Nidhal Zarrouk

Diurnal Variation in Wingate-Test Performance and Associated Electromyographic Parameters

The present study was designed to evaluate time-of-day effects on electromyographic (EMG) activity changes during a short-term intense cycling exercise. In a randomized order, 22 male subjects were asked to perform a 30-s Wingate test against a constant braking load of 0.087 kg·kg−1 body mass during two experimental sessions, which were set up either at 07:00 or 17:00 h. During the test, peak power (Ppeak), mean power (Pmean), fatigue index (FI; % of decrease in power output throughout the 30 s), and evolution of power output (5-s span) throughout the exercise were analyzed. Surface EMG activity was recorded in both the vastus lateralis and vastus medialis muscles throughout the test and analyzed over a 5-s span. The root mean square (RMS) and mean power frequency (MPF) of EMG were calculated. Neuromuscular efficiency (NME) was estimated from the ratio of power to RMS. Resting core temperature, Ppeak, Pmean, and FI were significantly higher (p < .05) in the evening than morning test (e.g., Ppeak: 11.6 ± 0.8 vs. 11.9 ± 1 W·kg−1). The results showed that power output decreased following two phases. During the first phase (first 20s), power output decreased rapidly and values were higher (p < .05) in the evening than in the morning. During the second phase (last 10s), power decreased slightly and appeared independent of the time of day of testing. This power output decrease was paralleled by evolution of the MPF and NME. During the first phase, NME and MPF were higher (p < .05) in the evening. During the second phase, NME and MPF were independent of time of day. In addition, no significant differences were noticed between 7:00 and 17:00 h for EMG RMS during the whole 30 s. Taken together, these results suggest that peripheral mechanisms (i.e., muscle power and fatigue) are more likely the cause of the diurnal variation of the Wingate-test performance rather than central mechanisms. (Author correspondence: n_souissi@yahoo.fr)

The acute effect of whole body vibration on repeated shuttle-running in young soccer players.

The aim of this study was to investigate the acute effects of whole-body vibration (WBV) on Repeated Sprint Ability (RSA). Seventeen male soccer players (16.71±0.47 y) performed three RSA tests (Randomized crossover study design). The second RSA test was done with WBV (RSA2) to assess the effect of WBV. The studied variables were: best time (BT), worst time (WT), total time (TT), the fatigue index (FI) of RSA, and post-test blood lactate (BLa). ANOVA with repeated measures showed no differences between RSA1 and RSA3, while there were significant differences in all variables studied. TT= [RSA2 0.93% and 1.68% lower than RSA1 and RSA3 respectively; p<0.05], BLa= [RSA2 16.97% and 14.73% greater than RSA1 and RSA3 respectively; p<0.001], WT= [RSA2 1.90% and 2.93% lower than RSA1 and RSA3 respectively; p<0.01], and FI = [RSA2 30.64% and 40.15% lower than RSA1 and RSA3 respectively; p<0.0001]. When comparing individual sprints, WBV showed a significant effect at the 5th sprint: RSA2 2.29% and 2.95% lower than RSA1 and RSA3 respectively (p<0.005), while at the 6th sprint: RSA2 2.75% and 4.09% lower than RSA1 and RSA3 respectively; p<0.005. In conclusion, when applying WBV during the recovery periods of Repeated Sprint Ability efforts, most of the performance variables improved.

Individuals with intellectual disability have lower voluntary muscle activation level

The aim of this study was to explore the voluntary activation level during maximal voluntary contraction (MVC) in individuals with intellectual disability (ID) versus individuals without ID using the twitch interpolation technique. Ten individuals with mild ID (ID group) and 10 sedentary men without ID (control group) participated in this study. The evaluation of neuromuscular function consisted in three brief MVCs (3s) of the knee extension superimposed with electrical nerve stimulation (NES) to measure voluntary activation. Muscle activity levels were also measured with surface EMG. The root mean square (RMS) was extracted from the EMG signal. The RMS/Mmax ratio and the neuromuscular efficiency (NME) were calculated. Our results reported that individuals with ID present lower muscle strength (p < 0.001), lower voluntary activation level (p < 0.001), lower RMS values of vastus lateralis (p < 0.05), vastus medialis (p < 0.05), and rectus femoris (p < 0.001) muscles. In addition, our results showed lower RMS/Mmax values in the ID group than in the control group for the VM (0.05 ± 0.01 mV vs. 0.04 ± 0.01 mV; p < 0.05) and the RF (0.06 ± 0.02 mV vs. 0.05 ± 0.02 mV; p < 0.05) muscles. However, no significant difference was reported for the VL muscle (0.05 ± 0.02 mV vs. 0.05 ± 0.02 mV; p=0.463). Moreover, Individuals with ID present smaller potentiated twitch (p < 0.001). However, no significant difference was reported in the NME ratio. These results suggest that the lower muscle strength known in individuals with ID is related to a central nervous system failure to activate motor units and to some abnormal intrinsic muscle properties. It seems that the inactive lifestyle adopted by individuals with ID is one of the most important factors of their lower voluntary activation levels. Therefore, physical activities should be introduced in life style of individuals with ID to improve their neuromuscular function.

