High Intensity Interval Training

More and more research continues to emerge supporting the benefits of performing low-volume exercise at 85-100% of calculated max HR. This style of workout once reserved for track athletes and ball sport athletes is now quickly becoming a trend in fitness communities and rehab settings alike.

High-intensity intervals are becoming a strongly validated clinical approach to treating some complex medical conditions. Everything from Parkinson's Disease, Dementia, Type 2 Diabetes, Heart Failure, and Osteoporosis have been shown to benefit from this low volume training. It should come as no surprise that this workout method is rising in popularity among the populous. 

I'm Dr. Allan Buccola, physical therapist and owner of Impetus PT in Greensboro, NC. In this post, I'll discuss some recent discoveries about the benefits of high intensity interval training (HIIT). This post is intended to serve as an educational tool only, but definitely not medical advice. I have not personally examined you and therefore cannot make specific recommendations for you: HIIT may not be safe for everyone!

What is High Intensity Interval Training (HIIT)?

High intensity interval training is a style of workout that can be applied to almost any activity you already consider 'aerobic' exercise. Whereas typical cardio exercise is usually performed at moderate efforts for prolonged intervals (25-50 minutes), HIIT workouts are shorter, with frequent breaks between efforts. 

A typical HIIT workout includes the repetition of short bursts of near maximal aerobic capacity exercise. To be done correctly, you'll probably need a calculator and a heart rate monitor. The targeted intensity should be between 85-100% of your aerobic capacity, but should still be below your maximal effort. Those who confuse these are on course for injury. 

How Many Intervals?

Depending on the person and the training goals, the number of intervals can vary from 3-10. High level athletes who perform these regularly may perform substantially more repeats and do so with specific training adaptations in mind. Their bodies are better conditioned to withstand such levels of stress. The number of repeats is often defined by the length of the total workout time, especially in fitness settings: in other words, these are often billed as 'express' workouts for those short on time. 

How Long Should the Intervals Be? 

The duration of the interval is also variable, but should always be balanced with the intensity level. Intervals 20-30 seconds long should be at a higher intensity than intervals lasting 2 minutes. A loss of balance in this equations will ultimately result in either wasted time or injury.

Sport-specific HIIT may include only one type of activity. For runners, you will see workouts vary from 10x100m, 6x800m, or even 4x1-mile, each serving a different physiological purpose. Generalized fitness versions may combine lots of different activities back-to-back. These may make more sense for generalized wellness and lower injury rates.  

What to do between Intervals?

The off or rest period between intervals, can also vary in both activity and time. The rest interval' is often performed at moderate efforts, walking or slow jogging, but an all-out cessation of activity is rare and strongly discouraged. Completely stopping between intense efforts can put dangerous stress on the heart. 

Performance of HIIT can be stressful on the body, even in trained athletes, and should be limited to 1 or 2 times each week to avoid injury. That being said, these can be performed in a variety of ways, including everything from running, stationary bike, jump rope, burpees, or rowing. The fitness gains will be similar. This is the beauty of cross-training: continued development of cardiovascular fitness, while muscles and tendons have a chance to rest.  

Sprint intervals don't mean being confined to the track.

Sprint intervals don't mean being confined to the track.

What are the benefits of high intensity intervals? 

Is High Intensity Interval Training Better for weight loss?

This is a hot topic in the fitness world. There are many 'expert' claims about the ability of HIIT to improve fat burning capacity or weight loss. Research has certainly asked this question quite a bit, as it turns out, and the answer in short is no: it is not 'better' for weight loss. 

This isn't necessarily bad news though. High intensity intervals were shown to be equally effective for weight loss as moderate intensity prolonged activity. This is actually really interesting, because the data support the notion that those short workouts at the gym are just as effective as the longer ones you used to have time for. 

A recent literature review tackled this topic in June 2017. It found that even though a reduction between body fat and waist circumference were near equal between these two workout groups, the HIIT group requires a 44% less time commitment. Interestingly, it also demonstrated that running-based protocols showed significant reductions in total body fat, whereas cycling-based protocols did not. 

VO2 Max, Aerobic Capacity in runners and cyclists

When performing HIIT with intent to improve aerobic capacity of the body, or VO2 max, intervals should be no shorter than 60 seconds to fully involve the aerobic physiological system. Efforts shorter than this are predominantly anaerobic and/or glycolytic in nature, and the greatest adaptations will be made toward shorter effort performance.

