Wednesday, July 16, 2014

HIIT Increases Post-Workout Growth Hormone and Sheds a Marginal Amount of Body Fat, While LISS Decreases GH and Does Nothing for the Physique of Previously Sedentary Men

The HIIT exercise in the study at hand was slightly less demanding ;)
The latest study from the Ritsumeykan University in Japan is another study that compares high intensity interval training (HIIT; 10 sets of 1 min pedaling at 85% of VO2max, 30 s rest between sets) and steady state (LISS; 22 minutes of pedaling at 45% of VO2max) aka classic "cardio" training, but it's a study with a unique twist.

Yes, the scientists determined the changes in whole body fat mass, abdominal fat area, and a handful of other parameters in response to the 4-week exercise program (3 sessions per week), but eventually Sasaki et al. were interested in the effects of HIIT on the exercised-induced GH secretion.

As a SuppVersity reader you are well aware that the growth hormone, testosterone & cortisol response to exercise alone does not determine the study outcomes.
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

Triple Your Energy Exp.
In fact, a seminal paper by West et al. revealed a correlation between high levels of the allegedly catabolic hormone cortisol and increases in skeletal muscle mass.
Figure 1: Growth hormone (top) and cortisol (bottom) response to HIIT & LISS (Sasaki. 2014).
As you can see in Figure 1, this would imply that the LISS regimen which left the study subjects, 24 healthy sedentary men (172.5 ± 1.4 cm, 71.2 ± 2.0 kg), with elevated cortisol levels 90 minutes after the workout was a good choice for anyone striving to build muscle. Needless to say that this is *bs* - the context in the previously mentioned study was a totally different one and the elevated cortisol levels may just have reflected a higher workout intensity in those who gained the greatest amount of muscle.
Figure 2: Changes in BMI, body fat and VO2max (fitness) in response to HIIT vs. LISS (Sasaki. 2014)
Accordingly, I suggest we are careful and don't overinterpret the transient increase in GH the Japanese scientists observed 30 minutes after the HIIT workout as the underlying reason of the measureable, yet not significant reduction in body fat you can see in Figure 2.
The high standard deviations in the study at hand confirm: HIIT is not for everyone | learn more
Bottom Line: The study at hand shows that HIIT is the better choice for previously sedentary men who want to improve their fitness and lose a minimal amount of body fat. It does also reveal that the loss of body fat goes hand in hand with a marginal increase in growth hormone ca. 30min after the workout. What it does not do, though, is provide significant evidence of a causal relationship between the increase in GH and the marginal loss of body fat. They correlate - that's all. And honestly, without dieting you are not going to make continuous significant improvements to your physique, anyway.