Fatigue PDF Lecture Notes (Curtin University)

17/05/2020 COMMONWEALTH OF AUSTRALIA Copyright Regulation 1969 WARNING This material has been copied and communicated to you by or on behalf of Curtin University of Technology pursuant to Part VB of the Copyright Act 1968 (the Act) The material in this communication may be subject to copyright und...

17/05/2020 COMMONWEALTH OF AUSTRALIA Copyright Regulation 1969 WARNING This material has been copied and communicated to you by or on behalf of Curtin University of Technology pursuant to Part VB of the Copyright Act 1968 (the Act) The material in this communication may be subject to copyright under the Act. Any further copying or communication of this material by you may be the subject of copyright protection under the Act. The pictures used in this lecture are only intended to be used as pictures and NOT the associated website or information attached to them Do not remove this notice 1 Fatigue 2 1 17/05/2020 Topics • Describe fatigue • Define the components of fatiguability and explain how these contribute to fatigue • Understand sense of effort 3 Fatigue Fatigue is a self‐reported disabling feeling of tiredness that results in decreased performance of a task (Enoka and Duchateau 2016; Kluger et al., 2013; Noakes 2012) When fatigued, a person has difficulty in initiating or sustaining voluntary activities (Tanaka and Watanabe, 2012) 4 2 17/05/2020 Fatigue – historical point of view Fatigue is due to a failure of the heart and skeletal muscle • peripheral fatigue ‐ lactic acid build‐up, lack of oxygen, failure of muscle contraction (A.V.Hill early 20th Century) Fatigue is due to responses in the central nervous system • sense of fatigue protects the body from damage (Mosso late 19th century, Bock and Dill 1930’s) • central fatigue – motor unit activation (Gandevia, 2001) A.V. Hill Integrated view: fatigue is due to both (Enoka and Duchateau 2016; Kluger et al., 2013; Noakes 2012) https://en.wikipedia.org/wiki/Archibald_Hill 5 What is fatigue? A self‐reported disabling symptom derived from two interdependent attributes: perceived fatigability and performance fatigability. • Specific to the person and their traits, capacity and experiences Performance fatigability • the decline in an objective measure of performance over a discrete period • Measured only during activity Perceived fatigability • change in sensations, homeostasis and the psychological state of the individual. • Measured at rest or during activity Enoka and Duchateau (2016) Kluger et al., 2013 6 3 17/05/2020 Factors that modulate fatiguability Enoka and Duchateau (2016) Kluger et al., 2013 7 Perceived fatiguability ‐ Psychological • 2004 Olympic Games held in Athens during the women’s eights rowing final, as the Australian team approached the final 400 metres Sally stopped rowing and slumped backwards, into the lap of her teammate Julia Wilson. She just… laid down. • Lack of psychological monitoring and intervention (AIS psychologist) https://punkee.com.au/lay‐down‐sally‐robbins/73911 8 4 17/05/2020 Dealing with fatigue Sensory input from the peripheral system to the central nervous system activates the inhibition system to limit the motor output; while a motivational input activates the facilitation system to increase the motor output. Tanaka and Watanabe (2012) Figure 1 9 Perceived fatiguability • Changes in the sensations that regulate the integrity of the performer • Can be assessed during activity or rest • Common in clinical settings (chronic fatigue, cancer fatigue, multiple sclerosis) • Fatigue severity scale Fatigue Severity Scale (FSS), which is a validated and reliable instrument that quantifies the impact of fatigue Fatigue Severity Scale 10 5 17/05/2020 Perceived fatiguability ‐ homeostasis • Homeostasis refers to the tendency of an organism to maintain a stable functional state. • Gabriela Andersen‐Schiess 1984 olympic marathon • Women’s marathon 1984 • What aspects did she mention? • Body homeostasis • Hydration • Temperature (core) • Psychological • pain • Recovered in a few hours • Prior experience and environmental conditions? 11 Performance fatiguability The decline in an objective measure of performance over a discrete period Objective performance usually considered to be the force a muscle can produce. A wider definition is any aspect of performance including velocity, duration of task, power production. The outcome measure must be valid. 12 6 17/05/2020 Enoka and Duchateau (2016) Kluger et al., 2013 13 Motoneuron firing is influenced by Motor unit recruitment and rate coding • recruitment order of MUs isn’t affected by fatigue (Henneman’s size principle is retained) but thresholds of recruitment can change • long endurance/low intensity tasks – MU rotation/substitution • rate coding tends to decline. In MVC as much as 50%. Motor neuron (MN) excitability decreases with repetitive activation • due to intrinsic changes in the MN • due to increased afferent feedback (pain and chemical receptors). Same receptors to the ANS increase blood flow and so oxygen supply. Taylor et al., (2016) 14 7 17/05/2020 Motoneuron firing is influenced by Muscle spindle input • usually increases 1a afferent firing to increase motor neuron firing • fatigue reduces spindle firing and efficiency of 1a facilitation of MN Cortical drive • initially increased excitatory drive form the cortex compensates for contractile failure and reduction in MN excitability • cannot be sustained and decreases ‐ supraspinal fatigue Taylor et al., (2016) 15 Contractile function – lack of fuel Glycogen is the carbohydrate energy store for ATP production. Excitation‐ contraction coupling is disrupted by a decreased ATP and increased ADP Excitation • Reduced ATP reduces Na+/K+‐pump function so alters the membrane potential so reduced graded potentials (reduced AP) https://en.wikipedia.org/wiki/Membrane_potential 16 8 17/05/2020 Contractile function – lack of fuel Glycogen is the carbohydrate energy store for ATP production. Excitation‐ contraction coupling is disrupted by a decreased ATP and increased ADP Contraction • decrease in ATP reduces Ca2+ release and reuptake by the sarcoplasmic reticulum • decrease in ATP slows the sliding filament 17 Blood flow • Muscle contraction increases the arterial blood pressure and decreases flow of blood into muscles • Reduced blood flow • reduces oxygen and glucose to muscle which is necessary for aerobic ATP production • reduces removal of by‐products of metabolic processes in working muscles • Chemical receptors to the ANS act to increase blood flow and so oxygen supply 18 9 17/05/2020 Factors that modulate fatiguability Enoka and Duchateau (2016) Kluger et al., 2013 19 Sense of Effort 20 10 17/05/2020 Sense of effort Rate of perceived exertion (RPE) be measured by the Borg Scale During exercise, afferent feedback from numerous physiological systems is responsible for the generation of the conscious RPE. 21 Summary • Describe fatigue • Define the components of fatiguability and explain how these contribute to fatigue • Understand sense of effort 22 11