Effect Of Fatigue Protocol Health Essay
Effect Of Fatigue Protocol Health Essay
In these survey 29 association football participants who were selected by convenience trying method and were indiscriminately divided into two experimental groups ( n=13 ) and control groups ( n=16 ) with ( age: 22.3±2.1 old ages and tallness: 176.5±4.4 centimeter ) volunteered as topics. Semi dynamic by Biodex balance system ( BBS ) and dynamic balance by Excursion Balance trial ( SEBT ) were taken earlier and after semi-soccer weariness protocol. For comparing of within and between agencies groups severally Paired and Independent t-test were used and the consequences were determined within the significance degree of ( P?0.05 ) .
Consequences: dynamic balance observed Anterior, Anteromedial, Medial, Posteromedial, Posterior, Posterolateral, Lateral and Anterolateral in both groups reduced significantly ( p=0.001 ) .Effect Of Fatigue Protocol Health Essay. The fluctuations of between groups were significantly in Anterior, Posteromedial ( p=0.033 ) in both groups reduced. Besides, the place of overall, anterior-posterior and Medial-lateral in semi-dynamic balance in both groups reduced significantly. Furthermore, the fluctuations of between groups were significantly in overall ( p=0.038 ) , anterior-posterior places in both groups.
Decision: Harmonizing to this consequences Finding of this survey showed that at the terminal of association football, the weariness can significantly cut down semi dynamic and dynamic balance, particularly in participants with functional mortise joint instability and later enhances hazard of hurt.
Cardinal words: Fatigue, Dynamic Balance, Ankle Instability, Soccer participant
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Introduction
Soccer, otherwise known as football, is a ball game which involves two squads of 11 participants each who attempt to impel the ball through a set of end stations while forestalling the other squad from making the same ( 1 ) . It is played by kicking, heading, or utilizing any portion of the organic structure except the weaponries and custodies with merely the goalie allowed utilizing custodies and weaponries. The game consists of two halves of 45 minute each, with a 15 minute remainder interval between the two halves ( 2 ) . This game requires explosions of velocity and power and includes frequent hits with other participants, the ball and the playing surface ( 3 ) . Hence, it is non surprising that as a consequence of its high strength and sum of hits among participants every bit good as the playing surface that the sum of hurts sustained will be high. It has been estimated that on norm, every elect male association football participant sustains about one public presentation restricting hurt each twelvemonth ( 4 ) . A bulk of the surveies into the prevalence of hurt observed that the lower appendages of the organic structures of association football participants were the most affected particularly the ankle articulation ( 5 ) . Hence, Junge and Dvorac ( 2004 ) reported that, the bulk of association football hurts are caused by injury. Based on the fact that the articulatio genus and mortise joint articulation have been observed to be the most affected organic structure parts, traumatic sprains to the mortise joint and articulatio genus were the most often encountered hurts ( 6 ) . In a survey conducted by Surve et Al. ( 1994 ) to look into the incidence of ankle sprains during one season among senior association football participants, it was observed that the usage of ankle orthosis had no consequence in participants without old mortise joint sprains, but significantly lower incidence of mortise joint sprains was observed in participants with antecedently history of mortise joint sprain ( 7 ) .Effect Of Fatigue Protocol Health Essay. Mattacola and Lloyd ( 1997 ) in their survey reported that 6-week strength and proprioception preparation plan on steps of dynamic balance: a single-case design effectual in bettering dynamic balance abilities assessed on a single-plane balance device ( 8 ) .
Osborne et Al ( 2001 ) stated that balance developing Ankle-disk preparation ( 15 min/d for 8 wk ) , injured side merely can decreased anterior tibialis musculus latency in both trained and untrained appendages, proposing a proprioceptive crossing over consequence ( 9 ) . McGuine et Al ( 2000 ) assessed balance through individual leg stance steps and found that topics who displayed hapless balance had about seven times more ankle hurts than topics with good balance. Ankle sprains are systematically the most common musculoskeletal hurt that occurs accounting for 10 % to 28 % of entire hurts ( 10 ) . Ankle sprains besides are the most common lower appendage hurt in jocks at the high school degree, with high association football participants showing the most ( 11 ) .
