Fatigue

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Posted by Cris (24.66.94.141) on November 05, 2003 at 11:03:17:

More from a paper on fatigue I wrote with all paper references at bottom:

Specific mechanisms of fatigue can be described in general terms that pertain to how the athlete feels: out of breath, losing strength, and losing mental focus. We might include “burning sensation”, as a warning that fatigue, although not yet present, is imminent if pace is maintained. We may also describe fatigue in more scientific terms. Currently there is no standardized consensus on specific categories of fatigue. The following categories are some of the more popular references to specific types of fatigue.

Types of Fatigue:

Neuromuscular Fatigue
Metabolic Fatigue
Structural Fatigue
Neuroendocrine Fatigue
Psychological Fatigue

Although we may be able to define scenarios where one of these systems is taxed causing fatigue, it is more likely that more than one system can be taxed to fatigue simultaneously during exercise, and that fatigue in one system may contribute to reduced function in another. Because of this it is important to view these categories as somewhat loose divisions of possibly interrelated-interdependent systems. For example an athletes muscles may stop working because they “hit the wall”, (depleted glycogen), or reached acidosis (measured by blood lactate accumulation). Both, in fact may be measurable at the same time. A runner may be pushing hard near the end of a long race. The increased intensity may push them deep into anaerobic glycolysis, saturating the muscle with lactic acid, or more precisely a reduction in muscle pH with increased muscle H+ disassociated from lactate. At the same time the athlete has all but depleted glycogen stores from exhaustive aerobic glycolysis. For the athlete it would feel like their legs are heavy, weak, possibly cramping, and losing speed, but inspired by the finish line being minutes away, they decide to pick up the pace and give everything they have. As they approach the finish line the burn is almost unbearable, and a feeling of muscles seizing is present. More than one source of fatigue has influenced this athlete’s performance.

Neuromuscular Fatigue

Involves the central nervous System and its ability to invoke the muscles; Motor endplates, Synapses, nerve tissue conduction. Attempts have been made to identify mechanisms of fatigue that are neural6-12. Our current understanding of neural fatigue translates into common broad-based training prescriptions such as; stop when fatigue is measurable, allow a recovery period before resuming; And to known parameters of time to peak force production in muscle that can be applied to strength and reactive power training such as resistance training and plyometrics respectively. Currently we are unable to make training prescriptions with integrity that specifically account for known predicted neural variables such as muscle fiber conduction velocity, quality of action potential, and physical location of neural fatigue be it cortical, in fibrous nerve tissue, at motor units, or elsewhere. Although it is known that neural fatigue occurs, the specific mechanisms be they local or central or both requires more research before a practical training prescription can be made from conclusions of these studies. With a large amount of study in this area a positive rather than speculative outlook should be held for finding more substantial conclusions in the near future.

Metabolic Fatigue

Involves reduced fuel (ATP/CP, glycogen) and accumulation of waste products and accompanying change in muscle chemistry such as increased H+, reduced pH, reduced Ca2+. Certain metabolic causes of fatigue are well studied such as glycogen depletion, and prolonged anaerobic glycolysis leading to H+ accumulation. Even though well studied, it is still possible to find a wide variance in conclusions as to exactly why time to fatigue is shorter with anaerobic glycolysis than with aerobic glycolysis. The discrepancy is in such factors as exactly how H+ accumulation decreases maximal tension development in muscle fiber, such as H+ competing for Ca+2 for troponin-binding sites.. Regardless of the academic argument of specific cause, the correlation of reduced physical performance with increased blood lactate accumulation (time to fatigue decreases exponentially along with exponential increase in blood lactate) is 100% repeatable, and occurs largely at and beyond a specific individual “threshold” of intensity/ metabolic function. This threshold is measurable through various protocols of fitness testing, the most reliable of which uses blood lactate samples at regular intervals throughout a ramped-stage test on an ergometer or treadmill. Field-testing should be used to confirm lab tests, and may replace some lab tests if the tester is proficient. Protocols can be created to be specifically adapted for any sport. The “lactate threshold” or “anaerobic threshold”, also referred to as “lactate balance point” are of great importance in prescribing training intensities for any athlete, and become essential for endurance athletes. Different test protocols can provide different lactate/ heart rate/ workload profile results for the same individual16-22. The tester must be well aquatinted with these variables to avoid using the wrong test, and causing erroneous advice to the athlete.

