Muscle fatigue exercise effects

Heart failure is due to defects in cardiac contractility (the vigor of heart muscle), leading to inadequate cardiac output. Signs and symptoms include decreased exercise tolerance and muscle fatigue, coupled with the results of compensatory responses (neural and humoral) evoked by decreases in mean BP. Increased SANS activity leads to tachycardia, increased arteriolar tone T afterload, 4- output, 4 renal perfusion), and increased venous tone (T preload, T fiber stretch). Activation of the renin-angiotensin system results in edema, dyspnea, and pulmonary congestion. Intrinsic compensation results in myocardial hypertrophy. These effects are summarized in Figure IH-4-1. 

A portion of the salvage pathway that is important in muscle is the purine nucleotide cycle (Fig. 41.13). The net effect of these reactions is the deamination of aspartate to fumarate (as AMP is synthesized from IMP and then deaminated back to IMP by AMP deaminase). Under conditions in which the muscle must generate energy, the fumarate derived from the purine nucleotide cycle is used anapleroti-cally to replenish TCA cycle intermediates and to allow the cycle to operate at a high speed. Deficiencies in enzymes of this cycle lead to muscle fatigue during exercise. 

Sugita M, Ohtani M, Ishii N, Maruyama K, Kobayashi K. Effect of a selected amino acid mixture on the recovery from muscle fatigue during and after eccentric contraction exercise training. Biosci Biotechnol Biochem 2003 67 372-375. 

Hypoperfusion of skeletal muscles leads to fatigue, weakness, and exercise intolerance. Decreased perfusion of the central nervous system (CNS) is related to confusion, hallucinations, insomnia, and lethargy. Peripheral vasoconstriction due to SNS activity causes pallor, cool extremities, and cyanosis of the digits. Tachycardia is also common in these patients and may reflect increased SNS activity. Patients will often exhibit polyuria and nocturia. Polyuria is a result of increased release of natriuretic peptides caused by volume overload. Nocturia occurs due to increased renal perfusion as a consequence of reduced SNS renal vasoconstrictive effects at night. In chronic severe HF, unintentional weight loss can occur which leads to a syndrome of cardiac cachexia. This results from several factors, including loss of appetite, malabsorption due to gastrointestinal edema, elevated metabolic rate, and elevated levels of proinflammatory cytokines. 

A number of studies have shown that caffeine may favorably affect long-term endurance performance (ref.3) but research results concerning high intensity, short-term exercise have been a bit mixed (ref.4). Still, it seems very likely from an analysis of the biochemical effects of caffeine that is has a beneficial effect on short-term fatigue and muscle fiber in high intensity, short-term exercise like weightlifting (ref.5 6). 

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