Latest revision as of 02:41, 21 August 2023

To run HIIT intervals requires a longer stride length, so other modes, such as a stationary bike may be more appropriate.

HIIT can be highly effective training, but involves a risk of injury. HIIT has been shown to improve aerobic capacity in untrained and moderately active individuals more quickly than Continuous Moderate Exercise, as well as having potential benefits for highly trained athletes. HIIT has also been shown to reduce body fat in untrained people more effectively than Continuous Moderate Exercise. However, there is no evidence to suggest that HIIT can replace other forms of training for endurance races. High Intensity Interval Training (HIIT) uses repeated short periods of very intense cardiovascular exercise separated by lower intensity recoveries. (I've found the Stryd estimate of power output is the best approach to gauging effort during HIIT, though Moxy can provide some interesting insight from Muscle Oxygen Saturation.) If you'd like to know more about the science behind HIIT, see The Science of High Intensity Interval Training.

1 What is HIIT?

High Intensity Interval Training is a form of Interval Training using short intervals of 10 seconds to 5 minutes at an intensity at or above 90% V̇O₂max^[1]. High Intensity Interval Training, abbreviated to HIIT or HIT, is sometimes called High-Intensity Intermittent Exercise^[2] or Sprint Training^[3].

2 HIIT Recommendations

Below are my recommendations based on my interpretation of the available evidence. These recommendations for incorporating HIIT in your training depend on your current fitness goals.

• To reduce injury risk, I strongly recommend performing HIIT on a stationary bike trainer rather than running. See "HIIT Training Methods" below for details.
• Ease into HIIT gently, following Safe Speedwork recommendations.
• For sedentary people, HIIT is probably more effective in building initial fitness than Continuous Moderate Exercise. Three sessions per week of Wingate HIIT on a stationary bike should provide an improvement in fitness for a modest time commitment. Using WinTab style HIIT may produce similar benefits for a lower time commitment.
• For people looking to lose weight, HIIT will probably produce a greater reduction in body fat than Continuous Moderate Exercise. Three sessions per week of Wingate HIIT on a stationary bike should help with Weight Loss and appetite control. The HIIT could be combined with other forms of exercise on the other days, which may further improve weight loss. (HIIT probably more effective than Continuous Moderate Exercise at improving insulin sensitivity.)
• Recreationally active people looking for rounded fitness may benefit from including HIIT in their overall training program. Adding 1-3 sessions per week of Wingate or WinTab HIIT on a stationary bike should provide an improvement in fitness.
• Athletes focused on improving their performance in endurance races lasting less than an hour will probably benefit from replacing some of their training load with a combination of both traditional HIIT and shorter Wingate or WinTab style HIIT. Up to one traditional HIIT or 1-3 shorter HIIT sessions could be included in a weekly training routine. Care should be taken to increase Training Load slowly with the additional HIIT and try to avoid increasing Training Monotony. The traditional HIIT should be performed by running on a track or other outdoor location. For the shorter HIIT, a stationary bike probably has a lower injury risk, but the additional benefits of outdoor running may outweigh the additional injury risk. However, the fast paces of the shorter HIIT should be introduced gradually, building up the pace over a number of workouts. See Cycling HIIT For Runners for details.
• There is no direct evidence to indicate if HIIT will help athletes focused on improving their performance in events lasting longer than an hour. However, it seems reasonable that HIIT would provide some benefits. Including 1 or 2 Wingate or WinTab HIIT sessions per week may be appropriate. Using HIIT followed immediately by endurance training may mimic some of the effects of longer training. As noted in the prior bullet point for shorter duration athletes, care should be taken to monitor Training Load and Training Monotony. As with athletes focusing on events lasting less than an hour, the stationary bike has the lowest injury risk, but there may be benefits to other training modes. However, athletes competing in longer duration events typically don't have the same need for the very high paces that are sometimes seen at the end of shorter events.
• There is no evidence to suggest that HIIT can be used to replace Continuous Moderate Exercise such as the Long Run that is a core part of endurance training.
• HIIT can rapidly deplete Glycogen stores, creating the possibility of using HIIT followed by lower intensity endurance training to mimic the effects of a much longer training session.
• While Glycogen stores are restored fairly quickly afterward, it seems like much of that may come from breaking down muscle protein. For the research behind this, see Glycogen Depletion and HIIT. Taking in calories in the form of carbohydrate and protein very soon after HIIT will help prevent muscle loss.
• For "all out" intensities, fewer intervals may be more effective. In my experience, 2 intervals, win the second at a slightly lower resistance (slope on the bike) is optimum for reaching and maintaining the highest workloads.

