September 19, 2023 • 2hr 51min

#082 The Science of Vigorous Exercise — Should We Train Hard or Train Long? | Martin Gibala, Ph.D.

FoundMyFitness

Dr. Martin Gibala is a professor and chair of the kinesiology department at McMaster University in Hamilton, Ontario. He is a world-renowned expert on high-intensity interval training (HIIT) and author of the book "The One-Minute Workout." In this episode, Dr. Rhonda Patrick interviews Dr. Gibala about the science behind HIIT, its health and performance benefits, and practical ways to incorporate it into exercise routines. The discussion covers a wide range of topics related to HIIT, from the physiological mechanisms driving adaptations to comparisons with other training modalities to considerations for different populations. Dr. Gibala provides evidence-based insights while acknowledging areas that need further research. The conversation aims to give listeners a comprehensive understanding of HIIT and how to apply it effectively.

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Key Takeaways

High-intensity interval training (HIIT) can provide similar or greater improvements in VO2 max compared to moderate continuous exercise in less time. As little as 20-25 minutes of HIIT 3-4 times per week can significantly boost cardiorespiratory fitness.
HIIT may be more effective than moderate exercise at eliminating "non-response" - where some people don't see improvements in VO2 max even with regular exercise. More vigorous exercise appears to potentiate adaptations.
VO2 max is one of the best predictors of longevity and health. Higher cardiorespiratory fitness is associated with reduced all-cause mortality and lower risk of many chronic diseases.
HIIT can rapidly increase mitochondrial content and function in muscle, improving metabolic health and the ability to oxidize fat. These adaptations occur even with very short duration high-intensity exercise.
Vigorous exercise may provide unique cognitive benefits through increased lactate production and blood flow/shear stress to the brain. This may enhance BDNF levels and neuroplasticity.
Even very short bursts of vigorous activity throughout the day (VILPA) can provide significant health benefits. Just 3-4 minutes total per day was associated with 25-30% lower mortality risk in one study.
There are many ways to incorporate intervals, from all-out sprints to gentler hills and valleys in intensity. The key is alternating between higher and lower intensities, which can be adapted for all fitness levels.
Resistance training can be incorporated into interval-style workouts for both strength and cardio benefits. Bodyweight exercises like squats and burpees can provide an effective full-body workout.
Current physical activity guidelines already encompass HIIT, but future guidelines may provide more specific recommendations as evidence accumulates. For now, HIIT can count towards weekly vigorous activity targets.

Introduction

The discussion covers a wide range of topics related to HIIT, from the physiological mechanisms driving adaptations to comparisons with other training modalities to considerations for different populations. Dr. Gibala provides evidence-based insights while acknowledging areas that need further research. The conversation aims to give listeners a comprehensive understanding of HIIT and how to apply it effectively.

Topics Discussed

Defining High-Intensity Interval Training (10:05)

HIIT generally involves working at about 80% of maximum heart rate
Alternates between periods of high and low intensity
Can be adapted for different fitness levels and goals
"Interval training as a more general catch-all term...provides a broader way of doing that." - Dr. Martin Gibala

HIIT vs Zone 2 Training for VO2 Max (11:54)

HIIT can provide similar or greater VO2 max improvements in less time
May eliminate "non-response" seen in some people with moderate exercise
Time-efficiency makes HIIT appealing for many people
20-25 minutes of HIIT 3-4 times per week can significantly boost cardiorespiratory fitness

Importance of VO2 Max for Health and Longevity (14:40)

VO2 max reflects integrated capacity of cardiovascular, respiratory, and muscular systems
Higher cardiorespiratory fitness associated with reduced all-cause mortality
Lowers risk of developing many chronic diseases
Elite performers can have up to 80% lower mortality risk compared to lowest fitness levels

Physiological Adaptations to HIIT (30:31)

Increases cardiac output - primary factor determining VO2 max differences
Improves stroke volume and heart rate
Enhances muscle's ability to extract and utilize oxygen
HIIT may lead to greater improvements in cardiac output compared to continuous moderate exercise

Mitochondrial Adaptations to HIIT (35:47)

Rapidly increases mitochondrial content and function in muscle
Can see measurable increases within days to weeks
Improves capacity to oxidize both carbohydrates and fats
HIIT appears to stimulate mitochondrial biogenesis more quickly than moderate exercise

Fat Oxidation and HIIT (40:06)

Mitochondrial content largely determines fat oxidation capacity
HIIT increases CPT enzyme levels, key for fatty acid oxidation
Don't need to be in "fat burning zone" during exercise to improve fat oxidation
HIIT increases overall capacity to burn fat, even if not primarily using fat during the workout

Autophagy and Exercise (45:56)

HIIT may be more potent for stimulating autophagy than fasting alone
Exercise promotes turnover and maintenance of cellular components
Supports overall mitochondrial health
High-intensity exercise can acutely disrupt homeostasis, leading to beneficial adaptations during recovery

VILPA and Health Benefits (57:55)

