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Eccentric Contractions And Increases In Muscle Mass

By Edited Nov 13, 2013 0 0

A common curiosity shared by the male population is the acquisition of skeletal muscle mass. The scientific term for increases in muscle mass is muscle hypertrophy - hypertrophy meaning an increase in cell size. Two underlying factors are associated with changes in body mass while training; the amount of calories ingested, and the intensity of the training stimulus. Countless articles circling the web claim to have originated routines which guarantee increased muscle mass. Firstly, if an individual is a novice to resistance training, ANY routine will generate results. Those who are accustomed to an exercise regimen may need to modify the F.I.T.T. principles of training, in order to overcome a plateau. This article will explain the basis of muscle fibre recruitment, the difference between muscle fibre types, the theory behind eccentric contractions (commonly referred to as performing a 'negative' rep), and why studies speculate this form of training has the potential to bring about a higher degree of hypertrophy.

Muscle Fibre Recruitment:

Muscle fibres across the body innervate with peripheral nerves extending from our central nervous system. These innervations are collectively identified as Motor Units. These Motor Units may be smaller or greater, depending on the diameter of a muscle fibre, or allocation within the body. The larger the muscle fibre, or greater the required force, the more motor units recruited.

Muscle Fibre Type:

Three muscle fibres types exist, each which differentiating levels of innervation. I've listed them below in order of recruitment while exercising.

• Slow twitch oxidative, or type I fibres, are recruited first during an exercise bout. These fibres have the lowest rate of firing while training. Higher proportions of type I fibres exist in frequently active muscles. Examples include the soleus or gastrocnemius, as they provide a higher resistance to fatigue.

• Fast twitch oxidative glycolytic (type IIa) fibres are recruited next, and are generally associated with resistance training. These fibres twitch more times per millisecond than type I fibres, and as such, are able to generate a greater force. The pectoral, latissimus dorsi, and vastus muscles are examples in which these fibres predominate.

• Fast twitch glycolytic (type IIx -formerly classified as type IIb) are the final fibre types found in human muscle. These fibres are recruited last, are activated when exerting a maximum amount of force, and exhaust relatively quickly.  

This information illustrates the fundamental principle behind resistance training. By using a heavier weight, one triggers the greatest potential for skeletal muscle growth by recruiting all fibre types. Novice individuals interested in gaining mass and strength should cater their weight lifting routine accordingly by following the guidelines listed below.

Training for hypertrophy:

1. Perform 9-12 repetitions with a resistance equivalent to 65% of your 1 RM (one repetition max)

Training for strength:

2.  Perform 5 repetitions with a resistance equivalent to 85% of your 1 RM (one repetition max)

Common criticisms regarding 'training for hypertrophy' argue that by training for strength, individuals will experience growth regardless. This article will not address the criticisms posed towards either method of training. Both work and work well.

Eccentric Training:

Strength training makes use of a resistance, or weight, which impedes muscle contraction. This causes the muscle to adapt, and as a result, increases its ability to generate force. The most intuitive muscle contraction is the concentric contraction; the shortening of a given muscle. An example of a concentric contraction is the stereotypical bicep curl. By gripping the weight and contracting the bicep, the weight is moved from a 180° angle, to something more acute (90° for example). An eccentric contraction is the exact opposite. Picture the same motion as the aforementioned bicep curl. When returning the weight to its original position, the bicep muscle lengthens back to a rested state. This motion is still a muscle contraction. Movements associated with muscle lengthening are speculated to bring about higher levels of adaptation in comparison to concentric contractions. An eccentric contraction is commonly referred to as performing a 'negative'. Here are some speculations as to why eccentric contractions, or negatives, bring about greater results:

1. A heavier, more potent resistance can be utilized when performing an eccentric contraction.

o Imagine performing a barbell bench press. With training, an individual is capable of moving a given weight, a certain amount of times, before fatigue ensues. Imagine the same exercise, except this time instead of forcing the weight upwards, one is to resist the force of gravity acting on the weight as it comes down. This action lengthens the pectoral muscles, and as such, causes an eccentric contraction. The amount of weight one is able to resist, is greater in comparison to the amount one can move.

2. A higher degree of muscle fibre recruitment ensues upon utilizing a heavier resistance.

o As mentioned above, an eccentric contraction is still a muscle contraction, and as a result, requires the recruitment of an appropriate number of muscle fibres. Muscle fibre recruitment is proportional to the resistance applied; a heavier weight means more fibres involved. The more fibres involved in a given contraction, the greater the degree of adaptation.

3. Eccentric contractions should be incorporated into a regular resistance training routine.

o Negatives can be performed with any routine, for any muscle group, on any training day of the week. Negatives are a good way of modifying the 'Type' and 'Intensity' factors of the F.I.T.T. principle. Some suggest a longer period of rest since heavier resistance is used, insuring a complete recovery.

 

A study performed by Daniel R. Moore, Mark Young, and Stuart M. Philips demonstrates the effects of eccentric training. Nine males aged 20 to 23 years were selected for this particular study. Measurements of an isometric, bicep, eccentric and concentric contraction, for each of the individuals were performed. The study lasted 9 weeks, with individuals 'exercising' twice a week. Results at the end of the study showed increases in work performed by both concentric, and eccentric contractions, as well as an increased bicep muscle mass. However, the measurements attained for eccentric contractions for both parameters were higher with respect to the concentric values. Below are two graphs illustrating the results (LC stands for lengthening or eccentric contraction, SC for shortening or concentric contraction):

 Notice the intrinsic force production of an eccentric contraction prior to exercise training. These results illustrate the potency of the eccentric contraction. Understanding the concepts outlined in this article will aid in diversifying any resistance training program.

Patience and perseverance
 
- Francesco

References:
Moore, Daniel M., Mark Young, and Stuart M. Phillips. "Similar increases in muscle size and strength in young men." (2011): n. pag. Web. 19 Jul 2011.


Total Work Per Repetition

Bicep Cross-Sectional Area

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