On the trail of Maffiuletti

electrostimulation, since for 15 years he has made great contributions at an international level. In this article we will go through some of the published articles in which this leading researcher has participated for many.

 In 2000, a publication by Maffiuletti and his colleagues was indexed in which the effects of electrostimulation were investigatedin basketball training and practice on muscle strength and jumping ability. This study presented a randomized clinical trial in which 20 young basketball players (mean 24.7 (3.9) years) underwent 4 weeks of training, with half being distributed in the control group, and the other half in the experimental electrostimulation group. The group that performed electrostimulation did it 3 times a week. Electrostimulation consisted of stimulation of the vastus quadriceps while the knee was fixed in a machine at 60 ° extension. The parameters were 100 Hz, at 400? S, with 3 seconds of impulse and 17 seconds of rest. During training each muscle performed 48 contractions. The intensity (milliamps) was monitored online and was determined based on 80% of the MCV (maximum voluntary contraction) that was detected at the beginning of the session with a special dynamometer. The results showed that EMS increased the isometric, concentric and eccentric forces of the knee extensors, in addition to the performance in vertical jump without stretching-shortening cycle (squatjump – SJ), since the improvement in the CMJ (counter-movementjump ) would be due to a better performance of the knee extensors, so after another 4 weeks of basketball training, without EMS, improvement was observed in the tests (Maffiuletti, Cometti et al. 2000).

Two years later he published, together with other colleagues from the University of Burgundy, a study onon the effects of electrostimulation combined with plyometric training on vertical jump height. The intervention was performed on 10 volleyball players for 4 weeks. The workouts, 3 times a week, consisted of 48 knee extensors contractions, 30 plantar flexor contractions, and finally 50 plyometric jumps. Maximum voluntary contraction increased significantly in just 2 weeks in both the knee extensors (+ 20%) and the plantar flexors (+ 13%). The jump height in different tests (SJ and sCMJ) also improved: in the jump without countermovement the improvement was 21%, while in the CMJ spike it was 8-10%.

When we really begin to see the conclusions that have made this researcher famous, it is as a result of the publication, in 2002, of a study that analyzed the activation of the plantar flexors after training with electrostimulation. Maffiuletti, Pensini and Martin subjected 8 subjects to 16 sessions in 4 weeks of training with electrostimulation, specific for the plantar flexors, in which involuntary contractions were caused at 75 Hz and 400? S of 4 seconds of duration and 20 of rest, while the hip, knee and ankle remained at 90 °. There were improvements in almost all the parameters, except in the contractile properties (with which we can link the results of the previous investigations of Maffiuletti and other authors in which there were significant improvements in the SJ and not so much in the CMJ). The conclusions after the improvements observed in the results were the following: a) the increase in voluntary torque after 4 weeks of EMS could be due to the increase in activation in the agonist muscles; b) the most obvious change is the increase in the amount of nerve impulse to the muscles from the supraspinal centers; c) the adaptation of motor units to preferentially activate type II fibers could explain the increases in post-activation potentiation and electromyographic activity in the gastrocnemius after short-term training (Maffiuletti, Pensini et al. 2002). b) the most obvious change is the increase in the amount of nerve impulse to the muscles from the supraspinal centers; c) the adaptation of motor units to preferentially activate type II fibers could explain the increases in post-activation potentiation and electromyographic activity in the gastrocnemius after short-term training (Maffiuletti, Pensini et al. 2002). b) the most obvious change is the increase in the amount of nerve impulse to the muscles from the supraspinal centers; c) the adaptation of motor units to preferentially activate type II fibers could explain the increases in post-activation potentiation and electromyographic activity in the gastrocnemius after short-term training (Maffiuletti, Pensini et al. 2002).

A year later, in 2003, the results of a study were shown in which the T and H reflexes were analyzed, with an intervention similar to that of the study summarized in the previous paragraph. The authors’ conclusions indicated that EMS training of the plantar flexor muscles did not affect alpha motor neuron excitability and / or presynaptic inhibition (Maffiuletti, Pensini et al. 2003).

