These episodes make great companion listening for a long drive.
Dr. Martin Gibala is a muscle physiologist and professor at McMaster University in Hamilton, Ontario, Canada. He is best known for pioneering research on the health benefits of high-intensity interval training (HIIT) and his profound understanding of HIIT's physiological mechanisms. He is a co-author of the book "The One-Minute Workout."
In this episode, Dr. Gibala and I discuss:
"VO2 max is the best objective measure of cardiorespiratory fitness and why fitness is essential… It protects you. It reduces your risk of dying and developing diseases. The best way to measure that is through a VO2 max test." Click To Tweet
High-intensity interval training (better known as HIIT) is an exercise protocol that revolves around alternating bursts of vigorous exercise and brief recovery periods. Pioneering studies, including those by Dr. Martin Gibala, underscore the transformative power of HIIT, revealing that its beneficial effects can rival, and at times even surpass, those derived from prolonged moderate-intensity endurance activities.
HIIT capitalizes on the principle of time efficiency, allowing you to achieve substantial fitness gains in considerably less time than traditional continuous exercise routines. Integrating HIIT into your workout routine optimizes time while triggering profound metabolic improvements that enhance your mitochondrial capacity and boost cardiovascular and cognitive health.
Driving these effects are what Dr. Gibala describes as the "intensity-duration trade-off" – a concept that reflects the non-linear relationship between exercise intensity (how hard you exercise) and duration (how long you exercise). As exercise intensity increases, the required duration can decrease without compromising cardiorespiratory benefits. In other words, you can achieve considerable fitness and health improvements in less time by engaging in high-intensity workouts compared to longer, lower-intensity workouts.
That's important because even a committed exerciser may run the risk of non-response – if you're not doing high-intensity training. That's because a surprising 40 percent of people might not see improvements in their VO2 max – even if they're meeting the guidelines for moderate-intensity exercise, roughly 2.5 hours per week.
VO2 max is a complex, multifaceted parameter that reflects the intricate coordination between the cardiovascular and musculoskeletal systems during exercise, based on various factors ranging from cardiac output (which can differ considerably between trained athletes and weekend runners) to muscle oxygen extraction. Put simply, it's the maximum oxygen uptake by the body and a definitive marker of cardiorespiratory fitness.
A person can approximate their VO2 max through equations and online calculators, but the most precise determination requires controlled laboratory testing involving incremental exercise protocols. However, accessible tools like the World Fitness Level calculator track changes in VO2 max over time, enabling anyone to monitor their fitness journey. And fitness trackers like the Apple Watch also offer tools to measure aerobic capacity by estimating VO2 max.
Some evidence suggests there is no upper benefit to cardiorespiratory fitness, with the most elite athlete having a nearly 80 percent lower risk of premature death compared to a less fit person of the same age. Given that up to 40 percent of people might not experience VO2 max improvements when adhering to standard exercise guidelines focusing on low-to-moderate intensities begs the question: Should we pivot toward the explosive benefits of HIIT, harnessing the power of vigorous intensities to unlock a new world of physiological adaptation?
"The most crucial adaptation in muscle is increasing mitochondrial content, which will allow a greater fat and carbohydrate oxidation capacity." Click To Tweet
Central to the physiological benefits observed with HIIT is its profound effects on the mitochondria – the cellular powerhouses that drive energy production. HIIT promotes mitochondrial biogenesis, contributing to the body's increased capacity for fat oxidation during exercise. A critical player in this process is carnitine palmitoyl transferase (CPT), an enzyme responsible for transporting fatty acids into the mitochondria for oxidation.
Dr. Gibala explains how exercise-induced adaptations, both through training and certain supplements like carnitine, enhance CPT levels, facilitating more efficient fat utilization and the preservation of carbohydrate stores. Exercise also promotes mitophagy (the turnover of dysfunctional mitochondria, fostering cellular resilience) and autophagy (the removal of cellular debris and damaged components).
Learn more about mitophagy in this clip featuring Dr. Guido Kroemer.
