How to Deliver a Fit HIIT to Your Pool

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High Intensity Interval Training is making waves because it gets results!

HIIT is an acronym for High Intensity Interval Training. The basic definition is pretty simple: “an intense phase of exercise followed by a period of recovery,” according to one Exercise Scientist. Cycle those “phases,” or intervals, into a short workout, and you’re doing HIIT!

HIIT workouts have been dominant for years. In 2014, they topped the list of the hottest fitness trends, according to the American College of Sports Medicine’s annual survey. They’re remained one of the top 5 trends every year since, including 2019. The reason: they work.


High Intensity Interval Training can deliver a host of health benefits. A significant body of research confirms HIIT’s effectiveness to:

Burn More Calories: Two published studies found that HIIT burns more calories in the same amount of time than other types of exercise. The research was performed at California State University, San Marcos, and University of Colorado, Denver, respectively.

And then Burn Some More: After finishing a HIIT workout, the body continues to burn more calories than other exercise formats … even when you’re resting! This metabolic boost from HIIT has been documented in multiple published studies from sports scientists in Singapore, Ontario, and Chapel Hill.

Burn Fat: After 12 weeks, adults had “significant reductions in abdominal fat” from HIIT workouts with no change in diet. The workouts took 20 minutes each, three times a week. The study documented a 17% decrease in visceral fat, the kind that surrounds internal organs and has been linked to many diseases. Other studies confirm that HIIT promotes fat loss with a surprisingly low time commitment.

Lower Blood Pressure: Overweight and obese people can lower their blood pressure with HIIT workouts – that’s according to a review of 65 published studies.

Release More Endorphins: They’re the hormones that kill pain and give us a natural high. When you engage in HIIT workouts, your body naturally releases more of them than when you do moderate exercise, according to a 2017 article in the journal Neuropsychopharmacology (say that three times fast!).


Of course, a HITT workout should be intense … within your personal limits. The goal is to build fitness as well as confidence. You should feel invigorated after a HIIT workout, not defeated.

If you’re new to HIIT, start slowly. Just add a few 15 or 30-second higher-intensity intervals to your existing cardio workout. Maybe your “higher” is someone else’s “moderate”; that’s fine. As you build your confidence and fitness level, you can add more intervals, raise the intensity, or reduce the length of the low-intensity/walking interval.

And keep it short; experts consistently recommend that HIIT workouts last 30-minutes or less, just two or three times a week at most; the intensity of these workouts can put you at risk of overuse injuries. With HIIT, a little goes a long way.


You can do HIIT Workouts with our swim current or Underwater Treadmill. The Endless Pools® Fit@Home app lets you program the pace of the current and treadmill; you can create HIIT workouts like the two listed below and save them for continued convenience.

The app works to control any Original Endless Pool, Endless Pools swim spa, or Endless Pools Hydrostride/Underwater Treadmill. WiFi-compatibility is required and can be added to new or existing models.


You might want to get started with a HIIT workout that’s as simple as:

  • 30 seconds walking + 30 seconds sprinting x 10 cycles = a 10-minute HIIT workout

If you have a higher fitness level, you could consider a more advanced HIIT workout:

  • Warm up: 9 minutes of brisk walking at 2 mph
  • 1 minute of running at 4.5 to 5 mph + 2 minutes of walking at 2.5 to 3 mph x 7 cycles

Including the warm-up, that’s a 30-minute HIIT workout. These suggested speeds are based on an Underwater Treadmill, where the water’s 360-degree resistance means that you can get a more vigorous workout at a lower speed than on dry land.

Before you take up any new exercise program, you should always check with your doctor. Aquatic exercise is low-impact, and many doctors and physical therapists recommend aquatic activity for seniors and even for patients recovering from surgery. HIIT workouts are more challenging, so listen to your body, and back off if need be.


Interval-based exercise: So many names, so many possibilities. Marcus Kilpatrick, Oct 26, 2017.


J Strength Cond Res. 2015 Mar;29(3):779-85. doi: 10.1519/JSC.0000000000000661. Caloric expenditure of aerobic, resistance, or combined high-intensity interval training using a hydraulic resistance system in healthy men. Falcone PH1, Tai CY, Carson LR, Joy JM, Mosman MM, McCann TR, Crona KP, Kim MP, Moon JR.

J Strength Cond Res. 2016 Jan;30(1):244-50. doi: 10.1519/JSC.0000000000001042. Dissimilar Physiological and Perceptual Responses Between Sprint Interval Training and High-Intensity Interval Training. Wood KM1, Olive B, LaValle K, Thompson H, Greer K, Astorino TA.

Sports Med Open. 2015 Dec;1(1):11. Epub 2015 Jun 5. The acute effect of exercise modality and nutrition manipulations on post-exercise resting energy expenditure and respiratory exchange ratio in women: a randomized trial. Wingfield HL1, Smith-Ryan AE2, Melvin MN1, Roelofs EJ1, Trexler ET1, Hackney AC1,3, Weaver MA4, Ryan ED1.

Appl Physiol Nutr Metab. 2014 Jul;39(7):845-8. doi: 10.1139/apnm-2013-0562. Epub 2014 Feb 6. High-intensity interval exercise induces 24-h energy expenditure similar to traditional endurance exercise despite reduced time commitment. Skelly LE1, Andrews PC, Gillen JB, Martin BJ, Percival ME, Gibala MJ.

British Journal of Sports Medicine 2017;51:494-503. Effects of high-intensity interval training on cardiometabolic health: a systematic review and meta-analysis of intervention studies. Batacan RB, Duncan MJ, Dalbo VJ, et al

Appl Physiol Nutr Metab. 2013 Feb;38(2):182-7. doi: 10.1139/apnm-2012-0136. Epub 2013 Feb 8. Oxygen consumption, substrate oxidation, and blood pressure following sprint interval exercise. Chan HH1, Burns SF.

J Obes. 2012;2012:480467. doi: 10.1155/2012/480467. Epub 2012 Jun 6. The effect of high-intensity intermittent exercise on body composition of overweight young males. Heydari M1, Freund J, Boutcher SH.

J Sports Med Phys Fitness. 2012 Jun;52(3):255-62. High intensity interval exercise training in overweight young women. Sijie T1, Hainai Y, Fengying Y, Jianxiong W.

Horm Mol Biol Clin Investig. 2015 Mar;21(3):165-73. doi: 10.1515/hmbci-2014-0038. The effects of short-term high-intensity interval training vs. moderate-intensity continuous training on plasma levels of nesfatin-1 and inflammatory markers. Ahmadizad S, Avansar AS, Ebrahim K, Avandi M, Ghasemikaram M.

PLoS One. 2015 Oct 21;10(10):e0138853. doi: 10.1371/journal.pone.0138853. eCollection 2015. High Intensity Interval- vs Moderate Intensity- Training for Improving Cardiometabolic Health in Overweight or Obese Males: A Randomized Controlled Trial. Fisher G, Brown AW, Bohan Brown MM, Alcorn A, Noles C, Winwood L, Resuehr H, George B, Jeansonne MM, Allison DB.

Neuropsychopharmacology v.43, p. 246–254 (2018) Opioid Release after High-Intensity Interval Training in Healthy Human Subjects. Tiina Saanijoki, Lauri Tuominen, Jetro J Tuulari, Lauri Nummenmaa, Eveliina Arponen, Kari Kalliokoski, Jussi Hirvonen