Boston Sports Medicine and Performance Group, LLC Blog

Evidence in Motion - Peak Activity

Posted by Boston Sports Medicine and Performance Group on Wed, Dec 18, 2013 @ 07:12 AM





“Muscle activity for the latissimus dorsi during the first pull showed a statistically significant increase when lifting heavy weights.

-S.-K. Chen et al., Journal of Mechanics in Medicine and Biology


A lot of confusion occurs when professionals interpret research and try to apply the findings from it to the clinical or performance setting.  Electromyography terms, such as mean and peak activation create confusion at times, especially when Maximum Voluntary Contraction (MVC) is thrown into the mix. In this article not only will we explain the differences between the three, but show how using surface EMG (SEMG) can unlock more than a few mysteries with training and rehabilitation. Practitioners need to migrate away from interpreting publications to actually implementing their own methodologies. 

Electromyography Terminology Made Simple

A quick synopsis of Electromyography can be summarized into three primary terms to clarify how surface EMG experiments are usually conducted and how practitioners can create their own methodologies internally.

▪      Maximum Voluntary Contraction - MVC is thought of as the maximal work a muscle can do during isometric contraction - voluntarily. Researchers and practitioners use MVC for normalizing comparisons of contractions and training. The MVC value can created in different ways, ranging from just tension of the muscle to very specific joint angles in an all-out isometric exercise like a mid-thigh pull for leg strength.


▪      Mean Activation – The average level of activity of a muscle over a specific period of time is the mean activation. The period of time can be anything the user wants to define, such as an entire repetition of a weighted exercise, an average of these repetitions, or movement patterns such as running, jumping, and throwing.


▪      Peak Activation – The maximal activity value of a muscle over a period of time is called peak activation. Peak activation is very useful for evaluating how intense an action is and comparing peak activation to mean activation is a common approach with EMG interpretation.

Now that those terms are explained let’s take a look using surface EMG to see how popular exercises such as the power clean and snatch can help both rehabilitation and performance enhancement.  



Musculature Contributions in Weightlifting

Sports medicine and sports performance is fusing together as an inverse relationship exists with performance and injury. When performance drops, often a risk to injury can increase if the body is compensating or using poor movement patterns. The traditional uses for weightlifting exercises have been thought of as only lower body power developers, not ways to increase injury resilience. The first pull in power cleans and snatches provide a lot of distraction forces to the shoulder that are great stimulators of the muscles around the joint system. One problem is that when a shoulder is dysfunctional and or the movement is done improperly, athletes miss the benefits of the exercise and increase risk of getting injured.

* Chen, Shen-Kai, et als. The Analysis of Upper Limb Movement and EMG activation During the Snatch Under Various Loading Conditions. Journal of Mechanics in Medicine and Biology, Vol. 13, No 1 (2013)

Using Noraxon’s wireless SEMG, researchers observed how increased loading recruited the latissimus dorsi in the first pull more than any other phase of the lift.  It can be assumed that heavier loads will increase the recruitment values but preserve similar patterns of muscle activity.

From a clinical and performance perspective, the information on musculature recruitment of the upper body suggests using only the lift off part of the exercise, but heavier weights. Additionally, comparing bilaterally is very useful to ensure that asymmetry was reduced, providing an objective way of tracking rehabilitation and return to play.

In the past, only researchers could complete analyses because the equipment and time demands were unavailable to clinicians and performance coaches. Now, however, with more powerful MyoMetric software it is possible, and even reporting and report comparison is fast and comprehensive. With less than a minute of set-up, users can get lab quality data real time, and make decisions that would not otherwise be possible. Many therapists and coaches are using SEMG to create protocols internally that improve patient outcomes and improve performance of their athletes.  


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