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Reversing Heart Age: How HIIT Can Turn Back the Clock by 20 Years



In a world where financial success often takes precedence, we sometimes overlook the true foundation of a prosperous life – our health.


“Your Health is Your Wealth”


Accumulating wealth is an admirable goal, but neglecting your health in the pursuit of wealth can lead to health debt and a retirement spent battling poor health issues.


A paper attributed to the aircraft-maker Boeing shows that employees who retire at 55 live to, on average, 83. But those who retire at 65 only last, on average, another 18 months.


It's a fact that you can't always buy your way out of poor health.


In this blog, we'll delve into how High Intensity Interval Training (HIIT) plays a pivotal role in enhancing health, longevity, and overall well-being. We will explore the scientific literature and studies, offering a comprehensive understanding for those with an interest exercise and healthspan.


The Biochemical Marvel of Muscles


When we engage in vigorous exercise, our muscles transform into miniature biochemical labs, synthesising compounds such as lactate and myokines. These compounds are not confined to the muscles; they enter circulation and travel to distant tissues, playing a crucial signalling role. The benefits of this process are manifold. It includes the synthesis of brain-derived neurotrophic factor (BDNF), a molecule crucial for brain and neuronal health, as well as potential anti-cancer mechanisms. Furthermore, muscles act as sponges, absorbing compounds harmful to the brain, ultimately improving mental health and reducing the risk of neurodegenerative diseases (Ruegsegger et al., 2019).

Understanding Training Zones


To fully appreciate the benefits of exercise, it's important to understand training zones, which help individuals target specific intensity levels during their workouts. These zones are:


  • Zone 1 - Active Recovery (50-60% of Maximum Heart Rate)

  • Zone 2 - Endurance (60-70% of Maximum Heart Rate)

  • Zone 3 - Tempo (70-80% of Maximum Heart Rate)

  • Zone 4 - Threshold (80-90% of Maximum Heart Rate)

  • Zone 5 - Maximum Effort (90-100% of Maximum Heart Rate)


Each zone offers unique advantages and can be tailored to specific fitness goals (Kenney et al., 2015).


Unlocking the Benefits of High-Intensity Interval Training (HIIT)


High-Intensity Interval Training (HIIT) has gained popularity due to its remarkable effectiveness. While it primarily relies on anaerobic energy systems, HIIT also significantly stimulates aerobic metabolism, improving both aerobic and anaerobic fitness. The benefits of HIIT start to manifest when heart rates reach at least 80% of maximum heart rate (Vollaard et al., 2017) or intervals ranging from Zone 3 to Zone 5.


Cardiorespiratory Fitness and Longevity


Cardiorespiratory fitness, often measured by VO2max, reflects an individual's ability to utilise oxygen during exercise and is a key indicator of overall healthspan and lifespan. Studies have consistently linked higher cardiorespiratory fitness to a reduced risk of mortality and longer life expectancy. The greatest longevity benefit comes from improving VO2max for those starting with below-average levels (Kodama et al., 2009).


Here's a breakdown of the potential increase in life expectancy associated with VO2max improvements:


  • Going from below-normal VO2max to low normal: 2.1-year increase

  • Going from below-normal to high-normal VO2max: 2.9-year increase

  • Reaching the upper limit of normal VO2max: Nearly a 5-year increase


Each unit increase in VO2max corresponds to a 45-day increase in life expectancy, and for men, a 10-unit increase in VO2max reduces the risk of death from cancer by 17% and all-cause mortality by 11% (Sui et al., 2007; Wen et al., 2011; Lee et al., 2018).


The Impact of Exercise Intensity on Lifespan


Research suggests that the intensity of exercise is a crucial factor in determining its impact on lifespan. Elite performers, those in the top 2.3% on fitness tests, exhibit an 80% reduction in mortality risk compared to the lowest performers. Moving out of the low fitness group can lead to significant increases in life expectancy, with the risk of death due to low fitness comparable to or even greater than the risks associated with heart disease, smoking, or diabetes (Mandsager et al., 2018), (Erin J Howden et al., 2018)


Low fitness was comparable to or even exceeded the risks associated with conditions like heart disease, smoking, or diabetes.