Aspects of neuromuscular control may be quantified through steps of postural control. Postural control can be defined as either inactive ( keeping a place with minimum motion ) , semi dynamic ( keeping a place while the base of support moves ) , or dynamic ( keeping a stable base of support while finishing a prescribed motion ) ( 12 ) . Fatigue is a really complex phenomenon that is non wholly understood. as any decrease in the neuromuscular ability to bring forth strength ( 13 ) is a usual phenomenon in opposition athleticss and is a common experience in the day-to-day activities ( 14 ) .Therefore, the muscular weariness can be the consequence of a failure in any procedure involved in the muscular contraction ( 14 ) . Fatigue consequences from an break in the concatenation of events from the CNS to the musculus fibre. Although all of writers seem to hold on the basic definition, there is still a batch of argument on whether weariness is strictly metabolic, or strictly neuromuscular related, or a combination of both ( 15 ) .
Previous researches have shown muscular weariness has a negative impact on balance and control of the organic structure place ( 16 ) . The survey of dynamic balance control system helps us to be able to hold a better apprehension of how the organic structure maps in the weariness and unstable conditions. Therefore, the intent of this survey was the consequence of weariness protocol on dynamic balance in association football participants with functional mortise joint instability.
Materials and Methods
Subjects
Twenty-nine physically active topics ( 13 experimental, 16 control ; average age 22.3±2.1 old ages, height: 176.5±4.4 centimeter ) volunteered as topics. All topics signed an informed consent signifier approved by the university ‘s institutional reappraisal board. Persons with self-reported vestibular upsets or mild head hurt in the old 6 months were excluded from the survey. The control group was free of any self-reported lower appendage hurt in the old 6 months. Subjects in the chronic mortise joint instability ( CAI ) experimental group were free from hurt to the lower appendage other than the mortise joint in the old 6 months ; had a history of at least 1 acute mortise joint sprain that resulted in puffiness, hurting, and impermanent loss of map ( but none in the old 3 months ) ; and a history of multiple episodes of the mortise joint ”giving manner ” in the past 6 months.
Protocol
After the obtained informations from questionnaires including ; single features, wellness history and Cumberland Ankle Instability Tools with internal dependability ( alpha=.83 ) ( 17 ) . Semi dynamic by Biodex balance system ( BBS ) and dynamic balance by Excursion Balance Test ( SEBT ) were taken earlier and after semi-soccer weariness protocol ( Bangsbo protocol ) . Measurements were taken from the topics ‘ dominant lower appendages. Effect Of Fatigue Protocol Health Essay. Leg laterality was determined by inquiring topics what leg they would utilize to kick a association football ball.
Star Excursion Balance Test Performance
The SEBT was performed with the topics standing in the center of a grid formed by 8 lines made with athletic tape widening out at 458 from each other33. For this undertaking, topics were merely making in the front tooth, median, and posterior waies. Each topic was asked to make every bit far as possible along the line, do a light touch on the line, and return the stretch leg back to the centre while keeping a single-leg stance with the other leg in the centre of the grid. The topics were instructed to do a light touch on the land with the most distal portion of the making pes and return to a dual leg stance without leting the contact to impact the base of support. Subjects were instructed to maintain their custodies on their hips and to maintain the heel of the stance leg on the land at all times.
Reach distances were recorded by puting a grade on a length of athletic tape on the floor matching to the touchdown point of the topic. We recorded the making distance as the distance from the centre of the grid to the point of maximal jaunt of the making leg. Based on our probe, 29 range distances were divided by leg length and multiplied by 100 to cipher a dependant variable that represents make distance as a per centum of leg length ( MAXD ) . A test was discarded and repeated if the research worker felt the topic used the making leg for a significant sum of support at any clip, removed the pes from the centre of the grid, or was unable to keep balance on the support leg throughout the test ( 18 ) .
Biodex Stability System Test
Biodex Stability System Test ( Biodex, Shirley, New York, USA ) and Star Excursion Balance were used in this survey. Biodex Stability System has a round platform that is free to travel about the anterior-posterior ( AP ) and medial-lateral ( ML ) axes at the same time. The BSS package sampled the divergences in the AP and ML waies at a rate of 20 Hz and calculated the anterior/posterior index ( API ) , medial/lateral index ( MLI ) , and overall balance index ( OBI ) utilizing the undermentioned expression. It was reported that these indexes are dependable and precise steps for postural stableness. The intra-tester dependability of BBS was 0.82 and 0.96, and the inter-tester dependability was 0.70 for OBI ( 19 ) .
Statistical Analysis
Finally, all the informations were analyzed utilizing SPSS version 16 The norm and standard divergence of informations were calculated after look intoing the information distribution normalcy utilizing Kolmogorov-Smirnov trial and Homogeneity of discrepancy method and so examined by Independent Samples Test and Paired Samples Test ( t-student ) , at a significance degree of P & A ; lt ; 0.05.
