Physiology Year 2

Explosive events Max effort Sustained sprinting

Muscles contract when stored chemical energy is converted into mechanical energy

ATP

Formed by bonding inorganic phosphate to ADP

ATP is stored in the resting muscle throughout the muscle fibres, but particularly in the cross bridge contractile sites Resting ATP levels can only sustain a few seconds of maximal contraction

Phosphagen system (400kj/min, 10-15s) Anaerobic glycogenolysis (200kj/min, 45-60s) Oxidation of glycogen/glucose (125kj/min, 2h) Fat oxidation (110kj/min, 8h+)

• biological catalyst • lock and key mechanism • body temp (37° is optimal working environment) • enzymes lower activation energy • a typical mitochondrion may have 10billion

• present in small stores within muscles • 80-100g in body at normal resting levels • ATP has high energy bonds which when broken down release free energy (30.6kj/mol) • we synthesise 60kg/day 1500times/day • synthesise ATP via bioenergetics • ATPase is responsible for the breakdown of ATP via hydrolysis • ATP + ATPase ➡️ ADP + P + energy • forming ATP from ADP is known as phosphorylation. ATP synthase catalyses this process

• in addition to small stores of ATP, skeletal muscle contains a larger reserve of a high-energy phosphate compound called phosphocreatine. • phosphocreatine= 1 creatine molecule and 1 phosphate molecule attached by a high energy bond. • when hydrolyzed by creatine kinase, phosphate is released and the energy released is used to phosphorylate ADP to ATP • thus, PCr is an important energy buffer that can maintain muscle ATP levels.

It’s resynthesized by reversal of the creatine kinase reaction, this phosphorylation energy is derived from oxidative pathways

• breakdown of either muscle glycogen or free glucose to lactate (lactic acid) • requires 11 chemical reactions, catalysed by enzymes (each one a potential limiting factor) • 3 ATP molecules are produced for each glycogen broken down to lactic acid (2 ATP for glucose) • most energy derived from glycogen as glucose conc is lower in muscles

Step 1- initial mobilisation of glycogen to glucose-6-phosphate (glycogen phosphorylase) Step 3- phosphofructokinase activity is stimulated or inhibited by metabolites (ADP, P or ATP). This is the main limiting factor to glycolysis Step 11- During high intensity exercise, pyruvate is converted to lactic acid, in the absence of oxygen by lactate dehydrogenase

• with training it’s possible to increase concentration of certain enzymes (phosphorylase, PFK, LDH) and substrates • muscle glycogen can be increased by training or by a high CHO diet • in brief efforts, amount of H produced won’t be sufficient to inhibit enzyme reaction rates, yet this may be a factor in repeated efforts • in repeated exercise bursts, it’s important to train for increased capacity to remove or buffer H ions.

• biggest change in muscular hypertrophy • increased resting glycogen and PCr • little effect on glycolytic and oxidative enzymes

• metabolic pathway for resynthesis of ATP derived from oxidation of pyruvic acid generated by glycolysis or from the oxidation of fatty acids. • potential energy in the hydrogen electron and proton released through the electron transport chain, which re-phosphorylates ADP to ATP • final step needs the proton and electron to be reunited and accepted by water. This can only occur in the presence of oxygen • max rate of ATP generation dependent on max rate oxygen is available to mitochondria • oxygen supply is the first rate limiting step.

Oxidation- the removal of hydrogen atoms Reduction- addition of an electron. Oxidation and reduction are always coupled reactions Often involves the transfer of hydrogen atoms rather than free electrons Hydrogen atom contains one electron Molecule that loses a hydrogen also loses an electron and therefore is oxidised.

• 1 ATP produced • 4 pairs of hydrogens removed (3NAD and 1FAD) • CO2 given off which dissolved in blood • 12 hydrogen pairs that move into the electron transport chain

• Nicotinamide adenine dinucleotide is a coenzyme found in all living cells. • exists oxidised and reduced • NAD carries energy from one reaction to another (accepts electrons from one molecule, becoming reduced NADH so can donate electrons. During glycolysis and Citric acid cycle, electrons carried by NADH are transferred into the mitochondria by mitochondrial shuttles. Then oxidised in turn by the electron transport chain, which pumps protons across a membrane and generates ATP through oxidative phosphorylation.

ETC transfers electrons from electron doners (NADH and FADH) to electron acceptors via redox reactions. Electron transfer is coupled with the transfer of protons across the inner mitochondrial membrane In a sequence of redox reactions, electrons are passed down a series of iron-containing carriers In the final step, electrons and protons are reunited to form hydrogen which combines with oxygen to form water High energy electron is passed through the etc and energy released pumps hydrogen out of the matrix space.

• Although ATP generation during high intensity exercise is predominantly glycogen, pathways for fat and protein are also available • during low to moderate exercise, up to 50% of energy may be made by fats. Fats stored in muscle and fat cells as triglyceride • triglyceride contains 1 glycerol and 3 fatty acids • hydrogen rich and energy dense • fatty acids mobilised by enzyme hormone sensitive lipase in fat cells. • splits triglyceride into glycerol and fatty acids which enter blood and transported to muscles. • FFAs combine with coenzyme A, forming acyl-CoA Carrier protein carburise and carnitine transferase transport fatty acyl CoA into mitochondria. • this is where the fatty acyl CoA undergoes beta oxidation

• the ability to oxidise fats instead of carbohydrates. • endurance athletes have an increased capacity to oxidise fatty acids • yet patients with obesity, insulin resistance and type 2 diabetes may have an impaired capacity to oxidise fat. Fat oxidation peaks at 65% of max heart rate

• we can estimate the proportional contribution of carbohydrate and fat oxidation • RER measures the difference between O2 consumed and CO2 produced within whole body • RQ reflects the ratio of CO2 produced by mitochondria to O2 consumed over the same time

• pathways exist in muscles that can remove nitrogen from amino acids that can then enter the Krebs cycle. • or amino acids can be converted to alanine which can in turn be converted in the liver to glucose • these pathways are more prevalent in starvation to sustain life rather than performance in fed athletes. • accelerated by decrease in glycogen and blood glucose and increase in cortisol

Outside cell: - oxygen deliver to muscle - hormone changes - delivery rate if glucose and FFAs Inside cell: - rate of fuel oxidation - availability of fuel - enzyme activity