Basics of Bioenergetics

bioenergetics

study of how energy is transformed through biochemical reactions

exercise metabolism

bioenergetics as it relates to the physiological changes during exercise

ATP synthesis and breakdown during exercise

• ATP broken down to ADP and a phosphate group

• releases energy for muscle contractions

• during exercise, ATP is regenerated via ATP-PCr system, glycolysis, and aerobic metabolism, using macronutrients (carbs, fats, sometimes protein)

ATP-PC system

high intensity ~ 5 sec, anaerobic

• regenerated during recovery

anaerobic glycolysis

high intensity ~ 30 sec-3 min

• glucose is supplied mainly from breakdown of glycogen (storage form of glucose in muscle and liver)

aerobic metabolism

lower intensity, longer duration

• glucose and fatty acids

• yields more ATP

carbs

4 kcal/g

→ glucose → metabolic pathways yielding ATP OR stored as glycogen

• metabolized faster and main fuel at higher intensities

fat

9 kcal/g (yields more ATP per gram)

→ fatty acids → metabolic pathways yielding ATP or stored as adipose tissue (potential to store is high)

• slower to break down

• used during lower-intensity, long-duration exercise

RER

respiratory exchange ratio

VCO2/VO2

CO2 produced to oxygen consumed

• higher indicates more carb use (~1) and lower indicates more fat use (~.7)

choice of fuel

• intensity

• training status

• diet

• as exercise duration increases, a gradual shift occurs from carb utilization to fat as a fuel source

high intensity

higher reliance on anaerobic systems :

ATP-PC and anaerobic glycolysisl

low intensity

use of aerobic metabolism more

endurance fuel

fat

• provides more ATP and is stored in large amounts

  • metabolized through B oxidation, aerobic glycolysis, krebs cycle, and ETC

krebs cycle and ETC in aerobic energy production

pyruvate (from glycolysis) is converted to acetyl-CoA → enters the krebs cycle → NADH and FADH2 generated → electrons are carried to ETC where ATP is synthesized with oxygen

protein

• minor fuel source

• must be broken down into amino acids

• mainly used during prolonged exercise or energy restriction when carbs/fats are depleted

how does the ATP-PC system regenerate ATP during high-intensity, short-duration activites?

PCr donates a phosphate to ADP to rapidly regenerate ATP without oxygen

byproducts of anaerobic glycolysis

lactate

• can be transported to the liver and converted back to glucose via Cori cycle

B oxidation

process of breaking down fatty acids into acetyl-CoA for ATP production

• key for long duration, low intensity

400 m sprint

• ATP-PCr at the start

• anaerobic glycolysis for sustained power (mostly)

• aerobic metabolism toward the end

short duration

ATP-PCr and glycolysis dominate

increased duration

aerobic system

ATP

molecule that serves as the primary energy currency of the cell

main processes of aerobic metabolism

1. aerobic glycolysis

2. krebs cycle

3. etc

anaerobic glycolysis

breakdown of glucose to pyruvate in the absence of oxygen

glycogen

primary storage form of carbs in muscle and liver

85% energy at rest

fat

15% energy at rest

carbs

CO2

primary byproduct of aerobic metabolism, removed by increased respiration

PCr

provides the energy required to re-synthesize ATP in ATP-PC system

marathon running

aerobic (oxidative) pathways

gluconeogenesis

process by which glucose is formed in the liver from non-carb sources like amino acids

pyruvate

what glucose is broken down into in anaerobic glycolysis, which can be converted to lactate

higher RER

more reliance on carbs