High intensity interval training with Dr. Martin Gibala

In this Masters in Exercise podcast episode, Dr. Martin Gibala, a kinesiology professor at McMaster University, discusses the efficiency and adaptability of high-intensity interval training (HIIT). He explains its benefits, including improved cardiorespiratory fitness and insulin sensitivity, while acknowledging the ongoing debate about its public health applicability. Dr. Gibala emphasizes that HIIT can be tailored to various intensity levels and modalities, making it accessible for different populations, including those with health conditions. He advocates for a collaborative, nuanced approach to exercise science, focusing on expanding options for physical activity.

• Dr. Martin Gibala discusses the physiological effects and time efficiency of high-intensity interval training (HIIT).
• HIIT involves short bouts of high-intensity exercise with periods of rest or active recovery.
• Recent studies indicate even 20-second bouts can trigger significant adaptations.

"High intensity interval training is a very time efficient type of training that is characterized by short bouts of high intensity exercise combined with short periods of rest or active recovery."

• HIIT is highlighted as a time-efficient exercise method, making it accessible for those with busy schedules.

• Dr. Gibala's interest in exercise prescription stems from personal experiences and teaching.
• He emphasizes the practical application of interval training for both performance and health.

"I've always been interested in physical activity, exercise for health. I think many in kinesiology get into the field for that reason, out of a personal interest."

• Personal interest and teaching experiences have driven Dr. Gibala's research focus on interval training.

• Interval exercise is a broader term encompassing various intensities and modalities.
• HIIT can range from light interval walking to all-out efforts, encompassing aerobic and resistance-based exercises.

"I like to use the term interval exercise. I think it's broader and more encompassing and so hit is one variation or one flavor on that."

• Interval exercise includes a wide range of intensities and types, not limited to extreme efforts.

• HIIT's popularity is partly due to its time efficiency, appealing to those with busy lifestyles.
• Despite time being a common excuse, the pandemic showed that time availability doesn't necessarily increase physical activity rates.

"There are definitely a segment of the population who legitimately are very time pressed. They're very regimented in their approach to life and they if they can schedule in a workout and it only has to take them 20 minutes rather than an hour. That really resonates."

• Time efficiency is a key factor in HIIT's appeal, especially for those with structured schedules.

• A debate exists on whether HIIT can effectively promote physical activity at the population level.
• Dr. Gibala advocates for a non-polarized approach, emphasizing the expansion of exercise options.

"I increasingly have little time for these polarized positions, and I understand why debates resonate. But I'm on Twitter sparingly. It is a cesspool and you're seeing scientists writing these polemics and just demonizing the work of others."

• Dr. Gibala stresses collaboration and expanding exercise options rather than engaging in polarized debates.

• Dr. Gibala supports collaborative research efforts to enhance exercise participation.
• He highlights a team science approach involving various disciplines to promote physical activity.

"I am also trying to engage in collaborative research efforts. And I think this really is the way of forward where we have medical professionals, scientists, behavioral scientists, physiologists, trying to work together."

• Collaboration across disciplines is crucial for advancing research and promoting physical activity effectively.

• The discussion highlights the limitations of research comparing high-intensity interval training (HIIT) and moderate-intensity continuous training (MICT).
• The design of many studies, including small sample sizes and varying levels of interaction, can bias results on motivation and enjoyment.
• Collaboration with experts in different fields is essential to improve study designs and reduce biases.

"Clearly, there are limitations. And so to answer, I guess, the original question first, that would be an example of where I attempted to collaborate with behavioral colleagues who are more expert than myself."

• Acknowledges the limitations in research and the importance of interdisciplinary collaboration to address these issues.

"But I readily admit that we have done underpowered studies in the past. We have probably over-interpreted our results."

• Admits past research shortcomings and emphasizes the need for more robust study designs.

• HIIT affects skeletal muscle through molecular signaling pathways, such as AMPK activation, which is crucial for energy availability in cells.
• The analogy of a fuel gauge helps explain how interval training impacts these pathways, leading to responses like mitochondrial biogenesis.
• HIIT can improve VO2 max, comparable to longer endurance training, possibly due to cardiovascular remodeling, though the exact mechanisms remain unclear.

