trial

This study investigated the effects of a ballistic training programme using an arm/shoulder specific strength device (ASSSD) on the upper body peak power (PP), muscle volume (MV) of the dominant arm and throwing velocity in junior handball players. Twenty-six players were randomly assigned to an experimental (EG = 15, age 17.6 ± 0.51 years) and control (CG = 11, age 17.36 ± 0.50 years) group. Over an 8-week in-season period, the EG performed a ballistic training programme (2 sessions/week) immediately before their normal team handball training. Both groups underwent tests on the ASSSD, which operates in consecutive accelerative and decelerative actions, for throwing characteristics determination. Peak power (PP), peak force (PF), peak velocity (PV), peak rate of power development (PRPD), muscle volume (MV), throwing velocity with runup, standing throw, and jump throw were also assessed before/after the training programme. The EG group showed significant post-training improvements in PP (52.50% – p < 0.001), PF (26.45% – p < 0.01) and PRPD (78.47% – p < 0.001) better than the CG (1.81, 0.67 and 1.64%, p > 0.05, respectively). There was also a post-training improvement in the velocity at PP (22.82% – p < 0.001) and PF (42.45% – p < 0.001) in the EG compared to the CG (4.18 and 8.53%, p > 0.05 respectively). There was a significant increase in acceleration at PP (51.50% – p < 0.01) and PF (69.67% – p < 0.001). MV increased (19.11% – p < 0.001) in the EG, with no significant change (3.34% – p = 0.84) in the CG. Finally, significant increases were obtained in the three throw types (3.1–6.21%, p < 0.05- < 0.001) in the EG compared to the CG. The additional ASSSD training protocol was able to improve muscle strength/volume and ball throwing velocity in junior handball players.     

Gender-related differences in maximum mechanical power output in short-term activities in children and adolescents

The study was designed to examine the gender-related differences in maximum mechanical power output in various short-burst activities during growth. The subject sample consisted of four subgroups: 9 boys (14.11 +/- 0.6 yr), 9 boys (10.67 +/- 0.71 yr), 7 girls (14.29 +/- 0.49 yr), 7 girls (10.57 +/- 0.54 yr). We measured peak power (PP), mean power (MP), fatigue index (FI) during 30-s WAnT, squat jump height (SJH) and power (SJP), and counter movement jump height (CMJH) and power (CMJP), maximum speed over 20-metre distance (S20). Lactation concentration was measured in the 3rd and 5th minutes after the WAnT Ratio normalisation and ANCOVA were used to remove the influence of the differences in muscle (MM) and body mass (BM). Male adolescents had higher absolute values of PP (P < 0.05), MP (P < 0.05) than female. Ratio normalisation showed that boys had higher PP/BM (P < 0.05), PP/MM (P < 0.05), MP/BM (P < 0.05), MP/MM (P < 0.06) than girls. The ANCOVA adjustment for MM showed differences between genders in PP (P < 0.001), MP (P < 0.001), SJH (P < 0.05), SJP (P < 0.05) and CMJP (P < 0.001), whereas the ANCOVA adjustment for BM showed differences only in PP (P < 0.001), MP (P < 0.001). Prepubertal boys had higher absolute values only in SJP (P < 0.05). We concluded that variations in body composition could not be the only key to gender-related differences in power output in short-burst activities.