Consequences
The consequences of dynamic balance, Star Excursion Balance Test ( SEBT ) after fatigue plan on functional mortise joint stableness and instability observed Anterior ( p=0.001 ) , Anteromedial ( p=0.001 ) , Medial ( p=0.001 ) , Posteromedial ( p=0.001 ) , Posterior ( p=0.001 ) , Posterolateral ( p=0.001 ) , Lateral ( p=0.001 ) and Anterolateral ( p=0.001 ) in both groups reduced significantly. Furthermore, the fluctuations of between groups were significantly in Anterior ( p=0.043 ) , Posteromedial ( p=0.033 ) in both groups ( functional mortise joint stableness and instability groups ) ( Table 1 ) .
Besides, the place of overall, anterior-posterior and Medial-lateral in semi-dynamic balance ( Biodex system ) after fatigue plan on functional mortise joint stableness and instability in both groups reduced significantly. Furthermore, the fluctuations of between groups were significantly in overall ( p=0.038 ) , anterior-posterior places ( p=0.040 ) in both groups ( Table 2 ) . Effect Of Fatigue Protocol Health Essay.
Discussion
The intent of this survey was to find the consequence of weariness protocol on dynamic postural-control undertaking in association football participants with functional mortise joint instability and to place a SEBT normalized cut-off mark that would connote hurt hazard to persons that scored below it. Harmonizing to the consequences of the informations aggregation, the consequences of dynamic balance observed Anterior, Anteromedial, Medial, Posteromedial, Posterior, Posterolateral, Lateral and Anterolateral in both groups reduced significantly. Furthermore, the fluctuations of between groups were significantly in Anterior, Posteromedial in both groups reduced.
Therefore, these findings correspond with findings from Olmsted et Al ( 2002 ) found similar consequences when comparing the public presentation of those with one-sided chronic mortise joint instability with matched control subjects during completion of all 8 making waies of the SEBT. Normalized making distances were reduced on the chronic mortise joint instability ; nevertheless, the writers did non analyze possible beginnings of public presentation shortages. Our consequences show reduced articulatio genus and hip articulation angles for Chronic mortise joint instability occurred at the same time with decreased MAXD, bespeaking a relationship between public presentation on the SEBT and altered neuromuscular control at the articulatio genus and hip due to ankle hurt ( 20 ) .A survey by Hadzic et Al ( 2009 ) determined that reduced dorsiflexion scope of gesture along with increased plantar flexure strength increased the comparative hazard of prolonging an mortise joint sprain by 22 % among female volleyball participants ( 21 ) . McLeod et Al ( 2009 ) found that their preparation plan improved tonss on the Balance Error Scoring System ( BESS ) and on SEBT range distances ( 22 ) . This survey, along with the other two McKeon et Al ( 2008 ) , and McGuine et Al ( 2000 ) , prove that traditional balance preparation intercessions can better the dynamic stableness and balance over a short-run plan of six hebdomads or less. It has besides been noted that balance betterments are still seen up to one twelvemonth after the completion of the intercession as this improved balance can take to a reduced hazard of hurt ( 10, 23 ) .Documented damages in inactive postural control consequence from musculoskeletal hurt to the mortise joint ( 24-25 ) . An hurt that disrupts joint unity, such as chronic mortise joint instability, is theorized to impair afferent-efferent tracts that allow for care of proprioception, kinaesthesia, and finally neuromuscular control. Most research workers who have examined this phenomenon have focused on neuromuscular damages merely at the injured articulation composite. Although this is a feasible agency of replying inquiries of impaired neuromuscular control trusting chiefly on single-joint nervous systems, functional activities of the lower appendage do non affect single-joint motions but instead coordinated actions throughout the full lower kinetic concatenation.
Harmonizing to this research, the place of overall, anterior-posterior and Medial-lateral in semi-dynamic balance in both groups reduced significantly. Furthermore, the fluctuations of between groups were significantly in overall ( p=0.038 ) , anterior-posterior places in both groups. Therefore, these findings correspond with findings from Nelson et al discovered that ankle hurts occurred more often in athleticss that involved both running and leaping with the highest hurt to exposure rates happening in football, association football, and hoops severally ( 9 ) .
