scholarly journals Is the notion of central fatigue based on a solid foundation?

2016 ◽  
Vol 115 (2) ◽  
pp. 967-977 ◽  
Author(s):  
Paola Contessa ◽  
Alessio Puleo ◽  
Carlo J. De Luca
Keyword(s):  
Muscle Fatigue ◽  
Muscle Force ◽  
Empirical Studies ◽  
Central Fatigue ◽  
Unit Force ◽  
The Central Nervous System ◽  
Solid Foundation ◽  
Exercise Induced ◽  
Voluntary Contractions ◽  
Central Factors

Exercise-induced muscle fatigue has been shown to be the consequence of peripheral factors that impair muscle fiber contractile mechanisms. Central factors arising within the central nervous system have also been hypothesized to induce muscle fatigue, but no direct empirical evidence that is causally associated to reduction of muscle force-generating capability has yet been reported. We developed a simulation model to investigate whether peripheral factors of muscle fatigue are sufficient to explain the muscle force behavior observed during empirical studies of fatiguing voluntary contractions, which is commonly attributed to central factors. Peripheral factors of muscle fatigue were included in the model as a time-dependent decrease in the amplitude of the motor unit force twitches. Our simulation study indicated that the force behavior commonly attributed to central fatigue could be explained solely by peripheral factors during simulated fatiguing submaximal voluntary contractions. It also revealed important flaws regarding the use of the interpolated twitch response from electrical stimulation of the muscle as a means for assessing central fatigue. Our analysis does not directly refute the concept of central fatigue. However, it raises important concerns about the manner in which it is measured and about the interpretation of the commonly accepted causes of central fatigue and questions the very need for the existence of central fatigue.

Spinal and Supraspinal Factors in Human Muscle Fatigue

2001 ◽  
Vol 81 (4) ◽  
pp. 1725-1789 ◽  
Author(s):  
S. C. Gandevia
Keyword(s):  
Muscle Fatigue ◽  
Muscle Force ◽  
Cortical Excitability ◽  
Central Fatigue ◽  
Muscle Afferents ◽  
Human Muscle ◽  
Voluntary Activation ◽  
Group Iii ◽  
Exercise Induced ◽  
Human Muscle Fatigue

Muscle fatigue is an exercise-induced reduction in maximal voluntary muscle force. It may arise not only because of peripheral changes at the level of the muscle, but also because the central nervous system fails to drive the motoneurons adequately. Evidence for “central” fatigue and the neural mechanisms underlying it are reviewed, together with its terminology and the methods used to reveal it. Much data suggest that voluntary activation of human motoneurons and muscle fibers is suboptimal and thus maximal voluntary force is commonly less than true maximal force. Hence, maximal voluntary strength can often be below true maximal muscle force. The technique of twitch interpolation has helped to reveal the changes in drive to motoneurons during fatigue. Voluntary activation usually diminishes during maximal voluntary isometric tasks, that is central fatigue develops, and motor unit firing rates decline. Transcranial magnetic stimulation over the motor cortex during fatiguing exercise has revealed focal changes in cortical excitability and inhibitability based on electromyographic (EMG) recordings, and a decline in supraspinal “drive” based on force recordings. Some of the changes in motor cortical behavior can be dissociated from the development of this “supraspinal” fatigue. Central changes also occur at a spinal level due to the altered input from muscle spindle, tendon organ, and group III and IV muscle afferents innervating the fatiguing muscle. Some intrinsic adaptive properties of the motoneurons help to minimize fatigue. A number of other central changes occur during fatigue and affect, for example, proprioception, tremor, and postural control. Human muscle fatigue does not simply reside in the muscle.

The Effect of Heating and Cooling on Time Course of Voluntary and Electrically Induced Muscle Force Variation

Medicina ◽  
2011 ◽  
Vol 47 (1) ◽  
pp. 6 ◽  
Author(s):  
◽  
◽  
◽  
◽  
Keyword(s):  
Muscle Fatigue ◽  
Time Course ◽  
Muscle Force ◽  
Peak Torque ◽  
Voluntary Contraction ◽  
Knee Extensors ◽  
Lower Body ◽  
Heating And Cooling ◽  
Force Variation ◽  
Voluntary Contractions

The aim of this study was to investigate the effect of heating and cooling on time course of voluntary and electrically induced muscle force variation. Material and Methods. Ten volunteers performed 50 maximal voluntary and electrically induced contractions of the knee extensors at an angle of 120 degrees under the control conditions and after passive lower body heating and cooling in the control, heating, and cooling experiments. Peak torque, torque variation, and half-relaxation time were assessed during the exercise. Results. Passive lower body heating increased muscle and core temperatures, while cooling lowered muscle temperature, but did not affect core temperature. We observed significantly lower muscle fatigue during voluntary contraction compared with electrically induced contractions. Body heating (opposite to cooling) increased involuntarily induced muscle force, but caused greater electrically induced muscle fatigue. In the middle of the exercise, the coefficient of correlation for electrically induced muscle torque decreased significantly as compared with the beginning of the exercise, while during maximal voluntary contractions, this relation for torque remained significant until the end of the exercise. Conclusion. It was shown that time course of voluntary contraction was more stable than in electrically induced contractions.

