Muscular Electrostimulation in Sport and Technological Advances

By Compex


Electrostimulation (ES) is no different to any other sports-related activity when it comes to the impact of recent technological advances and the more scientific approach now being taken to training. Both have radically changed our perception of this technique, and without the considerable scientific and technological advances we have seen, electrostimulation (ES) would not be available to the world of sport today.

The fundamentals governing the stimulation of nerve and muscle cells by electrical impulses have been known since the beginning of the last century. These laws were discovered and fully understood by eminent French physiologists like Lapicque and Weiss. Through a series of remarkable experiments, they succeeded in calculating a mathematical correlation between the quantity of current and duration of application required to stimulate motor nerves. More recently, the work of Hill has enabled an even better understanding of the processes involved. But the resources available at that time and the enormous size of electrical laboratory required meant that even obtaining a weak muscular response caused severe pain and burns. Today, with equipment no bigger than a large calculator, we can concentrate all the power of a bodybuilding gymnasium to express ourselves as we wish. As we will see later in this document, today's ES offers some very special additional benefits over and above those delivered by traditional muscle building training exercises.

However, no one is suggesting that active training no longer has a place, but neither is it an alternative to muscular stimulation. On the contrary ES is a complementary muscle working technique! Used as part of a sports preparation program, it can enhance the quality and performance of the overall training program. This is not based on choosing one technique in preference to another, but rather on methodology- based sequencing of the different training techniques to exploit their distinct and individual benefits. In this context, the benefits delivered by muscular stimulation can be substantial.

The results of advances in electronics

The first attempts at using ES in training were made at the Moscow Academy of Sports Science in the 1960s, directed by Professor Kotz. The results proved very encouraging, although they do look rather optimistic today. Rather than the 35% gain in strength then claimed to result from just three weeks of training, the real benefit (unless the circumstances are exceptional) was much more likely in the range of 5% to 15%, although this is still a remarkable achievement. The problem in Kotzs day was that the stimulation applied was quite uncomfortable and athletes found themselves subjected to something approaching torture sessions. If things had remained that uncomfortable, it seems unlikely that ES would ever have developed into an accepted sporting practice. As late as 1979, the physiologist, McDonnell, who had conducted a lot of research into the mechanisms that limit muscular performance, still thought of ES in these terms: "it cannot be used because of the very high voltages required and the impossibility of creating tetanic contractions".

The progress made in electronics, especially with the arrival of microprocessors, changed this situation radically. It became possible to be protected against the risk of burning and eliminate electrical pain, provided that the ES was applied using high quality equipment rather than some of the outlandish devices that seem better suited for creating aesthetic illusions than training muscle.

How exactly do electronics provide the type of stimulation that can be effective in increasing sporting performance? To understand this fundamental aspect of how stimulation works, we must first address the basic principles involved. In contrast to what many people thought for a long time (and which some of those involved in electrotherapy still teach) there is no magic current! Electricity has no particular innate ability to improve the condition of living tissue, especially muscle! All electricity can do is trigger the natural process of nerve stimulation to which the muscle fibers respond mechanically by doing a unit of work. ES is therefore just a means of imposing work on muscle fibers, which will, in turn, develop as a result of that work. But the fact is (and this is where the problem lies) that if it only makes a small percentage of muscle fibers do that work, we cannot expect to see that muscle progress significantly. Only working fibers will grow! The point is therefore to use ES to work the maximum number of fibers, i.e. as deeply into the muscle as possible. If only the surface fibers are worked, then the results obtained will also be fairly superficial. The basic problem of electrostimulation is therefore trying to work the maximum number of muscle fibers! In practical terms, thorough fiber stimulation means using powerful equipment whose current can be increased to maximize the number of fibers reached. But increased electrical current also means the risk of pain and burning. So the challenge was to exploit electronics to develop current pulses that were not only powerful and comfortable, but also risk-free. All of which is a long way away from the many gadgets seen on home shopping TV channels. Using technology very similar to that used by the best mobile phone systems and today's high quality electronic components, we can now generate the "optimum" electrical pulse. This pulse delivers maximum effectiveness (fulfilling Lapicque and Weisss fundamental laws on excitation) with maximum safety and comfort for the patient (by minimizing the number of electrical parameters contained in the pulse). This optimum pulse is now available to work the maximum number of muscle fibers, so the limitation on ES is no longer electrical pain, but the sensation produced by the power of contraction.