"Exercise is a stress. It temporarily disrupts or damages things. And then its all about the recovery that makes the cellular processes better. We continually do that, and over time, things get better." Click To Tweet
But HIIT's effects extend beyond mitochondrial dynamics, influencing multiple aspects of human physiology. For example, HIIT promotes the release of catecholamines, a group of signaling hormones released from the kidneys or brain during stress or physical activity to increase heart rate and prepare the body for action, facilitating the "fight or flight" response. Catecholamines serve dual roles as neurotransmitters and hormones and preserve homeostasis via the autonomic nervous system. They also signal adipose tissue to break down triglycerides and release them into the bloodstream, subsequently facilitating the uptake and oxidation of fatty acids within the muscle tissue.
Beyond its physical implications, HIIT has demonstrated potential cognitive benefits. Lactate, often misconstrued as a cause of muscle fatigue, is a significant player in these cognitive effects. Lactate is a weak base produced via the breakdown of glucose during exercise.
In zone 2 training, there's a deliberate effort to cap lactate accumulation. However, high-intensity workouts often produce more lactate than our muscles can handle. This surplus lactate can be "shuttled" to various tissues, including the muscles, heart, and brain, which use it as an energy source. Evidence suggests that lactate is the preferred fuel of the brain – pointing to its importance in maintaining cognitive function. Interestingly, HIIT-induced lactate promotes the release of brain-derived neurotrophic factor, a protein associated with cognitive function, pointing to the intricate interplay between exercise (particularly vigorous exercise), lactate metabolism, and cognitive health.
Exercise intensity also affects blood flow, creating shear force and playing a critical role in metastatic cancer resistance. One quality of cancer cells is that they sometimes have vulnerabilities that healthy cells do not, such as susceptibility to mechanical stress. In other words, when we exercise, we introduce cancer cells to a new type of stress. The turbulence created in our bloodstream can reduce the malignant cells' viability as they attempt to metastasize. Exercise may reduce the risk of cancer metastasis, and vigorousness may play a role, amplifying the effect.
"When we say high-intensity [effort], were talking [about] a relative heart rate of about 80 percent of your maximum. […] Youre working pretty hard, but its not an all-out sprint." Click To Tweet
An alphabet soup of HIIT protocols exists – HIIT, SIT, and REHIT, among them – with each form offering distinct advantages and outcomes. A common feature of all HIIT protocols is achieving an elevated heart rate of roughly 60 to 85 percent of one's maximum heart rate. You can determine your maximum heart rate using the Fox equation: 220 – your age in years.
HIIT involves intense but submaximal efforts, challenging a person to perform at an intensity below their maximum capacity. In contrast, SIT focuses on sprint-like training, replicating the intensity of sprinting from a perceived danger. REHIT takes this further, employing high power outputs surpassing VO2 max pace but for shorter durations, typically 10 to 20 seconds.
HIIT doesn't always translate to an all-out pace, however. In fact, the concept of resistance-style interval training, often referred to as functional training, underscores HIIT's versatility. Body-weight exercises like air squats, burpees, and push-ups performed in an interval manner can efficiently blend strength and aerobic conditioning. Although not a substitute for heavy weight lifting or endurance training, these body-weight exercises offer a time-efficient route to marked gains in both realms.
Dr. Gibala describes some of his favorite HIIT routines: "VO2 Max training interval," three five-minute intervals at maximum effort, including warmup, cool-down, and recovery in a 20-minute session. The minute-on/minute-off approach, repeated five or ten times, plus warmup and cool down. The "One-Minute Workout," featuring three sets of 20 seconds of intense exercise and two minutes of recovery, totaling 10 minutes – three times a week for optimal results. Tabata, Dr. Rhonda Patrick's favorite HIIT routine, consisting of a four-minute cycle with 20 seconds of maximum effort followed by 10 seconds of rest, repeated eight times. Dr. Patrick often opts for a 10-minute workout – doing two Tabatas back-to-back – a format that's also popular in Peloton programming.
"So, if youre just starting out getting into exercise, maybe you just want to start out by walking fast for a few light posts and then backing it off. Thats a form of interval training. Dont worry at all about whether youre at 80 percent." Click To Tweet
Novices might find starting an interval training regimen intimidating. However, Dr. Gibala explains that beginning with an alternating pattern can help, gradually progressing based on individual fitness levels and goals. Whether you're an athlete, relatively sedentary, or striving for time-efficient VO2 max optimization, interval training offers adaptable strategies to suit diverse objectives.
