lower intensities but increasing duration, while others will burn more calories exercising at higher
intensities for a shorter period of time. Ultimately dieters must find the optimal combination of
intensity and duration which maximizes caloric expenditure.
This partly explains why simply restricting calories while weight training causes fat loss.
Fat loss is primarily a function of calories in versus calories out. Weight training ‘signals’ the
body to keep muscle and the caloric deficit signals the body to lose fat. Whether a calorie deficit is
generated with a slight restriction in calories or through aerobic exercise, the end result is
basically the same. Additionally, the caloric cost of weight training, both during and after the
workout, will contribute to the overall calorie deficit. As long as weight training is being
performed and calories are not restricted too much, the majority of weight lost should be fat.
High-intensity aerobics and interval training
Interval training is an advanced exercise technique alternating short periods (15-90
seconds) of near maximal intensity activity with periods (1-2 minutes) of very low-intensity
activity. Several recent studies have found that either high-intensity endurance activity (38) or
interval training (39) yields greater fat loss than lower intensity continuous activity when diet is
not controlled. This is probably due to an appetite blunting mechanism or a greater EPOC from
higher intensity exercise.
Tremblay compared the effects of a high-intensity interval program to continuous exercise
(39). The interval group used a progressive program working up to 5 ninety-second intervals near
their maximum heart rate three times per week. The continuous exercise group worked up to 45
minutes of exercise five times per week. Although the interval training group only exercised one
hour per week, compared to 3.75 hours in the aerobic group, and expended only half as many
calories during the interval workouts, fat loss as measured by skinfolds was nine times greater.
Although fat loss per se was not measured, total bodyweight was. As both groups maintained
their overall weight, this suggests that the interval group gained more muscle as their fat loss
was greater.
For most individuals (excepting pre-contest bodybuilders who are addressed separately in
chapter 30), the primary goal of aerobic exercise should be on total caloric expenditure. For
individuals with limited time, maximizing calorie expenditure by working at the highest intensity
that can be maintained safely, and is compatible with a ketogenic diet, is the best choice. The
inclusion of interval training from time to time can raise fitness level and increase fat loss.
Specific guidelines for when and how to incorporate training techniques such as intervals are
discussed in chapter 25.
Summary
Contrary to popular opinion, there is no ‘fat burning zone’, at least not in terms of an
optimal intensity range which will maximize fat loss. The fat loss from aerobic exercise is tied
intimately to caloric expenditure, not the particular fuel which is used during exercise. Some
studies suggest that high-intensity aerobic exercise or interval training may actually cause