I'm pretty sure you knew EXACTLY what I meant. From wikipedia "Isometric exercise or isometrics are a type of strength training in which the joint angle and muscle length do not change during contraction (compared to concentric or eccentric contractions, called dynamic/isotonic movements)." But I suppose your comment gives you the chance to correct someone. Whatever.

Huh? It is more of a time/power equation.
For very short times from 10 secs for normal folk up to 20 secs for highly trained folk, energy comes from creatine phosphate and ATP stored within the muscle itself, therefore no lactate production until this is used up.
Once this is used up then outside help is needed, but with a continuous muscle contraction, circulation is greatly impeded and therefore there can be failure of the muscle without a lactate rise.

Hence why "dynamic" is a very imprecise term and not used in real, actual books that discuss skeletal muscle physiology (none I've read anyway).

When it's a topic outside your expertise, try not to think of it as a pissing match, but rather an opportunity to learn.

Isometric contractions produce LOADS of lactate and in fact this lactate is a very important source of energy to sustain the contraction (contributes to about 60% of its ATP turnover).

I can cite you my direct source if you like.

In order to neutralize the soaring accumulation of pyruvate and protons (from the splitting of ATP), each pyruvate molecule absorbs two protons into its structure, converting to lactate.

When it's a topic outside your expertise, try not to think of it as a pissing match, but rather an opportunity to learn.

I'd be interested in reading that source.

Jay

Lactate, when added to a solution, drastically reduces the pH of the solution which means in the normal pH of the body, it does contribute some H+ to the body.

"Muscle ATP turnover rate rate during isometric contraction in humans" J. Appl. Physiol. 60: 1839-1842, 1986 Katz, Sahlin & Hendriksson

Actually, I was looking for a source that shows that lactate is a major source of energy during anaerobic exercise. The article you cited shows that lactate accumulates during isometric exercise, which would suggest that it is not being utilized as an energy source.

Jay

so lactic acid is good for you, does that change anything in the way we should train or not?.

The reality is that we are never in really in "just" anaerobic metabolism or aerobic metabolism--we are usually in a blend of both, and anaerobic metabolism appears to be linked to aerobic metabolism through this direct lactate shuttle. Thus, greater lactate production could actually mean better performance.

I don't think it makes sense to talk about increasing lactate production to increase performance, because the only way to produce lactate is to burn glucose, and the stoichiometry is fixed: each glucose molecule burned produces two lactate molecules in the anaerobic pathway. What might make more sense, though, is to increase the cell's ability to utilize the lactate produced. Common sense suggests that training near the anaerobic threshold could increase the muscle cell's ability to utilize lactate.

Jay

Hey Tim, would that be a solution outside the body? Cause the last time I talked to an exercise physiologist researcher, he stated that new findings show lactate added to room temperature muscle biopsies (what all this muscle acidosis/fatigue theory has been based on) does not seem to replicate under actual muscle temperatures inside the human body when lactate is injected.