Christos Paizis

Effects of an Electrostimulation Training Program on Strength, Jumping, and Kicking Capacities in Soccer Players

Billot, M, Martin, A, Paizis, C, Cometti, C, and Babault, N. Effects of an electrostimulation training program on strength, jumping, and kicking capacities in soccer players. J Strength Cond Res 24(5): 1407-1413, 2010-The present study investigated the influence of a 5-week electrostimulation (EMS) training program on muscular strength, kicking velocity, sprint, and vertical jump performance in soccer players. Twenty amateur soccer players participated in the study, 10 in the electrostimulated group and the remaining 10 in a control group. Electrostimulation was applied on the quadriceps muscles over 5 weeks. Subjects were tested before, during (wk-3), and after (wk-5) the EMS training program. Maximal voluntary contraction using different contraction mode (i.e., eccentric, concentric, and isometric), vertical jump height, sprint running for 10 m, and ball speed were examined. We observed an increase in isometric and eccentric maximal knee extension torques and also a gain in ball speed performance without run up at wk-3. After 5 weeks of EMS training, eccentric, isometric, and concentric torques and ball speed had significantly improved. It appeared appropriate to conduct EMS training during at least 3 weeks to observe beneficial effects in specific soccer skills such as ball speed.

Effects of different unstable supports on EMG activity and balance

This study analysed the equilibrium strategies and EMG activity during postural equilibrium in four different unstable surfaces. Thirteen team sport males were tested on a FLAT surface and on three different wobble boards (JAKOBS(®) with easy multidirectional displacements, FREEMAN with strong multidirectional displacements and LATERAL with unidirectional lateral displacements). They had to maintain single-limb stance during 5s for each condition. The right foot centre of pressure (COP) position and its variability with concomitant EMG activity of soleus (SOL), tibialis anterior (TA), peroneus longus (PL) and extensor digitorum longus (EXD) muscles were recorded. Subjects maintained balance by making seesaw rotations. LATERAL and FREEMAN boards demonstrated significantly greater COP variability than JAKOBS(®) and FLAT in both anteroposterior and mediolateral directions. Similarly, PL, EXD, and TA muscles EMG activity were significantly greater using the LATERAL board, and in some cases using FREEMAN as compared with JAKOBS(®) and FLAT. These results highlighted new knowledge about central nervous system organisation while keeping equilibrium with a predominant anteroposterior control.

Dominant vs. nondominant arm advantage in mentally simulated actions in right handers

Although plentiful data are available regarding mental states involving the dominant-right arm, the evidence for the nondominant-left arm is sparse. Here, we investigated whether right-handers can generate accurate predictions with either the right or the left arm. Fifteen adults carried out actual and mental arm movements in two directions with varying inertial resistance (inertial anisotropy phenomenon). We recorded actual and mental movement times and used the degree of their similarity as an indicator for the accuracy of motor imagery/prediction process. We found timing correspondences (isochrony) between actual and mental right arm movements in both rightward (low inertia resistance) and leftward (high inertia resistance) directions. Timing similarities between actual and mental left arm movements existed for the leftward direction (low inertia resistance) but not for the rightward direction (high inertia resistance). We found similar results when participants reaching towards the midline of the workspace, a result that excludes a hemispace effect. Electromyographic analysis during mental movements showed that arm muscles remained inactivate, thus eliminating a muscle activation strategy that could explain intermanual differences. Furthermore, motor-evoked potentials enhancement in both right and left biceps brachii during mental actions indicated that subjects were actively engaged in mental movement simulation and that the disadvantage of the left arm cannot be attributed to the nonactivation of the right motor cortex. Our findings suggest that predictive mechanisms are more robust for the right than the left arm in right-handers. We discussed these findings from the perspective of the internal models theory and the dynamic-dominance hypothesis of laterality.

Effects of combined electromyostimulation and gymnastics training in prepubertal girls.