Plyometric Training Does Not Affect Central and Peripheral Muscle Fatigue Differently in Prepubertal Girls and Boys

2010 ◽  
Vol 22 (4) ◽  
pp. 547-556 ◽  
Author(s):  
Albertas Skurvydas ◽  
Marius Brazaitis
Keyword(s):  
Muscle Fatigue ◽  
Central Fatigue ◽  
Quadriceps Muscle ◽  
Voluntary Activation ◽  
Peripheral Fatigue ◽  
Plyometric Training ◽  
Peripheral Muscle ◽  
Before And After ◽  
Voluntary Contractions ◽  
Prepubertal Girls

The aim of the study was to evaluate the effect of plyometric training (PT) on central and peripheral (muscle) fatigue in prepubertal girls and boys. The boys (n = 13, age 10.3 ± 0.3 years) and girls (n = 13, age, 10.2 ± 0.3 years) performed continuous 2-min maximal voluntary contractions (MVCs) before and after 16 high-intensity PT sessions. PT comprised two training sessions per week of 30 jumps in each session with 20 s between jumps. The greatest effect of PT was on excitation–contraction coupling, (twitch force increased by 323% in boys and 21% in girls) and height of a counter–movement jump (increased by 37% in boys and 38% in girls). In contrast, the quadriceps voluntary activation index, central activation ratio, and MVC did not change significantly after PT. The thickness of the quadriceps muscle increased by 9% in boys and 14% in girls after PT. In conclusion, boys and girls demonstrated similar changes in indicators of central fatigue (50–60% decrease) and peripheral fatigue (45–55% decrease) after MVC before and after PT.

scholarly journals Accuracy of Force Repeatability in Relation to its Value and the Subjects’ Sex

2017 ◽  
Vol 18 (2) ◽  
Author(s):  
Ryszard Błacha ◽  
Agnieszka D. Jastrzębska
Keyword(s):  
Central Nervous System ◽  
Nervous System ◽  
Sex Differences ◽  
Muscle Force ◽  
Force Generation ◽  
Male Students ◽  
Minor Influence ◽  
The Central Nervous System ◽  
A Minor ◽  
Voluntary Contractions

AbstractThe purpose of the study was to determine the influence of force value and sex on force generation repeatability.The total of 17 female and 24 male students performed 3 maximal voluntary contractions for maximal force (FThe force generation repeatability rose with the increase of triggered force in both sexes; between force target 49 N vs. 98 N and 147 N (The influence of force value and a minor influence of sex on accuracy in generated forces might suggest that the control of muscle force by the central nervous system is similar in both sexes and the sex differences in muscle force generations are rather of muscle mass and structure.

scholarly journals AltitudeOmics: on the consequences of high-altitude acclimatization for the development of fatigue during locomotor exercise in humans

2013 ◽  
Vol 115 (5) ◽  
pp. 634-642 ◽  
Author(s):  
Markus Amann ◽  
Stuart Goodall ◽  
Rosie Twomey ◽  
Andrew W. Subudhi ◽  
Andrew T. Lovering ◽  
...  
Keyword(s):  
High Altitude ◽  
Muscle Fatigue ◽  
Muscle Activation ◽  
Acute Hypoxia ◽  
Central Fatigue ◽  
Constant Load ◽  
Peripheral Fatigue ◽  
Substantial Impact ◽  
Hypoxic Conditions ◽  
Exercise Induced

