PMID 25806146

Research
All papers

4 weeks of high-intensity interval training does not alter the exercise-induced growth hormone response in sedentary men

Sasaki H, Morishima T, Hasegawa Y, Mori A, Ijichi T, Kurihara T, Goto K

Question

Does 4 weeks of submaximal cycling HIIT alter exercise-induced growth hormone responses and body or ectopic fat in sedentary men?

Summary

In 24 healthy sedentary men, 4 weeks of cycling HIIT improved VO2max but did not change exercise-induced growth hormone response, whole-body fat, abdominal fat, intramyocellular lipid, or intrahepatic lipid. The authors noted the short, low-volume program and relatively lean healthy sample may have limited detectable endocrine or fat changes.

Methodology

  • Healthy sedentary men.
  • 24 participants.
  • Cycle ergometer.
  • Work intervals: 1 minute.
  • Recovery: 30 seconds rest.
  • Intensity: 85% VO2max.
  • About 14.5 minutes for HIT block.
  • 3 sessions/week.
  • 4 weeks.
  • Randomized two-group training study
  • Growth hormone, VO2max, and Abdominal and ectopic fat were tracked.

Outcomes

VO2max

VO2max increased significantly in both HIT and low-intensity groups, without a significant between-group difference.

HIT +8.3 +/- 2.6%; LT +4.7 +/- 1.3%; both p<.05 vs pre.

Improved

GH response

Acute exercise increased GH, but training did not change the GH response in either group.

GH AUC did not significantly change pre to post in either group.

No clear change

Fat depots

Body weight, BMI, percent fat, abdominal fat area, IMCL, EMCL, and IHL did not significantly change.

No significant pre-post changes reported for these measures.

No clear change

Insights

  • Short low-volume cycling HIT can improve aerobic capacity without changing fat or GH outcomes.
  • Growth-hormone claims are not supported by this 4-week protocol.
  • Body-composition effects may require longer duration, higher volume, or different populations.

Limitations

  • Small sample.
  • Male-only healthy sedentary participants.
  • Short 4-week duration.
  • Participants had relatively low fat accumulation and high baseline GH response.
  • No high-intensity continuous comparator.

Safety

  • No adverse events were reported in the reviewed text.
  • HR was continuously monitored during training sessions.