Deley, G, Cometti, C, Fatnassi, A, Paizis, C, and Babault, N. Effects of combined electromyostimulation and gymnastics training in prepubertal girls. J Strength Cond Res 25(2): 520-526, 2011-This study investigated the effects of a 6-week combined electromyostimulation (EMS) and gymnastic training program on muscle strength and vertical jump performance of prepubertal gymnasts. Sixteen young women gymnasts (age 12.4 ± 1.2 yrs) participated in this study, with 8 in the EMS group and the remaining 8 as controls. EMS was conducted on knee extensor muscles for 20 minutes 3 times a week during the first 3 weeks and once a week during the last 3 weeks. Gymnasts from both groups underwent similar gymnastics training 5-6 times a week. Isokinetic torque of the knee extensors was determined at different eccentric and concentric angular velocities ranging from −60 to +240° per second. Jumping ability was evaluated using squat jump (SJ), counter movement jump (CMJ), reactivity test, and 3 gymnastic-specific jumps. After the first 3 weeks of EMS, maximal voluntary torque was increased (+40.0 ± 10.0%, +35.3 ± 11.8%, and +50.6 ± 7.7% for −60, +60, and +240°s−1, respectively; p < 0.05), as well as SJ, reactivity test and specific jump performances (+20.9 ± 8.3%, +20.4 ± 26.2% and +14.9 ± 17.2% respectively; p < 0.05). Six weeks of EMS were necessary to improve the CMJ (+10.1 ± 10.0%, p < 0.05). Improvements in jump ability were still maintained 1 month after the end of the EMS training program. To conclude, these results first demonstrate that in prepubertal gymnasts, a 6-week EMS program, combined with the daily gymnastic training, induced significant increases both in knee extensor muscle strength and nonspecific and some specific jump performances.

Motor Asymmetry Attenuation in Older Adults during Imagined Arm Movements

Laterality is an important feature of motor behavior. Several studies have shown that lateralization in right-handed young adults (i.e., right versus left arm superiority) emerges also during imagined actions, that is when an action is internally simulated without any motor output. Such information, however, is lacking for elderly people and it could be valuable to further comprehend the evolution of mental states of action in normal aging. Here, we evaluated the influence of age on motor laterality during mental actions. Twenty-four young (mean age: 24.7u2009±u20094.4u2009years) and 24 elderly (mean age: 72.4u2009±u20093.6u2009years) participants mentally simulated and actually executed pointing movements with either their dominant-right or non-dominant-left arm in the horizontal plane. We recorded and analyzed the time of actual and mental movements and looked for differences between groups and arms. In addition, electromyographic activity from arm muscle was recorded to quantify any enhancement in muscle activation during mental actions. Our findings indicated that both groups mentally simulated arm movements without activating the muscles of the right or the left arm above the baseline level. This finding suggests that young and, notably, elderly adults are able to generate covert actions without any motor output. We found that manual asymmetries (i.e., faster movements with the right arm) were preserved in young adults for both actual and mental movements. In elderly adults, manual asymmetries were observed for actual but not for mental movements (i.e., equal movement times for both arms). These findings clearly indicate an age-related reduction of motor laterality during mental actions.

Direct Relation of Acute Effects of Static Stretching on Isokinetic Torque Production With Initial Flexibility Level

PURPOSEnTo examine the acute effect of a single static-stretching session of hamstring muscles on torque production in relation with individual flexibility.nnnMETHODSnMaximal voluntary concentric torque of hamstring muscles was measured before and after a static-stretching session (6 × 30 s). Torque changes were correlated with the flexibility level determined at the onset of the experimental procedure.nnnRESULTSnThe hamstring-stretching intervention significantly reduced maximal concentric torque in participants with low and high hamstring flexibility. Hamstring flexibility and torque decrease, determined immediately after the stretching procedure, were negatively correlated.nnnCONCLUSIONSnTorque decrease measured after the static-stretching session is dependent on participant flexibility. Participants with low flexibility are much more likely to demonstrate large torque decreases poststretching.

Changes in cortico-spinal excitability following uphill versus downhill treadmill exercise

HighlightsLocomotor exercise enhance corticospinal excitability in a non‐exercised muscle.No effect of the mode of muscle contraction in corticospinal excitability changes.After PAS25, exercise induced changes in corticospinal excitability were different. ABSTRACT An acute bout of aerobic exercise induces neuroplasticity in the motor cortex. Moreover, paired associative stimulation (PAS) is known to induce neuroplasticity in M1. However, the possible influence of the type of exercise on the neuroplastic changes remains unknown. The present study investigated the effects of two different modes of muscle contraction produced during locomotor exercise on changes in corticospinal (CS) excitability. Subjects performed two 30‐min treadmill exercises at an intensity corresponding to 60% of their maximal heart rate with either a +10% (uphill) or −10% (downhill) slope. These exercises were followed or not by paired associative stimulation method (PAS25) which consisted of 200 paired stimuli (0.25 Hz, 15 min) of median nerve electrical stimulation followed by transcranial magnetic stimulation of the hand M1 area (ISI 25 ms). Motor evoked potentials (MEP), assessed through abductor pollicis brevis (APB) activity were obtained before exercise, at 5 min, 15 min and 30 min after exercise. A significant (P < 0.05) increase of the MEP amplitude was observed 30 min after both exercises but was not different between the two modes of locomotion. On the contrary, MEP amplitude with PAS25 increased only 30 min after downhill exercise. We conclude that sub‐maximal treadmill exercise increases CS excitability within a period of 30 min. However, the predominant mode of muscle contraction during uphill versus downhill locomotion does not influence CS excitability when assessed using a non‐exercised muscle. However, results from PAS25 suggest that specific neuroplastic changes occur likely due to homeostatic mechanisms induced by exercise plus a PAS protocol.