Structural Fatigue

Involves any damage to physical structures such as sarcoplasmic reticulum, actin-myosin cross bridges, Z bands, mitochondria, triggerpoints, and any other cellular damage related to muscle function. Structural damage most likely influences all other types of fatigue listed here.

Neuroendocrine Fatigue

Involves hormonal responses to physical exertion. Typically, testosterone will drop and cortisol levels rise as a result of a training session/ race. This is transient and levels return to normal after recovery. In a state of overtraining, testosterone levels may remain low even during recovered states.

Psychological (or “central”) Fatigue

Involves lack of focus. Many times an athlete is fully capable of producing more power or performing at a higher level, but has difficulty achieving the mental state required to do so. Psychological training must be included as part of any successful training program. Also influenced by hormonal and neurotransmitter regulation, low blood sugar, and dehydration.

It is likely that combinations of neural, metabolic and mechanical variables are responsible for fatigue during exercise. Our unfamiliarity with fatigue factors may be due to limitations in testing devices, identifying which variables to study, and data computation methods.

Environmental influences on fatigue

Our bodies can be overtaxed in environmental conditions such as change in temperature, humidity, and altitude, leading to early fatigue in an otherwise fit and recovered individual. Acclimatization is required to remedy performance for altitude and moderate changes in temperature, but performance adaptation is limited to individual genetics14, and extreme environmental conditions are usually beyond unaided human adaptability.

1. J Pineal Res 1998 Dec;25(4):201-10 Altered circadian melatonin secretion patterns in relation to sleep in patients with chronic sleep-wake rhythm disorders. Rodenbeck A, Huether G, Ruther E, Hajak G. Department of Psychiatry, University of Gottingen, FRG.

2. Aviat Space Environ Med 1984 Nov;55(11):1031-5 The effect of sleep loss on high intensity exercise and recovery. McMurray RG, Brown CF.

3. Am J Physiol 1997 Jul;273(1 Pt 2):R364-70 Nocturnal melatonin onset is phase locked to the primary sleep gate. Shochat T, Luboshitzky R, Lavie P. Sleep Laboratory, Bruce Rappaport Faculty of Medicine, Technion-Israel Institute of Technology, Haifa, Israel

4. J Biol Rhythms 2002 Aug;17(4):364-76 Alteration of internal circadian phase relationships after morning versus evening carbohydrate-rich meals in humans. Krauchi K, Cajochen C, Werth E, Wirz-Justice A. Centre for Chronobiology, Psychiatric University Clinic, Basel, Switzerland.

5. J Biol Rhythms 1997 Jun;12(3):245-58 Sleepiness, performance, and neuroendocrine function during sleep deprivation: effects of exposure to bright light or exercise. Leproult R, Van Reeth O, Byrne MM, Sturis J, Van Cauter E. Department of Medicine, University of Chicago, IL 60637, USA.

6. Med Sci Sports Exerc 2002 Jan;34(1):105-16 Vertical jump coordination: fatigue effects. Rodacki AL, Fowler NE, Bennett SJ. Department of Exercise and Sport Sciences, Manchester Metropolitan University, Staffordshire, United Kingdom.

7. J Physiol 2002 Mar 15;539(Pt 3):913-25 Central and peripheral mediation of human force sensation following eccentric or concentric contractions. Carson RG, Riek S, Shahbazpour N. Perception and Motor Systems Laboratory, The University of Queensland, Brisbane, Queensland 4072, Australia. richard@hms.uq.edu.au

8. J Electromyogr Kinesiol 2001 Apr;11(2):85-94 Influence of contraction force and speed on muscle fiber conduction velocity during dynamic voluntary exercise. Masuda T, Kizuka T, Zhe JY, Yamada H, Saitou K, Sadoyama T, Okada M. National Institute of Bioscience and Human Technology, Agency of Industrial Science and Technology, MITI, Higashi 1-1, Ibaraki 305-8566, Tsukuba, Japan. masuda@nibh.go.jp

