My downward dog barked as I assumed the position, butt pointed to the ceiling, hands pressed into a rubber yoga mat. My shoulders throbbed from the effort to keep still. Sweat ran off my face like a flash flood, and my arms began to shake.

According to my doctor, this is how I would find the fountain of youth, or some measure of it. “Yoga,” he had told me, “is really great for old people.”

Doctors have made cracks about my age for years.

When I fell off the roof in my 40s, a doctor looked at my fractured elbow and said, “This would heal nicely if you were 13, but I can see you’re well past that.” When I tore the meniscus in my left knee, I was 50, and the doctor said, “You know, I’ve had teenagers run the day after surgery. But you’re not a teenager.” (He also said, post-surgery, “If you were a professional athlete, I would clear you for play right now, but no way are you a pro athlete.”)

Last summer, when surfing left me hobbling on a bum right knee, the diagnosis went something like this: “You have to expect this sort of thing at your age.”

My age, oh well. For the record, I’m 58. And arrogant as it sounds, I never imagined an age where I would have to slow down. I figured discipline and willpower would keep me going, and the rest would take care of itself. Exercise would give me a suit of armor, so I forged it like a blacksmith of the flesh.

When I ran, it was against the clock. When I lifted weights, it was about adding more of them. When I paddled my one-man canoe, it wasn’t about the sunset in the distance. It was about the effort involved to reach it.

But age creeps up on you, and my armor was wearing thin from overuse. I had limped into the doctor’s office, whining like a baby and insisting he prescribe an exercise to make it better.

When I was told I had early stages of arthritis in my knee and that it would never go away, I got angry. Exercise has always been my meditation, and having to stop because of pain has always been one of my greatest fears.

The doc’s solution was yoga. The healthiest of his older patients — I didn’t ask their age — were the ones who bent themselves into yoga pretzels, he said. I wasn’t a stranger to yoga, but I had never viewed it as a replacement for my old workouts.

Now I threw myself at it.

First, I joined a Saturday class at a city rec center to get my bearings. After a few months I added a weekday class at a Kaimuki studio where I discovered that half of the members were as flexible as Gumby and the other half could stand on their heads.

And that’s when I found a Holy Grail of exertion and suffering: hot yoga.

This class is done in a heated room. It’s like exercising in the Amazon. I’ve attended only one class and I almost passed out. It was so hard, I couldn’t imagine going back until I was in better shape.

This is real exercise, I thought afterward, as I waited for my endorphins to be replaced by pain. But instead I felt limber, although a bit lightheaded.

Not bad for an old guy, I thought, before asking myself, Was I doing this hard enough?

Reach Mike Gordon at 529-4803 or email mgordon@staradvertiser.com.