With a genuine ES system, the user is aware of a growing feeling of tension in the muscle even before sensing the electricity. This contraction force rises with the current until the maximum number of muscle fibers is activated. Although few training or bodybuilding specialists seem to be aware of the fact, it is possible, under certain stimulation conditions, to achieve a degree of contraction approaching or (in some instances exceeding) maximum isometric voluntary strength! The stimulation conditions are therefore fundamental to the effect. Strong training programs must be followed; programs that allow a sufficiently long period of tetanic contraction. High quality electrodes must also be used at precisely defined motor points and the sportsperson concerned must be trained in the technique to a point where he or she can tolerate the sharp rise in current. Since the mid-1980s, it has been possible to identify central neurological fatigue by measuring the difference between the subject's maximum voluntary contractions and the high levels achievable by ES. This aspect of activating the maximum number of fibers using ES can also be used as a test to identify overtraining. Frischknecht of the London Institute of Physiology has demonstrated that using ES on the muscles of overtrained athletes can activate more fibers and produce greater strength than it was possible for those athletes to achieve by voluntary contraction, thus demonstrating the central neurological component as an essential factor in performance reduction as a result of overtraining.

It is therefore the progress made in electronics that has enabled ES to go beyond being a superficial treatment to provide a means of working muscle fibers much more thoroughly. Without this essential progress, ES could be of no practical use in sports preparation, but that progress alone would not have been sufficient for ES to become such an essential training technique. Other scientific advances were needed to control this technique and to understand how it could be applied to enhance performance.

The results of advances in muscular physiology

Although the ability to use advances in electronics to impose work by stimulating the maximum number of muscle fibers is a vital part of the equation, it teaches us nothing about the nature of the work itself. Walking a dog involves a certain element of muscular work, as does an interval training session, but it is clear that the nature of the work done in these two activities is very different. In the first example, the muscular work involved is not the kind that will improve the performance of an athlete, but the second example, if repeated often enough, can result in improved performance. So, working the maximum number of muscle fibers by means of stimulation is clearly of interest only if we can control the nature and quantity of that work in such a way that it enhances a particular type of muscular performance.

Much recent research work, such as that done by Lieber, shows, predictably perhaps, that where identical quantities of the same work are done, the outcome for the muscle is the same regardless of whether that work is done voluntarily or by using ES. As muscle fibers are unconscious, they have no awareness of the source imposing the work, so whether the action potential is sent directly from the brain or applied by the stimulation equipment, the fibers progress in exactly the same way as long as work done is identical in quantity and quality. Given these conditions, it became vital to gather sufficient knowledge about the physiology of muscle contraction and the work done by different types of muscle fiber so that electrical pulses could be programmed to apply a quantity and rate of work appropriate to performance of the muscle to be improved.

This brings us to the problem of programming of the stimulation parameters that will enable the equipment to impose a range of work rates. This programming must be based on the most up-to-date physiological data. Bear in mind that there are two main types of muscle fiber: slow fibers and fast fibers. These two fiber types are differentiated by a series of morphological and functional differences. Slow fibers contract slowly using little force, but are highly resistant to effort, i.e. they do not tire quickly and are therefore capable of working for longer periods. Unlike slow fibers, fast fibers contract quickly and with great force, but tire quickly. Slow fibers are those that deliver endurance, while fast fibers are what we use for strength and speed. We know the precise tetanization frequencies for slow and fast fibers. Slow fibers tetanize at approximately 35 excitations per second (35 Hz), while the figure for fast fibers is approximately 70 Hz. This data can therefore be used to help determine the frequencies at which we must program our electrical pulses to tetanize fast fibers to their maximum, thus creating force stimulation (for example).

The discovery of many other fiber variants in addition to these two main types (slow and fast) has meant that we have been able to improve our stimulation programs considerably and develop different levels of strength, explosive strength, endurance and resistance programs. We can now identify no fewer than eight types of fiber: I, IIA, IIB, IIAB, IIC, IID, IIM and II∝. All of these fiber types have different characteristics and perform in different ways. For example, one type of IIM fiber is found in particularly strong, fast muscles, like the jaws of primates. The tetanization frequencies of these fibers are even higher than those of other fast fibers, allowing them to work at very high speeds, rather like the ocular muscles that move our eyes so quickly. These fibers, with their very high strength and speed, are responsible for what we commonly refer to as explosive strength. They are likely to be found in the quadriceps of the "supermen" capable of running a hundred meters in under ten seconds. It is also possible to measure the muscle fiber action potential conduction speeds in these athletes; speeds which correspond to the tetanization frequencies for these very fast fibers, which is why the stimulation programs now being used so successfully by most of todays top skiers and Italian soccer players are based on these frequencies. The benefits ES can deliver for this type of athlete are being seen much more clearly now that these new so-called "explosive strength" programs are in use.

So, the progress made in muscular contraction physiology has helped us understand how to program stimulation parameters in such a way that they can impose different work rates to match the type of performance required: resistance, endurance, strength, explosive strength, etc.