The Science Of Why You Can’t Sprint Forever

Exercise Physiology Geeks Gone Wild . . . This post is from Brian at the Wattage forum/Google Group.  No doubt some dope is being produced to spoof the bodies protective system, enabling you to product L7 power for 3 minutes at the end of a race and probably win, at the cost of frying your muscles/body at some terrifying level.  


A few points that may help in visualizing glycolysis (not requiring oxygen) and oxidative metabolism (kerbs and electron transport chain).

Glycolysis has relatively fast enzyme kinetics (Km) compared with PDH
and down stream kinetics. When energy demands are higher than
oxidative metabolism can provide ATP, glycolysis is still running
“fast”, with an increase in lactate via pyruvate that is in “excess”
of what can enter the oxidative downstream component. There is some
thought that the drop in pH causes fatugue by inhibiting
phosphofructokinase 2 (control step in glycolysis), which reduces the
abilty to produce ATP, thus lowering energy production (as a feed back
to protect the muscle).

 Pyruvate from glucose converted to acetyl-CoA and acetyl-CoA from fat
breakdown (beta-ox) are “competing” for citrate synthase. That is why
citrate synthase is used as a marker of increased abitliy to oxidaze
fat (and increased OBLA) because more can get past that step.

 Think of each system as its own complete loop or chain, but remember
that almost of the substrates can leave/enter the cycle at some
point. And that each control step is regulated by substrates and/or

 And relating back to substrate use during exercise, fasted/fed state
and compostion of the meal/food change metabolism as well.


Andy Scott | 140 Proof | | mobile: 415-509-5915 | @andyscott999

Marc Pro – Strava Racing Team Training Camp

+new (and old) teammates

+new (and old) sponsors



+massive bike geekdom, immersion, saturation

+Marc Pro ( and Strava ( sponsor presentations and demo’s/trainings


+MARC Pro unit — that thing works! #recovery #tech #nicehit . . . Strava service — social fitness service, really cool.

+bike rides for first time in 3 months where

a. time over 2 hours

b. above threshold efforts

c. more than 4k climing

d. mileage over 50

e. there was someone to talk to/ride with

f. Strava ride reports/profiles: 



The Marc Pro and Strava products are both very impressive.  Being a tech/innovation/start-up goon I can’t imagine a better fit — brands and companies I really identify with that marry those passions with another (cycling).  More to come on both of them in future posts.