By the good doctor's own expert diagnosis, the knee is shot.

Darryl Kan, a Honolulu orthopedist and offensive coordinator for the Punahou football team, first blew out his left knee during his junior year at Dartmouth College. A pro prospect at quarterback, he was about to scramble for a touchdown when he was clipped from the side.

Doctors placed his leg in a cast but didn't notice the torn anterior cruciate ligament he had suffered. The injury, which can severely affect stability, went unnoticed again the following year when Kan reinjured the knee and had to undergo surgery to remove torn cartilage.

By the time Kan learned about the tear, it was too late for repair. Yet, the balky knee was never much of a problem until a few years ago, when arthritis set in.

By that time, Kan, who grew up in San Francisco and spent summers in Hawai'i, had finished his undergraduate work at Dartmouth, competed for spots with the San Francisco 49ers and the San Diego Chargers, completed his medical degree at the University of Southern California (and a residency at Los Angeles County Hospital), and settled into private practice in Honolulu.

While the injury prevents Kan from running, jogging or doing any repetitive-stress activities — there is a small area where bone painfully meets bone — he's found ways to maintain his high level of muscular and cardiovascular fitness.

Just as Kan never stopped being an athlete, he's also never stopped being a student. He has a scholarly interest in human performance and cutting-edge training methods. And he's more than willing to put the ideas he's learned from Jay Schroeder, Dennis Thompson, Mel deLaura and others into personal practice.

"The workout changes pretty much every year," Kan says. "It's always a little bit different. If I did the same thing over and over every year, I'd just be bored. I'm always looking to learn new things and try new things. It might be the same exercise, but I'll do it differently."

Kan does much of his training in a gym he's set up in his 'Aina Haina home.

A typical workout begins with a set of exercises devoted to developing and maintaining dynamic flexibility. More than an average stretching warm-up, these exercises extend range-of-motion through active movement instead of held poses.

"When you have an arthritic joint, if you can keep it as mobile as possible, you can help prolong the life of the joint," he said. "From an athletic standpoint, the greater the range of motion, the greater the ability of that joint to apply force."

Kan will do 10 of these exercises, including walking lunges, to start.

Next, he moves to isometric holds — holding an isometric position for as long as five minutes.

"We do these in kind of extreme positions," he said.

For example, when concentrating on the hip flexors and quadriceps, Kan will hold a full-lunge position where the back leg is fully stretched.

"This requires you to not only fire the muscle and use it in a strength mode but also use it at its most elongated position," Kan said. It requires it to work in the most extreme condition. Holding these positions for long periods of time also requires cardiovascular work."

Next come rebounds and drops, where Kan quickly drops and catches weights. He'll hold a curl bar at chest level, let it drop, then stop the momentum before his arms are fully extended down, and curl the bar back up.

"You can use a lighter weight, but when you drop and catch it you're exposing your muscle to much, much greater force," Kan said. "Because it's a lighter weight to begin with, you can avoid overtraining the muscle and you can do it more often during the week."

The exercise — he does two or three at a time — has an added benefit for athletes.

"It seems to stimulate the nervous system in a different way," Kan said. "It teaches the brain to work at a much faster rate. This translates to athletics really well."

From there, Kan will move to "drops," wherein he starts from a height and drops into position. He'll start in a push-up position between chairs, drop to the ground and catch himself at a low position — "you try to stop yourself dead, like a gymnast sticking a landing."

Kan says this teaches muscles to absorb force quickly, again with direct athletic applications. He'll do three or four of these each workout.

Kan moves quickly from exercise to exercise, to maximize the cardiovascular benefits. He warms down with yoga stretches, as useful psychologically as they are physically.

"Yoga is great at refocusing you and allowing you to concentrate," Kan explains. "It's active meditation."

Reach Michael Tsai at mtsai@honoluluadvertiser.com.