Where balance refers to command of the cognitive in mention to the bounds of stableness ( i.e. the base of support ) , postural control refers to task specific control of position that is unconscious and stems from the acquisition, integrating and processing of afferent signals and the ensuing motorial response ( 26 ) . This definition, instead than concentrating on an result, describes a mechanism. Effect Of Fatigue Protocol Health Essay. Postural control refers to the uninterrupted feedback cringle that is the foundation of one ‘s ability to balance, nevertheless, postural control is non limited to one ‘s ability to equilibrate. The mechanism of control is used in any state of affairs where a section of the organic structure is maintained against gravitative forces and is non needfully remarkable to cases that straight affect changes in cognitive motions ( 26 ) .
Decision
Finding of this survey showed that at the terminal of association football drama, the weariness can significantly cut down semi dynamic and dynamic balance, particularly in participants with functional mortise joint instability and later the participant is prone to Injury. Presently there are four major factors that have consequence on postural control: Injury, chronic mortise joint instability, pes abnormalcies, and weariness. Lateral mortise joint sprains are one of the most common hurts in sports. Although argument exists on whether the functional instability that consequences is due to mechanical instability or proprioceptive shortages, it is clear that hurt to the mortise joint and other countries of the lower appendage can impact postural control. In a general decision, alterations in balance scheme were apparent during the latter phases of match-play, which may increase hurt hazard. It is good to urge that association football participants perform proprioceptional preparations during their preparation and remainder periods to develop neuromuscular control.
Abstract
Muscle fatigue is a common complaint in clinical practice. In humans, muscle fatigue can be defined as exercise-induced decrease in the ability to produce force. Here, to provide a general understanding and describe potential therapies for muscle fatigue, we summarize studies on muscle fatigue, including topics such as the sequence of events observed during force production, in vivo fatigue-site evaluation techniques, diagnostic markers and non-specific but effective treatments.
Fatigue is a common non-specific symptom experienced by many people and is associated with many health conditions. Often defined as an overwhelming sense of tiredness, lack of energy and feeling of exhaustion, fatigue relates to a difficulty in performing voluntary tasks.1 Fatigue accumulation, if not resolved, leads to overwork, chronic fatigue syndrome (CFS), overtraining syndrome, and even endocrine disorders, immunity dysfunction, organic diseases and a threat to human health.
There are many different fatigue classification methods. According to its duration, fatigue can be classified into acute fatigue and chronic fatigue. Acute fatigue can be quickly relieved by rest or life-style changes, whereas chronic fatigue is a condition defined as a persistent tiredness lasting >months that is not ameliorated by rest.2, 3, 4Fatigue can also be classified as mental fatigue, which refers to the cognitive or perceptual aspects of fatigue, and physical fatigue, which refers to the performance of the motor system.1
Muscle fatigue is defined as a decrease in maximal force or power production in response to contractile activity.5 It can originate at different levels of the motor pathway and is usually divided into central and peripheral components. Peripheral fatigue is produced by changes at or distal to the neuromuscular junction. Central fatigue originates at the central nervous system (CNS), which decreases the neural drive to the muscle.5, 6 Muscle fatigue is a commonly experienced phenomenon that limits athletic performance and other strenuous or prolonged activity. It is also increases and restricts daily life under various pathological conditions, including neurological, muscular and cardiovascular disorders, as well as aging and frailty. Effect Of Fatigue Protocol Health Essay.This review primarily focuses on muscle fatigue, particularly during intense exercise, to provide a basic understanding and potential therapies for muscle fatigue.
Factors that affect muscle contraction and fatigue
The production of skeletal muscle force depends on contractile mechanisms, and failure at any of the sites upstream of the cross-bridges can contribute to the development of muscle fatigue, including nervous, ion, vascular and energy systems.7Specifically, metabolic factors and fatigue reactants during the process of contraction, such as hydrogen (H+) ions, lactate, inorganic phosphate (Pi), reactive oxygen species (ROS), heat shock protein (HSP) and orosomucoid (ORM), also affect muscle fatigue.
Neural contributions
Central neurotransmitters, especially 5-HT, DA and NA, play important role during whole-body exercise and fatigue. 5-HT produces a negative effect, whereas methylphenidate, a DA-releasing enhancer and reuptake inhibitor, produces a positive effect in exercise performance.8 The so-called central fatigue hypothesis states that exercise induces changes in the concentrations of these neurotransmitters, and fatigue arises from changes within the CNS (or proximal to the neuromuscular junction). However, recent data have shown that drugs influencing the neurotransmitter systems scarcely perturb performance under normal ambient temperatures but significantly improve endurance under high ambient temperatures. For example, the NA reuptake inhibitor reboxetine and a dual DA/NA reuptake inhibitor, bupropion, have a negative effect9, 10, 11 on exercise performance under normal temperature. However, under heat, reboxetine decreases, whereas bupropion increases performance, thus suggesting that the thermoregulatory system may have an important influence on exercise performance.
