Unexplained exertional intolerance associated with impaired systemic oxygen extraction - 2019, by Melamed, Systrom et al

Patients on beta blockers will not be able to raise their HR higher than that. Ask me how i know

 

There are (otherwise healthy) participants who are on beta blockers who still can reach peak heart rates over 200, it's not that simple... But if I could only reach a peak heart rate of 140, I'd get the hell off the beta blockers.

 

I wonder if they consider the possibility of exercise-induced bronchoconstriction as a possible cause of hyperventilation. I say this because I've experienced this since childhood and only recently discovered what it was. I've had several treadmill tests over the years and no doctor has ever mentioned EIB as a cause of my low performance and prolonged hyperventilation, instead calling it "deconditioning," even when I was in relatively good shape.

 

The thing is that you can tell if someone give their best effort or if they don’t. And the Workwell CPET (Betsy Keller too) asks for the perceived exertion through a visual annalog scale, which is administered every 1-2 minutes or so. Then you have the Respiration Exchange Ratio (RER) which can tell you if the patient has gone anaerobic.

Being an endurance sport fiend before i got sick, i much agree that a max heart rate of 140 would seem quite weird to me as i remember my lactate balance point being 146. But the big advantage of the beta blockers i am currently taking is that i can stand up and do a few things. I am thankful for that.

 

Except that it isn't that specific, my RER flatlined for a few minutes while my VO2Peak still had yet to peak.

VO2Max is limited by cardiopulmonary factors, specifically, it is a measure of maximal oxygen delivery to the muscle, not the metabolic balance within the muscle which is determined by somewhat complex peripheral kinetic factors. To give a specific example, my performance at the ventilatory threshold on the first day was around 52% of my peak power output during the test. Hence, the shift towards anerobic metabolism occurs long before VO2Max.

The oxidative capacity of the large muscle groups that are activated during peak cycling or running always exceeds that which can be effectively delivered to the muscle by the cardiopulmonary system. But this occurs well past the ventilatory thresholds, the blood lactate accumulation threshold and the respiratory compensation point (where RER can flatline, despite a relative hypocapnia due to hyperventilation). Exercising past the respiratory compensation point in particular is quite difficult for untrained individuals and doubly so for CFS or ME patients.