Tuesday, September 27, 2016

Fact or Fiction: Lactate Causes Muscle Soreness

By: AJ Jagim

In this edition of "Fact or Fiction" we explore the topic of lactate and whether or not it is responsible for muscle soreness. Before we answer that question, let's first briefly cover lactate and what exactly we are dealing with. 

Lactate is a by-product of anaerobic metabolism or more specifically a metabolite of carbohydrate oxidation (burning carbs for energy).  At rest and lower levels of exercise intensity, we produce minimal levels of lactate as the rate of carbohydrate metabolism is relatively low. In addition, we are able to "clear" a lot of the lactate that we are producing by sending it out of the muscle cell and into the bloodstream where various other tissues and organs can actually use it as a fuel source.  As exercise intensity increase, our rate of lactate production also increases and our ability to clear lactate begins to become overwhelmed.  As a result, lactate levels within the muscle and blood begin to rise.  So, getting back to our original question of does lactate result in muscle soreness? The quick answer is: Not really. Let me explain why.  We actually produce lactic acid as a by-product of metabolism. In an aquesous environment, such as inside a muscle cell, it dissociates into lactate and a hydrogen ion (H+). Lactate can be used as a fuel source, used to make sugar which can also be used as fuel, and serves as a powerful stimulator for muscle growth. However, those H+ may begin to accumulate if high-intensity exercise is continued.

As that happens, it reduces the pH inside the muscle which is then perceived as that: "OMG, my legs are on fire" phenomenon during sustained muscle contraction.  When our muscle cells are exposed to an acidic environment they do not like to function properly.  Specifically the enzymes and contractile proteins responsible for movement do not work well in an acidic environment which means power output is diminished and fatigue is likely to set in. So moral of the story, don't blame lactate for acute muscle soreness and pain, blame the H+. Also, if we looked at the delayed onset muscle soreness (DOMS) effect that a lot of people may have heard of or encountered first hand; this is the soreness that presents itself about 24-48 hours AFTER an intense workout.  This soreness is not caused by lactate "trapped in the muscle" or any either myth you may have heard of.  This delayed muscle soreness is more a result of microscopic tears within the muscle cell in which some cells are damaged and even killed off resulting in an inflammatory response within your muscle(s).  Your nerve endings within the cells respond to this increase in localized swelling and various cell contents exiting the cell as pain.  There are active recovery strategies that can be utilized to improve or reduce sensations of pain but they help to facilitate the healing process not necessarily clear lactate out of the cell.  So again, lactate is not to blame for everything pain and soreness related that stems from exercise and simply serves as a metabolite from high-intensity exercise and can even be used as a substrate for fuel!

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