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Scientific Breakthrough: Understanding The Benefits of Intense Exercise

Folks, you are NEVER too old to engage in strenuous exercise! In recent years, a flood of scientific research has been reporting that the most efficient and most effective form of exercise is short intervals of high-intensity exercise. Some of the exercise programs that now utilize this approach include CrossFit, Tabata, Insanity and Sprint 8. However, up until now the mechanism of how or why intense exercise affects the body, especially at the cellular level, remained unknown. 

For decades, we have known that intense exercise engages the sympathetic nervous system.  When activated, the sympathetic nervous system releases powerful stress response hormones in both animals and humans which ignites our “fight or flight” survival mechanism. These stress hormones which are collectively called catecholamines include adrenaline, noradrenaline, and dopamine. They accelerate heart rate, increase alertness and prime muscles for battle or flight which enables us to respond to stress or danger. 

Scientists formerly believed that the primary benefit of intense stress or exercise was immediate rather than long-term. For example, a caveman is chased by a tiger; New York businessman is running to catch a bus or train; football player is running for a touchdown. Stress activates the sympathetic nervous system which pumps out the stress response hormones, allowing us to function at a higher level (fight or flight). 

Acute stress as in intense exercise improves performance by increasing blood pressure, muscle tension and blood flow to the muscles. But these are short-term effects which normalize soon after the exercise ends. Up until now, it was believed that the release of catecholamines following intense exercise did not contribute to the body’s long-term response to exercise, such as increased muscle size and endurance. But now, new research is forcing a paradigm shift in our understanding of the benefits of intense exercise.

Recently, scientists at The Scripps Research Institute in Florida have made a discovery which explains why intense exercise produces much greater benefits in far less time compared to mild to moderate exercise. Here’s what the new findings tell us.

The Scripps scientists have discovered that intense exercise causes something molecularly unique to happen at the cellular level. Their research reveals that igniting the sympathetic nervous system following intense exercise causes the activation of a unique protein called CRTC2. 

What is so special about CRTC2?  When the CRTC2 protein receives signals from the catecholamines that have been activated by intense stress or exercise, CRTC2 activates genes which deliver increased levels of blood sugar and triglycerides to the cells undergoing stress. This means muscles undergoing intense stress have more energy to perform better, and they recover much quicker after stress.  

Here is a summary these new findings. The Scripps scientists initially bred mice that were genetically programmed to produce much more of the CRTC2 protein than normal mice. When these mice were put on a program of frequent, high-intensity treadmill running, their endurance skyrocketed by 103% after only two weeks compared to an increase of only 8.5% in normal mice who followed the same exercise routine. The mice genetically altered to express more of the CRTC2 protein also gained an impressive 15% increase in muscle size.

There were also some unique metabolic changes in the CRTC2-expressing mice that enabled them to attain such impressive increases in muscle size and endurance in only two weeks.  The amount of fuel available to the muscles increased dramatically; triglycerides levels increased 48% while glycogen levels increased by an astounding 121%. 

It is important to realize that the CRTC2 protein only gets activated in cells and tissues that are undergoing intense stress. The resulting metabolic changes make more energy available to the muscles which enable them to grow bigger and stronger faster compared to normal exercise routines. Another BIG benefit is that the muscles undergoing intense exercise grow more mitochondria and the existing mitochondria grow larger. This means that over time, the muscles are able to produce more energy and more power…the muscles get bigger and you get stronger.


Aerobic fitness is incredibly important. Virtually everyone can benefit from engaging in aerobic high-intensity interval training (HIIT) a couple times a week. However, I want to stress that high-intensity strength training provides greater gains than high-intensity aerobic training. Here’s why. Like high-intensity aerobic exercise, high-intensity strength training also provides cardiovascular benefits and aerobic fitness. But, additional benefit(s) result from high-intensity strength training because it takes the muscles into a deep level of muscle fatigue. This activates CRTC2 proteins which send chemical signals to the genes in muscle cells. This initiates the metabolic changes that result in building larger, stronger muscles.

The findings of this study give new meaning to the old saying “no pain, no gain.” It is exercise that the body perceives as stressful that induces the catecholamine stress response hormones to activate the CRTC2 protein which signals genes to initiate the metabolic changes that result building bigger, stronger muscles.

This study also enables us to understand the importance of periodically reassessing the intensity of your workouts if you want to continue to improve your overall fitness. When you become stronger, exercises that were formally difficult become easier. The sympathetic nervous system ceases to perceive the exercise as a high-intensity workout. The lower stress means a reduced adrenaline response. This in turn fails to activate the CRTC2 proteins which reduce the opportunity to make significant gains in strength.

It is estimated that over 90% of people who do exercise regularly DO NOT engage in high-intensity exercises. By engaging in steady endurance-type exercises like jogging, running on a treadmill, riding a bike or swimming, you actually forfeit many of the most profound attainable benefits of exercise. However, integrating high-intensity intervals into the exercises I just mentioned will provide much greater benefits in the same (or less) amount of time. But, in closing, I want to re-emphasize that high-intensity strength training produces benefits that go beyond aerobic exercise. It is high-intensity strength training the activates the CRTC2 proteins resulting in rapid metabolic changes at the cellular level that accelerate the rate of building strength, endurance, and stamina. 

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