Add Two Pounds of Lean Mass in Three Weeks W/ HIIT. HIIT Sprint Training Builds Muscle & Anaerobic Power While Reducing the Exercise Induced GH Response by 64%

HIIT - A GH diminishing mass builder?

I know it sounds contradictory, at first. If you take into considerations that previous studies show that the post-exercise increase in growth (and other) hormones does not correlate with the beneficial adaptational effects of exercise, it's actually no longer that surprising that researchers from the Department of Exercise Physiology at the Winston-Salem State University found that "[o]ne week of HIT significantly decreased GH release, with a simultaneous significant increase in anaerobic power and lean body mass of the lower extremities." (Ritsche. 2014)

In their latest paper which appeared in the December edition of the Journal of Exercise Physiology Kevin Ritsche, Jason Smith, Paul Mellick, and Laurie Wideman report the results of a recent experiment in the course of which 19 recreationally active male subjects (24.9 ± 3.9 yrs) completed a one-week high intensity interval training.
The training protocol used in the study was based on similar high-intensity protocols published by Burgomaster et al. (2005) and Gibala et al. (2006) and began 24 hrs after the completion of a pre-test that was designed to measure the baseline fitness, body fat and lean body mass (by DEXA), as well as the acute GH response to high intensity exercise in the 19 young subjects.

The training protocol consisted of 4 to 6 repetitions of 30-sec maximal sprints and was performed three times per week for 3 weeks. One day of rest intervened each training session.

"The first 3 training sessions consisted of four 30-sec repetitions at 7.5% body mass with 4 min of active recovery at 50 W between each repetition. Training sessions 4 to 6 (wk 2) consisted of 5 repetitions, and sessions 7 to 9 (wk 3) consisted of six 30-sec maximal repetitions. During each repetition, each subject was encouraged verbally to provide maximal effort" (Ritsche. 2014).

At the end of each week, 48 hrs after the third training session for the week, subjects completed the acute sprint test protocol outlined previously (including blood draws).

Figure 1: Changes in body composition in response to the 3-week hiit-training protocol. the percentages above the bars indicate the relative difference between pre- and post-value. The light bars tell you that the corresponding changes were not statistically significant (Ritsche. 2014).

At least 48 hrs after the final blood profile, a post-training DXA scan was completed as outlined previously.

Figure 2: (a) Peak power; (b) peak power-corrected for subjects’ body mass; and (c) fatigue index during each 30-sec maximal cycle ergometer acute sprint (as) before and after 3 wks of hit; and (d) total combined workload of every sprint during each training week (Ritsche. 2014)

As you can see in Figure 1, the DXA-scans revealed significant increases in total and leg lean mass, albeit only non-significant reductions in body fat - changes which went hand in hand with a profound increase in exercise performance (see Figure 2) and a significant reduction of the initially observed post-exercise growth hormone spikes (see Figure 3).
References:

• Burgomaster, Kirsten A., et al. "Six sessions of sprint interval training increases muscle oxidative potential and cycle endurance capacity in humans." Journal of applied physiology 98.6 (2005): 1985-1990.
• Gibala, Martin J., et al. "Short-term sprint interval versus traditional endurance training: similar initial adaptations in human skeletal muscle and exercise performance." The Journal of physiology 575.3 (2006): 901-911.
• Ritsche, Kevin, et al. "Acute Exercise-Induced Growth Hormone is Attenuated in Response to Short-Term, High-Intensity Exercise Training." Journal of Exercise Physiology (2014).