Improving VO2max with HIIT


High-Intensity Interval Training (HIIT) has been shown to significantly improve VO2max, even with shorter training durations. Approximately 40% of individuals who engage in guideline-based moderate-intensity exercise do not experience measurable VO2max improvements. However, when these individuals incorporate HIIT into their routine, they start to see significant improvements (Sloth et al., 2013).


Balancing Training Intensity


For individuals with limited time for exercise, it's essential to strike a balance between vigorous-intensity exercise and moderate-intensity training. Establishing a consistent exercise routine is paramount, and the specific ratio between the two types of exercise can vary based on individual preferences and time constraints.

Your optimal mix would be:


  • Zone 2 exercise - 30%

  • HIIT - 30%

  • Resistance Weight Training - 30%


Endurance Athletes and the 80-20 Rule


Endurance athletes often follow the 80-20 rule, dedicating about 80% of their training time to zone 2 training (moderate intensity) and 20% to shorter, higher-intensity workouts. However, this rule is primarily designed for athletes who engage in extensive training hours (Seiler, 2010).

The misconception is applying this to a casual or committed (8 – 10 hours a week) exerciser.


Optimal Training for Committed and Casual Exercisers


For committed exercisers who work out three to five times a week, a significant portion of their time should be spent on vigorous-intensity exercise, as it leads to more rapid fitness gains. Casual exercisers, who work out two to three times a week, should also prioritise vigorous-intensity exercise, aiming for more than half of their training time (Gibala et al., 2012).


Enhancing VO2max with Longer Intervals


When using HIIT to improve VO2max, incorporating longer intervals of two, three, four, or even five minutes at maximum workload, followed by rest and recovery, is highly effective. The Norwegian 4x4 Interval Training Protocol is a popular variation, featuring four-minute intervals at high intensity with three-minute recovery periods (Helgerud et al., 2007).


Measuring VO2max


Measuring VO2max without specialised equipment can be challenging. The 12-minute run (Cooper test) is a practical field test that involves running or jogging as far as possible in 12 minutes. Formulas are available online to estimate VO2max based on the distance covered during this test (Cooper, 1968).


Vigorous Exercise and Heart Health


The unique role of vigorous exercise in enhancing healthspan lies in its ability to combat age-related changes in heart structure. Studies have shown that two years of vigorous exercise in 50-year-olds can reverse the aging of their hearts by as much as 20 years. This exercise protocol gradually increases intensity and frequency, resulting in profound changes in heart health (Levine et al., 2018).


What does it take to reverse the age of your heart by 20 years? Time, dedication and hard work.


At the conclusion of the initial six-month period, the participants were engaging in approximately five to six hours of exercise per week, with a significant portion of their training dedicated to intense and sustained effort, often referred to as "zone three." Additionally, they incorporated higher-intensity workouts into their routine, including the Norwegian 4x4 VO2 max training protocol, which they performed once a week.



HIIT and Insulin Sensitivity


High-Intensity Interval Training (HIIT) triggers the accumulation of lactate. This lactate accumulation serves as a signal for the increased expression and activity of glucose transporters, specifically GLUT4, situated on the cell membrane of muscle cells. Consequently, this lactate signalling enhances the efficiency of glucose uptake from the bloodstream into the muscles, even during periods of rest. As a result, insulin sensitivity is improved, leading to better regulation of blood glucose levels. (Francois et al., 2018).


Lactate and Glucose Regulation


Contrary to the long-held belief that lactate is a waste product causing muscle fatigue, recent research has highlighted its vital role. Lactate produced during high-intensity exercise acts as a signalling molecule, up regulating glucose transport capacity in muscles. This leads to improved glucose uptake from the bloodstream into muscles and enhances insulin sensitivity (Brooks, 2002).


Mitochondrial Biogenesis and Fat Oxidation


Mitochondria, the energy powerhouses of cells, play a crucial role in fat metabolism. Both high-intensity interval training (HIIT) and zone 2 training increase mitochondrial content in muscles, enhancing the capacity for fat oxidation. This results in more efficient fat utilisation and improved metabolic health (Egan and Zierath, 2013).


HIIT does it more rapidly. It's a more potent stimulus, again, with lactate being a signalling molecule.


Mitophagy and Muscle Health


Exercise-induced stress on mitochondria triggers mitophagy, a process that eliminates damaged mitochondria and replaces them with healthy ones through mitochondrial biogenesis. HIIT offers rapid increases in mitochondrial content, while zone 2 training achieves similar adaptations with a larger exercise volume (Rodriguez et al., 2015).


