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Query: UMLS:C0015672 (fatigue)
 51,768 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Nine trained cyclists were studied to determine the effects of caffeine (CAF), and glucose polymer (GP) feedings on work production (kpm) during two hr of isokinetic cycling exercise (80 rpm). Ingestion of 250 mg of CAF 60 min prior to the ride was followed by ingestion of an additional 250 mg fed at 15 min intervals over the first 90 min of the exercise. This treatment significantly increased work production by 7.4% and Vo2 by 7.3% as compared to control (C) while the subjects' perception of exertion remained unchanged. Ingestion of approximately 90 g of GP during the first 90 min (12.8 g/15 min) of the exercise had no effect on total work production or Vo2. It was, however, effective in reducing the rate of fatigue over the last 30 min of cycling. Although GP maintained blood glucose and insulin levels (P less than or equal to 0.05) above those of the C and CAF trials, total CHO utilization did not differ between treatments. During the last 70 min of the CAF trial, however, fat oxidation was elevated 31% and appeared to provide the substrate needed for the increased work production during this period of exercise. These data, therefore, demonstrate an enhanced rate of lipid catabolism and work production following the ingestion of caffeine.
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PMID:Influence of caffeine and carbohydrate feedings on endurance performance. 48 Nov 58

1. Latency relaxation and twitch tension were recorded simultaneously in single isolated muscle fibres of Xenopus laevis. 2. During low frequency (0.6 or 1 pulse/sec) repetitive stimulation, three successive phases of twitch tension were observed: negative staricase (a slight drop in tension), positive staircase (about 15% increase in tension) and fatigue. At the same time the amplitude of latency relaxation decreased monotonically, and near the peak of positive staircase, the amplitude decreased almost to an undetectable level. 3. The application of caffeine (0.1--1.5 mM) increased peak twitch tension by 15--200%, but decreased the latency relaxation amplitude by 30--93%. 4. The application of Ca-release inhibitors, deuterium oxide and dantrolene sodium, caused a 43--89% decline in peak twitch tension but no change in latency relaxation amplitude. 5. The lack of correlation between changes in peak twitch tension and latency relaxation amplitude suggests that latency relaxation is associated with the mechanism which triggers Ca2+ relase rather than with Ca2+ release itself.
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PMID:Latency-relaxation in single muscle fibres. 72 20

In excised, curarized and massively stimulated fast-twitch mouse gastrocnemius muscles the early twitch tension enhancements (treppe) during 1/s activity between 10 and 36 degrees C increase and affect more contractions as temperature increases. Tension output eventually declines at a temperature-independent rate. Half-relaxation time lengthens below 25 degrees C and shortens above 25 degrees C. During 1/0.63s twitches half-relaxation time lengthens even at 25 degrees C. In slow-twitch soleus muscles activity decreases twitch tension and half-relaxation time regardless of temperature. Activity shortens contraction times in both muscles. Oxygen lack induced by NaN3 cannot account satisfactorily for these results. Activation is apparently more plastic in the gastrocnemius than in the soleus, and the relationship between the rates of their activation and relaxation processes and the temperature sensitivities of these rates also seem to differ. In both muscles caffeine can convert activity-induced shortened of half-relaxation times into prolongations. In the soleus this effect is more pronounced at 30 than at 25 degrees C. At high temperature and twitch rates caffeine reduces treppe amplitude and duration without affecting the eventual twitch tension decline in the gastrocnemius while it greatly accelerates twitch tension decline in the soleus. In both muscles intrafiber Ca2+ movements are apparently major determinants of fatigue behavior.
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PMID:Fatigue and caffeine effects in fast-twitch and slow-twitch muscles of the mouse. 103 14