3 Incorporating HIIT In Your Training Regime

Here are some suggestions for adding HIIT to your training. These are not hard and fast rules, as there is a lot of individual variability.

• HIIT sessions should be considered hard workouts, so don't try to replace easy or rest days with HIIT while leaving your hard training as is.
• If your existing training is not already structured around hard days interspersed with rest days, then HIIT should be distributed through the week and you should take it easier on other days.
• If you are already structuring your workouts around hard days, you should replace a hard workout with HIIT rather than adding to your workload. (Monitoring your Training Monotony may help prevent Overtraining.)
• If you're looking to increase your training load, then HIIT may be an option. I would recommend starting off by replacing a hard workout with HIIT, then adding the original workload back over time. Remember that it can take several weeks for the additional fatigue to manifest itself, as fatigue builds up over a remarkably long time.
• One approach to using HIIT to increase your workload would be to incorporate a HIIT workout with a moderate length long run. There's not much evidence to know the optimum approach, or how this might change the effectiveness of HIIT. It seems likely that the HIIT would create additional fatigue and Glycogen Depletion, which would make the run seem much longer than the distance would suggest. For instance, a 16 mile moderately long run could be replaced by a HIIT and 10 miles. The exact details are going to be quite individual, so experiment based on feeling.
• Another way of increasing your training load via HIIT would be to use the HIIT workout as a second workout on a hard day. This may be of particular value if you're only running 3-4 days per week (as I recommend.)

4 Types of HIIT

There are various different protocols for performing HIIT. While the Tabata is probably the most widely recognized name in HIIT, it is one of the least studied and the least used.

4.1 Tabata

Main article: Tabata

The Tabata workout is one of the best-known protocols for HIIT and consists of 7-8 repeats of 20 seconds at 170% of V̇O₂max with 10 seconds rest. The number of repetitions is defined by how long the required intensity can be maintained. An athlete should be able to complete 7-8 intervals; if 9 can be performed, the intensity is increased. However, few people actually follow the Tabata protocol because it requires specialist equipment to measure V̇O₂max, then calculate 1.7x the V̇O₂max workload that should be used. In practice, most people do what I call the WinTab workout (see below).

4.2 4 x 4 (The Norwegian Method)

Main article: Medium Intensity High Volume Intervals

The original Norwegian Method is to perform four intervals, each of four minutes at 90-95% of maximum heart rate, with 3-minute recoveries, often called "4x4". At first glance this appears to be an odd specification, as it's impossible to immediately increase your heart rate to 90% of maximum, and the original definition^[4] talks about trying to get your heart rate to 90% or above in 60-90 seconds, then adjust the effort to keep your heart rate in range. This approach was refined by a more detailed study^[5] that used a range of 85-95% of max heart rate. In that study, the subjects increased their effort rapidly to 85-100% of the effort for their VO₂max. After their heart rate reached 95% of max, the effort was reduced to keep it in the 85-95% range. What's that mean in practice? Given the details below, you need to estimate your VO₂max, then either work out your pace or power.

• Power. Use the formula "weight in Kg * VO₂max * 0.097". You then start the 4-minute interval at 85-100% of that power.
• Pace. Luckily, it happens that pace in meters/second is roughly the same as power in watts/Kg. So you can use the formula to "VO₂max * 0.097" to estimate your target pace in meters/second, then use an online converter to change that to min/mile or min/Km.

