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Download Energy sources in skeletal muscle
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Energy sources in skeletal muscle Pathway 1. Direct phosphorylation 2. Glycolisis 3. Oxidative phosphorylation Rate Extent ATP/glucose Extremely fast Very limited - Very fast limited 2-3 Slow Unlimited 36 Muscle types • based on the speed of contraction – fast – slow • based on the source of energy – oxidative – glycolitic Basic classification of skeletal muscle fiber types Type I: slow oxidative Type IIB: fast glycolytic Type IIA: fast oxidative Slow Fast Fast SR Ca++ pumping capacity Moderate High High Diameter (diffusion distance) Moderate Large Small High Low Very high Moderate High High Fast Fast Slow Myosin isoenzyme (ATPase rate) Oxidative capacity (mitochondrial content, capillary density, myoglobin) Glycolytic capacity Mechanical response Components of muscle energetics • Phosphagen system 8 to10 second • Glycogen-lactic acid system 1 to 2 minutes • Aerobic system Unlimited time (as long as nutrients last) Components of muscle energetics • Phosphagen system 8 to 10 seconds • Glycogen-lactic acid system 1 to 2 minutes • Aerobic system Unlimited time (as long as nutrients last) Components of muscle energetics • Phosphagen system 8 to 10 seconds • Glycogen-lactic acid system 1 to 2 minutes • Aerobic system Unlimited time (as long as nutrients last) Muscle performance • the speed of contraction depends on the load – v = (A – B * F) / (F + C); where v0 = A / C; F0 = A / B – isotonic contraction – isometric contraction • the performance (P = F * v) of a muscle depends on the load – bell shaped curve → optimal load [~F0 / 3] – efficiency ~ 20% Effects of physical exercise demand: increased rate of metabolism Phosphocreatine pool anaerobic catabolism aerobic catabolism ATP (constant) Muscle contraction (20%) Heat production (80%) glucose, glycogen, FFA Increased O2 consumption • • • Respiratory rate ↑ Tidal volume ↑ O2 diffusion in the alveoli ↑ • • The maximum stroke volume ↑ The maximum AV O2 difference ↑ Responses of the cardiovascular system to the physical exercise • local responses: blood perfusion in the working muscles ↑ – vasodilation due to the sympathetic cholinergic activity – vasodilation due to the increased metabolism (hypoxia, hypercapnia, acidosis) – increased AV O2 difference (O2 extraction) • changes in the systemic circulation – – – – – – heart rate ↑ cardiac output ↑ pa ↑ stroke volume ↑ peripheral resistance ↓ redistribution of the circulating blood volume flow in the pulmonary vessels ↑ ? regulation: hyperkapnia, hypoxia, acidosis… → reflexes Circulatory changes during muscular exercise Brain vagus ↓ skeletal muscle activity ↑ sympathetic nerves ↑ arterial arteriolar pressure ↑ constriction ↑ • renal BF ↓ • splanchnic. BF ↓ • skin BF ↓↑ • resting muscle BF ↓ heart rate ↑ stroke volume ↑ cardiac output ↑ Venous return ↑ vasodilator metabolites ↑ exercising muscle BF ↑ • „muscle pump” • „respiratory pump” BF = blood flow Changes associated with exercise cardiovascular parameters Changes associated with exercise cardiovascular parameters • Increase in cardiac output – Heart rate ↑ – Stroke volume ↑ (in the beginning this is more pronounced) Changes associated with exercise cardiovascular parameters • end diastolic volume ↑ • end systolic volume ↓ • diastolic pressure ↓ • systolic pressure ↑ • mean arterial pressure ↑ Changes associated with exercise distribution of blood among the organs • during increased exercise – muscle BF ↑ – splanchnic BF ↓ – brain and heart BF = – skin BF ↑ ↓ Changes associated with exercise adaptation of the respiratory system • increased respiratory frequency (15/min – 40-50/min) • increased respiratory volume (0,5 l – 3 l) • increased respiratory minute volume (7-8 l/min – 150 l/min) regulation: reflexes activated by hypercapnia, hypoxia? Changes associated with exercise adaptation of the respiratory system • during an intermediate intensity exercise – the mean arterial pO2 does not change significantly – the mean arterial pCO2 does not change significantly – the venous O2 concentration decreases → • the reflex regulation is – breathing-synchronous changes in pO2 and pCO2 – stimuli coming from receptors found in the joints of the limbs Changes associated with exercise adaptation of the respiratory system • performance and oxygen uptake are linearly related • a maximal oxygen uptake is determined by the level of training Changes associated with exercise the „oxygen debt” • Increased O2 consumption following an exercise is used for – replenishing the O2 stores (myoglobin) – replenishing the phosphocreatine pool – elimination of lactic acid Changes associated with exercise training and the physical performance
