Can You Get Fit in Six Minutes a Week?

By Gretchen Reynolds

A few years ago, researchers at the National Institute of Health and Nutrition in Japan put rats through a series of swim tests with surprising results. They had one group of rodents paddle in a small pool for six hours, this long workout broken into two sessions of three hours each. A second group of rats were made to stroke furiously through short, intense bouts of swimming, while carrying ballast to increase their workload. After 20 seconds, the weighted rats were scooped out of the water and allowed to rest for 10 seconds, before being placed back in the pool for another 20 seconds of exertion. The scientists had the rats repeat these brief, strenuous swims 14 times, for a total of about four-and-a-half minutes of swimming. Afterward, the researchers tested each rat’s muscle fibers and found that, as expected, the rats that had gone for the six-hour swim showed preliminary molecular changes that would increase endurance. But the second rodent group, which exercised for less than five minutes also showed the same molecular changes.

The potency of interval training is nothing new. Many athletes have been straining through interval sessions once or twice a week along with their regular workout for years. But what researchers have been looking at recently is whether humans, like that second group of rats, can increase endurance with only a few minutes of strenuous exercise, instead of hours? Could it be that most of us are spending more time than we need to trying to get fit?

The answer, a growing number of these sports scientists believe, may be yes.




“There was a time when the scientific literature suggested that the only way to achieve endurance was through endurance-type activities,” such as long runs or bike rides or, perhaps, six-hour swims, says Martin Gibala, PhD, chairman of the Department of Kinesiology at McMaster University in Ontario, Canada. But ongoing research from Gibala’s lab is turning that idea on its head. In one of the group’s recent studies, Gibala and his colleagues had a group of college students, who were healthy but not athletes, ride a stationary bike at a sustainable pace for between 90 and 120 minutes. Another set of students grunted through a series of short, strenuous intervals: 20 to 30 seconds of cycling at the highest intensity the riders could stand. After resting for four minutes, the students pedaled hard again for another 20 to 30 seconds, repeating the cycle four to six times (depending on how much each person could stand), “for a total of two to three minutes of very intense exercise per training session,” Gibala says.

Each of the two groups exercised three times a week. After two weeks, both groups showed almost identical increases in their endurance (as measured in a stationary bicycle time trial), even though the one group had exercised for six to nine minutes per week, and the other about five hours. Additionally, molecular changes that signal increased fitness were evident equally in both groups. “The number and size of the mitochondria within the muscles” of the students had increased significantly, Gibala says, a change that, before this work, had been associated almost exclusively with prolonged endurance training. Since mitochondria enable muscle cells to use oxygen to create energy, “changes in the volume of the mitochondria can have a big impact on endurance performance.” In other words, six minutes or so a week of hard exercise (plus the time spent warming up, cooling down, and resting between the bouts of intense work) had proven to be as good as multiple hours of working out for achieving fitness. The short, intense workouts aided in weight loss, too, although Gibala hadn’t been studying that effect. “The rate of energy expenditure remains higher longer into recovery” after brief, high-intensity exercise than after longer, easier workouts, Gibala says. Other researchers have found that similar, intense, brief sessions of exercise improve cardiac health, even among people with heart disease.

There’s a catch, though. Those six minutes, if they’re to be effective, must hurt. “We describe it as an ‘all-out’ effort,” Gibala says. You’ll be straying “well out of your comfort zone.” That level of discomfort makes some activities better-suited to intense training than others. “We haven’t studied runners,” Gibala says. The pounding involved in repeated sprinting could lead to injuries, depending on a runner’s experience and stride mechanics. But cycling and swimming work well. “I’m a terrible swimmer,” Gibala says, “so every session for me is intense, just because my technique is so awful.”
Meanwhile, his lab is studying whether people could telescope their workouts into even less time. Could a single, two- to three-minute bout of intense exercise confer the same endurance and health benefits as those six minutes of multiple intervals? Gibala is hopeful. “I’m 41, with two young children,” he says. “I don’t have time to go out and exercise for hours.” The results should be available this fall.

Dieting is the practice of ingesting food in a regulated fashion to achieve or maintain a controlled weight. In most cases the goal is weight loss in those who are overweight or obese, but some athletes aspire to gain weight (usually in the form of muscle) and diets can also be used to maintain a stable body weight.

