Intensity or Duration: What makes fit happen faster?

It is a great question and, an important one because more and more it seems like there is less time in the day to get things done.  In a world of time crunches and deadlines, life is too busy for time to be wasted.  This is no truer than when working towards a healthier life because every moment we live takes us one step closer to death.  To obtain the highest quality of life, we must make every moment count. Exercise is no exception to this. So how does intensity and duration play into this? Are these interchangeable topics or do they exist independent of each other?

                This conversation can be viewed in two ways: what is best to achieve short-term goals and what will result in a lifetime of healthy living?  The second part of this question is the simplest to answer.  It takes a lifetime to live a healthy life.  Anyone who says otherwise is selling something.  If you believe anything different, I have beach front property in the Himalaya’s I would like to sell you.  Commit to making exercise a life time priority and you are one step closer to maximizing your health and quality of life.  Durable people last, it is that simple.

                The question then becomes; what is best for hitting specific goals along that journey and what is the best method for training to accomplish those goals?  On a side note, breaking down the overall goal of living a healthy life into several Specific, Measurable, Attainable, Realistic, Timely (SMART) goals makes achieving the big goal doable.  After the goal is identified duration is measured in two ways: the number of training sessions or weeks or months that will be completed between the initial establishing of the goal and the first progress evaluation.  The second consideration of duration is the length of time for specific training sessions.

                When I help a client establish a SMART goal, the time frame between initial evaluation and first progress evaluation is typically somewhere between four to twelve weeks after beginning the program.  If the client’s goal is to lose body fat, we test body fat percentage and take measurements every four weeks.  For someone looking to improve strength on a specific exercise or as a part of a sports performance program, evaluations are typically every eight to twelve weeks.  Specified goals with consistent, periodic evaluations are crucial to building a life time of health and fitness.

Among fitness professionals, the debate of the importance of Intensity and Duration in improving overall fitness can be quite heated.  The answer to this debate lies in another question: what is the desired performance goal?  The emphasis on intensity or the duration of training sessions is determined by the performance goal.  A person who runs marathons has a different performance goal than a power-lifter.  A person looking to lose ten pounds has a different goal than a person looking to lose one hundred pounds.

                It is pretty simple to understand that a person who wishes to successfully run 26.2 miles needs to focus, first and foremost on duration by basing training on building endurance.  Whereas a power-lifter needs to perform at a maximal intensity for just a few seconds, clearly high intensity training is more important than high levels of endurance.  So what is the average person, heading outside or into a local fitness center simply looking for a healthier body, to do?

                Two concepts of how the body responds to individual training sessions need to be understood: Excess Postexercise Oxygen Consumption (EPOC) and the hormonal response.  EPOC refers to the amount of oxygen the body needs following a training session.  During exercise the body needs more oxygen to aid in supplying energy for performance than when the body is at rest.  This is also true immediately after training. EPOC is a scientific way of referring to both the length of time and the extra amount of oxygen the body needs to return to its preexercise state.  In laymen’s terms this is called “sucking wind.”  How long and how much “sucking wind” a person does following exercise is one method of measuring the intensity of exercise.  The hard and longer a person remains in an elevated state of EPOC or, the longer you suck wind, the faster fitness levels, and overall health, will improve.

                Before establishing a specific length of time for an exercise session, a basic understanding of hormonal response to exercise needs to be understood; the hormonal goal of exercise is to create an anabolic response.  To put the body in an anabolic state, that is a state in which the body will become stronger and healthier as opposed to a catabolic state in which the body breaks down, becoming weaker and less healthy.  Excessively prolonged duration of exercise can take the body past an anabolic state and into a catabolic one.  Anabolic hormones promote healthy tissue growth and recovery from exercise.  The important anabolic hormones are insulin, insulin-like growth factors, testosterone, and growth hormone. The catabolic hormones are cortisol and progesterone. 

The objective of a quality training session is to work at an intensity that creates of high level of EPOC in short an enough amount of time that the hormonal response of the body stays in an anabolic condition.  So what is an appropriate time frame to maximize the mix of intensity and duration?  Testosterone, the most important of the anabolic hormones, peaks at around forty-five minutes into a training session and is beginning to drop off by sixty minutes.  If an exercise session goes beyond sixty minutes this drop off happens at a faster rate than if the session stopped at sixty minutes.  Prolonging exercise beyond sixty minutes accelerates the process of the body becoming catabolic.  If a training session lasts for two hours testosterone levels have dropped lower than testosterone levels would be one hour after the end of a sixty minute training session. 

The take away from all of this: for most people an intense training session lasting duration of forty-five to sixty minutes is the most beneficial combination.  This exercising at a high intensity for this time frame is more effective then decreasing intensity to the point of prolonging exercise beyond an hour.  Do forty-five to sixty minutes of challenging work not two hours of playing around.  Get in, get out of breath, break a sweat, and get on with life.