Why Interval Training Works

by Arnie Baker, M.D.

Intervals—periods of higher-intensity work interspersed with periods of lower-intensity work—are a common training technique and have been used by a variety of endurance athletes to improve performance for over 100 years.

Many cyclists benefit by changing their training. Past training results in physiologic strengths and weakness. Training differently strengthens weak links.

Cyclists who have never specifically trained by performing intervals almost always improve with an interval program. Cyclists who performed one type of interval benefit by choosing another type. Cyclists who have a strong background in interval training may benefit from long, endurance rides.

Intervals are classified by the workload and rest periods, or by the physiologic fitness system thought to be stimulated. For example, a popular interval prescription is a workout consisting of six 4-minute intervals, each separated by 3 minutes rest. Some might describe this workout as six VO2 max 30 intervals.

Although coaches currently commonly classify the benefits of intervals by the physiologic fitness system stimulated, what counts in the real world are results: What works in practice and in fact.

To expand: Although 30-second intervals are physiologically classified as creatine phosphate/lactic acid tolerance training intervals, and theoretically might be expected to help performance only in short events, studies show that these efforts also improve 40K time trial times. Again, what really counts is what works.

Science has so far not been able to predict ahead of time which interval-training method works best. Thus far, coaching wisdom and experimentation has been more important than science. Sure, later sports scientists might say: “Of course! And here’s why.”

Coaches, athletes, and sport scientists disagree about interval variables. Duration of work interval, effort strategy, number of repetitions and sets, best cadence, recovery interval types and training frequency are only a few of the many variables.

The most popular training approach starts with base or endurance training, moves to longer, low-intensity intervals, and finally includes shorter, higher-intensity intervals. I agree with this approach. A minority of coaches advocates a year-round interval program, adding endurance training when needed.

Arguments In Favor of Interval Training

• Interval training allows a greater volume of high-quality work.
• Interval training allows for controlled high-quality work. Workload can be systematically and precisely prescribed, administered, and recorded.
• Controlled intervals with feedback (power output, distance, cadence, or other measures of workload) allow athletes to develop a sense of pace.
• Interval training allows aspects of fitness to be trained that otherwise would not be trained.

Arguments Against Interval Training

• The individual response to interval training can be difficult to predict.
• Some cyclists find this type of exercise too complex or taxing.
• No scientific evidence exists that interval training is better than continuous training for mid-level aerobic work.
• Studies of interval training for high-level aerobic and anaerobic work are few and of marginal quality.
• Many professional riders do not consistently utilize interval training—yet some of these athletes possess high maximum aerobic capacities (VO2 max >75 ml/kg/min). A rebuttal: Although some elite athletes do not engage in formal interval-training sessions, nearly all cycling races and training rides are conducted in an intermittent manner and therefore represent a type of interval training. The exceptional aerobic fitness levels achieved by some elite cyclists may be due to the interval format of their frequent racing. This allows these athletes to follow many interval-training principles without a formal program.

3 Interval Training Basics

1. Spend some training time at or above event-specific intensity. Identify an interval-training session that will allow you to exercise at an intensity that is specific to the intensity at which you will compete (i.e., cycling speeds or power required during races).

2. Identify a duration of training at this intensity that will represent an overload (i.e., induce fatigue).

3. Determine how you will change your interval-training sessions as fitness improves over time, to progressively overload your body in a sport-specific manner.

Training Time at Race Intensity

Races represent the most specific type of physiological stress for cyclists. Unfortunately, races do not always progressively overload a cyclist in an optimal manner. Too much racing may promote overuse injuries and chronic fatigue.

How does one accumulate sufficient amounts of time at race intensities? A key is to recover appropriately so the body can adapt to intense efforts and to allow subsequent efforts to be of high quality.

Interval training can simulate race-specific intensities, be prescribed at appropriate frequencies to allow for adequate recovery, and can be altered to progressively overload the cyclist in a manner that will result in improved performance. Interval training can be used to promote overload with very specific control over the exercise intensity.