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Muscle Function and Exercise

The muscle cell is the basic unit that makes up a muscle.  When looking at a whole muscle, we are actually seeing a collection of muscle cells grouped together.  If we were to draw out one cell from the whole muscle, it would appear as a long " spaghetti " like strand.

Each strand is made up of sub-units called "sarcomeres".  These sarcomeres contain the  "contraction proteins” called actin and myosin.  The chemical interactions of these two proteins are responsible for the abilities of the muscle to contract (shorten), relax and produce force (necessary to move the body or objects).
 
Each muscle fiber or cell possesses what is called a " myoneural junction ".  This is the point where the nerve fiber, which originates in the brain and spinal cord, reaches the muscle, and passes -on the signal for the muscle to contract or relax.  This is an area of the muscle that can be trained, as well as the muscle itself.  The muscle fibers are grouped together and surrounded by a tissue sheath, much like the wrapper around a cable or wire.  Groups of many muscle fibers in their sheaths are collected together to form the whole muscle.
 
Muscle fiber recruitment
 
When the demand of lifting a weight or moving an object (the object can be your body itself ) is placed upon a muscle,  the nervous system will "recruit " or gather together as many muscle fibers as necessary to move the weight or object through the required distance.  Muscle fibers not needed will not contract or contract very weakly.  However, as a heavier and heavier weight is lifted, then more and more muscle fibers will be recruited until all of the muscle fibers within a muscle participate in the contraction necessary to move the weight.  If the weight is increased above the maximally recruited state of all the muscle fibers contacting at their highest tensions, the muscle will be unable to overcome the weight imposed upon it.
 
The repetition-maximum (RM) principal applies muscle fiber recruitment principals to establish safe limits to how much weight is lifted in a particular set and when it is safe to raise weights being utilized. .  For example, a 10 RM for the bench press exercise is the amount of weight that can be lifted "just 10 times", and No More, before fatigue or failure sets in.  That is, the particular weight being lifted is so heavy that an 11th repetition is not possible.
 
When a 10 RM weight of 100 lb is used in the bench press, if you can lift 9 repetitions but not complete a 10th repetition, then you can be sure maximal muscle fiber recruitment was reached.  The overload principal applies when you are able to lift for 10 repetitions.  To continue to stimulate maximal muscle fiber recruitment the weight must be increased for the next exercise set or workout session, that is, a new 10 RM weight has been established.
 
Forced Repetitions
 
When strength training, as you reach the RM of a particular set, that is when you reach the 10th repetition of a 10 RM set, the muscle and nerve-muscle units are experiencing momentary fatigue.  If, with the aid of an assistant’s help, you continue more repetitions, you are practicing forced repetitions.  These repetitions are impossible for you to do without the help of the assistant.  Usually, you are able to perform the eccentric or negative lowering part of the exercise alone, but then require the assistants help in the concentric or lifting phase.
 
In general, I do not recommend practicing forced repetitions in any strength building programs.  There is a much higher potential for injury when doing forced repetitions since the artificial aide of the assistant helping complete the repetitions is overriding the muscle’s natural fatigue mechanism.  The same fatiguing effect on the muscle desired by doing forced repetitions can be gained by lowering the weight and performing another set without resting between sets.

 

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