Diets to promote weight loss are generally divided into four categories: low-fat, low-carbohydrate, low-calorie, and very low calorie.^[1] A meta-analysis of six randomized controlled trials found no difference between the main diet types (low calorie, low carbohydrate, and low fat), with a 2–4 kilogram weight loss in all studies.^[1] At two years all diet types cause equal weight loss irrespective of the macronutrients emphasized.^[2]

Types of dieting

There are several kinds of diets:

• Weight-loss diets restrict the intake of specific foods, or food in general, to reduce body weight. What works to reduce body weight for one person will not necessarily work for another, due to metabolic differences and lifestyle factors. Also, for a variety of reasons, most people find it difficult to maintain significant weight loss over time. Among individuals that have lost 10% or more of body weight, only 20% are able to maintain that weight loss for a full year.^[3]

• Athletes participating in professional sports may sometimes undertake weight-gain diets to increase their body mass and gain advantage in their field.

• Individuals who are underweight, such as those recovering from anorexia nervosa or starvation, may adopt weight-gain diets which, unlike those of athletes, have the goal of restoring normal levels of body fat, muscle, and stores of essential nutrients.

• Actors, and people participating in similar activities, may pursue weight loss or gain in order to better portray a particular role.

In children and young adults

Receiving adequate nutrition through a well-balanced diet is crucial during childhood and adolescence. Some diets can deprive the body of necessary nutrients, for instance lipids. In addition, there are some indications that the harmful effects of starvation or extreme dieting during adolescence exceed the expected benefits, sometimes even leading to increased weight gains.^[4]

Research shows that putting children on starvation or extreme diets can be harmful. The brain is unable to learn how to correlate taste with nutritional value, which is why such children may consistently overeat later in their life despite adequate nutritional intake. ^[5]

Thermoregulation

As endotherms, humans expend energy to maintain their blood temperature at body temperature, which is approximately 37 °C (98.6 °F). This is accomplished by metabolism and blood circulation, by shivering to stay warm, and by sweating to stay cool.^[6]

In addition to thermoregulation, humans expend energy keeping the vital organs (especially the lungs, heart and brain) functioning. Except when sleeping, our skeletal muscles are working, typically to maintain upright posture. The average work done just to stay alive is the basal metabolic rate.

Physical exercise

Physical exercise is an important complement to dieting in securing weight loss. Aerobic exercise is also an important part of maintaining normal good health, especially the muscular strength of the heart.

Though the energy for muscle activity is primarily derived from the glycogen stored in the body, continued activity results in an increased use of the fatty acids as well. After the available glycogen stores are exhausted, fatty acids alone are used ^[7]. It is often recommended that muscle activity be maintained for 20 minutes or more for increased usage of fatty acids.

The energy burnt during physical exercise has only a limited effect on weight loss, since an hour of aerobic exercise for a man in reasonable physical shape would burn about 2 megajoules (500 kilocalories), which is equivalent to only 60 grams (2 oz) of fat.

Both aerobic and anaerobic exercise would increase the basal metabolic rate (BMR) for some time after exercising. This leads to an additional caloric loss.

Fat loss versus muscle loss

Weight loss typically involves the loss of fat, water and muscle. Overweight people, or people suffering from obesity, typically aim to reduce the percentage of body fat. Additionally, as muscle tissue is denser than fat, fat loss results in increased loss of body volume compared with muscle loss. Reducing even 10% body fat can therefore have a dramatic effect on a person’s body shape. To determine the proportion of weight loss that is due to decreased fat tissue, various methods of measuring body fat percentage have been developed.

Muscle loss during weight loss can be restricted by regularly lifting weights (or doing push-ups and other strength-oriented calisthenics) and by maintaining sufficient protein intake. Those on low-carbohydrate diets, and those doing particularly strenuous exercise, may wish to increase their protein intake. According to the National Academy of Sciences, the Dietary Reference Intake for protein is “0.8 grams per kilogram of body weight for adults.”

Excessive protein intake, may cause liver and kidney problems and may be a risk factor for heart disease.^[8]. There is no conclusive evidence that moderately high protein diets in healthy individuals are dangerous, it has only been shown that these diets are dangerous in individuals who already have kidney and liver problems.

Energy obtained from food

The energy intake from food is limited by the efficiency of digestion and the efficiency of utilization. The efficiency of digestion is largely dependent on the type of food being eaten, while efficiency of utilization is affected by individual factors, including body weight and hormones.

The effects of chewing, especially in elderly people, have been shown to affect the intake of micronutrients. However, there was no significant effect on the intake of macronutrients, such as sugars, fats, and proteins^[9].

