Pilot study: an acute bout of high intensity interval exercise increases 12.5 h GH secretion

The purpose of this study was to test the hypothesis that high‐intensity interval exercise ( HIE ) significantly increases growth hormone ( GH ) secretion to a greater extent than moderate‐intensity continuous exercise ( MOD ) in young women. Five young, sedentary women (mean ±  SD ; age: 22.6±1.3 years; BMI : 27.4±3.1 kg/m 2 ) were tested during the early follicular phase of their menstrual cycle on three occasions. For each visit, participants reported to the laboratory at 1700 h, exercised from 1730–1800 h, and remained in the laboratory until 0700 h the following morning. The exercise component consisted of either 30‐min of moderate‐intensity continuous cycling at 50% of measured peak power ( MOD ), four 30‐s “all‐out” sprints with 4.5 min of active recovery ( HIE ), or a time‐matched sedentary control using a randomized, cross‐over design. The overnight GH secretory profile of each trial was determined from 10‐min sampling of venous blood from 1730–0600 h, using deconvolution analysis. Deconvolution GH parameters were log transformed prior to statistical analyses. Calculated GH AUC (0–120 min) was significantly greater in HIE than CON ( P  = 0.04), but HIE was not different from MOD . Total GH secretory rate (ng/ mL /12.5 h) was significantly greater in the HIE than the CON ( P  = 0.05), but MOD was not different from CON or HIE . Nocturnal GH secretion (ng/ mL /7.5 h) was not different between the three trials. For these women, in this pilot study, a single bout of HIE was sufficient to increase 12.5 h pulsatile GH secretion. It remains to be determined if regular HIE may contribute to increased daily GH secretion.