The CNS, via a central neurotransmitter, produces various excitatory and inhibitory inputs on the spinal motoneurons, thus ultimately activating motor units (MUs) to achieve the force output. The strength and timing of contraction are controlled by the firing of the motoneurons. When first recruited in a healthy system, MUs usually fire at 5–8 Hz. Effect Of Fatigue Protocol Health Essay. During brief nonfatiguing voluntary contractions in humans, the mean MU firing rates are 50–60 Hz.12 MUs are recruited or derecruited in an orderly fashion on the basis of the motoneuron size, and they essentially control the amount of muscle tissue being activated.13
Slowing or cessation of MU firing contributes to the loss of force that marks fatigue. Motoneuron firing is influenced by intrinsic changes in the motoneuron properties, descending drive and afferent feedback. During fatiguing maximal contractions, motoneuron firing rates decrease because of the following factors: (1) Repetitive activation (repeated firing) of motoneurons leads to a decrease in their excitability to excitatory synaptic input;14 (2) the excitatory drive from the motor cortex or other supraspinal area to the motoneurons is lower;14 (3) the firing of group III/IV muscle afferents is increased,15, 16 thus decreasing motoneuron firing; (4) the firing of muscle spindles (sensory receptors) is decreased, thus decreasing firing of group Ia muscle afferents, increasing presynaptic inhibition, and finally decreasing motoneuron firing;17, 18 (5) specifically, group III/IV muscle afferents also exhibit feedback interaction with cardiovascular and respiratory processes via the autonomic nervous system, thereby improving muscle blood flow and oxygenation and consequently slowing the development of fatigue of the muscle itself.14
Ca2+
Neural activation results in signal transmission from the brain to the muscle’s transverse tubules, inducing calcium release from the sarcoplasmic reticulum (SR) into the cytosol and initiation of cross-bridge cycling. This excitation-contraction coupling process involves the following events: the action potential (AP) is generated at the neuromuscular junction and propagates along the surface membrane and into the transverse tubules, where it is detected by voltage-sensor molecules (the dihydropyridine receptors, VS/DHPRs), which in turn open the ryanodine receptor-Ca2+ release channels (RyR1 isoform in skeletal muscle) in the adjacent SR and cause release of Ca2+ into the sarcoplasm.19 The binding of Ca2+ to troponin moves tropomyosin away from the myosin-binding site on actin, thus permitting cross-bridge cycling. The removal of Ca2+ from the cytoplasm by Ca2+ ATPase results in the recovery of tropomyosin to its blocked position, and relaxation occurs.20
Impaired calcium release from the SR has been identified as a contributor to fatigue in isolated skeletal muscle fibers. Several possible mechanisms have been proposed: (1) AP involves Na+ influx, and the subsequent repolarization involves K+ efflux in muscle cells. High-frequency stimulation may lead to extracellular K+ accumulation, which may decrease voltage sensor activation and the action potential amplitude; (2) Most of the ATP in a rested fiber is Mg2+ bound. Fatigue can induce a decrease in intracellular ATP and an increase in free Mg2+, thus decreasing the effectiveness of SR Ca2+ channel opening; (3) Exposure to myoplasmic phosphate causes a sustained decrease in SR Ca2+ release in skinned fiber because inorganic phosphate can enter the SR and precipitate Ca2+, thus decreasing the free Ca2+ and amount of Ca2+ available for release.21
Blood flow and O2
Blood flow can bring oxygen necessary for aerobic ATP production and remove by-products of metabolic processes in working muscles, thus playing an important role in the maintenance of force output. Muscle voluntary contractions increase the mean arterial blood pressure,22 which consequently decreases the net blood flow to the working muscle and induces fatigue.23 The occlusion of blood flow to a working muscle substantially decreases the time to exhaustion 24, 25, 26 and increases the magnitude of the decline in force,27, 28 thus indicating the potential importance of blood flow in fatigue prevention. Effect Of Fatigue Protocol Health Essay. However, despite changes in blood flow accompanying the development of muscle fatigue, decreased blood flow does not seem to be a key factor in the development of fatigue. Wigmore et al.29 have used venous occlusion plethysmography to decrease blood flow of the ankle dorsiflexor muscles, and have found that the decline in MVC force precedes significant changes in blood flow to the muscle.
