She was coming back from knee surgery to repair age-related torn cartilage when her physical therapist delivered some bad news: "He said, 'You know what? You've got to stop teaching.' And I thought my world had just bottomed out."
After she slowly built up strength in her knee, the first thing her physical therapist let her do was climb on a bike.
That's where she found a new world.
Now, four years later, she teaches indoor cycling classes at the Manchester YMCA. Her students range from beginners who've never climbed on a bike to long-distance cyclists determined to stay sharp when the weather doesn't cooperate.
She's also licensed to teach Spinning, a high-powered kind of indoor cycling designed to duplicate road terrain.
In her classes, she rides right along with her students, and that, she says, is why she feels great.
There's a reason for that.
Her aerobic training exercise scientists prefer to call it cardio-respiratory training has raised her fitness level.
"Cardio-respiratory training trains the entire cardiovascular system to adapt to increasing workloads," Keith Shannon said. "It also trains the heart and lungs to become more efficient at supplying oxygen and nutrients to tissues around the body. You also get different muscle adaptations that you don't get from resistance training."
Shannon is a graduate research assistant in Virginia Commonwealth University's health and human performance laboratory. He is a master's degree candidate in the school's health and movement sciences program.
Aerobic training is one of the three components of a fitness program, besides resistance training and diet.
Who needs aerobic training?
"This is simple," Shannon said. "Unless you get sufficient moderate to vigorous physical activity in your daily life, you need to work out.
"If the words 'bicycle courier' are in your job description, you probably don't have to worry about cardio-respiratory training."
OK, then, what about the rest of us?
"Most of our jobs require us to remain inactive for the majority of the day," he said. "We use recreational activity to make up for this lack of physical activity."
Health benefits are huge and include reduced risk for diseases, as well as improvements for people already diagnosed with diabetes, high blood pressure, heart disease, depression, overweight and obesity.
Aerobic exercise can help you lose weight and change your body composition, but as Shannon noted, you can get fit without losing weight.
"Increases in cardio-respiratory fitness without significant weight loss are also shown to improve general health."
Guay isn't an exercise scientist, but she still understands how cycling has changed her body.
"My aerobic base went up. Plain and simple, my muscles got stronger. And cycling especially distance cycling has played an extremely important part in keeping my weight off."
She also follows what she calls a reasonable diet: "I'm not perfect. I don't do Spartan. I can't."
Besides teaching cycling classes, Guay, 47, works as a clinical social work counselor.
'Work your way up'
Indoor cycling is not the only aerobic exercise option on the road to fitness. What else qualifies?
"Anything that gets your heart rate up to a level that doesn't exceed your own physical capabilities," Shannon said. "I'd always consult a physician if you have any medical complications, just to make sure. If you are just starting an exercise program, start off at a lower intensity and work your way up."
You can work out inside at a gym or outside on a golf course (but leave the cart behind and walk). You can spend a little or a lot.
"It's all a matter of increasing energy expenditure," Shannon said. "We have a lot of flexibility in terms of where and how we make these changes."
Guay was a little surprised at her new fitness routine.
"I was not into indoor cycling at all, and I wasn't hooked immediately."
Still, she could see it was a way, as she put it, to reach for new horizons.
"In my healing process, my physical therapist would push me just a little bit, but not too much. That's how it was with cycling. If I paid attention to how my knee felt, I would get just a little stronger. With a higher-impact exercise, I would have pushed too far."
Inside or out
Some people like the workout you get at a gym, where the equipment measures distance and calories.
"If you like that kind of feedback or, for that matter, if you like being around people while you work out, then use it to your advantage," Shannon said. "Otherwise, you can get just as good a workout outside of a gym."
Something as simple as walking qualifies as aerobic training, and it's an especially good choice for sedentary people who are just beginning an exercise program.
"When you first start out, you want to choose activities that can be maintained at a constant intensity," said Robynn Shannon. "Walking is a very accessible exercise that is low impact and doesn't take a lot of coordination or endurance to get started."
She is a graduate research assistant in Virginia Commonwealth University's health and human performance laboratory and a master's degree candidate in the school's health and movement sciences program. She and Keith Shannon are married.
You build cardio-respiratory fitness, she said, through exercise that uses the large muscle groups, that is sustained, rhythmic and aerobic.
"To continue seeing improvements in your cardio-respiratory fitness," she said, "you need to challenge your body by changing intensities of your aerobic workout."
For instance, she said, "the same aerobic class over and over may not add any additional benefits to your fitness level once your body is accustomed to the intensity level of the class."
But once you reach the maintenance level in an exercise program, you don't have to pay as much attention to increasing intensity.
Oxygen to muscles
During an aerobic workout, she said, there's a lot going on inside your body, which stays busy getting the right amount of oxygen to the working muscles. Blood flow increases to these muscles and decreases to the ones that aren't exercising.
It's the heart's job to deliver nutrients like oxygen and to carry away wastes like carbon dioxide. At the same time, your energy requirements change during exercise, so the body has to make sure you have enough glucose and fat for fuel.
How do you know how hard to work? That's where measuring your heart rate comes into the picture. If you've done any exercise at all in a class or a gym, you've probably heard people talk about working within their target heart rate. The target heart rate is about 60 to 80 percent of your maximum heart rate, and it's within that range of intensity that you see your fitness level improve.
You'll get the most accurate target numbers from a treadmill stress test, which determines your maximum heart rate. But there are also math formulas some Web sites do the math for you that provide estimates based on average heart rates for different age groups.
It's important to work at an intensity that's appropriate for your fitness level, not the level of the person on the next treadmill or bike.
In Guay's cycling classes, resistance adjusts at the turn of a knob.
"You can turn it or not," she said, "depending on how you feel. The way I teach, I let people know they should listen first to their body, then to me."
Ys and fitness centers across the country also offer indoor cycling programs.
The Spinning routines she is licensed to teach were originally developed (and trademarked) by a long-distance cyclist named Johnny Goldberg as a training tool.
With adjustable seats and handlebars, the stationary bikes are designed to fit like a custom bike and to provide a ride that comes as close as possible to riding a real bike. It's the instructor's job to provide a ride that comes as close as possible to real road conditions, including hills.
Spinning also focuses on the mind-body connection.
"You can focus on yourself. You can think about barriers. What's keeping you back? Are you looking toward the end of the class now? Are you afraid? You can really find out about those things in this class."
In Guay's classes, visualization is a take-it-or-leave-it option, and more than half the class leaves it.
"Most people are into doing the exercise, and that's OK. They want to get in, and when they get out, they want to be sweaty."
And sweaty they're likely to be.
"I tell people I guarantee that no matter how hard I work, they will work harder than me."
How is that possible? "Because their aerobic base isn't up yet."
She's seen people new to cycling overdo it. "They think they've got to kill themselves, or they're not exercising. You're better off being at the low end for quite a while."
Experienced cyclists spend much of the class pedaling standing up, the way you power your own bike up a real hill.
"I tell the beginners it's really OK to sit anytime, because they're not there yet."
Guay is sensitive to beginners' struggles because she hasn't forgotten how she felt the first time she climbed on a bike.
"I thought I was in shape. I immediately got huge doses of humiliation.
"I can still remember that I couldn't stand up for very long, and a standing climb really left me winded. Now, I can do exactly what I thought was impossible, and I can do it for 20 minutes.
"That's amazing to me."
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