Two-minute intervals are an ideal length of time for development of the 13.1 or half marathon distance, and up to 4-minute intervals will place maximal effort on the development of the aerobic capacity for the marathon distance and beyond. Even though some evidence shows that shorter intervals are best at improving VO2 max, longer intervals may in fact be better at improving blood volume and hemoglobin levels. 

When it comes to development of aerobic fitness, there is strong evidence to suggest that although there is some personal variation, there is a fairly specific range of effort that best stimulates aerobic fitness development. Interval work that keeps an individual at a pace that is 80-90% of VO2 max, or roughly 90-95% max calculated heart rate provides the strongest stimulus.

Intensities greater than that have shown to not be nearly as effective. Even if you ultimately decide to partake in longer races, start with shorter timed intervals and gradually work your way up over the course of a few weeks. This allows time for your body to acclimate to these new stress levels gradually without increasing injury risk. 

High Intensity Exercise and chronic brain diseases

Fascinating research has emerged in the last 5-10 years on how HIIT may become one of the core interventions for patients with chronic brain diseases. In one paper, researchers concluded that such interventions improved all symptoms associated with Parkinson's Disease with exception to tremor, improving balance impairments, walking speed, walking quality, and fear of falling.

A study from 2015 assessed the ability of high-intensity training to help those with multiple sclerosis, a population typically unable to participate in such activities for fear of exacerbating symptoms. HIIT in this population resulted in higher mass of endurance muscle fibers, improvements in aerobic capacity, decreases in body fat, and increases in self reported physical activity.

Another study from March 2016 implies that HIIT may also improve levels of brain derived neurotrophic factor (BDNF), a protein critical for neuron growth and healing. I have had a chance to personally use HIIT with these populations clinically and watched it help make rapid changes in daily mobility. It should be noted that these individuals should perform HIIT under close medical supervision only, as they are more at risk of falling or sustaining other serious medical complications. 

HIIT can often involve weights and full body exercise. 

HIIT can often involve weights and full body exercise. 

Lifestyle induced metabolic disease: obesity, hypertension, & diabetes

A lit review of 10 studies looked at the effects of HIIT on the wellness of people in this population. Participants in these studies had diagnosed coronary artery disease, hypertension, morbid obesity, and/or heart failure. The use of HIIT was found to be superior (nearly double) in improving cardiovascular fitness in this population, when compared to moderate intensity continuous training.

A 2015 study, comparing HIIT with moderate-intensity continuous training in adults with pre-diabetes, found that the HIIT group had higher rates of compliance over the course of 4 weeks. Other studies have revealed HIIT to lead to softening of central arteries and improvements in whole body insulin sensitivity. A 2012 study comparing HIIT with moderate-intensity continuous training in college-aged obese females, found HIIT to be superior in improving both cardiovascular fitness and decreases in body fat percentage.   

concluding thoughts

All in all, it's becoming clear that high intensity intervals are the way to go when it comes to improving wellness, fitness, or function. Lines continue to be drawn between the important role of cardiovascular fitness and overall wellness. We all know the importance of regular exercise, but now we can possibly work it in more easily. 

I continue to personally enjoy these workouts for a couple of reasons. Firstly, they add some much needed variety to my typical week of hours of running at moderate intensities. Secondly, I know that I can get a solid workout if my hectic daily schedule limits my day is limited. 

I hope that this post has universal appeal for all. Whether you are an aspiring runner or cyclist preparing for the next personal record, or a someone simply trying to prepare for a big hiking trip this summer. If you're a person who has been struggling to get your health and habit in order, or just trying to find a way to fit a couple of workouts into the week, HIIT might be the answer.

High intensity intervals can be adapted to almost any equipment or person. As a father of two, I can assert that this appears to be the innate, preferred method of play for little ones. My kids will continuously sprint until hands-on-knees, out of breath, for hours on end. Ask a small one to run at a moderate pace for a prolonged period and they quickly lose interest. 

I am also reminded of playing fetch with the Ruby, my dog. Short explosive bursts with trotting and panting between. Even the most recent evidence on some of the benefit of CrossFit in development of fitness postulate the involvement of high intensity based activities, the latest version of circuit training.   

Consider how you might work this type of training into your regimen and see if it makes a difference in your performance or quality of life. If you have a complicated medical history, please seek consult from a PT or physician before attempting any of these workouts: safety must always take precedent.

Thanks for reading, and please contact me directly with any questions.

Until next time: don't stop moving! 


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Here's a fun video to give a different spin on the topic. Enjoy!