Once again, along the same lines, in a study with 12 volleyball players who were trained for 4 weeks, 3 times a week, it was possible to see how, the application of training in which there were only 20- 22 involuntary contractions through EMS, for the knee extensors and plantar flexors, did not modify the jump height in SJ and CMJ, but the height and power did increase after 15 seconds of consecutive CMJs. However, ten days after abandoning the intervention protocol, it was observed how then the jump height did increase significantly in SJ and CMJ (Malatesta, Cattaneo et al. 2003).

In 2005, with Boeiro at the head of the study, they published the results of a study in which they tried to glimpse the central and peripheral fatigue produced by EMS. According to these authors, the fatigue attributable to this type of training stimulus is both central and peripheral, with the most obvious alteration occurring in the CNS as a consequence of a decrease in the amount of nerve impulse from the supraspinal centers. On the other hand, neuromuscular propagation insufficiency was more evident for the muscle with the highest percentage of type II fibers (Boerio, Jubeau et al. 2005). However, the same authors, in another publication on this same research, add that a typical EMS session on the knee extensors mainly induces a failure in neuromuscular propagation, while the excitation-contraction coupling mechanisms and the neural mechanisms do not. they are significantly affected (Zory, Boerio et al. 2005). A year later they concluded, in another intervention, that EMS resistance training, in the short term, is accompanied by responses (by increasing EMG activation) and neural adaptations (by increasing the amplitude of the spinal reflex and decreasing coactivation), which would explain the increase and maintenance of maximum voluntary force (Jubeau, Zory et al. 2006). Later, in 2007, they verified how after a 4-week EMS training of the plantar flexors and after a 4-week detraining, there was a reduction in fatigue to a single EMS session. This leads the authors to think that it could be attributed to a failure in activation, decreasing central fatigue, probably as a result of the subjects having a greater tolerance of pain and discomfort produced by EMS (Jubeau, Zory et al. 2007) . In the short term, it is accompanied by responses (due to increased EMG activation) and neural adaptations (due to increased amplitude of the spinal reflex and decreased coactivation), which would explain the increase and maintenance of maximum voluntary force (Jubeau, Zory et al. 2006). Later, in 2007, they verified how after a 4-week EMS training of the plantar flexors and after a 4-week detraining, there was a reduction in fatigue to a single EMS session. This leads the authors to think that it could be attributed to a failure in activation, decreasing central fatigue, probably as a result of the subjects having a greater tolerance of pain and discomfort produced by EMS (Jubeau, Zory et al. 2007) . In the short term, it is accompanied by responses (due to increased EMG activation) and neural adaptations (due to increased amplitude of the spinal reflex and decreased coactivation), which would explain the increase and maintenance of maximum voluntary force (Jubeau, Zory et al. 2006). Later, in 2007, they verified how after a 4-week EMS training of the plantar flexors and after a 4-week detraining, there was a reduction in fatigue to a single EMS session. This leads the authors to think that it could be attributed to a failure in activation, decreasing central fatigue, probably as a result of the subjects having a greater tolerance of pain and discomfort produced by EMS (Jubeau, Zory et al. 2007) . it is accompanied by responses (due to increased EMG activation) and neural adaptations (due to increased amplitude of the spinal reflex and decreased coactivation), which would explain the increase and maintenance of maximum voluntary force (Jubeau, Zory et al. 2006). Later, in 2007, they verified how after a 4-week EMS training of the plantar flexors and after a 4-week detraining, there was a reduction in fatigue to a single EMS session. This leads the authors to think that it could be attributed to a failure in activation, decreasing central fatigue, probably as a result of the subjects having a greater tolerance of pain and discomfort produced by EMS (Jubeau, Zory et al. 2007) . it is accompanied by responses (due to increased EMG activation) and neural adaptations (due to increased amplitude of the spinal reflex and decreased coactivation), which would explain the increase and maintenance of maximum voluntary force (Jubeau, Zory et al. 2006). Later, in 2007, they verified how after a 4-week EMS training of the plantar flexors and after a 4-week detraining, there was a reduction in fatigue to a single EMS session. This leads the authors to think that it could be attributed to a failure in activation, decreasing central fatigue, probably as a result of the subjects having a greater tolerance of pain and discomfort produced by EMS (Jubeau, Zory et al. 2007) . which would explain the increase and maintenance of maximum voluntary force (Jubeau, Zory et al. 2006). Later, in 2007, they verified how after a 4-week EMS training of the plantar flexors and after a 4-week detraining, there was a reduction in fatigue to a single EMS session. This leads the authors to think that it could be attributed to a failure in activation, decreasing central fatigue, probably as a result of the subjects having a greater tolerance of pain and discomfort produced by EMS (Jubeau, Zory et al. 2007) . which would explain the increase and maintenance of maximum voluntary force (Jubeau, Zory et al. 2006). Later, in 2007, they verified how after a 4-week EMS training of the plantar flexors and after a 4-week detraining, there was a reduction in fatigue to a single EMS session. This leads the authors to think that it could be attributed to a failure in activation, decreasing central fatigue, probably as a result of the subjects having a greater tolerance of pain and discomfort produced by EMS (Jubeau, Zory et al. 2007) . verified how after a 4-week EMS training of the plantar flexors and after a 4-week detraining, there was a reduction in fatigue to a single EMS session. This leads the authors to think that it could be attributed to a failure in activation, decreasing central fatigue, probably as a result of the subjects having a greater tolerance of pain and discomfort produced by EMS (Jubeau, Zory et al. 2007) . verified how after a 4-week EMS training of the plantar flexors and after a 4-week detraining, there was a reduction in fatigue to a single EMS session. This leads the authors to think that it could be attributed to a failure in activation, decreasing central fatigue, probably as a result of the subjects having a greater tolerance of pain and discomfort produced by EMS (Jubeau, Zory et al. 2007) .