9. Med Sci Sports Exerc 2000 Nov;32(11):1880-6 Evidence of neuromuscular fatigue after prolonged cycling exercise. Lepers R, Hausswirth C, Maffiuletti N, Brisswalter J, van Hoecke J. Groupe Analyse du Mouvement, UFR STAPS, Universite de Bourgogne, Dijon, France. romuald.lepers@u-bourgogne.fr

10. J Appl Physiol 1994 Aug;77(2):802-6 Supernormal muscle fiber conduction velocity during intermittent isometric exercise in human muscle. Van der Hoeven JH, Lange F. Department of Clinical Neurophysiology, University Hospital Groningen, The Netherlands.

11. Exp Brain Res 2001 Jun;138(3):322-9 The effect of a fatiguing exercise by the index finger on single- and multi-finger force production tasks. Danion F, Latash ML, Li ZM, Zatsiorsky VM. Department of Kinesiology and Biomechanics Laboratory, Pennsylvania State University, University Park, PA 16802, USA.

12. Acta Physiol Scand 1999 Aug;166(4):319-26 Neuromuscular fatigue during repeated exhaustive submaximal static contractions of knee extensor muscles in endurance-trained, power-trained and untrained men. Paasuke M, Ereline J, Gapeyeva H. University of Tartu, Institute of Exercise Biology, Tartu, Estonia.

13. Periodization fourth edition 1999 ISBN 0-88011-851-2 Human Kinetics Publisher. (P.116 table 5.2) Tudor Bompa

14. The Physician and Sportsmedicine - VOL 29 - NO.5 - MAY 2001. Making a Difficult Diagnosis and Implementing Targeted Treatment. Arja L.T. Uusitalo, MD, PhD

15. Higher exercise performance and lower VO2max in Tibetan than Han residents at 4700 m altitude J Appl Physiol 1994 Aug;77(2):684-91. Ge RL, Chen QH, Wang LH, Gen D, Yang P, Kubo K, Fujimoto K, Matsuzawa Y, Yoshimura K, Takeoka M, et al. Qinghai High Altitude Medical Science Institute, Xining, Qinghai, China.

16. Eur J Appl Physiol Occup Physiol 1997;76(4):295-301 Stage duration and increase of work load in incremental testing on a cycle ergometer. Stockhausen W, Grathwohl D, Burklin C, Spranz P, Keul J. University Hospital Freiburg, Center for Internal Medicine, Department of Rehabilitation, Prevention and Sports Medicine, Germany.

17. Eur J Appl Physiol Occup Physiol 1989;58(4):411-8 Influence of cold exposure on blood lactate response during incremental exercise. Therminarias A, Flore P, Oddou-Chirpaz MF, Pellerei E, Quirion A. Laboratoire de physiologie, Faculte de Medecine de Grenoble, La Tronche, France.

18. J Sports Sci 1985 Autumn;3(3):189-95 The effects of prior exercise on the lactate and ventilatory thresholds. Neary PJ, Wenger HA

19. Med Sci Sports Exerc 1982;14(4):297-302 Blood acid-base and lactate relationships studied by ramp work tests. Hughson RL, Green HJ

20. Eur J Appl Physiol Occup Physiol 1984;53(3):260-6 Reproducibility of aerobic and anaerobic thresholds in 20-50 year old men. Aunola S, Rusko H.

21. Eur J Appl Physiol Occup Physiol 1993;67(6):518-22 The influence of blood sampling site on lactate concentration during submaximal exercise at 4 mmol.l-1 lactate level. el-Sayed MS, George KP, Dyson K. Department of Sport and Environmental Science, Manchester Metropolitan University, Alsager, Stoke-on-Trent, UK

22. Int J Sports Med 1985 Jun;6(3):163-8 Effects of pedal frequency on VO2 and work output at lactate threshold (LT), fixed blood lactate concentrations of 2 mM and 4 mM, and max in competitive cyclists. Buchanan M, Weltman A.

