|Image 1: The EU-940 EMS device the|
scientists used in their study to activate
the vastus medialis and lateralis (high-
lighted in the image) of their subjects, is
very different from the average EMS based
"abdominal toner" advertised on TV.
EMS? Now, many of you will probably remember those TV spots, where you were told that "Abmaster" & Co would transform your pot-belly into a "six-packed" attractant for the opposite sex, if you did not miss this "unique" opportunity and bought one of those electro-shockers no sane fitness professionals would voluntarily substitute his/her good old sit-ups and leg raises for. Yet, while these battery-powered torture instruments did, or I should say, were intended to electrically stimulate muscles (in fact in many of the obese buyers of these products, the abs were probably covered by a layer of fat that was way too thick for actually "stimulation" of the abdominal muscles to occur), both the devices, as well as the EMS protocol Seo et al. (Seo. 2011) employed in their double-blind randomized controlled trial at the Sports Science Research Laboratory of Kyungwoon University in Korea were a little more sophisticated.
Did you know? The fatigue index is a concept used in the study of fatigue during anaerobic activities. It is the ratio of power decline to the length of the time interval in seconds between peak power and minimum power. This means lower fatigue indexes equate lower declines of exercise intensity per time unit. When looking at the data in figure 1, you may want to keep in mind that higher starting values / greater overall workloads will entail greater declines in anaerobic power per time unit and thus present with higher fatigue indexesDuring and after 3 all out intervals on an ergometer (resistance: 0.8 x body weight Nm; active rest between intervals: 10 seconds) verbal feedback on perceived fatigue, fatigue indexes in W/s, mean power/weight, total work and lactic acid values (from serum drawn before, after and at 15 min and 25 min post exercise) were recorded in a group of 24 randomly selected collegiate Taekwando athletes (age: 19.8yrs, height; 177cm; weight: 66kg, training experience: 5yrs; mean values with non-significant differences between groups).
|Figure 1: Fatigue index, mean power (primary axis) and total workload (secondary axis) during Wingate ergometer test |
(data adapted from Seo. 2011)
- The control group received no regenerative treatment at all.
- The massage group was subjected to a massage protocol which had been shown to effectively improve exercise recovery in a previous study by the same authors (Lee. 1998).
- The EMS group was attached to an interferential current unit (EU-940, ITO CO., LTD, Tokyo, Japan), which applied an interferential current with a carrier frequency of 4kHz and a pulse duration of 125µs via four vacuum electrodes (vacuum pressure: 60ppm) to the vastus medialis and the vastus lateralis of the subjects.*
* "The current intensity was set within the range of the minimum visible contraction of the quadriceps femoris muscle", so that the muscle of the quadriceps were maximally stimulated, while the current was not so intense that cross-over effects to neighboring muscle groups would occur.
|Table 1: Outline of the massage |
protocol the athletes in the massage
group received after having performed
an exhaustive anaerobic Wingate
ergometer test (according to Lee. 1998)
|Figure 2: Relative reduction in lactic acid concentration after a wingate performance test followed by massage or EMS therapy compared to untreated control (data adapted from Seo. 2011)|
Edit (26 July): The lactate & Lactic acid confusion
After I posted this piece of information an interesting discussion around the physiological role of lactic acid broke lose on Facebook and I do not want to deny you the great information my buddy Sean Casey from CasePerformance brought to the table. So, here is what he had to say:
Lactic Acid is an interesting thing....During the 1970-1980’s various studies found lactic acid impaired strength and contraction velocity in samples of isolated muscle tissue (1). Based off these early findings, many researchers evaluated ...post workout recovery modalities on their ability to remove lactate from muscle tissue post workout. Similarly, coaches and athletes started employing post workout techniques aimed at removing lactate from muscular tissue. For instance, our high school track coach used to have us lie on our backs and rest our legs on an elevated surface w/ respect to our body. Usually we'd lie on the floor next to a wall & place legs on wall. The theory was that acid would “drain” out of our muscle tissue, allowing our legs to be fresher for the following day’s workout. (I know, a very bro-science approach; , but mentally felt good and you'd always get a cool tingly sensation when you set your legs down and the blood rushed back into them!)The only thing I would like to add to Sean's insightful dissertation is a criticism of the indiscriminate use of lactate, which is sort of 'recycled' muscle fuel, and lactic acid, which is its ugly 'degraded' relative. With the ever increasing H+ levels as they can be observed in the course of a long distance race, for example, more and more lactate gets degraded into lactic acid and thus works like a buffer similar to the beta-alanine derived intramuscular H+ buffer carnosine. Now it is no wonder that with H+ release being a measure of muscular exertion and lactic acid being a measure of H+ buffering, Faude et al. (Faude. 2009) found in what is one of the most recent reviews on the role of lactate in exercise metabolism that
Interestingly, it turns out that lactic acid may not be the best form of measurement with respect to evaluating the effectiveness of a PWRM [post workout recovery measures]. As pointed out by Cairns SP, it may have a much smaller effect on muscle fatigue than was previously hypothesized(1). Thanks to advances in technology, scientists are now able to study muscle tissue closer to physiological temperatures (old studies were completed at muscle tissue held at cooler temperatures, 50-68ºF). As shown by Westerblad et al., acid had little effect on contraction velocity when completed on muscle tissue held at 89ºF (2). On the other hand, a 2006 study by Knuth et al. did indicate that lactic acid decreased muscle contractile power even at warmer temperatures(3).
Although the lactate question is still being debated amongst scientist, athletes must ask themselves if the research is even applicable to their post training recovery protocol. Although lactate may induce muscular fatigue, its quickly metabolized within the body (1/2 life: muscle- 9.5 minutes; blood- 15 minutes), and eliminated from our system 90 minutes after an exercise session has been completed (4)(5). Thus, exercise induced lactic acid from one workout is likely not even present during a subsequent workout depending on when you complete it.
All this being said, don't misinterpret my comments and think that I'm trying to put down the role of EMS. I've had to use one a fair amount due to various issues and have found it to be effective. Anything that can get a muscle contracting and increase blood flow is always a good thing ;-)
1 Cairns SP. Lactic acid and exercise performance: culprit or friend? Sports Med. 2006;36(4):279-91.
2 Westerblad H, Bruton JD, Lännergren J. The effect of intracellular pH on contractile function of intact, single fibres of mouse muscle declines with increasing temperature. J Physiol. 1997 Apr 1;500 ( Pt 1):193-204.
3 Knuth ST, Dave H, Peters JR, Fitts RH. Low cell pH depresses peak power in rat skeletal muscle fibres at both 30 degrees C and 15 degrees C: implications for muscle fatigue. J Physiol. 2006 Sep 15;575(Pt 3):887-99. Epub 2006 Jun 29.
4 Karlsson J, Saltin B. Oxygen deficit and muscle metabolites in intermittent exercise. Acta Physiol Scand 1971; 82: 115-22.
5 Barnett A. Using recovery modalities between training sessions in elite athletes: does it help? Sports Med. 2006;36(9):781-96.
[t]hirty-two studies evaluated the relationship of LTs with performance in (partly simulated) endurance events. The overwhelming majority of those studies reported strong linear correlations, particularly for running events, suggesting a high percentage of common variance between LT and endurance performance.And, after all, it does not really matter in how far the established performance increases from massages and EMG therapy are related to their ability to accelerate lactate clearance, or more generally to their ability to increase blood flow and thus nutrient delivery and waste clearance in the respective tissue - does it?