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Is High-Intensity Interval Training for Everyone?

Updated: Sep 22, 2020

Why does frequency, volume, experience, fitness level, and supervision matter!

If you’ve been in a gym lately, you probably have picked up on the fact that High-Intensity Interval Training, or HIIT, has become the preferred method used by trainers of fitness classes, whether they be cardio-based dance classes, boot camps, or intense resistance training programs.

While the metabolic, health and cardiovascular benefits of HIIT are undeniable, personal trainers need to keep proper caution and application at the forefront when utilizing this method.  Using HIIT correctly can mean the difference between health and performance gains and injury and burnout.    As a personal trainer with your client’s interest, you should take precautions and understand the benefits, risks, and proper application of HIIT.

What is HIIT?  

HIIT is a training method that has been around since the early 1900’s that uses short, higher intensity intervals of an exercise interspersed with rest periods or active recovery. It was created as a tool for endurance athletes and recently become popular among a wide range of athletes. With that popularity comes an increased chance that key components will be overlooked or misconstrued.  Nowadays, it means a lot of different things to a lot of different people, but ultimately it is the process of using short, higher intensity intervals of a particular exercise interspersed with rest periods or active recovery.

The following are among the elements that call for the most attention:

The rest interval is an important part of interval training.  If you aren’t resting between intervals, you’re not doing HIIT!

Without adequate rest, the body is unable to recover from the short bursts of higher intensity work, which eliminates the possibility to sustain a high level of intensity for the entire length of the exercise session.1

Generally speaking, the higher the intensity of the interval, the shorter its duration, and the longer the recovery period. Interval training sessions usually last less an hour including rest periods and more intense sessions can be less than 25 minutes.

One popular method of training calls for “micro-intervals” in which both the work and rest periods are less than one minute. Another, known as Tabata Intervals, consists of 20 seconds of high-intensity work followed by 10 seconds rest interval.1,2

Benefits of HIIT

In a nutshell, short term, the benefit of low volume HIIT programs are: 

  1. Cause metabolic adaptations as longer term, higher volume endurance training.  

  2. Improve heart function

  3. Reduce the severity of type II diabetes

  4. Aid in weight loss in as little as one or two workouts per week. 

  5. Improve aerobic fitness, heart function, blood glucose levels, fat loss, and overall fitness in untrained individuals.  

Note "untrained individuals" above - But doesn't traditional endurance and resistance training have these same benefits?

Untrained individuals respond very well to training programs no matter what form they take.  Stacking firewood or playing hopscotch regularly would probably provide similar benefits.3,4,5,6

In contrast to untrained individuals, in highly trained individuals, HIIT does not improve VO2 max, a measure of how much oxygen an athlete can use.  This is because highly trained endurance athletes have already maximized improvements in VO2 max.  According to a few studies, it may improve their ability to buffer lactic acid.  HIIT does afford these athletes some performance gains, but only in small doses and for limited periods of time.  The most likely benefit is that the short work periods enable the athlete to practice good form at higher speeds and intensities.1

Regardless of the actual results, many people just seem to enjoy HIIT workouts more than regular, less intense workouts.  They work up a sweat, the work feels hard, and they feel that they are getting in a great workout in less time.  What’s not to love?  And as we all know, if a person likes the workout, they are more likely to do it.  And getting people to exercise is our job as trainers.  

What about the risks?

When trainers are considering implementing a HIIT workout for a client, they first need to determine how safe it is for each individual and how to tailor these workouts to benefit the clients with minimal risk.  Most studies have shown that performing HIIT workouts more than once or twice per week have no added benefit.

More is Not Always Better

More sometimes means tendonitis and muscle strains.  Training at higher intensities once or twice a week may be perfectly fine for any number of individuals, but in the fitness industry, many individuals are participating in HIIT style classes multiple times per week and higher intensity training, in general, is known to have a lot of risks. Higher intensities, when we’re talking about speed, means more repetitions in less time.

Even though your workout may be half the time on the clock, you may actually be doing just as many, if not more repetitions of your particular exercises. Increased speed means you are exerting more force on your joints. Poor exercise choices combined with more reps at higher speeds can lead to both overuse injuries and acute injuries, both of which will negatively impact the participant. In the literature, there are many causes for injuries sustained in fitness facilities, high-intensity training programs, military boot camps, and sports. Ultimately, both acute and overuse injuries in all these activities are primarily due to poor supervision, inappropriate increases in volume or intensity, failure to properly assess participants, overspecialization, and a failure to establish and maintain a proper strength and fitness base before participating in more intense activities.

All of these risk factors can be mitigated by proper supervision and an individualized approach to training activities. In other words, a well-informed, observant, and thoughtful coach can avoid most of these training errors.7,8,9,10,11

Not a Magic Formula

Tabata squats will only improve your ability to do Tabata squats, not run a 5k faster, or clean and jerk more weight. HIIT workouts are also no substitute for volume endurance training. Thirty-minute HIIT sessions only will not enable you to complete longer distance or duration endurance events unless you already have an established endurance base. Finally, the same health benefits and aerobic adaptations that HIIT can provide can also be developed through simple focused strength training and traditional endurance training.12,13

Why spend all your training time on intensity when you can also get strong and go long?

Simple Guidelines for Using HIIT

In a comprehensive review of the use of HIIT in the training of high-level athletes, Stephen Seiler, one of the world’s foremost experts in the practical use of HIIT, concludes several important points:

1. A 20%-80% volume ratio of HIIT to low-intensity exercise provides the most ideal benefit without the added risk of injury.

2. An established base of high volume, low-intensity training, may be an important precondition for tolerating a substantial increase in training intensity over the short term.

3. Although HIIT is an important part of training for exercisers and athletes alike, no more than two sessions per week are necessary for improving performance without causing excessive stress.1

HIIT in Group Fitness Class

From my own experience in the weight room and coaching group fitness classes, I would like to add some additional guidelines for using HIIT with resistance training:

1. Coaches must determine their client’s fitness level before starting them on a HIIT program that utilizes resistance training.  If the clients lacks foundational strength, can’t perform the exercises, or are severely out of shape, they will need to build strength and conditioning at lower intensities before participating.

2. As with all resistance training, the beginning signs of a break-down in form should signal the end of the work period.  Completing reps with bad form just means you’re teaching yourself to lift with bad form.  Training to failure is training to fail.


3. Trainers and coaches must be able to adequately teach, observe, and correct form on all movements being used in a HIIT circuit.   If you can’t teach it or correctly identify form breakdown, you shouldn’t be using it.  Anyone working with a trainer who expects them to complete a set with bad form needs to find a new trainer.

4. For resistance movements that are performed with heavier weights or require larger ranges of motions such as squats, push-ups, sit-ups, etc., limit the total number of repetitions in a session to under 75.


As we all know, many individuals value how sore and sweaty they are after a workout more than the quality of the workout.  But if your exercise session leaves you unable to walk u