Energy sources in skeletal muscle

Transcription

1 Energy sources in skeletal muscle Pathway Rate Extent ATP/glucose 1. Direct phosphorylation Extremely fast Very limited - 2. Glycolisis Very fast limited Oxidative phosphorylation Slow Unlimited 36

2 Muscle types based on the speed of contraction fast slow based on the source of energy oxidative glycolitic

3 Basic classification of skeletal muscle fiber types Type I: slow oxidative Type IIB: fast glycolytic Type IIA: fast oxidative Myosin isoenzyme (ATPase rate) Slow Fast Fast SR Ca ++ pumping capacity Moderate High High Diameter (diffusion distance) Moderate Large Small Oxidative capacity (mitochondrial content, capillary density, myoglobin) High Low Very high Glycolytic capacity Moderate High High Mechanical response Fast Fast Slow

4 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)

5 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)

6 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)

7 Muscle performance the speed of contraction depends on the load v = (A B * F) / (F + C); where v 0 = A / C; F 0 = A / B isotonic contraction isometric contraction the performance (P = F * v) of a muscle depends on the load bell shaped curve optimal load [~F 0 / 3] efficiency ~ 20%

8 Effects of physical exercise demand: increased rate of metabolism Phosphocreatine pool ATP (constant) Muscle contraction (20%) Heat production (80%) anaerobic catabolism aerobic catabolism glucose, glycogen, FFA Increased O 2 consumption Respiratory rate Tidal volume O 2 diffusion in the alveoli The maximum stroke volume The maximum AV O 2 difference

9 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 O 2 difference (O 2 extraction) changes in the systemic circulation heart rate stroke volume peripheral resistance cardiac output p a redistribution of the circulating blood volume flow in the pulmonary vessels? regulation: hyperkapnia, hypoxia, acidosis reflexes

10 Circulatory changes during muscular exercise Brain vagus sympathetic nerves skeletal muscle activity arteriolar arterial constriction pressure renal BF splanchnic. BF skin BF resting muscle BF vasodilator metabolites heart rate stroke volume Venous return exercising muscle BF muscle pump respiratory pump cardiac output BF = blood flow

11 Changes associated with exercise cardiovascular parameters

12 Changes associated with exercise cardiovascular parameters Increase in cardiac output Heart rate Stroke volume (in the beginning this is more pronounced)

13 Changes associated with exercise cardiovascular parameters end diastolic volume end systolic volume diastolic pressure systolic pressure mean arterial pressure

14 Changes associated with exercise distribution of blood among the organs during increased exercise muscle BF splanchnic BF brain and heart BF = skin BF

15 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?

16 Changes associated with exercise adaptation of the respiratory system during an intermediate intensity exercise the mean arterial po 2 does not change significantly the mean arterial pco 2 does not change significantly the venous O 2 concentration decreases the reflex regulation is breathing-synchronous changes in po 2 and pco 2 stimuli coming from receptors found in the joints of the limbs

17 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

18 Changes associated with exercise the oxygen debt Increased O 2 consumption following an exercise is used for replenishing the O 2 stores (myoglobin) replenishing the phosphocreatine pool elimination of lactic acid

19 Changes associated with exercise training and the physical performance