Dropping your effort as the interval progresses may result in a surprisingly large reduction, with the study showing that that most intervals ended at about 60% of the initial power. The study also showed that the second through fourth interval had a lower initial power requirement, roughly 10-15% lower than the first interval. Remember, you can estimate your VO₂max from a race performance using a Running Calculator. (Note that the more recent versions of the Norwegian Method use Medium Intensity High Volume Intervals.)

4.2.1 4x4 Conversion Details

The study had athletes with average VO₂max of 37, average weight of 72 Kg, and average peak power output of 260w, which is 3.6 w/Kg. A Stryd based study^[6] showed that there's a linear relationship between VO₂max and peak power. (Peak power at VO₂max varies with protocol). For this study, the peak power in w/Kg is VO₂max * 0.097.

4.2.2 4x4 Effort Worked Example

Assume your VO₂max is 53 and your weight is 60, then the initial target power is 53 * 0.097 * 60 = 309 watts. So the target range would be 260-309w at the start of the interval. Alternatively, the required pace is 0.097 * 60 = 5.14 meters/second, so the range is 4.37 to 5.14 m/s. That converts to 3:49-3:14 min/Km or 6:08-5:13 min/mile. The power or pace is then dropped to keep your heart rate below 95% max.

4.3 Wingate

This style of HIIT is based around the Wingate test, which is used to measure peak anaerobic power and anaerobic capacity^[7].

4.3.1 The Wingate Test

The Wingate Test typically uses a warmup of 10 minutes easy cycling, followed by 2-3x 15 second sprints to get used to the speed. Then the test is normally 30 seconds all out sprinting, though some researchers use a longer period of 40-120 seconds.

4.3.2 The Test on a Smart Trainer

The test is performed on a mechanically braked cycle ergometer, often a Monarch model. This makes converting the settings to a smart trainer tricky. The Monarch uses a weight to provide the resistance, and the Wingate Test uses 7.5% of your body weight. The formula for working out Watts for the Monarch is the resistance in Kg multiplied by the cadence. So, if you weigh 60 Kg, 7.5% is 4.5Kg, and at a cadence of 80 rpm is 360 watts. Setting your smart trainer's resistance so you get about 360 watts at 80 rpm is a good starting point for the test.

4.3.3 The Wingate as HIIT

The Wingate HIIT uses 30 seconds of 'all out' intensity, followed by ~4 minutes of recovery, repeated 4-6 times. A similar warmup procedure as the test seems reasonable, with 10 minutes easy, then 2-3x 15 second sprints.

4.4 WinTab (Tabata style Wingate)

Most athletes that use the Tabata workout do not use the 170% V̇O₂max intensity, but rather the Wingate style 'all out' intensity. Because the intensity is not fixed, the WinTab normally has 8 repetitions of 20 seconds all out plus 10 seconds rest, taking 4 minutes (plus Warmup), rather than the variable number of repetitions of the original Tabata protocol.

4.5 HillTab

Because the WinTab workout involves such fast paces, it can easily lead to injury as the stride length requires a greater range of motion than more common paces. You can reduce the pace while maintaining the intensity by running up hill, something I call HillTab (Hill Tabata). While similar to the WinTab in some ways, this workout has a variable length recovery, as you have to run down the hill after each time, and it uses different muscle groups. To perform a HillTab, find a hill that is moderately steep; about 10-12% gradient works well. Find a marker to use as the start point, such as a suitable tree or rock, then find an initial finish marker that is about 45 seconds up the path. You'll adjust the finish marker so that it takes about 30 seconds to cover the distance at your fastest speed. This will take a bit of trial and error, but don't worry if the first few intervals are too long or too short. You could use an audible timer, but I prefer a visible marker to aim for. If you want to time each interval, have a watch in your hand, held so you can press the lap button without fumbling. For each interval:

