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Physiological Basis of Brief Vigorous Exercise to Improve Health

Physiological Basis of Brief Vigorous Exercise to Improve Health

Authors and Affiliations

  • Martin J. Gibala: Department of Kinesiology, McMaster University
  • Jonathan P. Little: School of Health and Exercise Science, University of British Columbia

Overview of Brief Vigorous Exercise

  • Defined as exercise lasting around 15 minutes total, with 5 minutes of vigorous exercise.
  • Vigorous exercise is categorized as exceeding a percentage of maximal heart rate (≥ 77%), maximal oxygen uptake (≥ 64%), and/or a rating of perceived exertion (RPE ≥ 14) as per the American College of Sports Medicine.
  • The acute physiological mechanisms that enhance cardiorespiratory fitness (CRF) and glycaemic control post-exercise remain under investigation.

Key Concepts

  1. Improvement in Cardiorespiratory Fitness (CRF):
    • Evidence of increased VO2max after a few weeks of vigorous exercise, potentially without changes in maximal cardiac output, possibly due to greater oxygen extraction by active muscles (increased arterio-venous oxygen difference).
    • Protocols like Tabata (20s effort, 10s recovery repeated for 8 times) improve VO2max substantially.
  2. Impact on Glycaemic Control:
    • Some studies indicate vigorous exercise improves insulin sensitivity, with mixed results based on exercise type and duration.
    • Acute exercise can enhance insulin sensitivity for up to 24 hours but needs more detailed study.

Mechanisms of Improvement

Cardiorespiratory Fitness
  • Increased VO2max attributed to:
    • Expansion of red blood cell volume
    • Improvements in stroke volume independent of red blood cell volume.
  • Studies show increased VO2max even without changes in maximal cardiac output, suggesting other factors at play (e.g., increased capillary density, mitochondrial content).
Glycaemic Control
  • Structure and function of various tissues (muscle, liver, fat) adapt post-training, contributing to enhanced insulin sensitivity:
    • Acute bouts of exercise enhance glucose uptake via improved muscle sensitivity post-exercise.
    • Training effects vary with protocols and individual characteristics.

Studies and Findings

  • SIT (Sprint Interval Training) and its variants have shown promise, yet practical implementation outside labs could be challenging.
  • Protocols like REHIT (Reduced Exertion High-Intensity Training) show potential insulin sensitivity benefits similar to longer sessions.
  • Research in populations with type 2 diabetes demonstrates varied insulin sensitivity improvements:
    • Some studies support REHIT, others (e.g., Godkin et al. 2018) found no effect due to study design variations.
  • Acute responses such as glycemic control may be influenced by the timing of exercise in relation to meals.

Practical Implications

  • Brief vigorous exercise can improve CRF with commitments of around 30 minutes/week, suggesting it might substitute for longer forms of aerobic exercise.
  • The idea of exercise snacks (short, sporadic bouts of vigorous activity) offers potential for real-world applications.
  • Future studies should explore ways to standardize protocols for more effective results in improving overall health metrics, particularly regarding glycaemic control.

Conclusion and Future Directions

  • Brief vigorous exercise can effectively enhance CRF, yet its role in glycaemic control remains under scrutiny and requires further research.
  • Understanding the physiological adaptations to brief, intense training could provide insights into time-efficient exercise strategies for better health.