Table 1.

Temporal energetics of the glycogen shunt

Step 1. (0–15 msec) Breakdown of PCR to restore ATP used to fuel contraction

3ATP → 3ADP + 3 Pi

3PCR + 3ADP → 3ATP + 3Cr

Net: 3PCR → 3Cr + 3 Pi

Step 2. (15–100 msec) ATP from glycogen breakdown and glycolysis restores PCr

Glycogen (n + 1) + Pi → glycogen (n) + G6P

G6P + 3ADP + 2Pi → 2 lactate + 3ATP

3 Cr + 3ATP → 3ADP + 3PCR

Net: 3Cr + 3Pi + Glycogen (n + 1) → Glycogen (n) + 3 PCr + 2lactate

Step 3. Resynthesis of glycogen from ATP produced by lactate oxidation

glycogen (n) + glucose + 2ATP → Glycogen (n + 1) + 2ADP + 2 Pi

2lactate + 0.6 O2 + 2ADP + 2Pi → 0.6 CO2 + 2ATP + 0.6 H2O + 1.8 lactate

Sum of 3 steps: glucose + 0.6 O2 → 0.6 CO2 + 0.6 H2O + 1.8 lactate (note that 1.8 lactates per glycosyl unit transported out of muscle cell)