One of the important roles of blood flow is to provide O2 to the working muscles. It has been well documented that decreased oxygen availability to exercising muscle has profound consequences on muscle fatigue. Breathing hypoxic air can significantly increase muscle fatigue in vivo,30, 31 and enhanced O2 delivery to the exercising muscles32 directly attenuates muscle fatigue and increases muscle efficiency. However, O2 availability affects the fatigue process at moderate work intensities. Generally, oxygen uptake and ATP utilization are increased until the VO2max is reached. During exercise at a very high intensity (usually the VO2max is already reached), the demand for more ATP cannot be met by increases in oxygen delivery, thus resulting in an imbalance of metabolic homeostasis and leading to fatigue.33
Energy
Muscular work must be supported by a ready supply of ATP energy. There are three major ATPases that require ATP for muscle activity: Na+/K+-ATPase, myosin ATPase and Ca2+ ATPase. The Na+/K+-ATPase pumps Na+ back out and K+ back into the fiber after an action potential. The myosin ATPase uses ATP to generate force and do work, and the Ca2+ ATPase pumps Ca2+ back into the SR, thus allowing for muscle relaxation. The activities of these enzymes account for 10%, 60% and 30% of total ATP use, respectively.34
Glycogen is the carbohydrate energy store for ATP production. There are three distinct subcellular localizations of glycogen: (1) intermyofibrillar glycogen, located between the myofibrils and close to SR and mitochondria; (2) intramyofibrillar glycogen, located within the myofibrils and most often in the I-band of the sarcomere; and (3) subsarcolemmal glycogen, located beneath the sarcolemma and primarily next to mitochondria, lipids and nuclei. Approximately 75% of the total glycogen store in the cells is intermyofibrillar glycogen.35, 36
It is a fundamental concept in exercise physiology that glycogen is an important fuel during exercise.37 As early as the 1960s, a strong correlation between muscle glycogen content and exercise endurance was found.38 When glycogen stores are limited, exercise cannot continue.39 Glycogen oxidation is a major source for ATP regeneration during prolonged exercise (>1 h) and high-intensity intermittent exercise.40Furthermore, glycogen may be important because it produces tricarboxylic acid cycle intermediates, thus contributing to the maintenance of oxidative metabolism.41Excitation-contraction coupling and relaxation have been reported to be affected by glycogen levels.37, 42, 43 Low-muscle glycogen and/or glycolytic-derived energy are associated with impaired SR Ca2+ release, reuptake, and Na+/K+-pump function.43, 44However, how glycogen depletion affects the series of events and ultimately results in fatigue are not fully understood. Effect Of Fatigue Protocol Health Essay.
Metabolic factors
Muscle contractions activate ATPases and promote glycolysis, thus leading to an increase in intracellular metabolites, such as H+, lactate, Pi and ROS, which contribute to the changes in cross-bridge activity.
Historically, H+ has been thought to have a role in the development of muscle fatigue. Glycolysis leads to the production of pyruvate, which feeds into the TCA cycle for oxidation. If pyruvate production exceeds its oxidation, excess pyruvate is converted into lactic acid, which dissociates into lactate and H+. The accumulation of H+ lowers the pH, thus potentially interfering with SR Ca2+ release, troponin C sensitivity to Ca2+ and cross-bridge cycling and resulting in impaired muscle force.45 However, the role of decreased pH as an important cause of fatigue is now being challenged.46Several recent studies have shown that decreased pH may have little effect on contraction in mammalian muscle at physiological temperatures. Furthermore, there is a lack of association between changes in pH and MVC throughout fatiguing exercise and in recovery in humans.47
In addition to acidosis, anaerobic metabolism in skeletal muscle also involves hydrolysis of creatine phosphate (CrP) to creatine and Pi. The concentration of Pi can increase rapidly from approximately 5–30 mm during intense fatigue. Creatine has little effect on contractile function, whereas Pi, rather than acidosis, appears to be the most important cause of fatigue during high-intensity exercise.48 Increased Pi substantially impairs myofibrillar performance, decreases SR Ca2+ release and therefore contributes to the decreased activation.49
Mitochondrial respiration produces ATP and consumes O2, a process that generates ROS. The most important ROS include superoxide (O2•−), hydrogen peroxide (H2O2), and hydroxyl radicals (OH•). As the work intensity increases, ROS production increases. The most convincing evidence that ROS contribute to fatigue comes from experiments showing that pretreatment of intact muscle with a ROS scavenger significantly attenuates the development of fatigue. ROS affect muscle fatigue mainly through the oxidation of cell proteins such as the Na+–K+ pump, myofilaments, DHPR and RyR1,50 thus leading to the inhibition of SR Ca2+ release and myofibrillar Ca2+sensitivity. In addition, ROS activate the group IV muscle afferents51 and directly inhibit motoneurons.