"People who engaged in even three to four minutes… of VILPA-like activity [daily] had substantial reductions in all-cause mortality risk, were talking 25, 30 percent. So that would suggest that even brief, non-exercise, vigorous, intermittent physical activity can move the needle in terms of health outcomes." Click To Tweet
One strategy for incorporating vigorous exercise into your day involves "exercise snacks." These short bursts of vigorous-intensity exercise, lasting up to a minute and strategically dispersed throughout the day, include hopping on a stationary bike, performing a series of air squats, or engaging in bodyweight-style exercises at least four or five times daily.
Another strategy Dr. Gibala describes for engaging in more vigorous activity is VILPA, short for vigorous intermittent lifestyle physical activity. VILPA is non-structured exercise that involves short, vigorous bursts of activity that capitalize on ordinary, routine activities. Climbing uphill, briskly walking upstairs, and even vigorous housework all count toward your VILPA. Engaging in three to six minutes of VILPA-like activity daily may reduce the risk of early death by nearly half.
As research in the field of exercise physiology advances, the future of HIIT appears promising. Dr. Gibala and his colleagues advocate for rigorous trial designs and more extensive studies to provide robust conclusions about HIIT's effectiveness and the mechanisms that drive them. Additionally, ongoing investigations aim to decipher individual responses to HIIT, considering factors such as sex, age, and pre-existing medical conditions, acknowledging the nuanced nature of physiological adaptations, and taking steps toward personalized exercise recommendations.
Articles:
Episodes & Clips:
Exploring high-intensity training
Zone 2 vs. HIIT for improving VO2 max
The vital role of vigorous exercise
Why meeting exercise guidelines alone may not suffice for improvements in VO2 max for some people. Evidence indicates that vigorous training is important for adaptation and achieving better results. 1
Why VO2 max matters for longevity
How an epidemiological study showed an inverse relationship between VO2 max and all-cause mortality, with elite performers experiencing an 80% reduction in mortality compared to the lowest performers. 1
Why athletes vs. exercisers benefit from different intensity distributions
Elite endurance athletes often train extensively, with 15 to 20 sessions totaling 25 to 30 hours per week, dividing their efforts between 80% low-to-moderate intensity and 20% high-intensity to achieve exceptional cardiorespiratory fitness levels. This differs from the training approach of a fit, committed exerciser who trains a few hours each week.
Measuring maximum heart rate and VO2 max
How VO2 max can be estimated with equations or online calculators, which are useful to track changes over time. Dr. Gibala recommends World Fitness Level calculator. 1
How submaximal exercise tests like the 20-meter shuttle run and the 6-minute walk test are more accurate than online questionnaires in estimating cardiorespiratory fitness and VO2 max.1
How the heart adapts to HIIT to increase VO2 max
Why vigorous exercise accelerates mitochondrial adaptation
Mitochondrial content, essential for fat oxidation, can rapidly fluctuate in response to exercise or detraining.
Enhancing fat oxidation and mitochondrial growth with vigorous exercise
How intensive exercise boosts fat breakdown
Is high-intensity exercise better for autophagy than fasting?
How high-intensity exercise is a more potent stimulator of autophagy in skeletal muscle than an overnight fast. 1
Dr. Gibala discusses his use of Wingate tests to stimulate intense, short bursts of exercise in his early research. 1
Muscle adaptations from aerobic conditioning
During aerobic conditioning, two crucial muscle responses include increased mitochondria and improved capillarization, enhancing blood supply to support mitochondrial growth in skeletal muscle.
