Exercise is mandatory.  Walking 30-45 minutes per day at a brisk pace results in as much fitness as jogging, swimming, cycling, or doing more vigorous exercises at the gym.  Daily exercise, by increasing our muscle mass, raises our metabolic rates, not only during exercise, but also throughout the rest of the day.  This increased amount of energy spent on exercise reduces abdominal fat, which in turn reduces heart attacks and strokes.  Sedentary individuals have twice as many heart attacks and strokes, and their death rate is four times higher than those who exercise moderately.  

Excessive exercise, on the other hand, has been shown to be harmful to the joints, heart and arteries.  Survival benefits plateau after 45 minutes of moderate intensity exercise per day.  Recent studies have shown that strenuous exercise  by injuring the muscles, nerves, and arteries of the heart  may cause premature cardiac aging, atrial fibrillation and sudden cardiac death.  Moreover, except for young elite athletes, those who exercise strenuously and those who run marathons frequently have twice the rates of heart attack and strokes than moderate exercisers.  In the US, about 50% of people are sedentary and about 5% are exercise excessively, and both extremes suffer from higher mortality rates than those who exercise moderately.  “Everything in excess is opposed to nature,” said Hippocrates.

Prolonged sitting is harmful.  The longer periods we sit the less fit we become and prolonged sitting has shown to diminish the positive effects of exercise.  Before the Industrial and Electronic Revolutions, humans had to be physically active. From the mid-20th century onwards especially, however, mechanization and computerization have transformed humans from being active to leading a sedentary lifestyle.  With this transformation a global obesity epidemic has emerged.

Prolonged sitting is associated with diabetes, hypertension, high blood fats, backache, leg edema, blood clots, heart attacks, strokes and cancer.  Whereas agrarian societies tend to sit about three hours a day, city dwellers can spend as much as 13 hours sitting behind their desks, in cars and in front of TV and computer screens.  Daily exercise reduces but does not eliminate the potentially lethal effects of prolonged sitting.

Sitting is almost as bad as sleeping because we only spend 5% more calories when we use our muscles for sitting. In contrast, we spend 100% more calories when we engage in physical activities because we put our bigger, locomotion muscles to work.

Sitting kills more people than smoking because millions more people indulge in sitting and consequently suffer from serious health issues such as obesity, diabetes and cardiovascular disease.  To reverse this trend, we need to deliberately interrupt ourselves when we are sitting by using standup desks and by moving as often as we can away from our seats.  Recent studies show that if we would get up and walk five to ten minutes after every hour of sitting we would ameliorate the potentially deadly consequences of this sedentary posture.  Interrupting long periods of sitting or sedentem interrupta should become a global goal.  Achieving it will require massive public education and creative manipulation of the work or even home environment that would discourage prolonged sitting by promoting physical activity away from the desk or the screen.

Obesity, which is the cardinal consequence of sedentary life style more than it is of overeating, is both harmful and helpful.  Its negative effects on our health are numerous, but it also helps in building up our muscle mass.  Unlike morbid obesity, which is always harmful, moderate obesity requires the support of a larger muscle mass.  Hence, obese individuals who remain physically very active increase their muscle mass, which in the short run protects them from the serious metabolic consequences of obesity.  Active, obese individuals fare better than inactive, lean individuals, a phenomenon that has become known as the obesity paradox.

A less known consequence of obesity is cancer.  Obese individuals have more occurrences of cancer of the uterus, ovaries, kidney, stomach, liver, gall bladder, colon, pancreas, esophagus and the postmenopausal breast cancer.  Up to 2% of thyroid cancers and 41% of uterine cancers are associated with obesity.  Globally, obesity killed 3.4 million people in 2010, and the incidences are rising among adults as well as among children.

Diet is essential.  Eating fewer carbohydrates has been shown to be more beneficial than eating less fat.  Our eating habits have not changed that much over time but because our physical mobility has been reduced because of technology, the balance has shifted in favor of obesity.  

To contain this global obesity epidemic, people will need to eat less, sit less and undertake more physical exercise.  No strategy aimed at modifying these three risk factors has succeeded in stemming the obesity epidemic.  Prolonged watching of TV has caused a 42% increase in obesity and a 20% increase in diabetes.  Sitting for eleven or more hours per day has increased mortality by 40% compared to sitting less than four hours per day.

Achieving fitness entails fighting the obesity epidemic, fighting the prolonged sitting epidemic, fighting the carbohydrate epidemic and adding moderate exercise to our daily routine.