The Case Against High Intensity Cardio

We are all aware that we need to exercise in order to maintain an appropriate body weight, to be healthy, and increase our longevity.  However, the popular wisdom of the past 40-or-so years – that we would all be much healthier if we did 45-60 minutes of intense aerobic activity every day – has created a generation of overtrained, underfit exercise-a-holics.  In this blog post, I want to explore why high intensity aerobic training (think for marathon running or IronMan competitions) does not favor long term health or longevity.

Have you ever wondered why some people you know that exercise daily and complete ultra-marathons are not the healthiest people you know?  Years of spin classes and endless treadmill or elliptical sessions are not the answers to healthy, sustainable weight loss, and will do very little to contribute years to your life (in fact, they may decrease your overall healthy by harming your heart and your immune system).

There is a much easier, more effective, and fun way to burn fat, build and preserve lean muscle mass, maintain optimal health and increase your longevity.  But before we get to the details of how, we need to understand why this type of exercise is best for the human body.

Humans, like all mammals, have developed two primary energy systems that power our bodies.  They were developed as we evolved, in order to make our hunter-gatherer ancestors most efficient at their jobs of finding food, surviving, and producing and protecting offspring.

The 1st energy system: relies on the slow burning of fats to create energy (energy is also known as ATP).  This system keeps us fueled while we sleep or undergo low levels of aerobic activity (think of the gatherers – walking around looking for nuts, berries, and insects to eat).  Fats are very efficient fuels that are stored easily and burned easily when there is adequate oxygen present.  A well-adjusted hunter-gatherer could walk and forage for days without compromising his/her efficiency by using this slow fat-burning system.  Moderate intensity exercise has been shown to increase the amount of mitochondria (ATP producers in cells) in muscle cells over time.

The 2nd energy system: allows for short-term bouts of intense work that are accomplished in very brief bursts (think of the hunter who has to sprint for 20 seconds to get out of the way of an angry lion).  This system is called the ATP-PC system (ATP for energy, and PC for phosphocreatine – ATP in muscle cells provides the quick burst of energy, and PC replenishes the ATP as it is depleted).  Together, ATP and PC are a fantastic short-term fuel, but they don’t last long.  Our muscles can only store 10-20 seconds worth of this precious fuel to complete life-or-death tasks.  Within a minute or two, our bodies can replete ATP-PC stores for another 10-20 seconds of intense exertion.  This type of “interval” training causes an increased release of natural growth hormone,  which stimulates muscle growth to make the next intense bout of exercise easier.

If we think about it, running for hours on end wasn’t a smart way to be a human 40,000 years ago – squandering precious energy resources on running all day, with no promise of catching a prey for fuel, would be a quick way to exhaust yourself and become weak over time.  A weak human = another animal’s prey.  In the era of survival of the fittest, it was those humans who acted in accordance with these two energy systems – slow, continuous or intermittent walking/stalking interrupted by quick 10-20 second bursts of activity – that survived to pass on their genes to the next generation.  Further, much recent research has suggested that high intensity long distance endeavors (like marathon running) causes temporary damage to the heart, and may decrease one’s longevity.

So, what does this mean for you in 2014?

More and more research is coming to light that the current popular high intensity aerobic pursuit is not in the interest of long-term health and longevity.  It requires huge amounts of carbohydrate fuel (think: sugar, or foods that can be easily converted to sugar) to sustain, which promotes hyperinsulinemia (production of large amounts of insulin); over time, this increases oxidative damage (body “rust”) by a factor of 10-20x, and generates high levels of cortisol (the stress hormone) which increases susceptibility to injury, infection, depletion of lean muscle mass, and loss of bone density.  All while encouraging the body to deposit fat for future fuel!

Knowing about all of the above, we have to keep our hunter-gatherer ancestors in mind while devising the optimal exercise program for long-term health and longevity.  Ideally, our lifestyles would involve continuous or intermittent walking to maximize fat-burning systems, and intermittent sprints every once in awhile to generate growth spurts in our muscles.

Bottom Line: a combination of low level aerobic movement (walking, hiking, moderate intensity cycling) several times per week for 30-45 minutes (adding up to 250+ minutes per week), plus a few intense interval sessions (sprinting, or do any other activity intensely for 10-20 seconds at a time, with 1-2 minute rests in between) once or twice a week, is the most optimal strategy for fat loss, health and increased longevity.

In health,

K.

References:

Garber CE et al. American College of Sports Medicine position stand. Quantity and quality of exercise for developing and maintaining cardiorespiratory, musculoskeletal, and neuromotor fitness in apparently healthy adults: guidance for prescribing exercise. Med Sci Sports Exerc 2011;43(7)):1334-59.

Gerche AL  et al. Exercise-induced right ventricular dysfunction and structural remodeling in endurance athletes. Eur Heart J, 2011; doi: 10.1093/eurheartj/ehr397

Donnelley JE et al. American College of Sports Medicine position stand: appropriate intervention strategies for weight loss and prevention of weight regain for adults. Ed Sci Sports Exerc 2009;41(2):459-71.

Menshikova EV et al. Characteristics of skeletal muscle mitochondrial biogenesis induced by moderate-intensity exercise and weight loss in obesity. J of App Phys 2007; 103(1):21-27.

O’Keefe JH et al. Achieving hunter-gatherer fitness in the 21(st) century: back to the future. Am J Med, 2010; 123(12):1082-6.

Siegel AJ et al. Effect of marathon running on inflammatory and hemostatic markers. Am J Cardiol. 2001:;88(8):918-20.

Talanian, JL et al. Two weeks of high-intensity aerobic interval training increases the capacity for fat oxidation during exercise in women. J of Applied Phys 2007; 102(4):1439-47.

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