Joy's husband, Byron, is 60, an age when heart disease is diagnosed in many men. However, Byron is an ultra-marathon runner (an ultra-marathon is any distance longer than a marathon) and not a prime candidate for heart disease as running such extreme distances certainly requires a fit cardio-vascular system. He has had to slow down his running lately because of bad knee pain but Joy started to notice that he curiously seemed to lack energy. The family doctor did not consider these signs alarming, but Joy persisted and had her husband went through further tests. A blockage was found lurking behind the internal walls of his heart. They were lucky. Byron's heart was operated on in time, but as Joy said: "This was a heart attack waiting to happen."

"These research readings for today are all about how we need to exercise to prevent such illnesses as cardio-vascular disease and how each individual needs to take responsibility of his or her health," Joy notes and continues: "I never questioned this myself before, but now with Byron's heart condition, I wonder if this is even worth it any more. No amount of exercise seems to guarantee that we don't get these illnesses."

I don't know what to say... I have sometimes thought I might not exercise hard enough to gain the benefits of a disease-free existence: It is painful to exercise hard. I also had witnessed many exercisers quitting because their fitness program was too demanding or boring. In these cases, one might be more prone to heart disease. But Byron? He certainly engaged in strenuous enough exercise and did not fear pain.

Joy and I talk about the way we designed our group exercise class based on the components of health related fitness: an aerobic component for cardio-vascular fitness, toning for muscle fitness, some stretching for flexibility. We never challenged the necessity of such segments, but now Joy questions the entire rationale for exercising to prevent illnesses. One obviously gets ill anyway and it is impossible to know how and when. We remember several very fit people who have had heart disease: Jim Fixx died during a marathon and Alberto Salazar, another famous marathon runner, has had more than one heart attack. We know several friends who have lived healthily and exercised, but got cancer, heart disease, or osteoporosis. Scientists would call this anecdotal evidence: kind of isolated exceptions to the rule. However, when a loved one becomes ill, it is not much consolation to be an exception. It hits home at a very deep emotional level.

Joy no longer believes in defining health as the absence of illness and following exercise programs. However, such exercise programs are not usually critiqued of their lack of predictive value to prevent illness, but rather the huge drop-out rates from these programs. Namely, these types of exercise programs tend to be too demanding for beginners who can also find them repetitious and boring. Other critics have claimed that the emphasis on exercise puts all the responsibility for illness prevention entirely on the individual without considering environmental pollutants, long work hours, unsafe environments, poverty, or lack of access to fitness facilities.

It seems like we can do something about these criticisms: we can provide more interesting and suitable exercise programs, we can create policy to improve people's living conditions, we can provide more accessible fitness facilities. But the invisible illnesses seem to come from nowhere. What can one do about them if exercise is not helping?

"This seems hopeless," Joy says, "it means just accepting your fate. What do we say to our clients to motivate them to exercise? How do we educate our instructors to provide solid exercise programs if there is no hope?"

Scientific evidence that exercise prevents illness does not obviously guarantee that one can avoid all diseases. Exercise is not medicine similar to a pill or vaccination that cures or prevents illness. However, there is a stronger possibility for not becoming ill when one exercises enough. In addition, one is probably better prepared to combat the effects of an illness if one exercises. Joy and I start pondering how much we actually think about illness when we exercise. Do we exercise primarily to avoid, for example, heart disease? We probably should, but we seem to think more about how it feels, how our bodies adjust, or do we enjoy what we are doing. Perhaps it is the feel for physical activity that keeps us moving, not illness prevention? Perhaps this is not such a bad thing and it might give us some health benefits as a bonus.