Neuromuscular fatigue during high-intensity intermittent exercise in individuals with intellectual disability

This study examined neuromuscular fatigue after high-intensity intermittent exercise in 10 men with mild intellectual disability (ID) in comparison with 10 controls. Both groups performed three maximal voluntary contractions (MVC) of knee extension with 5 min in-between. The highest level achieved was selected as reference MVC. The fatiguing exercise consists of five sets with a maximal number of flexion-extension cycles at 80% of the one maximal repetition (1RM) for the right leg at 90° with 90 s rest interval between sets. The MVC was tested again after the last set. Peak force and electromyography (EMG) signals were measured during the MVC tests. Root Mean Square (RMS) and Median Frequency (MF) were calculated. Neuromuscular efficiency (NME) was calculated as the ratio of peak force to the RMS. Before exercise, individuals with ID had a lower MVC (p<0.05) and a lower RMS (p<0.05). No significant difference between groups in MF and NME. After exercise, MVC decreases significantly in both groups (p<0.001). Individuals with ID have greater force decline (p<0.001 vs. p<0.01). RMS decreased significantly (p<0.001) whereas the NME increased significantly (p<0.05) in individuals with ID, but both remained unchanged in controls. The MF decreased significantly in both groups (p<0.001). In conclusion, individuals with ID presented a lower peak force than individuals without ID. After a high-intensity intermittent exercise, individuals with ID demonstrated a greater force decline caused by neural activation failure. When rehabilitation and sport train ID individuals, they should consider this nervous system weakness.

Effect of Ramadan intermittent fasting on body composition and neuromuscular performance in young athletes: a pilot study

There is a conflict in the literature with regard to effects of the Ramadan intermittent fasting (RIF) on body composition and neuromuscular performance. The purpose of this pilot study was to examine the effect of the RIF on body mass/composition and neuromuscular performance during maximal voluntary contraction (MVC) and a muscle endurance exercise (Tlim ) of the knee extensors. Eight adolescents (17.2 ± 0.5 years) karate players were tested. Anthropometric variables (i.e. body mass, body mass index, fat mass and lean body mass) were evaluated 7 days before Ramadan (T1), and on days 7 (T2) and 28 (T3) of Ramadan. Each subject performed three MVC and a Tlim at 75% of MVC at T1, T2, and T3. Surface electromyographic (EMG) activity of vastus lateralis and vastus medialis was recorded during these neuromuscular tests. The anthropometric variables were unaltered by RIF. Likewise, there was no significant effect of RIF on the MVC (P = 0.29) and the Tlim (P = 0.22). This result was in accordance with the absence of change in both EMG activity level during MVC and in the rate of changes in EMG parameters (EMG activity level and frequency content) during Tli m . The results of the present study suggest that RIF does not impair maximal force generating capacity and muscle endurance at 75% of MVC. Therefore, Muslim experienced athletes could maintain their neuromuscular performance level by undertaking usual training loads during RIF.

Time-of-day effects on postural control and attentional capacities in children

The present study aimed to examine the effect of time-of-day on postural control, body temperature, and attentional capacities in 5-6 year old children. Twelve male children (5-6-year-old) were asked to maintain an upright bipedal stance on a force platform with eyes open (EO) and eyes closed (EC) at 07:00, 10:00, 14:00, and 18:00 h. Postural control was evaluated by center of pressure (CoP) surface area (CoPArea), CoP mean velocity (CoPVm), length of the CoP displacement as a function of the surface (LFS) ratio and Rombergs index (RI). Oral temperature and the simple reaction time were also recorded at the beginning of each test session. The one way ANOVA (4 time-of-day) showed significant time-of-day effects on CoPArea (p<0.001), CoPVm (p<0.01), LFS ratio (p<0.001) and RI (p<0.01). Childrens postural control was lower at 07:00 h and at 14:00 h in comparison with 10:00 h and 18:00 h. Likewise, the reaction time was significantly (p<0.001) better at 10:00 h and 18:00 h in comparison with 07:00 h and 14:00 h. Oral temperature was higher at 14:00 h and 18:00 h than 08:00 h and 10:00 h (p<0.001). In conclusion, the childrens postural control fluctuates during the daytime (i.e., better postural control at 10:00 h and at 18:00 h) with a diurnal rhythm close to that of body temperature and attentional capacities. Therefore, the evaluation of changes in postural control of 5-6-year-old children using force plate measures is recommended in the middle morning or the late afternoon to avoid the post-awakening and the post-prandial phases.