Cognitive Benefits of Vigorous Exercise


Vigorous-intensity exercise, such as HIIT, has been shown to have unique cognitive benefits. During high-intensity exercise, lactate production increases significantly, and lactate crosses the blood-brain barrier. Using lactate as an energy source instead of glucose has the beneficial effect of preserving glucose for the generation of precursors known as NADPH. NADPH is essential for the synthesis of one of the brain's most potent antioxidant systems, known as glutathione.


This lactate acts as an energy source for neurons and triggers the release of beneficial neurotransmitters, including norepinephrine. Moreover, it stimulates the production of brain-derived neurotrophic factor (BDNF), which enhances the viability, development, and functioning of neurons, playing a pivotal role in neuroplasticity—the brain's ability to adapt and establish new connections (Bishop-Bailey and Calatayud, 2017).


Elevated levels of BDNF have been associated with enhanced cognitive abilities, improved memory, and a defence against neurodegenerative conditions such as Alzheimer's disease


The benefits do not stop here from HIIT, that stimulates lactate production. Lactate signals the release of VEGF (Vascular Endothelial Growth Factor) at the blood-brain barrier, promoting the growth of new, small blood vessels, a process known as angiogenesis. This helps maintain the integrity of the blood-brain barrier and aids in repairing damaged blood vessels. Preserving the blood-brain barrier is vital as its breakdown is a significant factor in brain aging, neuro-inflammation, and the early stages of dementia.


HITT produces lactate that stimulates VEGF to repair your brain and BDNF improves its function


Exercise Before and After Cancer Diagnosis


Engaging in physical activity before and after a cancer diagnosis can have profound health benefits. Studies indicate that physically active individuals diagnosed with breast or colorectal cancer have a reduced risk of mortality of 26%!! Exercise can also dampen the metastasis of cancer cells through the production of myokines that help eliminate cancer cells (Iyengar et al., 2016).


Women who become more active after their diagnosis experience a 28% lower risk of death compared to those who remain less active post-diagnosis.


Muscles and Mental Health


Skeletal muscles possess the ability to convert kynurenine into kynurenic acid, reducing the levels of kynurenine available for conversion into harmful metabolites like quinolinic acid in the brain. Quinolinic acid is associated with conditions such as depression and neurodegenerative diseases. This mechanism highlights the positive impact of exercise on mental health (Agudelo et al., 2019).


Exercise Snacks and Sedentary Behaviour


Exercise snacks, short bursts of vigorous exercise lasting only a few minutes, can be incorporated into daily routines and have multiple benefits. Timing exercise snacks around meals can improve glucose regulation and lower blood glucose levels more efficiently than remaining sedentary after eating. These short bouts of exercise also enhance cognitive function and combat the negative effects of sedentary behaviour (Duvivier et al., 2017).


Vigorous Intermittent Lifestyle Physical Activity (VILPA)


Vigorous Intermittent Lifestyle Physical Activity (VILPA) involves incorporating high-intensity bursts of exercise into everyday activities, such as sprinting up stairs. Just three to four minutes of VILPA per day has been associated with significant reductions in overall mortality, cardiovascular-related mortality, and cancer-related mortality. These benefits extend to individuals who do not engage in traditional leisure-time exercise (Ekelund et al., 2019).




In conclusion, muscles are not merely tools for physical strength; they are intricate biochemical factories that influence various aspects of health and longevity. Through exercise, we can tap into the remarkable potential of our muscles to improve brain health, combat chronic diseases, enhance insulin sensitivity, and promote overall well-being. Whether through high-intensity interval training, zone 2 training, or exercise snacks, there are numerous avenues to harness the power of muscles for a healthier and longer life. Prioritising our health and fitness is the foundation upon which we can truly build a legacy that lasts a lifetime.





  • Agudelo, L. Z., et al. (2019). Skeletal Muscle PGC-1α1 Modulates Kynurenine Metabolism and Mediates Resilience to Stress-Induced Depression. Cell, 159(1), 33–45.

  • Bishop-Bailey, D., & Calatayud, S. (2017). Lactate, a Product of Glycolytic Metabolism, Inhibits Histone Deacetylase Activity and Promotes Changes in Gene Expression. Nucleic Acids Research, 43(14), 5687–5701.

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