1. Approach the start marker at an easy pace.
2. A few yards/meters from the start, shorten your stride and increase your Cadence. Your stride will be quite short at this point.
3. As you approach the start marker, lean forward so that your weight feels over the balls of your feet and toes.
4. When you cross the start marker accelerate hard, grabbing the ground with each stride and propelling yourself forward. You'll accelerate to your maximum velocity within a handful of strides, and you'll probably be acutely aware of each footstep as the adrenaline seems to slow time. For the first few intervals this phase often has a wonderful sense of euphoria and power.
5. Try to hold on to this pace to the end marker, which may seem to grow further away. Your legs will grow weak and distant as the lack of oxygen causes your vision to fade to gray.
6. By the time your reach the end, just 30 seconds later, your lungs are starting to burn and the ecstasy you felt just moments ago has turned to desolation.
7. Slow up carefully after the end marker. Do not let your form collapse or your feet slap the ground.
8. When your pace has dropped, turn around and descend. You may find your lungs burn more after the interval than before as you start to recover.
9. Run past the start marker, turn and repeat for a total of 8 intervals.

For HIIT, I suspect that the hard acceleration is a key to the benefits of the workout. The acceleration achieves high levels of muscle activation, mimicking the effects of Plyometrics. (There advantages to Downhill Running, but the risk of injury while running at HIIT pace downhill are much higher.)

4.6 Traditional Anaerobic Intervals

High intensity Interval Training has been in use since before the Tabata study made the term popular. The Jack Daniel's 'R' paced workouts are a classic example of this tradition of anaerobic interval training. The Jack Daniel's 'R' intervals are performed at around mile/1500m pace^[8], which is generally close to 100% V̇O₂max. The 'R' workouts are 12-40 repeats of 30-60 seconds with 1-4 min rests^[9]. Jack Daniels mentions once having his athletes perform over 1,000 repetitions of one-minute HIIT (4-minute rest) in a 14-day period, with two male athletes averaging 5:00 min/mile pace and therefore covering 250 miles^[9].

5 Fellrnr's Tabata Audio

I created a short audio file for my Tabata (WinTab), adding a countdown and interval counts. I started with Darude's Sandstorm, remixed it to 180 BPM and then extracted short snippets. I then recombined the snippets with voice countdowns so that I didn't need to look at a watch or timer to execute the workout. You can download or play the MP3 file of Fellrnr's Tabata. (I believe that I'm making fair use of Darude's work, given I am only using a short section of the original and modifying it heavily. If you want to enjoy the overall song, this MP3 file is not it!)

6 HIIT Training Methods

There are various ways that HIIT could be performed, each with their own pros and cons. As this site is dedicated to running, my assumption is that you're a runner primarily. If that's not the case, then you'll have to interpret the pros and cons slightly differently.

7 HIIT Running Paces

I don't generally recommend running HIIT workouts because of the high speeds required. Below is a sampling of the HIIT paces for different fitness levels (V̇O₂max). For each level, the 5K and marathon times are given, along with the pace that corresponds to 90%, 100% and 170% of V̇O₂max.

8 HIIT and Stryd

The Stryd footpod gives an extremely accurate measure of pace and incline, and from this it calculates an estimate of your power output in Watts. This power estimate responds much faster than Heart Rate, which is pretty useless for evaluating a HIIT session.

A graph of Heart Rate against Stryd power estimate for a HIIT session.

9 The HIIT Science

For details of the science around HIIT, see The Science of High Intensity Interval Training.

10 Crossfit Endurance

Crossfit Endurance is a training approach that reduces the normal endurance training volumes while increasing the training intensity^[10]. The reduction in volume is quite dramatic compared with other training plans; for instance, the Crossfit Endurance marathon training plan has a 10 mile time trial as its longest run, which is combined with weight training and interval training^[11]. Crossfit Endurance claims that eight 100 meter intervals "accomplishes everything you would by jogging 20 miles but doesn't put the same level of stress and damage on the body." There is the caveat that "some kind of stamina work that lost more than the 70 seconds is required to "dial in technique, just rhythm, and formulate pace strategy." While there are some testimonials to the Crossfit Endurance methodology^[12], their approach is controversial^[13]. The science that is used to support Crossfit Endurance does not support replacing traditional Continuous Moderate Exercise with HIIT for endurance events, only using HIIT as a supplementary form of training^[14]. Most of the anecdotal reports suggest that people have set personal records at 5K and 10K distances and completed half marathons using the Crossfit Endurance approach, but there are few reports of longer races. The anecdotal reports are hard to interpret objectively without knowing the individuals prior training methodology. (I have some other concerns with CrossFit, such as their emphasis on forefoot landing, then approach to hydration that includes the overly simplistic "sweat rate test", but that's outside of the scope of this article that focuses on interval training.)

