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Monday, June 10, 2013

The Meaning Behind Sets & Repetitions

Many moons ago I knew that I would eventually own either my own fitness facility or some kind of facility in which I would be able to do personal training and incorporate a well rounded body-mind-soul-work-play life style.  This was in 1983.  It was my first year in college at Scottsdale Community College.  The corporate wellness boom was in it's beginning years.  Health clubs were popping up such as Nautilus.  But I had something much more specific in mind.  It had to have just the right balance of education, promotion of fitness, prevention of injury...

Finally, in 2002 after receiving my Doctoral Degree I opened my very own clinic!  The name of my clinic was Specialized Exercise & Physical Therapy.  The Specialized Exercise designated that each person coming in is treated with a specific or special prescription just to suit their needs.  After all, physical therapy is specialized exercise mixed with other treatment modalities, manual therapy, etc.  

I began mentoring 1st & 3rd year physical therapy graduate students.  Many of the students did not have an undergraduate degree in healthcare, exercise science, or any other experience with human performance and rehab.  And then many of the graduate students did have exercise science degrees.  But with this one topic (sets & repetitions), there was a commonality with the non exercise science background and the students with business degree backgrounds.

Now, To My Point

Part of being an intern is to become competent with evaluating, assessing & problem solving, and diagnoses.  When it came time to prescribing a rehab protocol, I made it a point with every student to ask why they prescribed the number of repetitions and sets for this person with a specific exercise.  The most common reply was of course to strengthen the muscle, improve joint glide, decrease scarring and so on.

But what I was asking is "specifically, how did you come up with the number of repetitions and the specific number of repetitions?"  There was surely a reason behind it.  Never once did any of the students understand the science behind sets & repetitions.

Here's The Answer!  (Go To The Bottom For The Short Answer)

I'll use the example of performing and arm curl or flexing, pumping, working the biceps.  There is a massive amount of muscle fibers that "recruit" or work to perform this motion against resistance.  Each one of these muscle fibers has a certain amount of "fuel" (oxygen, blood glucose, stored glycogen converted to glucose, ATP, adipose, etc.).  The fuel source depends on the amount of resistance that is being applied and for how long the work is being done.  Again, for our purposes, we're going to be speaking of the blood glucose or ATP fuel source.

So far, we have:

Muscle fibers + Fuel source

Now, let's assume that every muscle fiber in the biceps muscle fired and spent it's fuel source on just one repetition.  If this were the case, there would be no fuel left in the muscle to perform a second repetition.  This raises the question of how is it then that more repetitions can be performed?

Let's go back to the muscle fibers and recruitment.  Out bodies will only use or recruit the amount of muscle fibers necessary to complete the movement against the resistance being used.  

Now we have:

Muscle fibers + Recruitment + Fuel source

Now there's one other component that needs to be added in.  How are repetitions figured in?  There is a very strong science background with regards to the amount of repetitions for developing specific properties of a muscle.

The equation now is: 

Muscle fibers + Recruitment + Fuel source + Repetitions =

Repetitions:      3             6              8             10              12              15              20               25
Per Set 
Weight:          Heavy                                  Moderate                                  Light

Intensity:       Hight Intensity                    Moderate Intensity                  Light Intensity

Results:         Strength                              Muscle Hypertrophy                Endurance                 
               Blood Glucose/ATP                Blood Glucose/Oxygen            Glycogen/Fat Stores

Deciphering The Above Table:

The above table is a general rule to follow when wanting to develop a the type of strength that repetitions indicate.  A very high resistance is going to recruit a much large amount of muscle fibers.  A more stronger motor is needed to move the weight.  When performing this type of repetition, the fuel that is being used is what is immediately available in the muscle fibers that are working.  The muscle needs instantaneous fuel.  There's no time to use oxygen as fuel.  Using oxygen takes time to process through the "Krebs Cycle" in order to convert it to ATP.  Therefore the repetitions that you'll be able to complete will be very low.  When working the muscle to develop raw strength, the rest time between sets will be much greater.  Often, an olympic power lifter will wait upwards of 8 - 12 minutes between sets of just 3 - 4 repetitions.  This time is needed in order for the muscle to evacuate lactic acid and replenish the muscle of fuel necessary for the next set.

As you can see, when moving to a lower resistance, more repetitions can be performed.  This is because fewer muscle fibers are being recruited per repetition.  So while one group of muscle fibers are working, a separate group is resting.  When the first group of muscle fibers have depleted their fuel and are unable to continue working against the resistance, then the resting fibers take over buy not until the subsequent set.

Sets are the last component of prescribing the sum of sets & repetitions.  

From the last paragraph above, only the necessary amount of muscle fibers will recruit or work depending on the resistance.  If the weight or resistance is light, then a large amount of repetitions will be able to be performed.  This is because the fuel source for the amount of resistance or work being done is plentiful.  Eventually though, the fuel will run out and the exhaust or waste product will takes it's place - Lactic Acid or plain overall fatigue.  The muscle fiber will fatigue, and you'll have to put the weight down and rest.  When this point is reached, you've just completed one set.

So, if you want to increase the size of a muscle (hypertrophy), then using a weight in which the muscle fatigues between 8 - 12 repetitions is perfect!  A rest of 40 seconds to 75 seconds is a good rest period between sets for this type of training.  The reason why you want to perform 2 - 5 more sets with this specific exercise is to recruit the total amount of muscle fibers in the biceps muscle.  Remember, during a set of repetitions, only a specifically determined amount of muscle fibers will be working.  The rest of the muscle fibers are resting.  On subsequent sets, the resting fibers work.  Multiple sets are performed to make sure all of the muscle fibers in that specific muscle belly are sufficiently worked in order to make the desired change.

Now Our Equation Reads:

Muscle fibers + Recruitment + Fuel source + Repetitions + Sets = Desired Outcome.  

Short Answer:

Weight lifting/strengthening is goal specific.  To improve the strength or power of a muscle there has to be a large enough force and workload applied to the muscle in order to make permanent change.  By performing multiple sets, this ensures that all of the muscle fibers in a targeted muscle belly are recruited and fatigued enough so that the desired change is made.  This means that by using, for example, a 20 lb. weight and you are only able to complete 10 repetitions, then this constitutes one set of 10 repetitions.  By repeating a set consisting of 10 repetitions even if you have to vary the weight to do so, you are still sufficiently working the muscle to cause an increase in strength and size (muscle hypertrophy).

As usual, email with any questions or concerns!

Good Health To All,

Brad Senska, PT, DPT, BS, ASTYM.

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