"So the way that I like to think of it is the, you know, the analogy of a fuel gauge."

• Uses a fuel gauge analogy to explain how HIIT affects muscle energy pathways.

"Our lab and others have shown that you can have the same activation of these molecular signaling proteins that are important for responses with these short, sharp exercise bouts or with the more prolonged approach to exercise."

• Indicates that both HIIT and continuous exercise can activate key molecular responses in muscles.

• HIIT can lead to improvements in VO2 max, but the mechanisms, particularly regarding cardiovascular remodeling, are not fully understood.
• The debate continues on whether limitations to VO2 max are central or peripheral, with some evidence pointing to central limitations.

"I generally, you know, subscribe to the saltine model and the classic work, although you would be aware of work coming out of Jose Calbe's lab and that reminding us of the importance of oxygen extraction."

• Discusses the ongoing debate about the factors limiting VO2 max improvements.

"Well, if you just do the math on the amount of blood that's flowing through with a series of short, hard bursts of exercise, it's nowhere close."

• Highlights the puzzling nature of cardiovascular adaptations to HIIT compared to expected outcomes.

• Interval training improves cardiorespiratory fitness and glycemic control/insulin sensitivity.
• Insulin sensitivity improvements can be seen with smaller volumes of interval training compared to traditional endurance training.
• Evidence for other benefits, like blood pressure and body composition, is less compelling.

"The two big ones to my mind, first of all, by far the biggest and best studied, and probably because it's easy to study, is the improvement in cardiorespiratory fitness."

• Emphasizes cardiorespiratory fitness as a significant benefit of interval training.

"But I think now there is strong evidence that interval training first certainly can enhance glycemic control, both in healthy individuals, to some extent, in particular in individuals who are with prediabetes or full-blown diabetes."

• Notes the strong evidence for glycemic control improvements through interval training.

• Elite athletes often use an 80/20 mix of moderate and high-intensity training for optimal performance.
• Traditional endurance training may offer unique benefits, such as different patterns of exercise, which can complement interval training.

"But I think the training of high-level athletes offer some clues. And if you, you know, the, the, the most elite athletes and most elite coaches who work with endurance athletes still pretty much use an 80, 20 mix."

• Indicates that a combination of moderate and high-intensity training is beneficial for elite athletes.

"For mere mortals who are performing a much smaller volume, I think that proportion can, can shift."

• Suggests that the balance of training types may vary for non-elite athletes based on volume and individual needs.

• A varied approach to fitness, incorporating different types of exercise, is considered optimal for both performance and health.
• The unpredictability of individual responses to exercise means that a diversified strategy, similar to spreading risk in stock investments, is advisable.

"I think a blended approach to fitness, whether it's for performance or health, is always going to be the best approach."

• Emphasizes that a mixed approach to fitness can cater to both health and performance needs.

"Could the athlete have gone a little bit faster if they trained a little bit differently? Well, we, we don't know. These are all experiments of, of one."

• Highlights the uncertainty in exercise outcomes, suggesting that individual responses can vary greatly.

• The structure of HIIT, including the duration of high-intensity and recovery intervals, can lead to different physiological adaptations.
• There is still a lack of comprehensive understanding of how varying HIIT structures affect long-term adaptations.

"If performance is the proxy for underlying physiological mechanisms, then clearly that work would suggest that, you know, varying up the training is important."

• Suggests that varying training stimuli could enhance performance by targeting different physiological mechanisms.

"There's still lots of good work to be done. If you ask good questions and come up with good designs, there's a lot of compelling questions that we still need to address."

• Indicates the need for further research to understand the specific adaptations resulting from different HIIT structures.

• Studies on stroke patients show a plateau in VO2 improvements, raising questions about the effectiveness of current HIIT protocols.
• The duration of high-intensity intervals might need adjustment to continue VO2 improvement in stroke rehabilitation.

"We normally start with moderate intensity cardiovascular training for four weeks and then we transition to heat... we clearly see a plateau after four weeks."

• Describes the observed plateau in VO2 improvements during stroke rehabilitation, suggesting a need for protocol adjustments.