Vigorous Intermittent Lifestyle Physical Activity (VILPA)
Brief bursts of activity during daily life, like climbing stairs vigorously
As little as 3-4 minutes total per day associated with 25-30% lower mortality risk
Provides option for health benefits even for those who don't engage in structured exercise

Protocols for Improving VO2 Max (1:00:39)

3-5 minute intervals at highest sustainable intensity seem optimal
Can also use 1 minute on, 1 minute off repeated 5-10 times
Tabata protocol: 20 seconds on, 10 seconds off for 4 minutes
Varying interval and recovery periods can provide different physiological challenges

Effects on Muscle Fiber Types (1:05:50)

HIIT recruits both slow and fast twitch muscle fibers
Can improve function of both fiber types
May help maintain fast twitch fibers with aging
Strength training remains important for preserving fast twitch fibers and muscle mass

Cognitive Benefits of HIIT (1:16:13)

Vigorous exercise may provide unique brain benefits
Increases lactate production, which can fuel the brain
Enhances blood flow and shear stress to the brain
May increase BDNF levels and promote neuroplasticity more than moderate exercise

Anti-Cancer Effects of Exercise (1:23:15)

Exercise may reduce risk of cancer metastasis
Shear forces from blood flow can disrupt circulating tumor cells
More intense exercise may amplify this effect
Another potential unique benefit of incorporating vigorous exercise

Comparing HIIT Protocols (1:50:23)

Wingate test: 30-second all-out effort, very demanding
Reduced-exertion HIIT (REHIT): Shorter 10-20 second sprints
4-second repeated sprints also being studied
Shorter sprints may provide benefits with less discomfort than traditional Wingate-style training

Perceived Exertion in HIIT (1:55:38)

Traditional RPE scales may not apply well to short, intense intervals
People often rate HIIT as less difficult than expected given the intensity
Intermittent nature allows for recovery between hard efforts
HIIT may be more tolerable than assumed, even for less fit individuals

Interval Walking for Diabetes (1:59:23)

Alternating between higher and lower walking intensities
Shown to improve glucose control more than continuous moderate walking
Accessible form of interval training for many people
Even gentle intervals can provide additional health benefits over steady-state activity

Contraindications and Risks of HIIT (2:01:06)

Vigorous exercise transiently increases risk of adverse event
Absolute risk remains low for most people
Some conditions like unstable angina contraindicate HIIT
Moderate preconditioning may be advisable before starting HIIT, especially for inactive individuals

Resistance Training as Aerobic Exercise (2:10:44)

Circuit-style resistance training can provide both strength and cardio benefits
Bodyweight exercises like burpees and air squats work well
Can keep heart rate elevated while building functional strength
Time-efficient way to combine resistance and aerobic training

Concurrent Training Interference (2:16:24)

Minimal interference effect for most people
May be slight blunting if done in same session
Separating by a few hours may be ideal if optimizing for strength/hypertrophy
Not a major concern for general fitness; combined training still very beneficial

Recommended HIIT Volume (2:18:45)

Current guidelines encompass HIIT under vigorous activity recommendations
75-150 minutes per week of vigorous activity for substantial health benefits
HIIT may allow achieving benefits in less total time
Even 30-60 minutes per week of very vigorous exercise may provide significant benefits

S*x Differences in HIIT (2:26:58)

Limited evidence for major s*x-based differences in HIIT responses
More research needed, controlling for factors like menstrual cycle
High individual variability may outweigh s*x-based differences
HIIT likely beneficial for both males and females; individual response may vary

HIIT for Postmenopausal Women (2:27:42)

No evidence HIIT is harmful for postmenopausal women
May help maintain muscle mass and bone density
Doesn't appear to chronically elevate cortisol levels
HIIT can be an effective part of exercise routines for postmenopausal women

Effects on Bone Density (2:34:16)

Impact-based HIIT (e.g. running) may benefit bone density more than cycling
Non-impact HIIT still beneficial for overall health
Low-impact options good for those with joint issues
Consider mix of impact and non-impact exercise for optimal bone and joint health

HIIT with Joint Issues (2:40:45)

Can modify HIIT for those with joint problems
Cycling and swimming good low-impact options
Maintaining activity important for joint health
Work with healthcare provider to find appropriate HIIT modifications if needed

Conclusion

High-intensity interval training offers a time-efficient and highly effective way to improve cardiorespiratory fitness, metabolic health, and potentially cognitive function and longevity. While more research is needed in some areas, the current evidence strongly supports incorporating some form of interval training for most people. HIIT can be adapted to different fitness levels and goals, from all-out sprints to gentler alternating intensities.

Key takeaways include the potent effects of HIIT on VO2 max and mitochondrial function, potential unique benefits for brain health and cancer prevention, and the accessibility of interval-style training even for less fit individuals. Current physical activity guidelines already encompass HIIT, but future recommendations may provide more specific guidance as evidence accumulates.

While HIIT is generally safe and beneficial for most people, those with certain health conditions or who are currently inactive should consult a healthcare provider before starting a HIIT program. Gradual progression and proper form remain important to maximize benefits and minimize injury risk. Overall, HIIT represents a powerful tool in the exercise toolbox that can help people achieve significant health improvements with relatively small time