1. Single fibres isolated from the anterior tibialis muscle of Rana temporaria (temperature, 2-5 degrees C; sarcomere length, 2.10 microns) were fatigued using two separate protocols that led to different degrees of depression of tetanic force. Under control conditions the fibre was stimulated to produce a 1 s fused isometric tetanus at 300 s intervals. A moderate degree of fatigue (tetanic force reduced to 70-80% of the control value) was produced by decreasing the intervals between tetani to 15 s ('fatiguing protocol 1'). A more pronounced depression of tetanic force (to 40-50% of the control value) was produced by evoking a single twitch at 1-2 s intervals ('fatiguing protocol 2'). 2. Fatiguing protocol 1 reduced the contracture response to submaximal and supramaximal concentrations of caffeine (3-15 mM) in proportion to the decrease in tetanic force. These results support the view that fatiguing stimulation according to protocol 1 leads to a true 'myofibrillar fatigue' with no failure of activation of the muscle fibre. 3. Fatiguing protocol 2 reduced the amplitudes of isometric twitch and tetanus to below 10 and 50% of the control values, respectively. By contrast, the maximal contracture response to caffeine (15 mM) was depressed by merely 2-3% of its prefatigue value. 4. Force and instantaneous fibre stiffness were recorded simultaneously during twitch and tetanus as fatigue was induced by protocol 2. During the initial part of fatigue (tetanic force reduced by 25% of control) stiffness was reduced by merely 9% in accordance with previous measurements during fatigue induced by protocol 1. However, with further depression of twitch and tetanus by protocol 2 there was a marked reduction of fibre stiffness. These results, together with the findings reported under point 3, strongly suggest that at an advanced state of fatigue induced by protocol 2 the decrease in active force is largely due to failure of activation of the contractile system. 5. Muscle fibres were quickly frozen for electron microscopical examination after shortening below slack length (to approximately 1.6 microns sarcomere spacing) during tetanic stimulation. In non-fatigued fibres, and in fibres fatigued according to protocol 1, the myofibrils exhibited a straight appearance throughout the preparation suggesting that the entire volume of the fibre was properly activated. In fibres fatigued by protocol 2, on the other hand, only the most peripheral layers of myofibrils remained straight after shortening, whereas the centre of the fibre showed marked waviness indicating failure of the inward spread of activation in this case.
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PMID:Myofibrillar fatigue versus failure of activation during repetitive stimulation of frog muscle fibres. 129 47

Genetic endowment and proper training are the major factors contributing to athletic success in endurance and ultraendurance events. Proper nutrition, primarily adequate carbohydrate and fluid, prior to and during the event is also critical. Endurance athletes often utilize other nutritional substances or practices, often referred to as ergogenics, in attempts to obtain a competitive edge by enhancing energy utilization and delaying the onset of fatigue. Numerous nutritional ergogenics have been used in attempts to enhance endurance performance, but with several exceptions most have been shown to be ineffective, including bee pollen, L-carnitine, CoQ10, inosine, amino acids, alkaline salts, and vitamin E at sea level. Research findings are equivocal relative to the ergogenicity of caffeine, phosphate salts, and vitamin E at altitude. Loss of excess body fat, a nutritional practice, may be an effective ergogenic. Conversely, some agents such as alcohol may impair performance, an ergolytic effect. Additional research is necessary to support the efficacy of several nutritional ergogenics to enhance prolonged endurance performance, such as caffeine, phosphates, specific amino acids, and various commercial products. Such research should involve exercise tasks comparable in intensity and duration to that experienced in the marathon and similar endurance events.
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PMID:Ergogenic and ergolytic substances. 132 3

Caffeine is the most widely consumed central-nervous-system stimulant. Three main mechanisms of action of caffeine on the central nervous system have been described. Mobilization of intracellular calcium and inhibition of specific phosphodiesterases only occur at high non-physiological concentrations of caffeine. The only likely mechanism of action of the methylxanthine is the antagonism at the level of adenosine receptors. Caffeine increases energy metabolism throughout the brain but decreases at the same time cerebral blood flow, inducing a relative brain hypoperfusion. Caffeine activates noradrenaline neurons and seems to affect the local release of dopamine. Many of the alerting effects of caffeine may be related to the action of the methylxanthine on serotonin neurons. The methylxanthine induces dose-response increases in locomotor activity in animals. Its psychostimulant action on man is, however, often subtle and not very easy to detect. The effects of caffeine on learning, memory, performance and coordination are rather related to the methylxanthine action on arousal, vigilance and fatigue. Caffeine exerts obvious effects on anxiety and sleep which vary according to individual sensitivity to the methylxanthine. However, children in general do not appear more sensitive to methylxanthine effects than adults. The central nervous system does not seem to develop a great tolerance to the effects of caffeine although dependence and withdrawal symptoms are reported.
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PMID:Caffeine and the central nervous system: mechanisms of action, biochemical, metabolic and psychostimulant effects. 135 51