"The type of heat that we're using is 1, 1, so 1 minute high intensity, 1 minute low intensity."

• Details the specific HIIT protocol used in stroke rehabilitation, highlighting the need to explore different interval durations.

• Traditional heart rate monitoring may not accurately reflect intensity during high-intensity training due to lag.
• Rate of Perceived Exertion (RPE) is recommended as a practical tool for gauging exercise intensity in applied settings.

"Heart rate becomes challenging as a marker of intensity, especially as intensity goes up."

• Points out the limitations of using heart rate as an intensity marker in high-intensity training.

"I think RPE has tremendous value and I think it makes it very, very easy because there is sometimes a tendency to overcomplicate interval training."

• Advocates for the use of RPE to simplify intensity measurement and make interval training more accessible.

• Low-volume HIIT can improve fitness markers like cardiorespiratory fitness and insulin sensitivity, comparable to traditional endurance training.
• Short, intense efforts, even as brief as 20 seconds, can be beneficial if performed multiple times a day.

"12 weeks of very brief intense internal exercise improve cardiorespiratory fitness, glucose tolerance, insulin sensitivity to the same extent as traditional endurance training."

• Highlights the effectiveness of low-volume HIIT in achieving significant health benefits.

"The exercise snacks idea is just these brief periods of exercise, very brief 20 seconds or so that you perform periodically throughout the day."

• Introduces the concept of "exercise snacks," emphasizing the potential benefits of very brief, frequent exercise bouts.

• The physiological mechanisms underlying exercise adaptation are consistent across different exercise types and durations.
• Short bursts of exercise activate similar molecular signaling pathways as longer exercise sessions.
• The optimal structure of exercise bouts for maximum adaptation is not fully understood.
• Public health guidelines now recognize the value of short exercise bouts.

"The adaptation is just the accumulation of successive exercise bouts and the best way to structure those together. You know, we don't know but I guess I would come back to."

• Exercise adaptation occurs through the accumulation of multiple exercise sessions, and the optimal structure for these sessions is still unknown.

"Every little bit counts. There's no optimal program for the vast majority of people. And so just get out there and do something you like and enjoy repeatedly and that's going to be the best prescription."

• Emphasizes the importance of regular physical activity, regardless of the specific program, for overall health benefits.

• HIIT has potential benefits for cardiac rehabilitation and other clinical conditions.
• Historical context shows the use of interval training in cardiac rehab settings.
• Interval training may be more feasible for individuals with certain pulmonary diseases.
• The narrative around exercise intensity can be reframed to encourage participation.

"I think clearly in a cardiac rehab situation, many cardiac associated diseases can benefit from an interval based approach."

• HIIT is beneficial for cardiac rehabilitation, offering a viable exercise approach for cardiac-related conditions.

"It's flipping the narrative there. And so rather than saying, you have to do 20 or 30 minutes at this low intensity, many of them just can't."

• Changing the narrative around exercise can help individuals with limitations engage in physical activity by focusing on what they can do.

• Professional success involves mentoring and supporting the success of students and trainees.
• Personal success is linked to family contentment and happiness.
• Success is about contributing positively to others' work and lives.
• The pandemic highlighted the importance of appreciating one's circumstances.

"Professionally, success is seeing my trainees and others go on to better things."

• Professional success is defined by the achievements and growth of mentees and colleagues.

"Personally, success is, you know, contentment in my family, right? And so if whatever I do at work, if my wife and two kids aren't happy with, you know, or if I'm putting too much in at work, they're going to let me know about it."

• Personal success is measured by the happiness and contentment of one's family and personal life.

• The speaker has a website and uses social media to communicate scientific work.
• Social media is used primarily for promoting work rather than engaging in debates.
• Science communication is important and can be achieved through various platforms.

"I do have a website and I made that and created it really, just for this. So it's a single point where individuals could go and learn a little bit about me."

• The speaker maintains a website to centralize information about their work and media appearances.

"I am on Twitter professionally. I tweet occasionally. I more read what others are putting on, but I do like having it as a platform if occasionally you have something to say or promote your work."

• Twitter is used as a platform for professional announcements and work promotion, rather than for extensive engagement.