What causes muscle fatigue? Is it simply overexertion, or is there something more? We know what causes muscle contraction. A stimulus is sent from the brain and down through the nerves of the body. This causes an increase of calcium ions into the sarcoplasm. This overload of calcium causes release channels in the sarcoplasmic reticulum to open. This causes acetylcholine (ACh) to be released into the synaptic cleft between the motor neuron and the motor end plate. The Ach causes sodium channels to open, letting sodium flood into the muscle fiber. The flow makes the inside of muscle more positively charged. This charge triggers and action potential. This muscle action potential then propagates along the sarcolemma into the T tubules. This causes the sarcoplasmic reticulum to release its stored calcium into the sarcoplasm and the muscle fiber contracts (Tortora).
Now although that was a wordy, scientific definition of what is going on the basic things you should take from that is that you need: a stimulus, calcium, acetylcholine, and sodium for a muscle to contract. During muscle contraction and relaxation the influx of sodium and potassium ions are constantly changing. The exact influx of the ions has never been known until recently. Tom Clausen from Aarhus University conducted a study that now gives us some insight into how the ions vary with muscle activity (Rockefeller).
Clausen’s study measured the changes in concentration of sodium and potassium ions in the extensor digitorum longus (ESL) muscles of rats. His study found that when these muscles were stimulated for about five minutes there was a sufficient loss of potassium. This loss would lead to an extracellular concentration that would interfere with further excitation (movement/exercise). This study shows that extracellular concentrations of potassium play a bigger role in muscle fatigue than previously though (Rockefeller).
Although this information does not lead to any solutions for muscle fatigue, it does give us insight into particular channelopathies that affect skeletal muscle such as hyperkalemic periodic paralysis (Rockefeller). This research allows us to look further into muscle fatigue and deeper into how our bodies work. This is particularly helpful insight to a highly complex and important working system of the body.
Rockefeller University Press. “New insights into the mechanics of muscle fatigue.” ScienceDaily, 17 Jan. 2013. Web. 31 Oct. 2013.
Tortora G.J. and B. Derrickson. 2012. Principles of Anatomy and Physiology. 13th ed., John Wiley and Sons