Why Do Muscles Fail?

Muscular failure is a complex phenomenon that stems from factors just as varied as the very ones that allow muscles to grow and strengthen under the same stressors. Despite the complexity of the factors involved, it’s possible to take some simple actions to be able to push muscular failure out as far as possible to increase performance. 

Failure or the point where muscles can no longer initiate or sustain a contraction is really just the end state of muscular fatigue building up to a state where where various physiological brakes get put on to stop further accumulation of fatigue.

The mechanisms of fatigue and failure are varied, but there are several distinct ones that are important to understand.

Mechanism: Muscles need fuel to contract and when the fuel runs out the muscle has to relax until it can be replenished. ATP is the actual fuel substrate your muscle uses for contraction, which is produced by the breakdown of phosophocreatine. This energy source doesn’t last long at all and can be completely exhausted inside of 30 seconds. At that point the body turns to glycolysis to generate more ATP from glycogen stored in the muscles to provide energy for up to a minute of exertion.

Solution: It doesn’t take PhD in sports physiology to understand that if you can maximize the available sources of energy you can extend the fatigue limits imposed by running out of fuel. While there isn’t much you can do to store more ATP, you can maximize the precursors by creatine supplementation. Creatine is the cheapest, most effective, and most well studied sports performance supplement on the planet (although caffeine would give it a run for its money) and maximizing creatine stores can increase production of ATP in time for those short bursts of maximal output before fatigue sets in. Further down the energy production cycle, ensuring your muscle glycogen stores are topped up by sufficient carbohydrate intake to support your activities is a close second in terms of pushing muscular fatigue out as far as possible.

Mechanism: After fuel depletion another key factor in muscular fatigue is the buildup of muscular metabolites. A long-held but recently disputed theory was that lactic acid (or actually lactate) buildup in the muscles was the cause of muscular fatigue. In reality, while there is certainly an association between increases in blood lactate and eventual fatigue or failure, the causal relationship between lactate buildup and fatigue has been debunked. In fact, lactate may have the opposite effect and may ultimately be ergogenic.

Solution: While you can’t directly manipulate lactic acid buildup through supplementation or anything like that, you can use monitoring and testing of lactic acid to help guide your training program. Lactate testers are relatively inexpensive and can be used to plot out performance levels for cardiovascular training.

Here’s a bit of fun physiological trivia. Typically with high muscular output you’re going to see an increase in blood lactate. But, given sufficient specific training it’s possible to actually buffer lactate faster than it’s produced while maintaining high force output. 

Mechanism: A second form of muscular metabolite buildup that is now thought to be one of the main biochemical causes of fatigue is the “leaking” of calcium in the muscle cells. While calcium is a vitally important chemical in terms of controlling muscle contractions, when it starts to leak out of the proper channels it weakens the ability for the muscle to contract.  

Solution: Unfortunately this is one area where the answer for now is simply “train more.” While there may be some drugs on the horizon it will be a long time, if ever, before the knock-on effects of artificially muting the fatigue signals in muscle are understood well enough to know if it’s a good idea to do so or not.

Mechanism: As with most systems in the body the brain and nervous system maintains a high level of control. An interesting example of this as it relates to muscle fatigue is evidence that the intention of a task actually affects fatigue. In one study, participants were able to maintain a low-force output much longer when they were intentionally maintaining force rather than intentionally maintaining a joint position against a matched resistance.

( https://www.ncbi.nlm.nih.gov/pubmed/16044306/ )

Solution: One of the physiological priorities of the nervous system you see throughout functions of the body is to maintain survival. When things are dangerous, the nervous system puts on the brakes to prevent or reduce damage. So for performance while we certainly want to push that envelope of fatigue and failure, we have to remember that it’s there for a reason and the goal needs to be to expand it, not to circumvent it. The best way to expand it is to train within it. Training to failure is training to fail. There may be times when it’s appropriate, such as dedicated hypertrophy cycles or for physique athletes, but when it comes to the combat athlete where one more rep might actually be the difference between life and death you should always be optimizing for increasing fatigue tolerance.

Understanding the mechanisms of muscular failure can help you understand how to put together a smarter and more effective training program. As always in good training, the whole is greater than the sum of the parts and no single factor is going to be worth more than a smart and comprehensive approach to training and recovery.

David Dellanave is a lifter, coach, and founder of The Movement Minneapolis in the Twin Cities. He implements biofeedback techniques, teaching his clients, ranging from athletes to general population, to truly understand what their bodies are telling them. He writes articles to make you stronger, look better naked, and definitely deadlift more at http://www.dellanave.com/.

He holds several world records, including one in the Jefferson deadlift, and his alter ego, Dellanavich from Dellanavia, has a penchant for coaching classes wearing a weightlifting singlet and speaking with a (terrible) Eastern European accent. David and his wife, Jen Sinkler, currently reside in Philadelphia, PA having recently moved there on a grand adventure of reinvention.

Twitter: http://twitter.com/ddn

Facebook: http://facebook.com/movementminneapolis

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