EMS Research Update
Hi everyone, now Xmas is here and I have time off of work I can finally get around to writing up a few things for the Forum. Starting with this very interesting talk I attended back in March… :eek: TC
This is a review of information presented by Nicola A. Maffiuletti of the University of Burgundy at Bijon, France during the UK Strength and Conditioning conference in May 2005. I found his talk quite interesting because he suggests some different opinions to those most of us on the CF Forum currently hold on EMS.
Just for reference Maffiuletti uses the terms ES = Electro stimulation and EMS to = Electromyostimulation. I can’t remember exactly what the difference is but apparently it was important to make the distinction!
Motor Unit Recruitement
Firstly, Maffiuletti suggests that while it was originally believed that motor unit recruited during ES occurs in the opposite order  to voluntary contraction (e.g. large/fastest motor units first down to smallest/slowest motor units last), in reality this is not the case. He believes the motor unit recruitment is affected by:
- Axon diameter – the largest are recruited first
- Anatomical positioning – the largest superficial axons are recruited first
- Cutaneous receptors – the recruitment order is altered 
One study suggests that while voluntary contraction appears to show that 6% of motor units are recruited in reversal during voluntary contraction, during ES this increases to about 30% . From this and his own work Maffiuletti suggests that during ES motor unit recruitment doesn’t occur in reversal but it does occur in an order that is different to voluntary contraction.
When comparing the acute effects of ES contractions with voluntary contractions it has been shown that the drop off in the force of contraction during an ES session varies between 10-20% (depending on the muscle group) during 30 isometric repeated contractions . This is pretty similar to what occurs during voluntary muscular contractions.
Metabolic Cost of EMS
The same study  also showed that anaerobic glycolysis also increased during ES sessions (basically the subjects started to develop lactic acid as a result of ES).
From several studies the metabolic cost of ES in comparison to Voluntary contraction can be summarised as:
02 consumption is believed to be some 500-900% less than voluntary work
Pi:Pcr ration is some 300-400% less than voluntary work
ATP turnover decreases by 200-500% compared to voluntary work
It is believed the increased metabolic effects associated with voluntary contractions result because of the rotation and need for synchronisation of the fastest motor units during voluntary contraction.
[Please note that this part of my notes are not very clear so it might be the other way around! – I just can’t tell!]
Interestingly it is also suggested that muscle soreness (DOMS) is greater and peaks more abruptly on the second day after training with ES than with voluntary contractions. This increase in DOMs seems to correlate with an increase in muscle damage (CK activity) .
Personally I havn’t found ES with Compex to create any soreness what so ever! Though a dull ache (feeling of fatigue) does occur but it is nothing like DOMS.
MRI scans have shown that there is significant activation of the CNS during ES ! This has been shown to lead to a drop off in activation of around 4.5% and contractile force is reduced by about 6% .
Maffiuletti was pretty decided on the issue that EMS does not bypass the CNS and creates central and peripheral fatigue!
Practical training applications
In terms of the basic question: should the athlete voluntarily contract the muscle during EMS or not? It has been shown that voluntary contraction increases the force output and reduced the pain perceived by the user. However, voluntary contraction during ES makes it hard to define intensity.
For healthy populations research suggests that ES on its own is not as effective as voluntary contraction for increasing strength but in unhealthy populations ES is better. However, he suggest the two are complementary because of the different motor unit recruitment patterns.
In terms of neural adaptations, ES seems to increase surface EMG, Activation Level and H reflex, while reducing coactivation of antagonists.
In terms of muscular adaptations there appears to be conflicting ideas with some studies showing an increase in the cross sectional area and other not. However, High Frequency activation via ES seems to lead to a shift from type IIx > IIa and I > IIa which is similar to voluntary resistance training.
In short Maffiuletti believes ES does increase muscle strength and the neuromuscular effects are very similar to voluntary contractions.
EMS as a practical strength training device for Team Sports
Having described a number of studies relating to the use of EMS as a method of strength training for athletes (basketball, volleyball, soccer, tennis) the conclusions were that EMS increased muscular strength but did not translate to sport specific performance improvements (specific power).
However, the effects of EMS are more specific if combined with plyometrics. From this Maffiuletti’s general recommendations were that ES should be used during GPP and not the competitive season and should not be used as the sole method of strength/power training.
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