“From left, Amber Imburgia, Jarina Moss, Jim Porter, and Kurt Johnson sprint hard during a Cruizin’ stationary bike drill at Island Athletic Club.Matt Johnson / staff photosBecome a pedal pusherBoth Momentum and Island Athletic Club offer their cycling classes to club members and non-members. Members do have to pay extra for the classes at both clubs. At Momentum, members can ride in an unlimited number of sessions for $12 a month, while non-members can pay $75 for 10 sessions. IAC charges members $25 for 10 sessions, while non-members pay $45. Drop-in, single class rates range between $3 and $10, depending on membership status. Both clubs offer at least five classes per week.It’s really an old idea.Take a bicycle and remove one of its wheels. Weld the bike to a stable stand. Then, tighten the brake pads against the wheel. Now you’ve got a stationary bike. Get on, pedal and sweat.The stationary bike is nothing new. At this moment, thousands of them are sitting in garages and basements all over South Whidbey, stashed away after their owners lost interest in riding alone. But at South Whidbey’s two athletic clubs, Momentum and the Island Athletic Club, riding a new breed of stationary bikes has become the hottest adult fitness movement going. Called spinning — along with several other names — the activity is now nationally known as one of the best calorie-killing workouts available at athletic clubs.Early last year, both clubs began offering group classes in which about 10 people get astride high-tech stationary bikes in a cozy workout room and ride to the beat of rock and roll music until they are soaked in sweat. Imagining themselves on a long ride through the countryside or in the middle of a sprint at the Tour de France, the dozens of people who have become fans of this new workout say the time they spend spinning the pedals is some of the hardest physical work they do all week.I think that class works me harder than any class I take, said Amber Imburgia, an IAC member who has taken the club’s Cruizin’ class for the past few months.That is high praise from Imburgia, who has spent the past year working everything from weights to aerobics at the club. Jodi DiMartini, the Cruizin’ instructor, said she is not surprised to hear it. A fitness and aerobics instructor for the past 14 years, DiMartini said the low-impact exercise routine helps people shed pounds and build cardiovascular endurance like almost nothing else. It is also more appealing than many aerobics classes, which are often perceived to punish participants’ joints.It’s not intimidating, DiMartini said, noting that the class attracts as many men as it does women. Conventional aerobics classes tend to attract mostly women. Phil Pearl, a new IAC member, took his inaugural Cruizin’ class last week. Pearl said he does a good deal of cycling on the road, but was attracted to the Cruizin’ class by the quality of the cycling equipment.I just wanted to give it a try, he said.At Momentum, a few miles down the road at Ken’s Korner in Clinton, three different kinds of Spin classes draw a wide cross-section of riders. In addition to offering a straight fitness riding course, the club has a Social Cycle conversational riding course and a Pedal and Pump course, in which riders spend the last 15 minutes of their ride lifting small hand weights and pulling on resistance cords.Momentum owner and fitness instructor Kim Helpenstell said she got hooked on the Spin workout when she discovered how fit it could make her without the pounding of the aerobics courses she has taught almost daily for more than a decade. She said the classes have drawn plenty of people who want to get away from pounding their joints.They just want to stop jumping up and down, she said.Devin Hibbard, a Spin regular, said the class is the only way she will get on a bike during a rainy Whidbey winter.It’s very social and it makes you sweat, Hibbard said.During the classes, riders use a tension-adjustment knob to make riding easier or more difficult. The instructor tells the riders when to turn the knob and how much. The bikes are stable on their steel bases, allowing class members to ride with a high cadence while sitting, or to stand up and push hard against a high-tension adjustment.The classes at both clubs attract experienced cyclists, aerobics buffs, and people who are new to fitness, said Helpenstell and DiMartini. They also keep riders motivated with the camaraderie that develops among class members, say the instructors. “