In a team led by Brocherie, five researchers, including Maffiuletti and Cometti, embark on an intervention in 17 ice hockey players. Nine of them performed electrostimulation training 3 days a week for 3 weeks, where the electrodes were placed on the knee extensors with 85 Hz and 4 seconds of impulse to perform a total of 30 contractions per session. Isokinetic strength improved significantly, as did the 10-meter sprints with skates, while jump height decreased in SJ, CMJ, and DJ (Brocherie, Babault et al. 2005). These results differ with respect to other studies, where there is no decrease in height, and it is even improved in the squatjump, a jump where there is no requirement for contractile properties.It is possible that this is a consequence of the lack of training with EMS of the plantar flexors, or perhaps because the requirements of the sport are not oriented towards jumping, so sessions in which there was a greater volume of these were not included.

In 2006, together with Spanish researchers such as Herrero and Izquierdo, an intervention with a larger sample of 40 subjects was launched, who were randomized into four different groups: EMS, plyometrics, EMS and combined plyometrics and control group. The trainings were carried out 4 times a week. Training with EMS alone and combined with plyometrics induced increases in maximal strength and hypertrophy of the trained muscles. However, training with only EMS did not produce improvements in jumping, and even interfered with sprinting (Herrero, Izquierdo et al. 2006).

 A curious case study concluded that plastic changes in neural control confirm the possible involvement of both the spinal and supraspinal structures when contractions are induced by EMS. In addition, the changes at the fibrillar level, caused by EMS training resistance to force, in this case they preferentially affected type I (Maffiuletti, Zory et al. 2006). One year later, in a study that showed an intervention in 16 healthy men to evaluate the recruitment of muscle fibers, it was concluded that during EMS the fibers are activated without an obvious sequence in relation to the type of fiber, that is, they do so randomly, moving away from the reversibility of the Henneman principle proposed for EMS (Jubeau, Gondin et al. 2007).

One of Maffiuletti’s featured articles from 2008 reported on the differences between men and women with respect to sensory and pain thresholds. Women take longer to feel the stimulus, but the pain threshold arrives much earlier (Maffiuletti, Herrero et al. 2008). Three years later, in another investigation that stratified by woman / man and by obese / non-obese, it was found that the sensory threshold was lower in women than in men, whether or not they were obese. Sensory and motor thresholds were higher in obese patients, with body mass index being a strong predictor of motor excitability (Maffiuletti, Morelli et al. 2011).

A year later, continuing in the first line on performance that began in 2000, Maffiuletti investigated the effects of electrostimulation training on tennis players’ preseason performance, concluding that it can be included to induce improvements in anaerobic power and in the stretch-shortening cycle (Maffiuletti, Bramanti et al. 2009).

