High Intensity Interval Training, or HIIT, has exploded in popularity over the past few years, but not everyone is familiar with what it is that makes it so great.
HIIT is also referred to as just interval training and refers to alternating repeats of a short period of relatively intense exercise followed by a short period of low-intensity exercise or active rest. HIIT makes the body work harder than it does during steady state training.
The main benefit of interval training is that you get maximum effect in a minimum amount of time. If you’re focused on losing weight, it burns maximum kilojoules with a minimum amount of workout time. Studies show that interval training yields more significant improvements in most measures of fitness and cardiorespiratory health than steady state training.
For clarity, steady state training would be considered the opposite of HIIT, and it generally reflects exercise we’re most familiar with including jogging, running, riding, or swimming. It is longer periods of exercise at a moderate intensity.
Science shows that a 20 minute HIIT workout will most likely improve your health and fitness more than going for a longer run.
WHY DOES INTERVAL TRAINING WORK?
To know why interval training works so well you need to know and understand muscle metabolism and muscle fibers.
Principally, interval training engages more type II muscle fibers, the muscle fibers used when performing strong and powerful bursts of movement. It provides more stimulus of the anaerobic system and neurological system as a whole. This leads to more positive motor unit adaptation and burns through more energy.
The anaerobic system, the body’s function of producing energy without oxygen, is much less efficient than the aerobic system. This is because the anaerobic system sacrifices efficiency for speed and power. Replenishment of the anaerobic energy system happens via EPOC (informally called afterburn) which in turn elicits higher aerobic fitness.
Beyond burning through more energy and eliciting higher aerobic fitness, interval training improves muscle mass (tone), strength, and power to a larger degree than steady state training.
You can apply interval training/HIIT to just about any form of exercise; running, cycling, swimming, rowing, stair climbing, elliptical cross trainer, skipping, squat jumps, burpees, boxing, kettlebell swings and so on.
During the rest period, you are best to continue moving by doing the same form of exercise at a low intensity to help remove accumulated lactate from your system.
HOW TO BEGIN INCORPORATING HIIT INTO YOUR WORKOUTS
You should not be doing a HIIT workout every day as recovery is paramount for long-term success. You also need to take a cautious approach towards highly intense workouts and what form of exercise you choose.
Rather than launch straight into a new HIIT program, it’s best to build up your conditioning gradually. I would avoid running or jumping exercise until I was confident that my body can tolerate the stress of these forms of training put on my body.
A common assumption is that you should always go at your maximum effort or speed during interval training. However, this isn’t true unless you are doing a HIIT program aimed at 100% effort for short bursts of about 5-10 sec.
Most HIIT programs require submaximal effort to maintain the same intensity throughout the entire set. Refer to exercise safely for risks.
HIIT isn’t always a good idea. It is easy to overtrain with HIIT, especially if combined with other forms of exercise. HIIT will produce high levels of lactate and high hormonal stress response in the body, which may be problematic for those with chronic fatigue. For more on HIIT and chronic fatigue, refer to fitness strategies for ME/CFS and FMS.
UNDERSTANDING “TABATA” AND OTHER STUDIES IN HIIT
Izumi Tabata became famous for his contributions to studying certain forms of High Intensity Interval Training and subsequent publications of these findings. “Tabata regimen” basically mimics the High Intensity Interval Training program used for these studies. This is eight cycles of 20-second intense ‘work’ followed by 10 seconds of low intensity work (this does not include a warm-up or cool down).
While these studies have been of great benefit, there is a lot more science on High Intensity Interval Training to consider before formulating an exercise program.
WHAT INTERVAL TIMES AND EXERCISE VS. REST RATIOS SHOULD YOU FOLLOW?
The interval times and ratios you should train to depend on your goals. If you want to improve your aerobic fitness, you can focus on your aerobic system. However, training both of your anaerobic systems will also improve your aerobic fitness.
To push harder and improve your long duration sprint speed, then you train your anaerobic glycolytic system. If you’re going to go all out and improve your short duration sprint speed, then you train your anaerobic ATP-PC system.
To improve power, you need to add resistance. To do strength training and improve your aerobic fitness without compromising strength gains, then refer to combining forms of exercise and compatibility issues.
HIGH INTENSITY INTERVAL TRAINING (HIIT) OR (HIT) DEFINED
HIIT describes protocols in which the training effort is ‘near maximal’ or the workout intensity is between 80-100% of maximum heart rate. If you can converse during the workout, then you aren’t working hard enough.
SPRINT INTERVAL TRAINING (SIT)
SIT describes protocols that involve ‘all out’ or ‘supramaximal’ efforts in which the target intensities correspond to workloads greater than what is required to elicit 100% of VO2max.
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