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The Physiological Effects of Interval Training

author image Michelle Matte
Michelle Matte is an accomplished fitness professional who holds certifications in personal training, pilates, yoga, group exercise and senior fitness. She has developed curricula for personal trainers and group exercise instructors for an international education provider. In her spare time, Matte writes fiction and blogs.
The Physiological Effects of Interval Training
A woman is sprinting. Photo Credit: BONNINSTUDIO/iStock/Getty Images

A traditional cardiovascular endurance training routine consists of exercising for a predetermined length of time at a steady state that keeps your heart rate in its training zone. But always working at the same pace can get you into a training rut where you are just maintaining and not really getting anywhere. Adding interval training to your workout is an ideal way to break a training plateau and improve speed and performance.

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Interval Training

University of New Mexico researchers Len Kravitz, PhD and Lance Dalleck, MS define Interval training as high-intensity short duration training sessions performed at workloads above the lactate threshold, marked by an abrupt increase in blood lactate that forces the muscle to revert from aerobic to anaerobic metabolism. While it is impossible outside of a laboratory environment for the average exerciser to know the precise moment of blood lactate increase, Kravitz and Delleck assert that it can most accurately be identified based on a perceived exertion rating of "somewhat hard" to "hard." In other words, interval training means interspersing intervals of higher intensity that take you outside your comfort zone during steady-state cardiovascular training.

Work-to-Rest Ratio

Interval training programs are designed using a ratio of work to rest, or the length of the intensity interval compared with time at your normal pace. For cardiovascular endurance training, the work-to-rest ratio often ranges from 1:1 to 1:4. For example, a 1:1 ratio for cycling might include 1 minute of all-out effort followed by 1 minute of cycling at your usual pace. A 1:4 ratio for running may involve 30 seconds at an all-out sprint followed by 2 minutes at your normal pace. The length of your intensity intervals is largely determined by your fitness level. As you adapt, you will be able to maintain the higher intensity interval for a longer period of time. The long-term goal of interval training is to enable you to perform at higher intensities at a faster pace.

Respiratory Training Adaptations

A significant physiological effect of interval training is improved respiratory function, including improved blood flow through the lungs and an improved exchange rate of oxygen and carbon dioxide. A 2005 study of 38 elite cyclists published in the “Journal of Strength and Conditioning Research” showed that high intensity interval training improved the athletes' performance by improving ventilatory threshold and VO2 max, both measures of the cyclists' ability to take in and utilize oxygen to generate energy.

Muscular Training Adaptations

Another study published in the July 2006 issue of the "Journal of Physiology" found improved adaptations in muscle cells after interval training as compared to traditional steady-state endurance training. The study compared two groups of active young men over a two-week period. One group engaged in traditional long-duration training for 90 to 120 minutes, while the other did four to six sets of sprint-intervals involving 30 seconds at an all-out pace with 4 minute rest intervals. The study revealed superior adaptations in muscle tissue of the sprint interval group, indicating that interval training for endurance performance can be an effective and time-efficient alternative to long-duration steady-state training. Fat-burning is reportedly higher during interval training and/or during post-workout recovery.

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