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Interval Training Advantages

by Jason Karp, PhD on Mar 24, 2011

One of the main reasons for all of the attention being given to interval training in the fitness industry is that it can improve fitness quickly, which is great news for busy people who don’t want to spend 2 hours in the gym.

Designing Interval Workouts

Interval training manipulates four variables: time (or distance), intensity, time of each recovery period and number of repetitions. With so many possible combinations of these four elements, the potential for variety is nearly unlimited. Possibly the greatest use of interval training lies in its ability to target individual energy systems and physiological variables, improving specific aspects of clients’ fitness levels.

Aerobic (Cardiovascular) Intervals
One of the best methods for improving the heart’s ability to pump blood and oxygen to the active muscles is interval training using work periods lasting 3–5 minutes and recovery periods equal to or slightly shorter than the work periods (see the sidebar “Sample Interval Workouts”). The cardiovascular adaptations associated with interval training increase clients’ VO2max, raising their aerobic ceiling. Since VO2max is achieved when maximum stroke volume and heart rate are reached, each work period should be performed at an intensity that elicits maximum heart rate.

Anaerobic Capacity Intervals
Anaerobic capacity refers to the ability to regenerate energy (ATP) through glycolysis. Work periods lasting 30 seconds to 2 minutes target improvements in anaerobic capacity by using anaerobic glycolysis as the predominant energy system. These short, intense work periods with recovery intervals two to four times as long as the work periods increase muscle glycolytic enzyme activity. As a result, glycolysis can regenerate ATP more quickly for muscle contraction and can improve the ability to buffer the muscle acidosis that occurs when there is a large dependence on oxygen-independent (anaerobic) metabolism.

Anaerobic Power Intervals
Anaerobic power refers to the ability to regenerate ATP through the phosphagen system. Work periods lasting 5–15 seconds target improvements in anaerobic power by using the phosphagen system as the predominant energy system. These very short, fast sprints with 3- to 5-minute recovery intervals that allow for complete replenishment of CP in the muscles increase fast-twitch motor unit activation and the activity of creatine kinase, the enzyme responsible for breaking down creatine phosphate.

Sample Interval Workouts

Incorporating interval training into your clients’ programs will dramatically improve their fitness. Ensure that clients warm up before each workout and cool down afterward.

Aerobic (Cardiovascular) Intervals

  • 5 x 3 minutes @ VO2max intensity (95%–100% HRmax) with 2½–3 minutes of active recovery
  • 3 x 4 minutes @ VO2max intensity (95%–100% HRmax) with 3½–4 minutes of active recovery
  • 3, 4, 5, 4, 3 minutes @ VO2max intensity (95%–100% HRmax) with 2½–3 minutes of active recovery

Anaerobic Capacity (Glycolytic) Intervals

  • 4–8 x 30 seconds at 95% all-out with 2 minutes of active recovery
  • 4–8 x 60 seconds at 90% all-out with 3 minutes of active recovery
  • 2–3 sets of 30, 60, 90 seconds at 90%–95% all-out with 2–3 minutes of active recovery, 5 minutes of recovery between sets

Anaerobic Power (Phosphagen System) Intervals

  • 2 sets of 8 x 5 seconds all-out with 3 minutes of passive rest, 5 minutes of rest between sets
  • 5 x 10 seconds all-out with 3–4 minutes of passive rest
  • 2–3 sets of 15, 10, 5 seconds all-out with 3 minutes of passive rest, 10 minutes of rest between sets

For additional information, please see “Interval Training: The New and Better Way to Train Your Clients” in the online IDEA Library or in the February 2011 issue of IDEA Fitness Journal.

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About the Author

Jason Karp, PhD

Jason Karp, PhD IDEA Author/Presenter

Dr. Jason Karp is owner of, a state-of-the-science running coaching and personal training company in San Diego, California. He is a frequent presenter at national coaching, fitness, and academic conferences, including U.S. Track and Field and Cross Country Coaches Association, American College of Sports Medicine, American Society of Exercise Physiologists, IDEA Fitness Fusion, IDEA World Fitness Convention, SCW Fitness MANIA, ECA World Fitness Convention, and the San Diego State University Writers' Conference, among others. He has taught USA Track & Field's highest level coaching certification and was an instructor at the USATF/U.S. Olympic Committee’s Emerging Elite Coaches Camp at the U.S. Olympic Training Center. He is also the founder and host of the VO2max Distance Running Clinic, the San Diego Personal Training Summit, Dr. Karp's Run-Fit Boot Camp, and Running Clinics in the Park. He is a prolific writer, with over 100 articles published in numerous international coaching, running, an