I am 76 , with a pre-diabetic condition, but otherwise in excellent health, very active year round ( gym, swimming, windsurfing)

AS detailed below, I noticed a totally unexpected but real and considerable improvement in my jogging endurance three months after being put on metformin and, I should add, after a three months’ interruption of my cardiovascular training, with the exception of a few windsurfing sessions and some laid-back cycling, certainly not as effective as jogging for cardio-vascular training.
I even expected to be a bit rusty, as I usually am after prolonged inactivity. Indeed, I get the measure of my cardio efficiency when I compare my normal h.r at rest ( 75 b.p.m) with the h.r. after a few weeks of training, which goes down to 63 b.p.m.

In terms of intensity of effort, at least perceived intensity, I’d rate my cardio training in jogging as moderate, between 70-80 % of my allowed maximum range.

Technically, going by the age charts, training at 80 % means in my case 115 b.p.m, but, subjectively, I find this rate much below 80%, probably the same as brisk walking and I usually go up to 135 -140 b.p.m. without much strain . Sometimes , by my cardio-watch, I even hit 150 b.p.m. ( probably 100% + ) , but I slow down immediately as a precaution.
Incidentally, there is a formula, proposed by Karvonen, which corrects the allowed age-related maximum b.p.m. rates of the usual charts by taking into account the decreased heart rate at rest brought about by training.
In other words, if you decrease it by 10 b.p.m. , you create a reserve allowing you to safely increase your maximum allowed b.p.m. accordingly, i.e. by the same amount.
Probably this explains why I can safely go well over 115 b.m. if I want to train at 80% of my theoretical maximum.

To come to the point, in what consists my improvement and what is my question?
Usually, at the beginning of my training cycle, on the very same 500 m outdoor jogging track my h.r. goes up rather quickly to 140 b.p.m by the third or fourth lapse and my leg muscles feel kind of aching and strained, especially the first few training sessions. Then I either end the session or I stop for a while.

This time instead, after three months of low cardiovascular activity, I could do, to my surprise, 10 lapses already on the first training session and my h.r. kept at a comfortable 130-135 b.p.m. rate all along, with little or no discomfort on the leg muscles.
For lack of a better explanation, I thought it may be because improving insulin sensitivity facilitates the transport of glucose to the muscle cells, therefore making more energy available to them.

I submitted this to a Diabetes Forum, but the only response I received was that metformin hasn’t ( and cannot have ) anything to do with this, because, while exercising, the bulk of glucose absorption and use by the “ skeletal muscles” is absolutely insulin-independent. Only the glucose needed for the “ standing, basal function” of the these muscles would be , according to this person, insulin-dependent.

I wonder if this is right, because, based on some readings on the issue, I understand it is just the opposite.
May be somebody familiar with the issue can comment on this.

But then, if that person is right, another question comes in from the back door: what could explain this perceived improvement? I neither made any drastic changes in my diet, nor was I an overweight person who has gained a lot of energy by losing weight.

The placebo effect is sometimes invoked to explain such subjective perceptions and in some cases even bodily effects by the subtle and still mysterious body-mind interplay, as some bio-feedback feats indicate.

On the other hand, the cardio-watch readings are there and they confirm that my improved physical performance is real.

In essence my question is :

can metformin, by increasing insulin sensitivity, make more glucose available to the ( muscle) cells therefore resulting in more energy available when exercising? If not, whatever the reasons are, is it true that muscle activity, when exercising, is insulin-independent, as that reader contends?

Thank you for your comments and clarifications


P.S perhaps an administrator may be interested to know that I could not register on your Forum with Chrome, because the antispam captcha test fails me after repeated attempts, even though I have done it many times elsewhere with no problems..I had to register from the Firefox browser. Kind of frustrating. I am not a bot!

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