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: More from a paper on fatigue I wrote with all paper references at bottom: : Specific mechanisms of fatigue can be described in general terms that pertain to how the athlete feels: out of breath, losing strength, and losing mental focus. We might include “burning sensation”, as a warning that fatigue, although not yet present, is imminent if pace is maintained. We may also describe fatigue in more scientific terms. Currently there is no standardized consensus on specific categories of fatigue. The following categories are some of the more popular references to specific types of fatigue. : Types of Fatigue: : Neuromuscular Fatigue : Metabolic Fatigue : Structural Fatigue : Neuroendocrine Fatigue : Psychological Fatigue : Although we may be able to define scenarios where one of these systems is taxed causing fatigue, it is more likely that more than one system can be taxed to fatigue simultaneously during exercise, and that fatigue in one system may contribute to reduced function in another. Because of this it is important to view these categories as somewhat loose divisions of possibly interrelated-interdependent systems. For example an athletes muscles may stop working because they “hit the wall”, (depleted glycogen), or reached acidosis (measured by blood lactate accumulation). Both, in fact may be measurable at the same time. A runner may be pushing hard near the end of a long race. The increased intensity may push them deep into anaerobic glycolysis, saturating the muscle with lactic acid, or more precisely a reduction in muscle pH with increased muscle H+ disassociated from lactate. At the same time the athlete has all but depleted glycogen stores from exhaustive aerobic glycolysis. For the athlete it would feel like their legs are heavy, weak, possibly cramping, and losing speed, but inspired by the finish line being minutes away, they decide to pick up the pace and give everything they have. As they approach the finish line the burn is almost unbearable, and a feeling of muscles seizing is present. More than one source of fatigue has influenced this athlete’s performance. : Neuromuscular Fatigue : Involves the central nervous System and its ability to invoke the muscles; Motor endplates, Synapses, nerve tissue conduction. Attempts have been made to identify mechanisms of fatigue that are neural6-12. Our current understanding of neural fatigue translates into common broad-based training prescriptions such as; stop when fatigue is measurable, allow a recovery period before resuming; And to known parameters of time to peak force production in muscle that can be applied to strength and reactive power training such as resistance training and plyometrics respectively. Currently we are unable to make training prescriptions with integrity that specifically account for known predicted neural variables such as muscle fiber conduction velocity, quality of action potential, and physical location of neural fatigue be it cortical, in fibrous nerve tissue, at motor units, or elsewhere. Although it is known that neural fatigue occurs, the specific mechanisms be they local or central or both requires more research before a practical training prescription can be made from conclusions of these studies. With a large amount of study in this area a positive rather than speculative outlook should be held for finding more substantial conclusions in the near future. : : Metabolic Fatigue : Involves reduced fuel (ATP/CP, glycogen) and accumulation of waste products and accompanying change in muscle chemistry such as increased H+, reduced pH, reduced Ca2+. Certain metabolic causes of fatigue are well studied such as glycogen depletion, and prolonged anaerobic glycolysis leading to H+ accumulation. Even though well studied, it is still possible to find a wide variance in conclusions as to exactly why time to fatigue is shorter with anaerobic glycolysis than with aerobic glycolysis. The discrepancy is in such factors as exactly how H+ accumulation decreases maximal tension development in muscle fiber, such as H+ competing for Ca+2 for troponin-binding sites.. Regardless of the academic argument of specific cause, the correlation of reduced physical