Physiological Responses to Sprint Interval Exercise in a Fasted State in Active Men

Articles in Press

Document Type : Research Paper

Authors

1 Ms Graduate, Department of Exercise Physiology, Faculty of Physical Education and Sport Sciences, University of Guilan, Rasht, Iran.

2 Professor, Department of Exercise Physiology, Faculty of Physical Education and Sport Sciences, University of Guilan, Rasht, Iran.

3 Assistant Professor, Department of Exercise Physiology, Faculty of Physical Education and Sport Sciences, University of Guilan, Rasht, Iran.

Abstract

Introduction: Fasting is a method used to enhance metabolic flexibility toward lipid utilization. However, there are concerns about hypoglycemia or protein breakdown in exercise. The present study investigated the physiological responses to sprint interval exercise with different rest durations in a fasting state. Methods: For this randomized crossover study, 10 healthy active men (aged 22.70 ± 1.15) were selected from eligible volunteers. In 2 separate sessions, following 14 hours of fasting, participants randomly performed 5×15s all-out sprints on an E894 MONARK ergometer with 30 or 60s rest intervals. Results: Diastolic blood pressure and heart rate were lower with longer rest intervals. Blood glucose, insulin, and urea remained unchanged after both protocols compared with baseline levels. There was a marked increase in lactate levels after both protocols, independent of the rest duration. The immune response was significantly higher with longer rest intervals than with short rest intervals or baseline levels. Conclusion: Sprint interval exercise performed in a fasted state did not induce hypoglycemia or evidence of protein degradation, suggesting that such training may be safe for active men. Longer rest intervals were associated with lower post-exercise heart rate and diastolic blood pressure, as well as an enhanced immune response. These findings suggest that coaches and practitioners may consider manipulating rest intervals to achieve targeted physiological adaptations.

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References

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Journal of Nutrition,Fasting and Health

Articles in Press, Accepted Manuscript
Available Online from 18 August 2025

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History

  • Receive Date: 10 June 2025
  • Revise Date: 11 August 2025
  • Accept Date: 17 August 2025

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