Above: “Whew – I do believe my intramuscular pH levels have taken a nose-dive. Damn those H+ ions!!!”
What happens when we reach muscular exhaustion? What is it, really?
“True” muscular exhaustion occurs when physiological reasons (as opposed to say, psychological ones) conspire to impair and shut down muscular contraction. For example, if one runs out of stored glycogen, then anaerobic metabolism cannot take place (no fuel) and muscular contraction stops. Or, when the pH within a muscle lowers too far – the acidic environment impairs cross-bridging of myosin and actin (prevents muscle shortening, in plain English).
We see the first phenomenon quite often in long races, such as a marathon. The runner, gasping, crosses the finish line, only to collapse in a heap. What has probably happened is that he has exhausted all intramuscular and liver glycogen, leaving his body with no more sugar to burn. Even if he still possesses fuel (fat reserves) to burn, the process cannot be started without glycogen. The glycogen acts as kindling to start the “burning” of substrates for fuel.
“Fat burns in a sugar flame.”
Interesting, no? Think about that the next time your muscles are burning and you don’t think you can achieve one more rep. Go for “true” muscular exhaustion*!
*As a consequence of inability of the muscle fibers to produce force, or inability to contract due to low pH, not through the mechanism I previously described. You’d be lifting for an awfully long time to do that one.