Monday, May 18, 2015

Study Offers New Insights into the Effect of Interval Length & Intensity on the Metabolic Effects of HIIT - 16x1 at 95% or 4x4 at 90%? What is Right for You and Your Goals?

While tire (or sled) pulling can be effective and motivating, I would suggest you start with the basics. Good running shoes and a soft surface like grass or a tartan track are all it takes to do 4x4 or 16x1 sprints. If you get bored or feel that you don't make further progress you can still start to pull tires, sleds or tractors ;-)
Wesley J. Tucker, Brandon J. Sawyer Catherine L. Jarrett, Dharini M. Bhammar, and Glenn A. Gaesser from the Arizona State and Point Loma Nazarene Universities, the Texas Health Presbyterian Hospital Dallas and UT Southwestern Medical Center Dallas have recently conducted an experiment to compare the VO2, HR, and blood lactate responses during two commonly used HIIT protocols - the 4x4, or “Norwegian” HIE protocol, which consists of four, 4-minute intervals at 90-95% of peak heart rate (HRpeak), interspersed and its "quick fix" alternative with ten, 1-minute high-intensity intervals at 95% of the HRmax with 60-75 seconds of active recovery.

In order to equate the two protocols for total amount of active interval duration, Tucker et al. used a 16x1 protocol to compare with the 4x4 protocol. Secondarily, we also assessed ratings of perceived exertion (RPE) and enjoyment of each protocol with the physical activity enjoyment scale.
You can learn more about HIIT at the SuppVersity

Never Train To Burn Calories!

Tabata = 14.2kcal /min ≠ Fat Loss

30s Intervals + 2:1 Work/Rec.

Making HIIT a Hit Part I/II

Making HIIT a Hit Part II/II

HIIT Ain't For Everyone
In that, the researchers hypothesized that the two protocols would elicit similar VO2 and blood lactate responses, and similar values for RPE and PACES, because they used the same target HR range (90-95% HRpeak) for each protocol, and adjusted power output continuously in order maintain HR in the desired range.
Figure 1: Graphical overview of the exercise protocol (Tucker. 2015).
On separate days, 14 recreationally active males performed the previously mentioned 4x4 (four, 4-minute intervals at 90-95% HRpeak, separated by 3 minutes recovery at 50 W), and 16x1 (16, 1-minute intervals at 90-95% HRpeak, separated by 1 minute recovery at 50 W) protocol on a cycle ergometer.
Five Good Reasons Why At Least 50% of Your 2015 'Cardio' Training Should Be High Intensity Interval Training (HIIT) | read the full article.
This is what works for me: I am a science guy, so I am always open to put the results of scientific research into practice, but practice has taught me that I am not the average subject of study X, which is why the things that works for this "virtual guy or gal" must not necessarily work for me. It is thus not surprising that I've found that speed, not resistance is what makes my HIIT workouts (a) worthwhile and (b) productive. This does also imply that crosstrainers are a no-go for my HIIT sessions, because going really fast is virtually impossible on these devices. If you want to bring your heart rate up, you would have to increase the resistance. This, however, tends to burn me out and makes my HIIT workouts counterproductive.

So, my suggestion for you is: "Go fast not hard, but if you feel that this doesn't work for you, don't be a fool and stick to something that works for me, yet not for you!"
As the data in Figure 2 indicates, the 4x4 protocol elicited a higher mean VO2 (2.44 ± 0.4 vs. 2.36 ± 0.4 L·min-1) and “peak” VO2 (90-99% vs. 76-85% VO2peak) and HR (95-98% HRpeak vs. 81-95% HRpeak) during the high-intensity intervals. Average power maintained was higher for the 16x1 (241 ± 45 vs. 204 ± 37 W), and recovery interval VO2 and HR were higher during the 16x1.
Figure 2: Comparison of the relevant parameters | values expressed relative to inter-group means (Tucker. 2015)
In contrast, no differences were observed for blood lactate concentrations at the midpoint (12.1 ± 2.2 vs. 10.8 ± 3.1 mmol·L-1) and end (10.6 ± 1.5 vs. 10.6 ± 2.4 mmol·L-1) of the protocols, or ratings of perceived exertion (RPE; 7.0 ± 1.6 vs. 7.0 ± 1.4) and physical activity enjoyment scale scores (PACES: 91 ± 15 vs. 93 ± 12). Furthermore, the mean HR during each protocol was the same, and both protocols were rated similarly for perceived exertion and enjoyment, despite the 4-fold difference in interval duration that produced greater between-interval transitions in VO2 and HR, and slightly higher mean VO2 during the 4x4.
The stop watch is your friend, when it comes to HIIT optimization. Learn more in the "Making HIIT a Hit" Series at the SuppVersity - "Training Optimization? Where Do I Start? Theoretical Considerations & 10 Rules of Thumb" | read more.
So what do I do? In view of the fact that the 4x4 protocol yielded higher heart rates at identical workloads, the latter appear to be preferable for (endurance-)athletes who are trying to improve their physical fitness. The shorter and "lighter" 1 minute sprints, on the other hand, may be the better choice for people who do their HIIT exercise mainly to maintain their current fitness level and shed some body fat.

Still, if you belong to the last-mentioned group, I would still suggest you try both and pick the exercise format that suits you best. After all, being able to stick to your regimen is significantly more important for long-term success than the potentially higher rate of fatty acid to carbohydrate oxidation on the "short" 1-minute intervals | Comment on Facebook!
  • Tucker, et al. "Physiological Responses to High-Intensity Interval Exercise Differing in Interval Duration." Journal of Strength and Conditioning Research (2015): Publish Ahead of Print.