Corticospinal changes induced by fatiguing eccentric versus concentric exercise

Abstract The present study assessed neuromuscular and corticospinal changes during and after a fatiguing submaximal exercise of the knee extensors in different modes of muscle contraction. Twelve subjects performed two knee extensors exercises in a concentric or eccentric mode, at the same torque and with a similar total impulse. Exercises consisted of 10 sets of 10 repetitions at an intensity of 80% of the maximal voluntary isometric contraction torque (MVIC). MVIC, maximal voluntary activation level (VAL) and responses of electrically evoked contractions of the knee extensors were assessed before and after exercise. Motor evoked potential amplitude (MEP) and cortical silent period (CSP) of the vastus medialis (VM) and rectus femoris (RF) muscles were assessed before, during and after exercise. Similar reductions of the MVIC (−13%), VAL (−12%) and a decrease in the peak twitch (−12%) were observed after both exercises. For both VM and RF muscles, MEP amplitude remained unchanged during either concentric or eccentric exercises. No change of the MEP amplitude input–output curves was observed post-exercise. For the RF muscle, CSP increased during the concentric exercise and remained lengthened after this exercise. For the VM muscle, CSP was reduced after the eccentric exercise only. For a similar amount of total impulse, concentric and eccentric knee extensor contractions led to similar exercise-induced neuromuscular response changes. For the two muscles investigated, no modulation of corticospinal excitability was observed during or after either concentric or eccentric exercises. However, intracortical inhibition showed significant modulations during and after exercise.

Performance determinants of fixed gear cycling during criteriums

Abstract Nowadays, fixed gear competitions on outdoor circuits such as criteriums are regularly organized worldwide. To date, no study has investigated this alternative form of cycling. The purpose of the present study was to examine fixed gear performance indexes and to characterize physiological determinants of fixed gear cyclists. This study was carried out in two parts. Part 1 (nu2009=u200936) examined correlations between performance indexes obtained during a real fixed gear criterium (time trial, fastest laps, averaged lap time during races, fatigue indexes) and during a sprint track time trial. Part 2 (nu2009=u20099) examined correlations between the recorded performance indexes and some aerobic and anaerobic performance outputs (VO2max, maximal aerobic power, knee extensor and knee flexor maximal voluntary torque, vertical jump height and performance during a modified Wingate test). Results from Part 1 indicated significant correlations between fixed gear final performance (i.e. average lap time during the finals) and single lap time (time trial, fastest lap during races and sprint track time trial). In addition, results from Part 2 revealed significant correlations between fixed gear performance and aerobic indicators (VO2max and maximal aerobic power). However, no significant relationship was obtained between fixed gear cycling and anaerobic qualities such as strength. Similarly to traditional cycling disciplines, we concluded that fixed gear cycling is mainly limited by aerobic capacity, particularly criteriums final performance. However, specific skills including technical competency should be considered.

Neuromuscular and perceptual responses to moderate-intensity incline, level and decline treadmill exercise

PurposeTo describe the neuromuscular and perceptual responses to incline, decline or level treadmill exercise.MethodsFifteen healthy subjects performed on separate days 45xa0min treadmill exercise at 75% heart rate reserve in a level (+u20091% slope), incline (+u200915%) or decline condition (−u200915%). Neuromuscular function of the knee extensors (KE) was assessed before and after exercise. Perception of effort, muscle pain and pleasure were measured during the exercise. Muscle pain was also reported up to 96xa0h after exercise.ResultsAt the same heart rate, the decline exercise was performed at a higher velocity. This higher velocity was associated with a higher perceived effort and muscle pain, as well as lower pleasure. Maximal isometric KE peak torque and maximal voluntary activation similarly decreased in the three conditions (~u200915u2009±u200912 and ~u20094u2009±u20094%). M-wave amplitude of the vastus medialis muscle decreased in the three conditions (~u2009−u200912u2009±u200913%). M-wave amplitude of the rectus femoris muscle decreased only after the decline exercise (−u200912u2009±u200916%). Peak twitch torque of the electrically evoked contractions was reduced after incline and decline exercises for both 10 and 100xa0Hz doublets (−u20098u2009±u20099 and −u200917u2009±u200918%). The Dt10/Dt100 ratio was reduced only after decline exercise (−u200924u2009±u200919%).ConclusionAt the same moderate intensity, decline exercise induced a greater level of muscle fatigue associated with a higher perceived effort and muscle pain than incline and level exercise. Exercise intensity should be carefully monitored during decline locomotion for training or rehabilitation purposes.