5 questions with Abbie Smith-Ryan, Ph.D. about HIIT training


Abbie, you’ve been a phenom with regard to obtaining grant funding and publishing, and one of your laboratory’s main focuses is high intensity interval training (or HIIT), so let’s hiit it (pun intended):

Q1: Could you briefly describe HIIT, and is there a “right” way to do it?

High intensity interval training is essentially repeated bouts of high-intensity work (i.e. above lactate threshold or >80% max) interspersed by periods of low-intensity exercise or complete rest.  I like to think of it as increasing your heart rate to a level you couldn’t sustain for a long period of time (i.e. 30 sec-4 min), rest briefly, bringing heart rate back up before you’re ready to go again. 

A few key elements of how to do it ‘right’ is really making sure the intensity is high enough. To see all of the reported benefits, intensity must be high.  I also always say, if someone is doing true HIIT more than 3-4 times per week or for more than 30 minutes, they are likely not doing it correctly.  

Q2: What seems to be great about HIIT is that someone can experience the same benefits of cardiovascular exercise in a fraction of the time.  Can you explain some of these training adaptations?  

Exactly!  The benefits from HIIT match traditional aerobic training, but can occur in a quarter of the time (i.e. 2 weeks vs. 10-12 weeks).  Key improvements result in aerobic fitness, mitochondrial density—which helps with glycogen sparing and improvements in fat utilization, as well as improvements in insulin sensitivity. There also appear to be positive effects on fat storage, with HIIT preferentially reducing visceral fat. Lastly, HIIT has recently been shown to stimulate an increase in muscle mass (which is not shown in traditional aerobic exercise).  

Q3: A misnomer about exercise in general is that it’s “risky” for folks that have chronic diseases (e.g., obesity and/or hypertension). Relating that perceived risk to HIIT, most folks would think it’s crazy to put someone with these chronic diseases through HIIT training. Is this a perceived or real risk? 

Absolutely not. Since the intensity of each work bout is relative to each individual, it is very feasible and effective for a number of clinical populations. My lab specifically has demonstrated it to be effective and safe among obese, cancer, cardiovascular disease, and knee osteoarthritis populations. Due to the low volume of exercise, it actually may be safer than traditional lower intensity, higher volume aerobic exercise. 

Q4: You recently gave a phenomenal lecture at Dr. Marcas Bamman’s Exercise is Medicine Conference on HIIT.  Another perception, again, is that people dread doing HIIT, and would rather jog at low exercise intensities for a long time.  Based on your research is this true?

Thank you. Based on our data and others, enjoyment levels for HIIT are actually very high.  They do tend to increase with more training, and are also higher in those that are more fit, but I’ve found that once you teach someone what hard exercise feels like, they truly enjoy it, and keep coming back.  Part of this may also be due to the quick adaptations—they may feel the fitness changes more quickly.

Q5: What are some future research areas that have been untapped with regard to HIIT? 

Broadly, there is unique potential for the implications of HIIT on muscle protein synthesis and neuromuscular function that have yet to be explored.  There is some debate on sex-based responses which need to be evaluated, and lastly, I think HIIT has the potential to be an impactful therapeutic approach to medicine, but pragmatic clinical trials evaluating this are needed. 

Thanks so much for your time and expertise, Dr. Smith-Ryan.

Abbie Smith-Ryan, Ph.D. is an Associate Professor in the Department of Exercise and Sports Science at the University of North Carolina-Chapel Hill.

To find out more about Smith-Ryan’s research, check out:

Twitter: @asmithryan

Website: UNC Applied Physiology Laboratory

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