How exercise adaptations also involve increased muscle glycogen storage and improved glucose transporter capacity on cell membranes, aiding blood sugar regulation, especially in people with diabetes. 1
Exercise snacks
How "exercise snacks," brief bouts of vigorous-intensity exercise lasting less than one minute, spread throughout the day, may impact insulin sensitivity and blood glucose control, providing a time-efficient strategy for improving overall health and fitness. 1
Vigorous Intermittent Lifestyle Physical Activity (VILPA)
VILPA involves incorporating intense physical activity into daily routines, such as taking stairs instead of elevators, brisk walking, and carrying a backpack with effort. 1
How as little as three to four minutes of VILPA-like activity per day significantly reduces the risk of all-cause mortality. In essence, even short bouts of non-exercise, vigorous, intermittent activities can improve health outcomes. 1
The effect of HIIT on muscle fiber types
Dr. Gibala explains muscle fiber types and their recruitment during exercise, highlighting distinctions between elite athletes and the general population.
How aging affects muscle fibers
Dr. Gibala discusses the potential impact of high-intensity interval training on body composition, specifically addressing its role in fat loss or lean mass gains. 1
Does high-intensity training produce an "afterburn" effect?
How the lactate shuttle theory proposes that lactate produced in one cell can fuel another cell, positively affecting brain health by elevating BDNF levels, which promote neurogenesis and better brain function. 1
Why Vigorous Workouts are Better for BDNF and Cognition
How lactate produced from vigorous exercise increases BDNF and neurotransmitters, potentially offering distinct cognitive benefits unique to high-intensity workouts.
Anti-metastatic cancer effects
Why the mechanical forces of vigorous exercise may impart cognitive benefits and anti-metastatic cancer effects. 1
Dr. Gibala describes the concept of the "sprint from danger" pace and compares it to the Wingate test or sprint interval training. 1
Dr. Gibala proposes that incorporating a mix of training techniques, including longer intervals, tempo training, and sprint-from-danger pace efforts, could be more efficient for enhancing overall fitness.
How recent evidence indicates that elite endurance athletes who include sprint training experience performance and VO2 max improvements. 1
Dr. Gibala explores training protocols and offers strategies for combining diverse exercises to improve both performance and VO2 max.
Wingate training vs. reHIIT — A comparison of protocols
How Dr. Edward Coyle's research demonstrates that frequent four-second all-out efforts can lead to high power outputs, even for deconditioned individuals, who can easily repeat this process after a short recovery. 1
High-intensity interval training challenges the traditional perceived effort model measured by the Borg Rating of Perceived Exertion scale, as sometimes, older adults and individuals with obesity experience low perceived exertion despite high % Max HR and output during short efforts. 1
Perceived exertion vs. HRmax
Interval walking for people with type 2 diabetes
Contraindications of HIIT
Interval training can boost cardiorespiratory fitness, yet it might pose short-term risks to unconditioned individuals or those with specific health challenges. In light of this, Dr. Gibala questions whether the benefits might outweigh the risks of inactivity. 1
Why preconditioning reduces risks from exercise
Can resistance training be a type of aerobic exercise?
Does cardio and strength training interfere with each other?
Dr. Gibala asserts that performing aerobic and strength training simultaneously is unlikely to produce a substantial interference effect for most people. Furthermore, evidence suggests that aerobic conditioning before resistance training boosts muscle growth, satellite cell content, and capillarization in healthy young adults. 1, 2
How many minutes per week of high-intensity training?
Recent guidelines no longer require physical activity to last at least 10 minutes due to a lack of scientific support, emphasizing that all activity, even short bursts, can contribute to health improvements. 1
Are there sex differences and misconceptions in high-intensity training, for women?
Should post-menopausal women do HIIT?
Does intense exercise raise cortisol?
While exercise can temporarily increase cortisol levels, consistent interval training seems to help maintain lower basal cortisol levels. Moreover, after a HIIT workout, cortisol rises within the first 60 minutes, falls below baseline by 180 minutes, and then returns to baseline after 24 hours. 1
In women with polycystic ovary syndrome (PCOS), those who performed HIIT training had significantly higher pregnancy rates compared to the non-exercise control group. 1
Bone density and osteoarthritis
Atrial fibrillation risk
Hypoxic training and blood flow restriction
Tips for training with joint issues
FoundMyFitness Members get access to exclusive content not available anywhere else, including a transcript of this episode.
You wouldn't believe how cool being a premium member of the world's best cross-disciplinary science-focused website and podcast really is.
Learn more about the advantages of a premium membership by clicking below.
Every other week premium members receive a special edition newsletter that summarizes all of the latest healthspan research.