performance with increased blood lactate accumulation (time to fatigue decreases exponentially along with exponential increase in blood lactate) is 100% repeatable, and occurs largely at and beyond a specific individual “threshold” of intensity/ metabolic function. This threshold is measurable through various protocols of fitness testing, the most reliable of which uses blood lactate samples at regular intervals throughout a ramped-stage test on an ergometer or treadmill. Field-testing should be used to confirm lab tests, and may replace some lab tests if the tester is proficient. Protocols can be created to be specifically adapted for any sport. The “lactate threshold” or “anaerobic threshold”, also referred to as “lactate balance point” are of great importance in prescribing training intensities for any athlete, and become essential for endurance athletes. Different test protocols can provide different lactate/ heart rate/ workload profile results for the same individual16-22. The tester must be well aquatinted with these variables to avoid using the wrong test, and causing erroneous advice to the athlete. : Structural Fatigue : Involves any damage to physical structures such as sarcoplasmic reticulum, actin-myosin cross bridges, Z bands, mitochondria, triggerpoints, and any other cellular damage related to muscle function. Structural damage most likely influences all other types of fatigue listed here. : Neuroendocrine Fatigue : Involves hormonal responses to physical exertion. Typically, testosterone will drop and cortisol levels rise as a result of a training session/ race. This is transient and levels return to normal after recovery. In a state of overtraining, testosterone levels may remain low even during recovered states. : Psychological (or “central”) Fatigue : Involves lack of focus. Many times an athlete is fully capable of producing more power or performing at a higher level, but has difficulty achieving the mental state required to do so. Psychological training must be included as part of any successful training program. Also influenced by hormonal and neurotransmitter regulation, low blood sugar, and dehydration. : It is likely that combinations of neural, metabolic and mechanical variables are responsible for fatigue during exercise. Our unfamiliarity with fatigue factors may be due to limitations in testing devices, identifying which variables to study, and data computation methods. : Environmental influences on fatigue : Our bodies can be overtaxed in environmental conditions such as change in temperature, humidity, and altitude, leading to early fatigue in an otherwise fit and recovered individual. Acclimatization is required to remedy performance for altitude and moderate changes in temperature, but performance adaptation is limited to individual genetics14, and extreme environmental conditions are usually beyond unaided human adaptability. : 1. J Pineal Res 1998 Dec;25(4):201-10 Altered circadian melatonin secretion patterns in relation to sleep in patients with chronic sleep-wake rhythm disorders. Rodenbeck A, Huether G, Ruther E, Hajak G. Department of Psychiatry, University of Gottingen, FRG. : 2. Aviat Space Environ Med 1984 Nov;55(11):1031-5 The effect of sleep loss on high intensity exercise and recovery. McMurray RG, Brown CF. : 3. Am J Physiol 1997 Jul;273(1 Pt 2):R364-70 Nocturnal melatonin onset is phase locked to the primary sleep gate. Shochat T, Luboshitzky R, Lavie P. Sleep Laboratory, Bruce Rappaport Faculty of Medicine, Technion-Israel Institute of Technology, Haifa, Israel : 4. J Biol Rhythms 2002 Aug;17(4):364-76 Alteration of internal circadian phase relationships after morning versus evening carbohydrate-rich meals in humans. Krauchi K, Cajochen C, Werth E, Wirz-Justice A. Centre for Chronobiology, Psychiatric University Clinic, Basel, Switzerland. : 5. J Biol Rhythms 1997 Jun;12(3):245-58 Sleepiness, performance, and neuroendocrine function during sleep deprivation: effects of exposure to bright light or exercise. Leproult R, Van Reeth O, Byrne MM, Sturis J, Van Cauter E. Department of Medicine, University of Chicago, IL 60637, USA. : 6. Med Sci Sports Exerc 2002 Jan;34(1):105-16 Vertical jump coordination: fatigue effects. Rodacki