11 References

1. ↑ Stephen H. Boutcher, High-Intensity Intermittent Exercise and Fat Loss, Journal of Obesity, volume 2011, 2011, pages 1–10, ISSN 2090-0708, doi 10.1155/2011/868305
2. ↑ EG. Trapp, DJ. Chisholm, J. Freund, SH. Boutcher, The effects of high-intensity intermittent exercise training on fat loss and fasting insulin levels of young women., Int J Obes (Lond), volume 32, issue 4, pages 684-91, Apr 2008, doi 10.1038/sj.ijo.0803781, PMID 18197184
3. ↑ MJ. Gibala, JP. Little, M. van Essen, GP. Wilkin, KA. Burgomaster, A. Safdar, S. Raha, MA. Tarnopolsky, Short-term sprint interval versus traditional endurance training: similar initial adaptations in human skeletal muscle and exercise performance., J Physiol, volume 575, issue Pt 3, pages 901-11, Sep 2006, doi 10.1113/jphysiol.2006.112094, PMID 16825308
4. ↑ J. Helgerud, K. Høydal, E. Wang, T. Karlsen, P. Berg, M. Bjerkaas, T. Simonsen, C. Helgesen, N. Hjorth, Aerobic high-intensity intervals improve VO2max more than moderate training., Med Sci Sports Exerc, 39 !!V̇olume!!, issue 4, pages 665-71, Apr 2007, doi 10.1249/mss.0b013e3180304570, PMID 17414804
5. ↑ Justin J. Acala, Devyn Roche-Willis, Todd A. Astorino, Characterizing the Heart Rate Response to the 4 × 4 Interval Exercise Protocol, International Journal of Environmental Research and Public Health, publisher MDPI AG, volume 17, issue 14, date 2020-07-15, ISSN 1660-4601, doi 10.3390/ijerph17145103, page 5103
6. ↑ https://blog.stryd.com/2019/12/06/how-to-use-stryd-power-to-calculate-your-vo2/, How to use Stryd power to calculate your VO2, Accessed on 2023-08-21
7. ↑ H. Vandewalle, G. Pérès, H. Monod, Standard anaerobic exercise tests., Sports Med, volume 4, issue 4, pages 268-89, PMID 3306867
8. ↑ Jack Daniels, Daniels' running formula, date 2005, publisher Human Kinetics, location Champaign, IL, isbn 0-7360-5492-8
9. ↑ ^{9.0 9.1} Jack Daniels, Daniels' running formula, date 2005, publisher Human Kinetics, location Champaign, IL, isbn 0-7360-5492-8, pages 132
10. ↑ About Crossfit Endurance, http://www.crossfitendurance.com/whatiscfe, Accessed on 26 February 2013
11. ↑ http://www.outsideonline.com/fitness/endurance-training/CrossFit-Endurances-Unconventional-12-Week-Marathon-Training-Plan.html, http://www.outsideonline.com/fitness/endurance-training/CrossFit-Endurances-Unconventional-12-Week-Marathon-Training-Plan.html, Accessed on 26 February 2013
12. ↑ Testimonials, http://www.crossfitendurance.com/testimonials, Accessed on 26 February 2013
13. ↑ Science of Running: Crossfit endurance, Tabata sprints, and why people just don’t get it, http://www.scienceofrunning.com/2012/01/crossfit-endurance-tabata-sprints-and.html, Accessed on 26 February 2013
14. ↑ CrossFit MPH - Washington, DC, http://metamorphitness.wordpress.com/nutrition-enrichment/running-faqs/is-there-any-science-to-support-crossfit-endurance/, Accessed on 26 February 2013