Comparison of Recovery Strategies on Maximal Force-Generating Capacity and Electromyographic Activity Level of the Knee Extensor Muscles

CONTEXT With regard to intermittent training exercise, the effects of the mode of recovery on subsequent performance are equivocal. OBJECTIVE To compare the effects of 3 types of recovery intervention on peak torque (PT) and electromyographic (EMG) activity of the knee extensor muscles after fatiguing isokinetic intermittent concentric exercise. DESIGN Crossover study. SETTING Research laboratory. PATIENTS OR OTHER PARTICIPANTS Eight elite judo players (age = 18.4 ± 1.4 years, height = 180 ± 3 cm, mass = 77.0 ± 4.2 kg). INTERVENTION(S) Participants completed 3 randomized sessions within 7 days. Each session consisted of 5 sets of 10 concentric knee extensions at 80% PT at 120°/s, with 3 minutes of recovery between sets. Recovery interventions were passive, active, and electromyostimulation. The PT and maximal EMG activity were recorded simultaneously while participants performed isokinetic dynamometer trials before and 3 minutes after the resistance exercise. MAIN OUTCOME MEASURE(S) The PT and maximal EMG activity from the knee extensors were quantified at isokinetic velocities of 60°/s, 120°/s, and 180°/s, with 5 repetitions at each velocity. RESULTS The reduction in PT observed after electromyostimulation was less than that seen after passive (P < .001) or active recovery (P < .001). The reduction in PT was less after passive recovery than after active recovery (P < .001). The maximal EMG activity level observed after electromyostimulation was higher than that seen after active recovery (P < .05). CONCLUSIONS Electromyostimulation was an effective recovery tool in decreasing neuromuscular fatigue after high-intensity, intermittent isokinetic concentric exercise for the knee extensor muscles. Also, active recovery induced the greatest amount of neuromuscular fatigue.

Effect of heavy isokinetic intermittent exercise on acute neuromuscular fatigue in knee extensors

This study aimed at quantifying maximal voluntary force-generating capacity of the quadriceps femoris and its EMG output after an isokinetic concentric intermittent exercise. Another objective was to find out whether the amount of neuromuscular fatigue was velocity-dependent. Eight males judo players (age: 18.4 ± 1.4 years; height: 1.80 ± 0.03 m; body mass: 77.0 ± 4.2 kg) performed a fatiguing exercise composed of five sets of ten maximal knee extension at 120°/s, with 3min recovery in between. Peak torque (PT) at three angular velocities (60, 120 and 180°/s) and EMG from the vastus lateralis, rectus femoris and vastus medialis were evaluated before and after the fatiguing exercise. EMG was analyzed for root mean square (RMS) and median frequency (MF). The fatiguing exercise induced PT decrement (P< 0.01) irrespective of the test velocity, in conjunction with decreased RMS (P< 0.001) and a decrease in MF (P< 0.01). In addition, although EMG activity demonstrated no velocity effect, the loss of PT after the fatiguing isokinetic intermittent exercise was more pronounced at the lower velocity (P< 0.05). The combination of decreased PT, RMS and MF suggests a reduction of the neural drive under the present fatiguing protocol.

Long-term basketball playing enhances bone mass and isokinetic muscle strength

Aim: To evaluate bone mass in female basketball players and the relationship between bone mineral density (BMD) and isokinetic muscle strength. Methods: We investigated 29 female basketball players, age 21.9± 9.1 years, training for about 6–8 hours per week. The reference group consisted of 22 non-active female, age 21.4 ± 1.5 years. BMD was measured using dual-energy-X-ray absorptiometry in total body, lumbar spine, the whole femur and humerus. Isokinetic peak torque of the quadriceps and hamstring muscles were measured at 60 and 180◦/s. Osteocalcin (OC) and cross-linked C-telopeptide (CTX) were measured by radioimmunoassay and electrochimiluminescence, respectively. Results: Compared to the controls, the basketball group had significantly (P < 0.001) a higher BMD in the total body (11.6%), the lumbar spine (9.83%), the dominant femur (16.8%), the non-dominant femur (15.8%) and the dominant humerus (8.47%). The female basketball players had also significantly higher peak torques at both isokinetic velocities (60 and 180◦/s) and for both lower limbs. All muscle peak torque measured for the female basketball players were significantly correlated with correspondent leg BMD and for both velocities tested. However, no significant correlations were noted for the control group. Values of formation (OC) and resorption (CTX) markers were significantly higher in the athletic females (P < 0.01 and P < 0.05, respectively). Conclusion: Our results show clearly that practice of basketball is associated with the improvement of bone mass. In addition, the most important finding of our study is that isokinetic muscle strength seems to be correlated with correspondent BMD in female basketball players.

Biomechanical Model of the Knee to Estimate the Musculotendinous Forces during an Isometric Extension

In this work, we present an improved biomechanical model of the knee and the muscle group involved to ensure the movement of extension of the knee joint, under an external load. The problem of redundancy is solved by presenting the problem as an optimization procedure. In order to identify the best objective function to be optimized, we carried out some experimental tests during which measurements of some tendon forces were performed using EMG sensors.