The instructor yells out, not so much from authority but so as to be heard above the blaring mix tape of pop, country and rock and roll songs playing for peak inspiration.

“Pick it up,” he says. “C’mon, c’mon, c’mon.”

This is the regular Tuesday morning spin interval class at Blitz Fitness in West Tisbury. Eleven women sit atop stationary bicycles, pedaling at the top of their lungs, going nowhere except to a fitter body. Though known to the fast pedaling women in the class as their relentless fitness instructor, he is better known and recognized when wearing a uniform.

He is Oak Bluffs chief of police Erik Blake.

Their crime? Not cycling outdoors. — Maria Thibodeau

Chief Blake took the outside route to inside bicycling. In 2009, as part of his duties in the Massachusetts Chiefs of Police Association, he got to know several colleagues who rode in the Pan-Mass Challenge, a bicycle fund-raising event in which people ride from Sturbridge to Provincetown to raise money for cancer research and treatment.

“I’ve got to lose 10 or 100 pounds, so I might as well go out and try it,” Chief Blake said, remembering his decision to sign up. “We got going and I was like, I love this. I loved outdoor riding.”

Though an accomplished road rider with thousands of miles under his belt, the transition to indoor spinning did not come easy. A few years ago he told his future wife, Katy, owner of Blitz Fitness, that he needed some cardio work in the winter, when riding outside wasn’t always possible. She introduced him to a spin class.

“It killed me,” Chief Blake said. “Wow, I couldn’t believe the spin class. I was dying, absolutely dying.”

He kept at it, got in better shape and decided he might like to lead a class.

“I’ve taught everything from firearms to problem-solving,” he said. “I don’t mind actually instructing. So I tried it without having the certifications. [Katy] then took me to fitness conferences, I got all the certifications and now this is my regular class.”

Mr. Blake's first spin class was a killer. — Maria Thibodeau

The chief explained that spinning is a lower body and cardio workout that is adaptable to the ability and fitness level of the participants. The resistance of the bike pedals can be set on the fly, allowing simulation of hills. The group effect also helps inspire fitness.

“The benefit of this is, we’re going to have eight or 10 people in here, everyone can get the same workout at different levels,” Chief Blake said. “It’s not like you run a mile and I have to wait eight minutes for you to finish the mile. If you’re sitting here and it’s a recovery day for you, or you’re not feeling that good, you can still do the entire workout and be with the class.”

The class has been spinning for about 20 minutes, when it’s time for the interval part of the spin interval class.

“Off the bikes, grab the weights,” Chief Blake yells.

He leads the exercise class through a series of push-ups, sit-ups and boxing drills with light weights. As the sweat flies and the muscles burn, he leads them through another set of drills in a squatting pose that he calls the horse dance.

With hardly a chance to catch a breath, it is back on the bikes for more spinning.

“Crank the resistance up to eight,” Chief Blake yells to the class, while he jumps back on his own bike and cranks the music controls up a notch to match the effort.

“We go from a range of one to 10, one meaning no resistance, 10 meaning you can’t turn the pedals. I always go around and try to crank them up.”

The riders stand up on the spin bikes, then sit down to pedal in a kind of exercise dance choreographed from the front of the room by Chief Blake’s commands.

There is no slacking off among the squad. Chief Blake said he has never threatened to arrest anyone for lack of effort, but he does joke with one rider about the possibility of being placed in custody for refusing to do push-ups.

The next song kicks in, an upbeat rock ‘n’ roll number. He exhorts the spinners to work harder still.

“Okay, double the beat, almost there, almost there.”