The development of muscle fatigue is oxygen (O2)-delivery sensitive [arterial O2 content (CaO2) × limb blood flow ( QL)]. Locomotor exercise in acute hypoxia (AH) is, compared with sea level (SL), associated with reduced CaO2 and exaggerated inspiratory muscle work (Winsp), which impairs QL, both of which exacerbate fatigue individually by compromising O2 delivery. Since chronic hypoxia (CH) normalizes CaO2 but exacerbates Winsp, we investigated the consequences of a 14-day exposure to high altitude on exercise-induced locomotor muscle fatigue. Eight subjects performed the identical constant-load cycling exercise (138 ± 14 W; 11 ± 1 min) at SL (partial pressure of inspired O2, 147.1 ± 0.5 Torr), in AH (73.8 ± 0.2 Torr), and in CH (75.7 ± 0.1 Torr). Peripheral fatigue was expressed as pre- to postexercise percent reduction in electrically evoked potentiated quadriceps twitch force (ΔQtw,pot). Central fatigue was expressed as the exercise-induced percent decrease in voluntary muscle activation (ΔVA). Resting CaO2 at SL and CH was similar, but CaO2 in AH was lower compared with SL and CH (17.3 ± 0.5, 19.3 ± 0.7, 20.3 ± 1.3 ml O2/dl, respectively). Winsp during exercise increased with acclimatization (SL: 387 ± 36, AH: 503 ± 53, CH: 608 ± 67 cmH2O·s−1·min−1; P < 0.01). Exercise at SL did not induce central or peripheral fatigue. ΔQtw,pot was significant but similar in AH and CH (21 ± 2% and 19 ± 3%; P = 0.24). ΔVA was significant in both hypoxic conditions but smaller in CH vs. AH (4 ± 1% vs. 8 ± 2%; P < 0.05). In conclusion, acclimatization to severe altitude does not attenuate the substantial impact of hypoxia on the development of peripheral fatigue. In contrast, acclimatization attenuates, but does not eliminate, the exacerbation of central fatigue associated with exercise in severe AH.

Amino Acids and the Brain: Do They Play a Role in “Central Fatigue”?

2007 ◽  
Vol 17 (s1) ◽  
pp. S37-S46 ◽  
Author(s):  
Romain Meeusen ◽  
Phil Watson
Keyword(s):  
Amino Acids ◽  
Perceived Exertion ◽  
Acute Exercise ◽  
Prolonged Exercise ◽  
Central Fatigue ◽  
Good Evidence ◽  
Plasma Concentration Ratio ◽  
The Central Nervous System ◽  
Pass Through ◽  
Exercise Induced

It is clear that the cause of fatigue is complex, infuenced by both events occurring in the periphery and the central nervous system (CNS). It has been suggested that exercise-induced changes in serotonin (5-HT), dopamine (DA), and noradrenaline (NA) concentrations contribute to the onset of fatigue during prolonged exercise. Serotonin has been linked to fatigue because of its documented role in sleep, feelings of lethargy and drowsiness, and loss of motivation, whereas increased DA and NA neurotransmission favors feelings of motivation, arousal, and reward. 5-HT has been shown to increase during acute exercise in running rats and to remain high at the point of fatigue. DA release is also elevated during exercise but appears to fall at exhaustion, a response that may be important in the fatigue process. The rates of 5-HT and DA/NA synthesis largely depend on the peripheral availability of the amino acids tryptophan (TRP) and tyrosine (TYR), with increased brain delivery increasing serotonergic and DA/NA activity, respectively. TRP, TYR, and the branched-chained amino acids (BCAAs) use the same transporter to pass through the blood-brain barrier, meaning that the plasma concentration ratio of these amino acids is thought to be a very important marker of neurotransmitter synthesis. Pharmacological manipulation of these neurotransmitter systems has provided support for an important role of the CNS in the development of fatigue. Work conducted over the last 20 y has focused on the possibility that manipulation of neurotransmitter precursors may delay the onset of fatigue. Although there is evidence that BCAA (to limit 5-HT synthesis) and TYR (to elevate brain DA/NA) ingestion can influence perceived exertion and some measures of mental performance, the results of several apparently well-controlled laboratory studies have yet to demonstrate a clear positive effect on exercise capacity or performance. There is good evidence that brain neurotransmitters can play a role in the development of fatigue during prolonged exercise, but nutritional manipulation of these systems through the provision of amino acids has proven largely unsuccessful.

Unilateral isometric muscle fatigue decreases force production and activation of contralateral knee extensors but not elbow flexors

2014 ◽  
Vol 39 (12) ◽  
pp. 1338-1344 ◽  
Author(s):  
Israel Halperin ◽  
David Copithorne ◽  
David G. Behm
Keyword(s):  
Muscle Fatigue ◽  
Force Production ◽  
Voluntary Activation ◽  
Knee Extensors ◽  
Elbow Flexors ◽  
Post Intervention ◽  
Nonlocal Effects ◽  
And Performance ◽  
Voluntary Contractions ◽  
Isometric Muscle