This researcher has not been able to forget about the oxygenation of the tissues, being able to corroborate together with other of his colleagues how, at 30 Hz and with the maximum tolerated intensity, the biceps brachii requires an oxygen demand comparable to a voluntary contraction at maximum intensity (Muthalib, Jubeau et al. 2009). In another intervention, with 10 young subjects, they compared the oxygenation index of the tissues with voluntary and involuntary contractions in the biceps brachii (EMS at 75 Hz, 50 contractions, 4 seconds of impulse, 15 seconds of rest). The results of this experiment reported that the local oxygen demand of the biceps brachii was similar in both conditions (Muthalib, Jubeau et al. 2010).

Returning to inquire about the effects of electrostimulation on muscle enhancement, in 2010 an article was published comparing how a maximum voluntary contraction or a contraction produced by transcutaneous nerve electrostimulation (TENS) affected subsequent muscle activation. All this for the quadriceps muscle, both the rectum and the vastus. The TENS parameters were 80 Hz at 500 µs and the intensity was associated with 40% of the maximum voluntary contraction; therefore, the voluntary contraction with which it was compared was also 40%, and was performed for approximately 10 seconds. The 16 young subjects who completed the intervention had an amplitude M _maxsignificant greater, for the rectus femoris, from 3 seconds after contraction to 600 seconds in the voluntary condition; while in the vastus lateralis, until the 60 second, the amplitude M _max was greater, but not significant, when the previous contraction was produced by TENS. However, despite the fact that only the results appear to be clear for the rectus femoris, the authors conclude that for potentiation it would be more advisable to choose voluntary contractions (Jubeau, Gondin et al. 2010).

In 2010, Maffiuletti launched only a systematic review on the use of muscle electrostimulation, in which it was indicated that it could be for: preserving muscle mass and functions during injury or immobilization, recovering muscle massand the functions during an injury or immobilization, improve the functions of the healthy musculature or prehabilitate it. Thus, it is also indicated that its use has been reported in cardiovascular, orthopedic, neurological, general, geriatric, spatial and sports medicine. The insistence between the differences between a voluntary contraction and one produced by NMES stands out in this review: asynchronous vs. synchronous, sparse vs. superficial (near the electrodes), selective (from slow to fast fibers) vs. random (messy between slow and fast fibers), partial fatigue vs. extreme fatigue, etc. It highlights the importance in training with neuromuscular electrostimulation of the parameters (frequency, intensity, impulse, rupture, ramp), the characteristics of the contraction (dose, duration of contraction, muscle length, type of electrostimulation – alone, combined or superimposed-), the characteristics of the hardware (electrodes, electrostimulation unit), details of the program (contractions per session, sessions per week, weeks, tolerance, adherence). But, above all, at the end, the disorder in the recruitment of muscle fibers stands out as a limitation (Maffiuletti 2010).

The programming of electrostimulation training should be introduced with care when it comes to sports performance, since a study over 2010 indicates that after 4 weeks of training with electrostimulation (4 times a week) for the quadriceps there was no change in the strength of the quadriceps. maximum voluntary contraction, and there was even a decline in contractile properties, but muscle activation (EMG) did improve. However, after 4 weeks of detraining, muscle activation was maintained, contractile function recovered, and maximal voluntary contraction force increased (Zory, Jubeau et al. 2010).

One of the most spectacular investigations consisted of analyzing, through biopsy, the quadriceps of 8 young men after having undergone electrostimulation training for 8 weeks, in which they performed 25 sessions. The subjects were divided into two subgroups, those who were sedentary, and those who were active. The analysis focused on the phenotypic adaptations produced. EMS training has been shown to be an effective modality for increasing muscle mass, maximal voluntary strength, neural drive, and oxidative metabolism, as well as enhancing antioxidant defense systems. The atypical adaptations that occur with this type of training combine the characteristics of resistance training (“resistance”) and cardiovascular resistance (“endurance”), which could be attributed to the non-selective recruitment of motor units. In addition to improving in active subjects, in sedentary people it seems especially suitable, since it counteracts in a higher way the disuse atrophy typical of hypoactivity (Gondin, Brocca et al. 2011).

