Physiology Year 2 Flashcards
Possible sites for metabolic limitations to performance
Explosive events
Max effort
Sustained sprinting
What must occur to initiate movement for exercise
Muscles contract when stored chemical energy is converted into mechanical energy
Main source of chemical energy
ATP
How is ATP formed
Formed by bonding inorganic phosphate to ADP
Where is ATP stored and how long can it supply forceful contractions
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
Metabolic pathways and their power/duration
Phosphagen system (400kj/min, 10-15s)
Anaerobic glycogenolysis (200kj/min, 45-60s)
Oxidation of glycogen/glucose (125kj/min, 2h)
Fat oxidation (110kj/min, 8h+)
Enzymes
- biological catalyst
- lock and key mechanism
- body temp (37° is optimal working environment)
- enzymes lower activation energy
- a typical mitochondrion may have 10billion
ATP- the ultimate energy currency
- 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
ATP-PC system
- 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.
Once PCr is depleted
It’s resynthesized by reversal of the creatine kinase reaction, this phosphorylation energy is derived from oxidative pathways
Anaerobic glycolysis
- 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
Rate limiting steps (anaerobic glycolysis)
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
How can training influence metabolic performance
- 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.
Major adaptations during resistance training
- biggest change in muscular hypertrophy
- increased resting glycogen and PCr
- little effect on glycolytic and oxidative enzymes
Aerobic metabolism
- 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.
