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 precaution and understand the benefits, risks and proper application of 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.
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 period 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]
In a nutshell, short term, the benefit of low volume HIIT programs are:
Cause metabolic adaptations as longer term, higher volume endurance training.
Improve heart function
Reduce the severity of type II diabetes
Aid in weight loss in as little as one or two workouts per week.
Improve aerobic fitness, heart function, blood glucose levels, fat loss, and overall fitness in untrained individuals.
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.
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.
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 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]
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?
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:
A 20%-80% volume ratio of HIIT to low intensity exercise provides the most ideal benefit without added risk of injury.
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.
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.
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:
Coaches must determine their client's fitness level before starting them on an 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.
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.
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.
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 up the stairs or function on a daily basis, you need to reconsider your workouts. HIIT can still be very effective without leaving you virtually crippled at the end of the session.
The formats outlined below can easily be incorporated into a person's weekly training schedule twice per week to enhance conditioning, fat loss, and strength endurance.
Pick an endurance exercise: walking, cycling, rowing, running, etc. Establish a baseline pace that you can sustain for 30-60 minutes. To use HIIT, start with an easy work-to-rest ratio such as 1 minute of work to 1 minute of "rest". After warming up, increase your pace to slightly higher than your normal sustained pace for one minute. Then go back to your normal pace for one minute.
In this way, you are effectively working harder for half the time you are exercising. Over time, lengthen the work interval such that you may be sustaining your higher pace for 3-4 minutes with one minute of rest at your lower pace. Eventually, you will be able to sustain the higher pace for the duration of your workout and then you can start again with an even more challenging pace.
For circuit style resistance training HIIT, pick 3-5 full body exercises that you can execute with good form. Remember, you will want to keep your total reps of each exercise under 75 so choose a set/rep scheme that keeps you within these parameters. Five to eight sets of 6-10 or 10-15 reps works well with this format. Choose weights that allow you to complete repetitions within the given rep range.
Complete the number of reps you can do with good form before moving on to the next exercise. If you can't complete the minimum number, the weight is too high. Likewise, if you are throwing the weight around and can obviously complete significantly more repetitions than the rep range max, the weight is too light.
An example of some exercises that work well in this circuit are: Pushups, goblet squats, ring rows, standing Russian twists, and back extensions. Remember to utilize a rest interval between each exercise, typically 30-60 seconds, or between each set, typically 1-2 minutes.
Micro-intervals are one of the more popular HIIT formats with the Tabata interval being the most well known. The benefit of micro-intervals is that their relatively short duration keeps lactic acid from building up in the blood as rapidly as in other longer interval formats. The Tabata interval is 8 rounds of 20 seconds on, 10 seconds off, but you can use other formats as well.
When using a single movement such as jumping rope or swinging a kettlebell, I like to use a 30 seconds on, 30 seconds off format for 5-10 rounds. As fitness improves, I change that to 45 seconds on, 15 seconds off. You can use these intervals for full body movements, sprints, or calisthenics. Just be sure to limit your reps when using heavier resistance movements.
For the more fit individual, barbell, dumbbell, kettlebell, and sandbag complexes are incredibly useful exercise formats for conditioning and strength. You can allow your rest period to be an untimed "complete recovery" segment if you are trying to focus more on strength or limit it to 1-2 minutes if you want to focus more on conditioning. With the limited recovery times, you will want to use lighter weights.
Complexes are a specific method of circuit training that utilizes a single implement. Typically they involve a series of movements that flow intuitively from one to the next in a logical fashion. Each movement is performed for a designated number of reps until the series of complete.
With an appropriate warm-up, complexes can be a stand-alone workout or serve as a finisher on a short lifting day. Complexes can be rather taxing both from a cardiovascular standpoint and endurance-wise, so be sure that you can handle the workload of the complex itself and any other work you may have planned for the session.
HIIT is a valuable tool, but it does come with some risks and limitations. As a weightlifting and powerlifting coach, I have never seen someone optimize their strength by doing only HIIT workouts. They get stronger with focused strength training. Nor have I ever seen a person dramatically increase their running distances by only doing HIIT workouts. They actually have to work on running farther.
HIIT can help with running faster and having more power, but distance is built on the road. HIIT can help improve one's conditioning, but it does not improve one's sports skills. Ultimately, HIIT should be thought of as a tool that fits into a broader program that addresses strength, endurance, cardiovascular fitness and flexibility.
There are a lot of ways to implement HIIT into your training practice, but remember that it is one of many tools and may not always be the best one. The development of a strength and endurance base using traditional methods is still superior for safety and efficacy in improving one's general fitness and performance. HIIT, if used intelligently, is a great tool for enhancing those developments and keeping workouts fun and interesting.
For a comprehensive look at how HIIT fits into both fitness and endurance training, check out this ISSA CEU course.
Stephen Seiler, E. T. (2009). Intervals, Thresholds, and Long Slow Distance: the Role of Intensity and Duration in Endurance Training. Sports Science, 32-53.
Izumi Tabata, K. I. (1997). Metabolic Profile of High Intensity Intermittent Exercises. Medicine and Science in Sports and Exercise, 390-395.
Kirsten Burgomaster, K. H. (2008). Similar metabolic adaptations during exercise after low volume sprint interval and traditional endurance training in humans. Journal of Physiology, 151-160.
Jasmin Ma, T. S. (2013). Extremely low volume, high-intensity interval training improves exercise capacity and increases mitochondrial protein content in human skeletal muscle. Open Journal of Molecular and Integrative Physiology, 202-210.
Simon Adamson, R. L. (2014). High Intensity Training Improves Health and Physical Function in Middle Aged Adults. Biology, 333-344.
Jonathan P. Little, J. G. (2011). Low-volume high-intensity interval training reduces hyperglycemia and increases muscle mitochondrial capacity in patients with type 2 diabetes. Journal of Applied Physiology, 1554-1560.
Shannon Gray, C. F. (2015). The causes of injuries sustained at fitness facilities presenting to Victorian emergency departments - identifying the main culprits. Injury Epidemiology, 1-8.
Benjamin Weisenthal, C. B. (2014). Injury rate and patterns among crossfit athletes. The Orthopaedic Journal of Sports Medicine, 1-7.
Tamara McLeod, L. D. (2011). National Athletic Trainers' Association Position Statement: Prevention of Pediatric Overuse Injuries. Journal of Athletic Training, 206-220.
Thomas Wyss, L. R.-C. (2014). Impact of training patterns on injury incidences in 12 Swiss army basic military training schools. Military Medicine, 49-55.
Jill Inouye, A. N.-W. (2013). A survey of musculoskeletal injuries associated with Zumba. Hawaii Journal of Medicine and Public Health, 433-436.
Mads Holten, M. Z. (2004). Strength training increases insulin-mediated glucose uptake, GLUT4 content, and insulin signaling in skeletal muscle in patients with type 2 diabetes. Diabetes, 294-305.
Randy Braith, K. S. (2006). Resistance Exercise Training: Its Role in the Prevention of Cardiovascular Disease. Circulation, 2642-2650.
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