HIIT or LISS - A Question of Efficacy? High Intensity Interval Training Kickstarts Fatty Acid Oxidation & Metabolism to Make Up for the Higher Energy Exp. During LISS in 24h

If you ever wondered why you're huffing and puffing for hours after your HIIT sessions, here is the answer!

Your oxygen consumption can be used as a measure of fatty acid oxidation and total energy demands. It is one of the frequently used output variables in training studies and it is often cited as one of the arguments of the friends of "classic" cardio training like jogging on a treadmill or cycling at a medium intensity. Why? Well, if you cycle for one hour you will obviously consume more oxygen (O2), than you'd do within 10 minutes of high intensity interval training, right?

In a recent study scientists from the Department of Kinesiology at the Ivor Wynne Centre of the McMaster University in Hamilton, Ontario (Canada), Lauren E. Skelly and colleagues tested whether this initial advantage, i.e. the increased VO2 consumption and thus energy expenditure in response to the exercise, would last 24h (Skelly. 2014).

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

To this ends, the researchers recruited nine healthy young men (age = 21 ± 1 years, body mass = 91 ± 15 kg) and had them perform 3 trials in random order in a repeatedmeasures design.

• The HIIT treatment involved 10 × 60-s intervals at a workload that elicited 90% HRmax with 60 s of active recovery at 50 W. 
• The END protocol consisted of cycling at a workload that elicited 70% of HRmax for 50 min. 
• Control protocol: No exercise was performed in the control trial (CON). 

The HIIT and END protocols were selected, because previous research has reported similar changes in body composition between HIIT and longer (40–60 min) bouts of END (Macpherson et al. 2011).

"Also, given that HIIT studies typically involve 3 training sessions per week, and given current physical activity guidelines are calling for 150 min of moderate-intensity exercise per week, a comparable END training program would consist of 3 × 50-min sessions per week." (Skelly. 2014)

A 3-min warm-up at 50 W was performed prior to the main exercise bout in both, the HIIT and END trials. All trials commenced following a 10-h overnight fast (all meals were standardized for a given subject across all trials) and subjects were advised to perform no physical activity other than the prescribed exercise and normal activities of daily living for 24 h prior to each trial and over the course of the 24-h collection period. 

Figure 1: Total oxygen consumption at each measurement point (A) and over 24 h (B). CON, control; HIIT, high-intensity interval training; END, continuous moderate-intensity training; HRmax, maximal heart rate. *,p< 0.05 vs. CON; †,p< 0.05 vs. HIIT

Due to the "no breakfast" + "no other exercise" framework, the results are not per se generalizable, but it seems prudent to assume that we will see a similar "catch up" in O2 consumption after the workouts under different circumstances, as well.

Suggested Read: Some HIIT For Life & Less LISS For More! How to Burn 27,300 Kcal Extra W/out Losing a Single Extra Pound of Fat | more

Bottom line: The study at hand underlines hat HIIT is more than just 10 min of all out exercise. It's a metabolic trigger with long lasting consequences and a real alternative to classic "cardio" training. HIIT is time-efficient and effective, but it's not exactly resistance training compatible. The constant CNS overload you'd suffer if you add 3 HIIT sessions on the off days to a 3-day split resistance training regimen is much more likely to fry your nerves than a "lazy" walk on an incline treadmill. Keep that in mind and be weary of sleep problems, a lack of drive and motivation if you decide to incorporate additional high intensity interval work into your routine | Comment on Facebook!

Reference: 

• Macpherson, R. E., et al. "Run sprint interval training improves aerobic performance but not maximal cardiac output." Medicine and science in sports and exercise 43.1 (2011): 115-122.
• Skelly, Lauren E., et al. "High-intensity interval exercise induces 24-h energy expenditure similar to traditional endurance exercise despite reduced time commitment." Applied Physiology, Nutrition, and Metabolism 39.999 (2014): 1-4.