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Q: Do you have any thoughts on HIIT’s effect on cancer survivorship versus MICT, or can you reference any researchers working in this area?

A: I believe there are large trials in prostate cancer and breast cancer ongoing with HIIT — I am not sure of all the details regarding inclusion/exclusion and cancer outcomes. Kerry Courneya at the University of Alberta is a leader in Exercise RCTs in cancer. A recent example showing promise of HIIT in prostate cancer from his group can be found here.

Q: Based on the SMARTEX study and the intensity overlap, is intensity between 80-85% of peak heart rate still classified as HIIT?

A: Great question. I don’t think we have a great answer on how to classify HIIT where intervals reach ~80-85% peak heart rate. The data from the 4 X 4-min “Norwegian” HIIT model do suggest that reaching 90-95% is important, but these types of studies comparing intervals that are this “close” in intensity are difficult to conduct. Pragmatically, and from experience, the RPE and subjective experience of intervals reaching 90-95% do feel “harder” than ~80-85%, and likely there are some benefits to going a little harder if that is the goal of your HIIT workout.

Q: %HR is predominantly used to prescribe HIIT, but for patients taking beta blockers, HR may not reach target %HR? Any other strategies to better prescribe HIIT in this population, instead of using heart rate response or RPE?

A: There are some modified peak HR equations in the practical guidelines article from Jenna Taylor and colleagues I discussed in the presentation. RPE is probably the best in this case, but if you are monitoring participants and have access to treadmill speed or ergometer wattage, you could use % of peak workload as another possibility.  

Q: With exercise snacks, how much time do you need to warm up/cool down?

A: Great question. We have used a 2-3 minute warm-up in our published studies but have recently completed a stair-climbing snacks intervention in the workplace with no warm-up (other than walking to the stairwell), and in ongoing studies using whole-body exercise snacks that can be performed at your desk (or anywhere with a little bit of space) we do not incorporate a warm-up in order to make the exercise more time efficient and accessible.  

Q: Can you give a protocol for exercise snacks? How much time between?

A: We don’t know if there is an “optimal” protocol, but our published and ongoing studies use 20-60 seconds of “hard” exercise (at least 4/5 on Borg CR-10 RPE scale) performed as cycling sprints, stair-climbing, bodyweight exercises, etc. performed at least three times per day with at least one hour in between. Pragmatically, I don’t think it matters as long as some minimal dose of “hard” exercise is accumulated. We don’t know what this minimal dose of hard exercise is, but in our studies I suppose it was ~1 minute per day (3 X 20-seconds). I don’t want this to be misconstrued to suggest I am saying that one minute per day is sufficient to achieve all the health benefits of physical activity! Of interest on this “minimal dose” idea, a recent epidemiological study suggests as little as two minutes per day of vigorous “unplanned” activity (i.e., not part of a specific exercise session) was associated with reduced mortality. So I think the dose of vigorous exercise that confers health benefits might be quite small — which makes the exercise snacks approach intriguing!

Q: You might’ve touched on this. Sorry if I missed it. What about the calculation 220-age for HR max?

A: I think this equation works okay on a population basis but certainly is not perfect for an individual. We only use it as a starting point if we don’t have max test information for a participant.  

Q: What is the evidence and outcomes between AIT & a 10 x 1 model?

A: There are a few studies comparing the 4 X 4 AIT “Norwegian” model and the 10 X 1-min low-volume HIIT model. It probably depends on the outcome you are interested in. Some studies report no substantial differences between the two, whereas there is some indication that the improvement in VO2peak might be greater with the 4 X 4 model, and as I mentioned in the presentation, there are more high-quality RCTs in clinical populations using this style of HIIT. I think it makes some sense that the time spent at a very high intensity (e.g., time spent above 90% peak heart rate) is likely greater in the 4 X 4 vs. 10 X 1 HIIT, so if that characteristic of training is important for improving VO2peak then 4 X 4 may be superior for this outcome. The main potential benefit of 10 X 1 HIIT is the lower time commitment — there are really not a lot of studies supporting superiority of this HIIT format compared to standard endurance-oriented training (e.g., MICT) but appears to elicit similar adaptations/responses with less time.

Q: How do you implement exercise snacks in daily life, considering a person’s normal routine (work, study, etc.)?

A: We are currently working on this, but some ideas are to couple exercise snacks with other “habits” or activities that you do each day. For example, couple an exercise snack before/after you (a) brush your teeth, (b) make a coffee, (c) take a coffee break, (d) finish a Zoom meeting at your desk, (e) when you arrive at your office/desk, (f) before you leave your desk/office. We are also working on technology to send push notifications or text messages as reminders at pre-defined times of day according to participant schedules.

Q: Exercise snacks! Can you give an example for adding exercise snacks in daily life?

A: Some of my favorite examples/suggestions are to ascend stairs as fast and safely as possible if you work or have a meeting on a different floor, use the restroom on a higher (or lower) floor and ascend the stairs quickly on your way, or perform 20-30 seconds of jumping jacks, star jumps, or air squats in between Zoom meetings.

Q: In terms of metabolism, is it true that it boosts metabolism up to 24 hours after the session?

A: There are some studies that may show some elevation in resting metabolic rate (what is commonly called “metabolism”) for up to 24 hours after a HIIT session. However, the “extra” calories you would burn is not a lot, and if you compared this to performing a few more minutes of exercise, it would not amount to much. It is my opinion that a boost to metabolism 24 hours after a HIIT session is not a major mechanism for the health or performance benefits of HIIT.  

The views presented here are of the author, and do not necessarily reflect the positions of ACSM.