Muscle Fatigue: How to Blast Through the Dreaded Muscle Failure

We typically use the term muscle fatigue to describe general sensations of tiredness and the accompanying decreasing muscular performance. If you’ve been working out for any amount of time, you’re probably well acquainted with fatigue: that sensation of your muscles being "cooked", "toast", "done… You know, the "please have mercy before I’m permanently trapped under this weight," or "you might just have to drag me off the track because I’ve collapsed" feeling.

It’s like when we "hit the wall" and can no longer perform reps on a particular lift; we can no longer produce the optimal output of muscular contractions as we did at the beginning of the set of workout and can’t no longer run any farther.

What is Muscle Fatigue?

The underlying causes of fatigue fall into one of two categories:

1. central (neuromuscular: the mind/central nervous system),
2. and local (peripheral: the actual muscle site).

It’s a very complex phenomenon in which multiple sites fail during muscular work.

The central nervous system (CNS) acts much like an automobile engine regulator. Most cars are made with a regulator that causes them to "shut down" when the engine revs too high for too long. This mechanism protects the engine from "over-heating." In the same way, our brains attempt to protect our muscles from tearing by reducing the rate nerve impulses are sent to our working muscles.

In most cases, you’ll experience central fatigue before local fatigue.
In other words, when you think you simply can’t do any more work because you’re so tired, what happens essentially is that your mind is telling your body (muscles) to shut down. But in fact, you’re probably able to continue for another couple of reps.

Local fatigue is related to local factors that limit the ability to perform muscular work. These include the energy systems (ATP-CP, glycolysis, and oxidation); the accumulation of metabolic byproducts (such as lactic acid); and the failure of the muscle fiber’s contractile mechanisms. The energy systems act much the same way as fuel in a car or a battery in a flashlight. However, humans are different in that we have three energy systems within the muscle’s cells that are called upon at different times depending on the intensity and duration of an activity.

The first energy system is called the ATP-CP system

It is called upon during extremely short and intense bouts of exercise (e.g., weight training, sprinting, and jumping). It works by repeatedly breaking down ATP (the basic currency of energy in the body) and rebuilding ATP using CP (creatine phosphate). During repeated maximal contractions, fatigue coincides with CP depletion.

The other two energy systems are called into play during exercises that last longer than 30 seconds. They are known as:

1. anaerobic (or glycolytic)
2. and aerobic (or oxidative)

These energy systems are very dependent on the availability of glycogen (the stored form of glucose-sugar). As with CP use, the rate of glycogen depletion is controlled by the intensity (i.e., how hard you train) of the exercise.

First Example: During sprinting

During sprinting, muscle glycogen may be used 35 to 40 times faster than during walking. Glycogen depletion and hypoglycemia (low blood sugar) limit performance in activities lasting longer than 30 minutes. Long-distance runners often speak of "bonking" or "hitting the wall." This refers to a perceived fatigue usually related to glycogen depletion. At this point, the body begins to use other forms of energy, such as fat and protein (which are not as efficient sources, thus making it harder to sustain energy levels).

2nd Example: During high-intensity anaerobic exercise

During sprinting and weight training for example, our bodies produce metabolic byproducts such as lactic acid and CO2. As these accumulate in our bodies, our ability to maintain the duration and intensity of exercise diminishes. And when they finally reach a point of saturation, our muscle capacity comes to a screeching halt. This is often referred to as the "burn," whereby the muscle feels like it’s on fire: signaling you to stop.

Even if it sounds like some fairly complex processes -which they are, so here are a few instances you can surely relate to; they will help clarify how these energy systems work in our bodies, and more importantly: how we can assist our bodies to increase their output and delay (or temporarily overcome) the onset of muscle fatigue.

With this information at hand, you’re now armed with practical, safe, scientifically sound methods to overcome muscle fatigue. Though, you’ll be able to train harder (possibly even longer) and to become stronger, both mentally and physically: making every workout that much better.

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