Muscle Fatigue

We use the term fatigue to describe a general feeling of the overall effects of an exercise on the body or the inability to continue with an exercise. So what causes this sensation of fatigue? The reason has to do with several factors including the availability of fuel for the muscles and the mechanism of hydrogen ions and calcium in muscle cell action.

Fuel

Muscles require ATP (adenosine triphosphate) as an energy source. During intense activity we rely on the anaerobic pathway but this has a limited store (ATP/CP pathway approximately 10 seconds and the Anaerobic Lactic pathway approximately 2 minutes). The aerobic pathway produces ATP copiously (with the breakdown of glucose and glycogen) and requires oxygen, carried by the blood, to support the process. The cardiovascular system is limited in its ability to deliver blood and oxygen to the working muscles.

Hydrogen ions

The breakdown of glucose or glycogen produces lactate and hydrogen ions. If insufficient oxygen is available to the working muscles then hydrogen ion concentrations increase and the blood and muscle become acidic. This acidic environment start to block the nerve signals from the brain to muscle fibres so the legs begin to feel heavy and we slow down in order to allow more oxygen to get to the working muscles.

Calcium

One of the functions of calcium is to help control muscle contractions. Researchers at the Columbia University Medical Centre conducted a study which found that muscle fatigue after long intense exercise may be caused by tiny leaks of calcium inside muscle cells. The researchers found that after extended high intensity exercise, 3 hours of cycling by experienced cyclists, small channels in the athlete's muscle cells were leaking calcium. This calcium leak weakens muscle contraction and stimulates an enzyme that attacks muscle fibres resulting in muscle fatigue. These calcium leaks stopped after a few days rest.

Reference: Bellinger AM, Reiken S, Dura M, Murphy PW, Deng SX, Landry DW, Nieman D, Lehnart SE, Samaru M, Lacampagne A, Marks AR. Remodeling of ryanodine receptor complex causes "leaky" channels: A molecular mechanism for decreased exercise capacity, The Proceedings of the National Academy of Sciences, February 11, 2008

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Associated Pages

The following Sports Coach pages should be read in conjunction with this page:

Associated Books

The following books provide more information related to this topic:

Principles of Anatomy and Physiology, G.J. Tortora et al., ISBN 0 06 046704 5
Strength Training Anatomy, F. Delavier, ISBN 0 7360 4185 0
Atlas of Skeletal Muscles, R.J. Stone et al., ISBN 0 697 13790 2
The Muscle Book, P. Blakey, ISBN 1 873017 00 6
Advanced Studies in Physical Education and Sport, P Beashel et al., ISBN 0 17 4482345
Physical Education and the Study of Sport, B. Davis et al., ISBN 0 7234 31752
Essentials of Exercise Physiology, W.D. McArdle et al., ISBN 0 683 30507 7
Physical Education and Sport Studies, D. Roscoe et al., ISBN 1 901424 20 0
The World of Sport Examined, P. Beashel et al., ISBN 0 17 438719 9
Advanced PE for Edexcel, F. Galligan et al., ISBN 0 435 50643 9
Examining Physical Education, K. Bizley, ISBN 0 435 50660 9
Sport and PE, K Wesson et al., ISBN 0 340 683821
PE for you, J. Honeybourne, ISBN 0 7487 3277 2

Keywords: muscle, fatigue, calcium, lactate, blood, physiology, hydrogen, anaerobic, energy, ions, lactic, aerobic, fuel, endurance, obla, thresehold, onset, accumulation, cell, mechanism, exercise, sport, several, factors, including, availability, action, pathway