But do these beliefs have certain merit and even have a current evidence basis?
Within these articles I hope to shed light on some of the common bodybuilding beliefs.
Shaping A Muscle
The Argument Against
Most anatomists will tell you that a muscle and its shape are determined through genetics and to a point this is undeniably true. A muscle has an origin and an insertion and where these affix upon the body is genetically determined and there's nothing you can do about this.
This pretty much lays waste the belief that you can shape a muscle, after all it can not become longer if its end and start point are undeniably fixed and considering that physical variables such as peak to a bicep and flare to your lats depend upon insertion points it would appear these variables are beyond your control.
However as with anything in the human body there are almost unlimited variables in governing a single structure and as such the topic becomes slightly more grey than the black and white belief espoused above. Considering that for a long time bodybuilders have laid claim that certain exercises are 'shaping' movements do they have any substance to this claim?
Shape Of A Muscle Or Shape Of An Area
Firstly when most people think of the shape of a certain muscle they are in fact actually envisioning a body part or grouping of muscles rather than a single muscle itself.
Considering this it's now easy to see that preferential hypertrophy of a single muscle within a cluster of muscles can give an appearance of a bodypart changing its shape due to a single area developing, which is in fact just a single muscle developing more than its surrounding musculature.
There are a myriad of examples that can be used to prove this point. One case in point would be developing the rhomboids and trapezius rather than the lats in order to develop thickness within the back as opposed to more width. A second example would be development of the brachilis rather than the bicep in order to create thickness in the lower area of the upper arm.
Two Heads Are Better Than One
The second factor which allows an area or muscle to be preferentially shaped through differing areas is if the muscle has more than one head. Muscles that have two or more heads to their structure will either usually cross two joints and perform more than one action or allow a particular action to be performed from more than one angle.
A case in point is the sternal head and clavicular head of pectoralis major which allows adduction or horizontal flexion with the arm in a variety of ways.
With this muscle group there is a tendency for the sternal head to take more of the workload during movements were the arm is inferior to the shoulder joint, where as the clavicular head tends to take more of the workload with adduction or horizontal flexion actions when the arm is superior to the shoulder.
This is the case with many of the multiheaded muscles within the body, for example the quadriceps and squat depth effects recruitment of either the vastus medialis or vastus lateralis.
Considering the vastus lateralis gives a greater appearance of sweep to the thigh and the vastus medialis gives greater thickness around the knee and the teardrop look, it's easy to see how altering an exercise or its range of motion can give the thigh a different apparent shape.
Proximal Vs Distal Hypertrophy
Typically it's thought that a fiber will run a long the length of a muscle and according to the all or nothing principal it will contract along its entire length or not all. Considering this it is presumed that the entire fiber will adapt and hypertrophy to any given stimulus, however several studies have shown that a fiber may end intrafascicularly or in other words mid way through the length of a muscle (loeb 1987, chaunaud 1991, ounjian 1991, trotter 1995, young 2000).
This means that if these motor units' fibers are preferentially hypertrophied they will cause greater hypertrophy either proximally or distally along the muscle. This lends credence to the belief of being able to build either the lower or upper, inner or outer segments of certain muscles.
Considering that different exercises recruit motor units in different patterns it may be presumed that certain exercises will recruit these short fibers and aid in either proximal or distal hypertrophy of a muscle.
Another interesting point is that it has been found that certain motor units have fibers which taper in diameter through the length of the fibers so as to have a larger cross sectional area at one end or another (ounjian1991, trotter1995, eldred 1993,trotter 1991, sheard 1999 2000, young2000).
Evidence for Distal or proximal hypertrophy was found with a study which found greater distal hypertrophy with Isokinetic style training (housh1992) and greater proximal hypertrophy with weight training (smith 1995).
This may indicate that differing types of contractions such as isotonic and auxotonic versus isokinetic are responsible for possible non uniform hypertrophy. This was supported by a study that showed weight training which typically uses isotonic or auxotonic contractions produced uniform hypertrophy within the leg musculature (narcici 1996).
What Does It All Mean?
The jury is still out on whether you can shape a muscle or not, with most anatomists believing that a muscle either hypertrophies or atrophies and the resultant shape is genetically determined.
But as stated above there is some evidence to believe that preferential recruitment of certain sub populations of motor units will alter the shape of a given muscle.
Even if this is not true, it's a definite that certain muscles are bio mechanically loaded more than other muscles which perform similar functions during different movements.
As such the development of different areas of the body can be achieved through careful exercise selection.
Considering this it would seem prudent to choose a wide variety of exercises and training modalities in your pursuit of physique development as long as this does not interfere with the corner stone of training which is progression in weight used over time. Within Part two we will look at more bodybuilding myths and try to uncover the truth behind them.
- Ounjian, M. Roy R.R, eldred E et al 1991. physiological and developmental implications of motor unit anatomy. Journal of neurobiology 22, 547-559
- Loeb G.E, Pratt, .A Chanuad C.M Richmond F.J 1987. distribution and innervation of short, interdigitated muscle fibers in parallel fibered muscles of the cat hind limb. Journal of morphology 191, 1-15
- Chanaud , C.M, Pratt, C.A Loeb G.E 1991. functionally complex muscles of the cat hind limb. II. Mechanical and archeticural heteogenity within the biceps femoris Experimental Brain research 85, 257 270
- Trotter, J.a Richmond, F.J.r and Purslow 1995. functional morphology of force transmission in skeletal muscle. A brief review. Acta Anatomica 146 205-222
- YoungM, Paul A. Rodda J, Duxson M, Sheard P 2000. examination of intrafascicular muscle fiber terminations; implications for tension delivery in series-fibered muscles. Journal of morphology 245, 130-145
- Trotter J.A 1991 Dynamic shape of tapered skeletal muscle fibers. Journal of morphology 207, 211-223
- Eldred E, Ounjian M, Roy R.R Edgerton V.R 1993. Tapering of the intrafascicular endings of muscle fibers and its implications to relay force. Anatomical record 236 390-398
- Sheard. P.W, Mchannigan P,Duxson M.J 1999. single and paired motor unit performance in skeletal muscle: comparisons between simple and series-fibered muscles from the rat and guinea pig. Basic and applied mycology 9 79-87
- Sheard P.W 2000 tension delivered from short fibers in long muscles. Exercise and sport science reviews 28, 51-56
- Housh, D.J. Housh T.J. Johnson, G.O and Chu, W.K. 1992 Hypertrophic response to unilateral concentric resistance isokinetic resistance training. Journal Applied physiology 73, 65-70.
- Smith R.C. and Rutherford, O.M 1995. The role of metabolites in strength training. I. A comparison of eccentric and concentric contractions. European journal of applied physiology 71, 332-336.
- Narici M.V. Hoppeler, H. Kayser, B. et al 1996. human quadriceps crosssectional area. Torque and nueral activation during six months strength training. Act Physiologica Scandinavica 157, 175-186.