Proper nutrition

Food provides nutrients from six broad classes: proteins, fats, carbohydrates, vitamins, dietary minerals, and water. Carbohydrates are metabolized to provide energy. Proteins provide amino acids, which are required for cell construction, especially for the construction of muscle cells. Essential fatty acids are required for brain and cell membrane construction. Vitamins and trace minerals help maintain proper electrolyte balance and are required for many metabolic processes. Dietary fiber is another food component which influences health even though it is not actually absorbed into the body.

Any diet that fails to meet minimum nutritional requirements can threaten general health (and physical fitness in particular). If a person is not well enough to be active, weight loss and good quality of life will be unlikely.

The National Academy of Sciences and the World Health Organization publish guidelines for dietary intakes of all known essential nutrients.

Sometimes dieters will ingest excessive amounts of vitamin and mineral supplements. While this is usually harmless, some nutrients are dangerous. Men (and women who don’t menstruate) need to be wary of iron poisoning. Retinol (oil-soluble vitamin A) is toxic in large doses. As a general rule, most people can get the nutrition they need from foods. In any event, a multivitamin taken once a day will suffice for the majority of the population.

Weight-loss diets which manipulate the proportion of macronutrients (low-fat, low-carbohydrate, etc.) have not been found to be more effective than diets which maintain a typical mix of foods with smaller portions and perhaps some substitutions (e.g. low-fat milk, or less salad dressing).^[10] Extreme diets may, in some cases, lead to malnutrition.

How the body gets rid of fat

All body processes require energy to run properly. When the body is expending more energy than it is taking in (e.g. when exercising), the body’s cells rely on internally stored energy sources, like complex carbohydrates and fats, for energy. The first source the body turns to is glycogen (by glycogenolysis). Glycogen is a complex carbohydrate, where 65% of it is stored in skeletal muscles and the rest in the liver (totaling about 2000 kcal in the whole body). It is created from the excess of ingested macronutrients, mainly carbohydrates. When those sources are nearly depleted, the body begins lipolysis, the mobilization and catabolism of fat stores for energy. In this process, fats, obtained from adipose tissue, or fat cells, are broken down into glycerol and fatty acids, which can be used to make energy. The primary by-products of metabolism are carbon dioxide and water; carbon dioxide is expelled through the respiratory system.

Fats are also secreted by the sebaceous glands (in the skin).

Psychological aspects of weight-loss dieting

Diets affect the “energy in” component of the energy balance by limiting or altering the distribution of foods. Techniques that affect the appetite can limit energy intake by affecting the desire to overeat.

Cognitive Behavior Therapy has been effective in producing long term weight loss ^[11]. Judith S. Beck has been one of the most prominent practitioners and writers to bring this method to a popular audience.

Consumption of low-energy, fiber-rich foods, such as non-starchy vegetables, is effective in obtaining satiation (the feeling of “fullness”). Exercise is also useful in controlling appetite as is drinking water and sleeping.

The use of drugs to control appetite is also common. Stimulants are often taken as a means to suppress hunger in people who are dieting. Ephedrine (through facilitating the release of adrenaline and noradrenaline) stimulates the alpha(1)-adrenoreceptor subtype, which is known to act as an anorectic. L-Phenylalanine, an amino acid found in whey protein powders also has the ability to suppress appetite by increasing the hormone cholecystokinin (CCK) which sends a satiety signal to the brain.

Weight loss groups

There exist both profit-oriented and non-profit weight loss organizations who assist people in their weight loss efforts. An example of the former is Weight Watchers; examples of the latter include Overeaters Anonymous, as well as a multitude of non-branded support groups run by local churches, hospitals, and like-minded individuals.

These organizations’ customs and practices differ widely. Some groups are modelled on twelve-step programs, while others are quite informal. Some groups advocate certain prepared foods or special menus, while others train dieters to make healthy choices from restaurant menus and while grocery-shopping and cooking.

Most groups leverage the power of group meetings to provide counseling, emotional support, problem-solving, and useful information.

Food diary

A July 2008 study, published in the American Journal of Preventive Medicine, showed dieters who keep a daily food diary (or diet journal) of what they eat lose twice as much weight as those who do not. The researchers concluded, “It seems that the simple act of writing down what you eat encourages people to consume fewer calories.”^[12] Diet journaling software and websites have become popular to help people track calorie consumption, calorie burning, weight loss goals, and nutritional balance.