Other metabolites with probable roles in fatigue include ATP, ADP, PCr and Mg.52 For example, muscle ADP increases with intense contractile activity. In skinned fibers, ADP decreases fiber velocity but increases force, presumably because of more cross-bridges in the high force states. However, the more important role of ADP in eliciting fatigue appears to be related to the inhibition of the SR Ca2+ pump and the resulting disturbances in ECC rather than direct effects on the cross-bridge.53
Fatigue reactants
Organisms have different levels of adaptive responses to fatigue stress, including the CNS nervous system, sympathetic nervous system, endocrine system (hypothalamus-pituitary-adrenal axis, HPA axis), and innate immune system (that is, non-specific cytokines, complement system and natural killer cells). Effect Of Fatigue Protocol Health Essay. Many fatigue reactants, such as cortisol, catecholamine, IL-6 and HSPs, may have roles in muscle function.54
HSPs are involved in the adaptation to fatigue stress. Within the family of HSPs, HSP25 protein is abundantly expressed in skeletal muscle and increases with muscle contractile activity.55 Interestingly, Jammes et al. have reported that a widespread HSP25 response to fatigue in a single hindlimb muscle is responsible for a global adaptive response to acute localized stress and have demonstrated that group III and IV muscle afferents play an important role in the fatigue-induced p-HSP25 response; moreover, the sympathetic nerve supply to the muscles and kidney comprises the efferent arm of the p-HSP25 activation.56 Skeletal muscle HSP25 has been reported to stabilize muscle structure and repair damaged muscle proteins,57 as well as to decreases apoptosis in cultured muscle C2C12 cells by inhibiting the intrinsic and extrinsic apoptotic cell death pathway.58
Orosomucoid (ORM) is an acute-phase protein, with a very low pI of 2.8–3.8 and a very high carbohydrate content of 45%. It is predominantly synthesized in the liver, and many extra-hepatic tissues have also been reported to produce ORM under physiological and pathological stress.59 Our studies have found that the expression of ORM is markedly increased in the serum, liver and skeletal muscle in response to various forms of fatigue, including sleep deprivation, forced swimming and treadmill running. Interestingly, exogenous ORM increases muscle glycogen and enhances muscle endurance, whereas ORM deficiency results in decreased muscle endurance, thus indicating that ORM is an endogenous anti-fatigue protein. Further studies have demonstrated that ORM binds to C–C chemokine receptor type 5 (CCR5) on muscle cells and activates AMPK, thus promoting glycogen storage and enhancing muscle endurance, and representing a positive feedback mechanism for resisting fatigue and maintaining homeostasis.60, 61 Modulation of the level of ORM and CCR5 signaling may be a novel strategy for the management of muscle fatigue. Effect Of Fatigue Protocol Health Essay.
Non-invasive techniques for the ASSESSMENT OF sites of muscle fatigue
Muscle fatigue is manifested most naturally in the intact organism. Non-invasive techniques of site-specific stimulation can now be used to evaluate the potential sites of the entire system for force production in human studies. All evoked muscle responses are recorded via electromyography (EMG) electrodes placed on the muscle.
Transcranial magnetic stimulation
Transcranial magnetic stimulation involves applying magnetic stimulation to the motor cortex and is optimized to activate the muscle of interest.1 The stimulation-induced muscular response recorded by EMG is known as the motor-evoked potential (MEP). MEP is influenced not only by cortical excitability but also by spinal cord motor neuron excitability and muscle factors. MEP depression can occur in the relaxed muscle after a fatiguing exercise, possibly as a result of afferent input from the fatigued muscle. MEP is increased in the upper- and lower-limb muscles during sustained submaximal isometric contractions and is regarded as an augmentation of the central drive to the lower motoneuron pool that allows a constant level of force to be maintained despite the development of peripheral fatigue. During sustained MVC, MEP has been reported to increase during the first seconds and then to level off, increase linearly or remain stable, depending on the protocol used (that is, continuous vs intermittent) and the muscle investigated.1
Cervicomedullary region electrical stimulation
Electrical stimulation in the cervicomedullary region aims to activate the corticospinal tract at a subcortical level, thereby eliminating cortical contributions to the evoked muscle response. The muscular response recorded by EMG is known as the cervicomedullary motor-evoked potential (CMEP). Comparison of MEP and CMEP is helpful for the localization of excitability at the cortical or subcortical level.Effect Of Fatigue Protocol Health Essay. During a sustained 30% MVC of the plantar flexors, a large increase in MEP and only a slight increase in CMEP have been reported, thus suggesting a small contribution of spinal factors to the increase in corticospinal excitability during submaximal fatiguing contractions. In contrast, during 50% MVC of the elbow flexors to task failure, similar MEP and CMEP kinetics has been found, thus indicating that central changes occur almost entirely at the spinal level.62, 63, 64
Peripheral nerve low-intensity electrical stimulation
Low-intensity electrical stimulation of the peripheral nerve preferentially activates the Ia sensory fibers, which synapse with the α-motoneuron in the spinal cord. The signal is then carried along the motor neurons to the muscle, generating a response in the muscle known as the Hoffmann reflex (H-reflex). The H-reflex is used to assess spinal excitability and inhibition. Although there are several of an increase65 or no change,66the general consensus is that there is an overall decline in the amplitude of the H-reflex with the development of muscle fatigue, thus indicating a decrease in spinal excitability.67, 68 The rate and degree of decrease in H-reflex amplitude appear to be dependent on the type of fatiguing task.
