How to Recognize Fatigue

Looking for fatigue during any exercise is not as simple as it would seem possible on the surface.  The causes will vary based on the intensity and duration of the exercise done.

Your fatigue is different in a 20 minute even where you are working Zone 5b than for a 10 hour even with a heart rate that is in Zone 2.  There are many different causes of fatigue.

There is more than overheating and dehydration that will slow down or stop your ability to exercise.  There are at least four different common physiological causes of fatigue during the endurance events that are generally accepted by sports science.

Increasing Body Acidity

The hydrogen ions accumulated in and around the muscles that are working hard.  This fatigue is common when steady exercise or events that last less than 1 hour and are high intensity with variable paced event putting the heart rates in Zones 5a, 5b or 5c.

Fatigue is marked by labored and heaving breathing along with a burning sensation in the limbs that are doing the work, which are usually the arms and legs.  Your body also feels like you have “redlined”.

Any workout that is done in Zone 5 is to help prepare the body for this kind of fatigue by being able to produce buffers to offset the acid and also by removing the hydrogen ions from the body.

Depletion of Muscle Glycogen

This is the body’s way of storing carbohydrates.  Glycogen is a fuel source that is limited.  The body has only enough of this stored for an event that is between 90 and 120 minutes of intense exercise.

It is necessary to either replace it using something like a sports drink or other similar items in events that are longer than an hour.

If you don’t then you are going to begin to really feel tired and heavy along with finding it difficult to continue.  There will also be a strong desire to stop moving.  In many sports this is referred to as ‘bonking.’

Neuromuscular Junction Failure

The nervous system will transmit the electrochemical impulses that go from the spinal cord to the muscle fiber.  When a nerve axon meets the muscle fiber is when the muscle innervations occur.

When this happens late in an exercise session if may fail for many different unknown reasons.  When this does happen, athletes are unable to fully stimulate a muscle group from contracting right, which will result in what many believe as fatigue.

This is also associated with cramping.  Neuromuscular junction failure can occur when an even, regardless of the duration or heart rate intensity.  Since there isn’t a lot known about this type of fatigue, it is hard to avoid it and is a mystery.

Possibilities can include making sure to be adequately hydrated, eating a diet that is full of electrolytes and making sure you have had a lot of workouts related to the event you are going to be participating in.

Tryptophan Buildup

This is another one of the fatigue factors we don’t know a lot about either.  Here is what we do know about it.  In long duration activities, usually something that is three hours or more with low intensity, there seem to be changes that take place in the blood amino acid levels.

Usually these changes are a subtle, chemical reaction that will increase the tryptophan levels to the brain that will cause the athlete to feel sleepy and/or lethargic.  Tryptophan is what helps people sleep at night.

You might feel like yawning, lying down or even have problems keeping your eyes open.  Finishing the event can become a struggle.  You aren’t going to be able to train to prevent this type of fatigue from happening.

More than likely you will need a supplement for your diet that has branched chain amino acids before this particular exercise session even begins if you see that you experience this type of fatigue regularly while training.

Hard/Easy Cycle

The fatigue during exercise that was mentioned above is best described as short term fatigue.  There is also long term fatigue that biological causes are not completely understood.

It could be something as simple as chronically low levels of glycogen or even as complex as something called neuromuscular or hormonal shifts.

This is a type of fatigue that accumulates over time if it is not checked out.  A good way to avoid this type of fatigue would be to make sure you follow the principle that is called hard/easy training cycles.

Hard training days include high heart rate zones or training that are long duration workouts that are in the low heart rate zones should be followed by easy days.

Easy days are considered short workouts done with the heart rate in Zone 1 or even days with no exercise at all.  It the same way, if you have had a few weeks with hard training there should be several days of easy workouts or no workouts.

When you have had several months of hard training it may be wise to take a few weeks off doing easy workouts.

In order to make sure you prevent overtraining you need to make sure you are aware of fatigue, the causes and the appropriate actions needed to be taken when you experience it.

Good luck!

Terry

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