Nonlocal muscle fatigue occurs when fatiguing 1 muscle alters performance of another rested muscle. The purpose of the study was to investigate if fatiguing 2 separate muscles would affect the same rested muscle, and if fatiguing the same muscle would affect 2 separate muscles. Twenty-one trained males participated in 2 studies (n = 11; n = 10). Subjects performed 2 pre-test maximum voluntary contractions (MVCs) with the nondominant knee extensors. Thereafter they performed two 100-s MVCs with their dominant knee extensors, elbow flexors, or rested. Between and after the sets, a single MVC with the nondominant rested knee extensors was performed. Subsequently, 12 nondominant knee extensors repeated MVCs were completed. Force, quadriceps voluntary activation (VA), and electromyography (EMG) were measured. The same protocol was employed in study 2 except the nondominant elbow-flexors were tested. Study 1: Compared with control conditions, a significant decrease in nondominant knee extensors force, EMG, and VA was found under both fatiguing conditions (P ≤ 0.05; effect size (ES) = 0.91–1.15; 2%–8%). Additionally, decrements in all variables were found from the first post-intervention MVC to the last (P ≤ 0.05; ES = 0.82–2.40; 9%–20%). Study 2: No differences were found between conditions for all variables (P ≥ 0.33; ES ≤ 0.2; ≤3.0%). However, all variables decreased from the first post-intervention MVC to the last (P ≤ 0.05; ES = 0.4–3.0; 7.2%–19.7%). Whereas the rested knee extensors demonstrated nonlocal effects regardless of the muscle being fatigued, the elbow-flexors remained unaffected. This suggests that nonlocal effects are muscle specific, which may hold functional implications for training and performance.

On the dimensionality of intragroup conflict

2017 ◽  
Vol 28 (5) ◽  
pp. 538-562 ◽  
Author(s):  
Lin Ma ◽  
Baiyin Yang ◽  
Xueli Wang ◽  
Yan Li
Keyword(s):  
Factor Analysis ◽  
Empirical Studies ◽  
Cognitive Conflict ◽  
Content Type ◽  
Intragroup Conflict ◽  
Four Dimensions ◽  
Coding Schemes ◽  
Standard Scale ◽  
Solid Foundation ◽  
Initial Scale

Purpose The purpose of this paper is to explore the dimensionality of intragroup conflict and to develop an instrument with acceptable psychometric properties for the comprehensive measurement of conflict. Design/methodology/approach This paper strictly follows the standard scale-developing method: first, establish theoretical dimensions of intragroup conflict; then, develop the initial scale through in-depth interviews and coding schemes; third, revise and verify the scale through exploratory factor analysis and confirmatory factor analysis; and, finally, examine the predictive validity of the new intragroup conflict scale. Findings This study identifies four dimensions of intragroup conflict – cognitive conflict, affective conflict, behavioral conflict, and interest-based conflict – and provides evidence of construct validity for a new measure. The results show that cognitive and interest-based conflict affect group innovation performance positively, whereas affective and behavioral conflict affects it negatively. Originality/value This study first detects interest-based conflict as a new dimension and explores a more comprehensive scale (ABCI) that reflects all the connotations of conflict, which deepens the understanding of intragroup conflict, laying a solid foundation for empirical studies of conflict.

Fatigue of intermittent submaximal voluntary contractions: central and peripheral factors

1986 ◽  
Vol 61 (2) ◽  
pp. 421-429 ◽  
Author(s):  
B. Bigland-Ritchie ◽  
F. Furbush ◽  
J. J. Woods
Keyword(s):  
No Reduction ◽  
Rest Period ◽  
Central Fatigue ◽  
Voluntary Contraction ◽  
Adductor Pollicis ◽  
M Wave ◽  
Generating Capacity ◽  
Target Force ◽  
Voluntary Contractions ◽  
Muscle Contractile

Central and peripheral factors were studied in fatigue of submaximal intermittent isometric contractions of the human quadriceps and soleus muscles. Subjects made repeated 6 s, 50% maximal voluntary contractions (MVC) followed by 4 s rest until the limit of endurance (Tlim). Periodically, a fatigue test was performed. This included a brief MVC, either a single shock or 8 pulses at 50 Hz during a rest period and a shock superimposed on a target force voluntary contraction. At Tlim, the MVC force had declined by 50%, usually in parallel with the force from stimulation at 50 Hz. The twitches superimposed on the target forces declined more rapidly, disappearing entirely at Tlim. In similar experiments on adductor pollicis, no reduction of the evoked M wave was seen. The results suggest that, during fatigue of quadriceps and adductor pollicis induced by this protocol, no central fatigue was apparent, but some was seen in soleus. Thus the reduced force-generating capacity could result mainly or entirely from failure of the muscle contractile apparatus.

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