Twenty-four-hour ambulatory electrocardiographic monitoring was used to determine the incidence of arrhythmia while on-call and its relationship to stress and fatigue in 20 healthy medical interns. Mitral valve prolapse was present in 8 of 19 interns (42%). Heart rates ranged from a maximum of 103-167 beats/min (135 +/- 16) to a minimum of 38-61 beats/min (47 +/- 5). Interns had at least one episode of sinus tachycardia/h during 57% +/- 21% (range, 8-88%) of their hours on-call. Atrial premature beats (APB) were present in 19 of 20 (95%) and ventricular premature beats (VPB) in 12 of 20 (60%) subjects. APB/h ranged from 0 to 1.2 (0.4 +/- 0.3) and VPB/h from 0 to 23 (2 +/- 6). Three interns had multiform VPB and two had ventricular couplets. More APB/h occurred in interns under greater stress (0.5 +/- 0.4/h vs 0.3 +/- 0.1/h, p < 0.05) and combined stress and fatigue (0.6 +/- 0.4/h vs 0.2 +/- 0.2/h, p < 0.01). More VPB/h (5 +/- 9/h vs 0.5 +/- 0.6/h, p < 0.05) and higher (Lown) grade ventricular ectopy (2.3 +/- 1.6 vs 0.8 +/- 1.1; p < 0.05) occurred in interns under greater combined stress and fatigue. Mitral valve prolapse, sleep deprivation and caffeine intake were not associated with increased arrhythmia. The authors conclude that (1) rapid sinus tachycardia is frequent in interns while on-call and (2) interns experiencing greater stress and fatigue have more APB/h, VPB/h, and higher grade ventricular ectopy. These data support the notion that stress and fatigue may contribute to arrhythmia in healthy normal subjects.
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PMID:The effect of stress and fatigue on cardiac rhythm in medical interns. 140 19

The effects on measures of anxiety from two doses of oral caffeine (250 and 500 mg) and placebo were compared in 12 patients with generalized anxiety disorder (GAD), 12 patients with panic disorder, and 12 normal subjects. Caffeine produced significantly less decrease in electroencephalographic alpha wave activity, greater decrease in N1-P2 auditory evoked potential amplitude, and greater increased in skin conductance level, systolic and diastolic blood pressure, critical fusion flicker frequency, and self-ratings of anxiety and sweating in patients with GAD than in normal patients. Patients with panic disorder showed different reactivity than normal patients did with respect to electroencephalographic alpha waves, N2 latency, N2-P2 auditory evoked potential amplitude, and physical tiredness but were less reactive than patients with GAD on several variables. It is concluded that patients with GAD are abnormally sensitive to caffeine and that the data support the view that panic disorder is a separable disorder from GAD.
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PMID:Anxiogenic effects of caffeine in patients with anxiety disorders. 144 24

Studies in adult animal and human subjects have suggested that the methylxanthine drugs can delay the onset or attenuate the severity of diaphragmatic fatigue. We have investigated the effect of aminophylline and caffeine on the pressure-generating capacity of the fatigued diaphragm in 1-mo-old piglets. Measurements of ventilation, transdiaphragmatic pressure, blood gases and pH, diaphragmatic electromyogram, diaphragmatic pressure-frequency curve (PdiFC), diaphragmatic blood flow, and end-expiratory lung volume were obtained at baseline, after 90 min of inspiratory resistive loaded breathing (IRL), and again 30 min after methylxanthine infusion while still on IRL. IRL resulted in a significant decrease in minute ventilation secondary to a fall in tidal volume. Spontaneously generated transdiaphragmatic pressure increased 7-fold from baseline. EMG activity increased to both segments of the diaphragm. Abdominal expiratory muscle activity was noted after the onset of IRL and was accompanied by a fall in end-expiratory lung volume. The PdiFC was significantly decreased from baseline after 90 min of IRL, demonstrating diaphragmatic fatigue. Aminophylline did not alter the PdiFC of the diaphragm. Diaphragmatic electromyogram and tidal volume increased. No change in diaphragmatic blood flow was demonstrated after infusion of aminophylline. Serum theophylline levels averaged 117 +/- 11 mumol/L (21 +/- 2 micrograms/mL). Caffeine administration did not alter the PdiFC or the diaphragmatic electromyogram during IRL. Blood flow to both segments of the diaphragm decreased after caffeine infusion. Serum caffeine levels averaged 86 +/- 30 mumol/L (16.6 +/- 5.9 micrograms/mL).(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Effect of methylxanthines on diaphragmatic fatigue in the piglet. 148 Apr 60

Elderly women in subjectively good health--free of acute illness and major sleep pathologies--who were self-identified as good (n = 22) and poor (n = 16) sleepers were compared on measures of physical health, psychological symptoms, psychosocial status, and life-style. Poor sleepers reported longer sleep latencies, less total sleep time, more nonrestorative sleep, and more daytime fatigue than did good sleepers. Sleep recordings confirmed subjective reports, with shorter total sleep times and trends for lower sleep efficiency, longer sleep latencies, and more wake-after-sleep onset among women with subjective poor sleep. Poor sleepers also were more frequent users of sedative-hypnotic medications in the past. Current medication use, alcohol and caffeine use, daytime napping, and exercise were equivalent in both groups. Psychosocial status failed to discriminate groups. Poor sleepers reported significantly more psychological symptoms than did good sleepers. The levels of both psychological symptoms and sleep disturbance were mild.
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PMID:Factors related to sleep quality in healthy elderly women. 155 9


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