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The benefits and risks of internal training
Improve your fitness
with intervals "I just started taking the interval training aerobics class two months ago," you overhear a member telling a friend, "and it's great! I've enjoyed aerobics for several years and am in pretty decent shape. I think the classes I used to take helped me maintain my fitness, but I had sort of reached a plateau. This new class really pushes me! I appreciate a challenging workout, and I can already see an improvement in my fitness." One intensity doesn't fit all Current exercise recommendations from public health organizations, including the American College of Sports Medicine, the Centers for Disease Control and Prevention and the office of the Surgeon General, take an "exercise light" approach, designed to encourage sedentary people to engage in regular physical activity.4 (Specifically, they recommend that people perform about 30 minutes of moderately vigorous physical activity most days.) The greatest good for the largest number of Americans would result if these recommendations were followed. Of course, many people are already fairly active and are eager to reach even higher levels of fitness. Most exercise physiologists agree that while some exercise is better than none, more is better still,2 and most fitness centers have a number of members who fall into the "more is better" group. High intensity in tolerable doses Interval training has been used by serious athletes for decades. As you know, fitness improves when you ask physiological systems to do more than they are accustomed to doing. The musculoskeletal system gets stronger when you ask it to exert force against a resistance. Energy systems improve when they are asked to work harder. Interval training can increase the ability of the anaerobic and aerobic energy systems to provide energy for physical activity. |
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Interval training refers to
workouts that include periods of high-intensity exercise
interspersed with periods of active (lower-intensity exercise)
or passive (resting) recovery. The length of the high-intensity
exercise and recovery periods vary depending of the energy
system targeted for training.2 Athletes training for a specific sprint-type event will choose an exercise duration that is similar to that of their event, usually between 10 and 30 seconds. For example, sprinters training the immediate energy system (ATP/phosphorcreatine) might alternate a sprint at maximal intensity for 10 seconds, followed by at least 30 seconds of recovery. This 1:3 ratio is a minimum that allows sufficient time for the high-energy phosphates to be restored so that the athlete will have energy for the next sprint. Athletes whose events last longer than 10 seconds will want to train the lactic acid system (where ATP is manufactured from ADP through anaerobic glycolysis) and might use a 60-second exercise period with at least a 1:2 exercise to recovery ratio. The recovery phase must be long enough to allow adequate lactic acid removal so that the athlete can begin the next high-intensity bout with little fatigue. Active recovery helps lactate clearance and increases training volume. To improve the aerobic energy system, high-intensity exercise intervals of one to two minutes are recommended, with exercise to recovery ratios of at least 1:1 or 1:1.5, although longer recovery periods are commonly used. The duration of the recovery interval should be long enough to allow the next interval to begin without undue fatigue. |
Don't get lost in the ratios. The important thing is to
perform a number of high-intensity intervals in a row to stimulate energy
system improvement. Even four or five high-intensity intervals will
stimulate improvement. Athletes might perform up to 10 in a hard workout.
I-T for recreational exercisers
Most adult recreational exercisers are interested in improving their lactic
acid and aerobic energy systems. An example of interval training that might
occur during an aerobics class is 90 seconds of maximal intensity drills,
alternating with several minutes of moderate-intensity movement. Swimmers
might alternate sprints with slower swimming. Joggers and cyclists can add
high-intensity sprints into their workouts. Most pieces of aerobic equipment
now have interval training protocols available that alternate high-intensity
and more moderate-intensity exercise.
Vary training on alternate days
Interval training is physically and psychologically demanding, and should
only be performed two or three days a week. Alternate interval days with
days of rest or more moderately-paced exercise.
Be alert to signs of overtraining
Signs of overtraining include fatigue, depression, irritability, increase in
resting heart rate, muscle pain, increased susceptibility to colds and
gastrointestinal problems, insomnia, weight loss, overuse injuries and
unexpected decline in athletic performance.
Slow and steady still preferred
High-intensity exercise is not appropriate for middle-aged and older men and
women with fairly low fitness levels. Studies have shown that exercise
intensity is related to risk of orthopedic injury and heart attack in
middle-aged and older men.1 The same is probably true for women. People with
lower fitness levels often find high-intensity exercise uncomfortable and
unappealing, and just plain too hard.
Indeed, in addition to being safer, physical activity of moderate intensity
may have more health benefits than high-intensity exercise, the health
benefits for which many adult exercisers visit fitness centers. Some
evidence suggests that physiological benefits such as enhanced immune
function, decreased blood pressure and lower platelet aggregation are more
likely to occur in response to moderate, rather than high-intensity,
exercise.1 A possible explanation for this is that the lactate threshold
also serves as an "adrenaline threshold," an exercise intensity at which
plasma concentrations of the catacholamines norepinephrine and epinephrine
(adrenaline) begin to increase. These hormones produce a stress response
that does not appear to be harmful for healthy, young people, but may be
counterproductive in people who already have cardiovascular disease,
including atherosclerosis and hypertension.
REFERENCES
1. Haskell, W.L. Health consequences of physical activity: Understanding and
challenges regarding dose-response. Medicine and Science in Sports and
Exercise, 26: 649-660, 1994.
2. Lee, I.M., & R.S. Paffenbarger Jr. How much physical activity is optimal
for health? Methodological considerations. Research Quarterly for Exercise
and Sport, 67: 206-208, 1996.
3. McArdle, W.D., F.I. Katch & V.L. Katch. Exercise Physiology: Energy,
Nutrition and Human Performance. Baltimore: Williams & Wilkins, 1996.
4. Pate, R.R., M. Pratt, S.N. Blair, et al. Physical activity and public
health: A recommendation from the Centers for Disease Control and Prevention
and the American College of Sports Medicine. Journal of the American Medical
Association, 273: 402-407, 1995.
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