Peripheral nerve high-intensity electrical stimulation
High-intensity stimulation of the peripheral nerve directly activates the α-motoneuron, evoking a motor response (m-wave) from the muscle. The m-wave is a compound action potential recorded with surface EMG and is used to assess peripheral excitability of the muscle membrane and transmission at the neuromuscular junction. A change in the twitch force without a change in the m-wave indicates a failure of excitation-contraction coupling. Effect Of Fatigue Protocol Health Essay.
Short-duration fatiguing contractions (~20 s) induce an enhancement in the amplitude and area of the m-wave.69 A longer (4-min) sustained maximal contraction does not induce changes in the amplitude of the m-wave70 but results in a significant decline in the central activation, thus suggesting that central factors contributing to fatigue can occur in the absence of a peripheral change in membrane excitability. However, more longer-duration contractions that induce fatigue (~17 min) can also induce a decline in the muscle membrane excitability and m-wave size.69
Biomarker for the diagnosis of muscle fatigue
At present, there are still no specific factors that have been consistently associated with a particular type of fatigue. Exercise types (for example, aerobic/anaerobic, short or long term), contraction type (for example, incremental/constant, isometric/non-isometric, concentric/eccentric), and fatigue degree and duration all affect the biomarker profile. According to the mechanism and metabolic changes during muscle fatigue, three categories of biomarkers have been determined: (1) ATP metabolism biomarkers, such as lactate, ammonia and hypoxanthine; (2) Oxidative stress biomarkers (ROS), such as lipid peroxidation, protein peroxidation, and antioxidative capacity; and (3) Inflammatory biomarkers, such as TNF-α, leukocytes, and interleukins.71
ATP metabolism biomarkers
Under normal circumstances, the total adenine nucleotide pool (ATP+ADP+AMP) remains constant. When the ATP supply fails to meet the consumption of ATP during exercise, fatigue occurs. To maintain the ATP/ADP ratio, two molecules of ADP may be converted to one molecule of ATP and one molecule of AMP. AMP is subsequently degraded by AMP-deaminase to IMP and ammonia.72 IMP is degraded to inosine and hypoxanthine, and ammonia is further converted to urea nitrogen (BUN), thus increasing blood BUN.Effect Of Fatigue Protocol Health Essay. In the case of inadequate oxygen supply, oxidative phosphorylation of ADP to generate ATP fails to meet the energy requirement, and the ATP production shifts from aerobic processes (the processing of glucose/glycogen, lipids or amino acids) to anaerobic glycolysis or glycogenolysis,73 thereby resulting in lactate accumulation. The best-known biomarkers of muscle fatigue from ATP metabolism include lactate, ammonia, and hypoxanthine.74, 75 Lactate and ammonia are usually determined in the serum. Hypoxanthine is usually analyzed in the serum or urine.
Serum lactate increases with exercise intensity in healthy and diseased subjects.76However, serum lactate does not appear to be related to age, sex, and physical fitness. Under the conditions of workload standardization, serum lactate appears to be a promising biomarker of muscle fatigue.73 Serum ammonia closely follows the lactate response during exercise 73 and increases during exercise. Serum ammonia is not associated with age77 and remains low in physical fitness, but is higher in men than in women.78 Serum hypoxanthine significantly increases immediately after exercise.79There exists a sex difference 80 but a lack of reliable data on age- or physical fitness-dependency on serum hypoxanthine. Effect Of Fatigue Protocol Health Essay.
