Week 2 - Anaerobic Exercise

What builds up in muscle?

  • ammonia

  • PCr

  • Lactic acid

ATP: unstable due to crowded negative charges = phosphoanhydride bonds

  • nucleotide

    • adenine + ribose + three phosphate groups

  • universal energy currency

    • biosynthesis

    • transport

    • movement

ATP is unstable due to negative charges, alpha, beta and gama (1st, 2nd, and 3rd of the triphosphate) the breakdown of those bonds release energy.

essentially = sugar, base and 2 phosphates w an extra part

  • in cells ATPs functional form is energy ATP 2, has a binding to magnesium, its function is inherently linked to it.

  • Chemcially accurate drawing of ATP

Cleaving off the phosphate, hydrolysis via ATPase separates a phosphate to release energy; a triphosphate turns into a diphosphate by cleaving off that one inorganic phosphate

lysis = breaking down

hydro = water

hydrolysis = breaking a bond by adding water

ADP +Pi is more stable that ATP, change in free energy is less that 0 meaning the reaction is downhill, driving something forward. This can then be used in another step

Hydrolysis of ATP, releasing energy and changing the free energy.

extra step = adds in magnesium and ionic charges *nor required to know

ATP synthesis:

  1. phosphagen system = anaerobic

  2. anaerobic glycolysis = anaerobic

  3. aerobic glycolysis

Anaerobic - without air

Required for everyday life - Anaerobic energy production

Involves the breakdown of:

  • glucose /glycogen

  • PCr

Rapid ATP w/out oxygen

where do PCr and glycogen get broken down?

glycolysis = purpose of glycolysis is to phosphorylate ADP, to add a phosphate to ADP

  • glycolysis w/ glucose

  • glycogenolysis w/ glycogen

key points in the chain:

glycolysis is when you start w glucose, not glycogen.

Glycolysis Step 1:

Phosphorylate glucose at C-6 (add a phosphate)

energy investment of 1 ATP

traps guel

G6P cant leave via glucose transporters (glut)

hexokinase inhibited by G6P—> hexokinase turns glucose into glucose-6-phosphate. The glucose comes from the blood, self regulatory step is put in place to not use all of our blood glucose

if glycogen is considered, extra steps must take place

glycogen phosphorylase (enzyme) releases G1P

phosphoglucomutase —> G6P

energy investment = 0 ATP —> uses inorganic phosphate instead of using ATP, blood glucose will cost 1 energy investment this doesn’t

Step 3 of glycolysis:

rate limiting step, once this occurs it must follow through

  • phosphorylate F-P at C-1

    • energy investment of 1 ATP

  • committed, rate-limiting step

PFK activates

  • AMP/ADP, F-2, 6-BP, when there is low energy

PFK inhibited

  • ATP, Citrate, H+, when there is high energy or too much ATP

Step 6 of glycolysis: hydrogen is what changes the pH of a muscle

  • only oxidation step in glycolysis

    • there is a loss of electrons

  • glyceraldehyde - 3 - phosphate dehydrogenase

  • ADds pi without ATP

flux depends on cytocolic

LDH regenerates NAD+ when O2 limited

Step 7:

substrate level phosphorylation

  • +2 ATP per glucose

  • reversible and depends on step 6

Step 10:

  • subtrate level phosphorylation 

    • +2 ATP per glucose 

    • irrevesible 

  • Activated by F-1, 6BP

  • requires Mg2+ and K+

pyruvate in anaerobic conditions will be converted into lactate 

Phosphocreatine

  • fastest ATP buffer, rapid synthesis ATP via creatine kinase

  • cytosol

  • finite capacity

  • if there is more ADP, thats going to drive the reaction

  • PCr pool —> can be improved, for example when taking creatine as a supplement

  • each kg is storing 5mmol of ATP and 15 mmol of PCr

studies show that inhibited creatine kinase is essential to facilitate muscle contraction and the use of PCr. Long term adaptations when blocking phosphagen system (ATP-PCr); make anaerobic pathways more efficient, make more mitochondria to increase aerobic respiration.

how we are studying anaerobic metabolism:

  • percutaneous needle biopsy: it shows you the change in muscle, great for measuring pre and post cycling for example, fiber type and activation, phosphorylation and muscle adaptation. quite invasive and does not show full transition

  • magnetic resonance spectroscopy: measures rest, exercise and recovery as well as measuring PCr, ATP and Pi. Allows us to watch change over time.

square brackets means concentration of

  • ramp test; gets harder over time, as it increases, PCr concentration decreases slowly, PCr does not go to 0 at the end of exercise, never going to reach 0 due to systems being in a state of flux

  • step test: PCr is maintained

    • oxygen uptake and use mirrors the pathway

Importance of ATP - Pcr

  • fastest ATP buffer —> supports the first seconds of high intesntiy work

  • stabalises ADP and preserves change in free energy, helps maintain force

  • buys time until glycolysis and xoidative phosphorylation reach steady flux

  • direction set by ADP.ATP concentration, pH, Mg and Pi

  • recovery is aerobic; PCr resynthesis rate reflects mitochondiral capacity; training shortens

  • creatine can improve availability of PCr/Cr pool

Summary:

Phosphocreatine (PCr) System – Key Points

  • Role:

    • Acts as the fastest ATP buffer in muscle.

    • Provides immediate ATP resynthesis during the first seconds of high-intensity work.

    • Stabilizes ADP concentration and maintains free energy for contraction.

  • Reaction:

    • Creatine kinase catalyzes:
      PCr + ADP ⇌ ATP + Cr

    • Direction depends on [ADP]/[ATP], pH, Mg²⁺, and Pi levels.

  • Capacity & Adaptation:

    • Small storage pool: ~5 mmol ATP and ~15 mmol PCr per kg of muscle.

    • PCr supply is finite but can be improved by creatine supplementation, which increases the PCr/Cr pool.

    • PCr does not fully deplete during exercise; system stays in flux.

  • Function in Exercise:

    • Buys time until glycolysis and oxidative phosphorylation reach steady state.

    • Supports force output at the start of intense efforts.

    • Recovery of PCr is aerobic → rate of resynthesis reflects mitochondrial capacity. Training enhances this recovery rate.

  • Research Tools:

    • Muscle biopsy: invasive, provides detailed biochemical info.

    • Magnetic resonance spectroscopy (MRS): non-invasive, measures ATP, PCr, Pi in real time during exercise/recovery.

    • Ramp tests vs. step tests: PCr falls progressively during ramp tests; remains steady in step tests at submaximal levels.

✅ Main Takeaway:
The PCr system is the body’s rapid-response ATP supplier, crucial for short bursts of high-intensity effort. It doesn’t last long but stabilizes energy balance and bridges the gap until slower pathways (glycolysis, oxidative phosphorylation) can contribute. Its recovery depends on aerobic metabolism, and both training and creatine supplementation can expand or speed up PCr availability.