Continuando con las revisiones, se publicó una en 2011 que recogía la evidencia sobre las adaptaciones neurales al entrenamiento con EMS. En esta se confirmaba la hipótesis de que en las primeras fases, en adultos jóvenes sanos, el entrenamiento con EMS, al igual que en el convencional, el aumento de la fuerza de máxima contracción voluntaria se produce a través de los mecanismos neurales, sin hipertrofia muscular. En esta revisión no se encontraron a penas evidencias sobre la participación de mecanismos espinales (médula) para mediar esos incrementos en la fuerza. Sin embargo, sí hay fuerte evidencia para sugerir que las contracciones con EMS pueden activar áreas sensoriales, sensoriomotoras y motoras, y caminos interhemisféricos en el cerebro (Hortobagyi and Maffiuletti 2011).

In 2012 they published an intervention in which they compared the muscle damage produced by maximal voluntary and electrostimulated isometric contractions in the elbow flexors. Twelve men, aged 23 to 39, untrained. Two test sessions were carried out, separated by 2 weeks, in which voluntary contractions were performed with one arm and electrostimulated contractions with the other. 50 contractions were performed, with the elbow at 160 °, at 4 seconds of contraction and 15 seconds of rest, in the case of EMS at 75 Hz at 250? S. Measurements were taken immediately after, at one hour, at 24 h., At 48 h., At 72 h. and at 96 h. Maximum voluntary contraction decreased more with EMS and recovered more slowly. The levels of CK (creatine kinase) increased only after EMS, in addition the muscles were more sore and more sensitive.

Entering the world of rehabilitation, Maffiuletti and his colleagues concluded, after an intervention published in 2013, that adding electrostimulation to the care of critically ill patients makes a big difference to just performing the usual care. loss of muscle mass (Maffiuletti, Roig et al. 2013).

It has been noted that the area to be stimulated determines the responses and adaptations of EMS training .For this reason, several investigations in which Maffiuletti has participated have shown how quadriceps training is more effective when electrostimulated on the femoral nerve trunk, than when it is done on the muscle belly (Rodriguez-Falces, Maffiuletti et al. 2013; Rodriguez-Falces, Maffiuletti et al. 2013). This is why, theoretically, they support that finding the motor point prior to electrode placement would maximize results and minimize discomfort sensations (Botter, Oprandi et al. 2011; Gobbo, Maffiuletti et al. 2014). In this regard, not only the placement of the electrodes is important, but also their size, which is why a 2014 intervention investigated the difference between conventional electrodes and large and multiple electrodes to electrostimulate the quadriceps.

Thus, we cannot forget the latest contributions, in which EMS is compared at 25 Hz and 100 Hz, resulting in differences in fatigue and potentiation (Neyroud, Dodd et al. 2014; Regina Dias Da Silva, Neyroud et al. 2014). In addition, following this line it has been possible to see how large the inter-subject differences are, suggesting that there are responders and non-responders to the different proposed stimuli (Wegrzyk, Foure et al. 2014).

Benefits of electrostimulation

 Taking into account all these contributions, we can summarize Maffiuletti’s work as follows:

• EMS improves the strength of maximal voluntary contraction.
• EMS does not produce improvements in contractile properties. However, short-term detraining (4 weeks), especially if it is accompanied by other training that requires jumping ability (basketball, volleyball …), achieves improvements in these.
• Sensory thresholds are modified by gender and body mass index.
• EMS can be used as a potentiation method, but under certain conditions it does not exceed the effectiveness of performing maximal voluntary contractions.
• EMS in the biceps brachii at low frequencies (30 Hz) has effects on oxygenation similar to performing a voluntary contraction at maximum intensity, however there are no differences with voluntary contractions of similar intensity when the frequency is high (75 Hz).
• In sedentary people it counteracts the effects of hypoactivity more effectively than in active people.
• EMS produces neural adaptations, since there is evidence of the participation of the supraspinal centers, but not of the spinal ones.
• In EMS the recruitment of muscle fibers is random, and does not fulfill the reversibility of the Hennrman principle.
• EMS produces more muscle damage than voluntary contractions.
• There are responders and non-responders at the different EMS frequencies.
• The motor point is important to increase effectiveness.
• It is more effective to stimulate at the level of the nerve trunk than in the muscle belly.
• Large, multiple electrodes are more effective and provide less discomfort.

 By Carlota Díez Rico. Collegiate 52838. Physical Educator.