AL, Fowler NE, Bennett SJ. Department of Exercise and Sport Sciences, Manchester Metropolitan University, Staffordshire, United Kingdom. : 7. J Physiol 2002 Mar 15;539(Pt 3):913-25 Central and peripheral mediation of human force sensation following eccentric or concentric contractions. Carson RG, Riek S, Shahbazpour N. Perception and Motor Systems Laboratory, The University of Queensland, Brisbane, Queensland 4072, Australia. richard@hms.uq.edu.au : 8. J Electromyogr Kinesiol 2001 Apr;11(2):85-94 Influence of contraction force and speed on muscle fiber conduction velocity during dynamic voluntary exercise. Masuda T, Kizuka T, Zhe JY, Yamada H, Saitou K, Sadoyama T, Okada M. National Institute of Bioscience and Human Technology, Agency of Industrial Science and Technology, MITI, Higashi 1-1, Ibaraki 305-8566, Tsukuba, Japan. masuda@nibh.go.jp : 9. Med Sci Sports Exerc 2000 Nov;32(11):1880-6 Evidence of neuromuscular fatigue after prolonged cycling exercise. Lepers R, Hausswirth C, Maffiuletti N, Brisswalter J, van Hoecke J. Groupe Analyse du Mouvement, UFR STAPS, Universite de Bourgogne, Dijon, France. romuald.lepers@u-bourgogne.fr : 10. J Appl Physiol 1994 Aug;77(2):802-6 Supernormal muscle fiber conduction velocity during intermittent isometric exercise in human muscle. Van der Hoeven JH, Lange F. Department of Clinical Neurophysiology, University Hospital Groningen, The Netherlands. : : 11. Exp Brain Res 2001 Jun;138(3):322-9 The effect of a fatiguing exercise by the index finger on single- and multi-finger force production tasks. Danion F, Latash ML, Li ZM, Zatsiorsky VM. Department of Kinesiology and Biomechanics Laboratory, Pennsylvania State University, University Park, PA 16802, USA. : 12. Acta Physiol Scand 1999 Aug;166(4):319-26 Neuromuscular fatigue during repeated exhaustive submaximal static contractions of knee extensor muscles in endurance-trained, power-trained and untrained men. Paasuke M, Ereline J, Gapeyeva H. University of Tartu, Institute of Exercise Biology, Tartu, Estonia. : 13. Periodization fourth edition 1999 ISBN 0-88011-851-2 Human Kinetics Publisher. (P.116 table 5.2) Tudor Bompa : 14. The Physician and Sportsmedicine - VOL 29 - NO.5 - MAY 2001. Making a Difficult Diagnosis and Implementing Targeted Treatment. Arja L.T. Uusitalo, MD, PhD : 15. Higher exercise performance and lower VO2max in Tibetan than Han residents at 4700 m altitude J Appl Physiol 1994 Aug;77(2):684-91. Ge RL, Chen QH, Wang LH, Gen D, Yang P, Kubo K, Fujimoto K, Matsuzawa Y, Yoshimura K, Takeoka M, et al. Qinghai High Altitude Medical Science Institute, Xining, Qinghai, China. : 16. Eur J Appl Physiol Occup Physiol 1997;76(4):295-301 Stage duration and increase of work load in incremental testing on a cycle ergometer. Stockhausen W, Grathwohl D, Burklin C, Spranz P, Keul J. University Hospital Freiburg, Center for Internal Medicine, Department of Rehabilitation, Prevention and Sports Medicine, Germany. : 17. Eur J Appl Physiol Occup Physiol 1989;58(4):411-8 Influence of cold exposure on blood lactate response during incremental exercise. Therminarias A, Flore P, Oddou-Chirpaz MF, Pellerei E, Quirion A. Laboratoire de physiologie, Faculte de Medecine de Grenoble, La Tronche, France. : 18. J Sports Sci 1985 Autumn;3(3):189-95 The effects of prior exercise on the lactate and ventilatory thresholds. Neary PJ, Wenger HA : 19. Med Sci Sports Exerc 1982;14(4):297-302 Blood acid-base and lactate relationships studied by ramp work tests. Hughson RL, Green HJ : 20. Eur J Appl Physiol Occup Physiol 1984;53(3):260-6 Reproducibility of aerobic and anaerobic thresholds in 20-50 year old men. Aunola S, Rusko H. : 21. Eur J Appl Physiol Occup Physiol 1993;67(6):518-22 The influence of blood sampling site on lactate concentration during submaximal exercise at 4 mmol.l-1 lactate level. el-Sayed MS, George KP, Dyson K. Department of Sport and Environmental Science, Manchester Metropolitan University, Alsager, Stoke-on-Trent, UK : 22. Int J Sports Med 1985 Jun;6(3):163-8 Effects of pedal frequency on VO2 and work output at lactate threshold (LT), fixed blood lactate concentrations of 2 mM and 4 mM, and max in competitive cyclists. Buchanan M, Weltman A.

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