Interval Training

Interval training
Interval training is a type of physical training that involves bursts of high intensity work. This high intensity work is alternated with periods of recovery (which may involve complete rest and/or lower intensity activity).The term can refer to any cardiovascular workout (e.g. boxing, running, circuit, etc.) that involves brief bouts at near-maximum exertion interspersed with periods of lower-intensity activity.

Interval training is prominent in many sports training. It is a technique particularly employed by runners, but athletes from several other backgrounds have been known to use this type of training.

Interval training can be an effective means of enhancing an athlete’s lactate threshold – i.e. increase the threshold at which lactate starts to accumulate in the blood. Lactate threshold has been shown to be a significant factor determining performance for long distance running events.

This method of training may be more effective at inducing fat loss than simply training at a moderate intensity level for the same duration. This is due the metabolism boosting effects of high intensity intervals.

High-intensity interval training (HIIT)
Or sprint interval training is an exercise strategy that is intended to improve performance with short training sessions. HIIT is a form of cardiovascular exercise which is beneficial to burning fat in a short and intense workout. Usual HIIT sessions may vary from 9–20 minutes. The original protocol set a 2:1 ratio for recovery to work periods. For example, a runner would alternate 30–40 seconds of jogging or walking with 15–20 seconds of hard sprinting.

HIIT session consists of a warm up period of exercise, followed by six to ten repetitions of high intensity exercise, separated by medium intensity exercise, and ending with a period of cool down exercise. The high intensity exercise should be done at near maximum intensity. The medium exercise should be about 50% intensity. The number of repetitions and length of each depends on the exercise. The goal is to do at least six cycles, and to have the entire HIIT session last at least fifteen minutes and not more than twenty.

HIIT is considered to be an excellent way to maximize a workout that is limited on time.

Tabata Method
A popular regimen based on a 1996 study uses 20 seconds of ultra-intense exercise (at an intensity of about 170% of VO2max) followed by 10 seconds of rest, repeated continuously for 4 minutes (8 cycles). In the original study, athletes using this method trained 4 times per week, plus another day of steady-state training, and obtained gains similar to a group of athletes who did steady state (70% VO2max) training 5 times per week. The steady state group had a higher VO2max at the end (from 52 to 57 ml/kg/min), but the Tabata group had started lower and gained more overall (from 48 to 55 ml/kg/min). Also, only the Tabata group had gained anaerobic capacity benefits.

Little Method
An alternative regimen based on a 2009 study uses 60 seconds of intense exercise (at 95% of VO2max) followed by 75 seconds of rest, repeated for 8–12 cycles. Subjects using this method trained 3 times per week, and obtained gains similar to what would be expected from subjects who did steady state (50–70% VO2max) training for five hours per week. While still a demanding form of training, this exercise protocol could be used by the general public with nothing more than an average exercise bike.

Studies by Tabata, Tremblay and others have explored the effectiveness of this method compared to traditional endurance training methods. A study by Gibala demonstrated 2.5 hours of sprint interval training produced similar biochemical muscle changes to 10.5 hours of endurance training and similar endurance performance benefits. According to a study by King, HIIT increases the resting metabolic rate (RMR) for the following 24 hours due to excess post-exercise oxygen consumption, and may improve maximal oxygen consumption (VO2 max) more effectively than doing only traditional, long aerobic workouts.

Long aerobic workouts have been promoted as the best method to reduce fat, as fatty acid utilization usually occurs after at least 30 minutes of training. HIIT is somewhat counterintuitive in this regard, but has nonetheless been shown to burn fat more effectively. There may be a number of factors that contribute to this, including an increase in RMR, and possibly other physiological effects.

High-intensity interval training has also been shown to improve athletic performance. For already well-trained athletes, improvements in performance become difficult to attain and increases in training volume can potentially yield no improvements. Previous research would suggest that, for athletes who are already trained, improvements in endurance performance can be achieved through high-intensity interval training.

Recently it has been shown that two weeks of HIIT can substantially improve insulin action in young healthy men. HIIT may therefore represent a viable method for prevention of type-2 diabetes.

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