Pectoral development: The kinesiology of muscular action and development

[digitorum]

Pectoral development: The kinesiology of muscular action and development

By digitorum (AKA Flexor)
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Introduction

Welcome to my article on kinesiology applied to chest development and muscle action in general. This is the first public article I have written, but it is one of many in the style I have written for A level coursework and Degree assignments. It is based on the research I have done in my spare time and has not been submitted as an assignment, it is a separate piece of work. It may be the first of many that I will post here. It doesn't propose anything revolutionary, I have just tried to explain why the various grips have certain effects on pectoral development. The principles can be applied to various other parts of the body as well. The reason for writing this article was primarily for bettering my knowledge as well as for the enjoyment of it. I hope this proves that not all "teens" present their viewpoints without having research to support it!

I posted this at another forum initially about a year ago, but the traffic was so low there and very few read it. So here it is, only bigger and better, with more research, references and hypotheses. My conclusion is an obvious one, but I wanted to explore what the reasons were for it and I thought I would share them with you. Perhaps you have your own viewpoints, in which case they are welcome!

Effects of muscle fibre shortening on fibre damage - concentric action

Firstly, the "sticking point" of a muscle occurs where the muscle fibres shorten to a specific point where maximum force can be produced, although this won’t mean maximum force is produced mechanically because leverages will vary (6). Anyway, as the fibres go past this sticking point as it is called, tension decreases across the length of the fibre and if tension decreases, force is reduced and less damage can be done to the fibres in that portion of the rep (4). This is because the myosin cross bridges involved with binding to the actin within the fibres, become disrupted (4). So, on the concentric portion of your lift, tension will vary (5), meaning it is not the most effective part of your lift to cause fibre damage.

Effects of muscle fibre lengthening on muscle damage - eccentric action

When a muscle fibre lengthens under contraction, the situation is different. The greater the stretch in the muscle fibres, the greater the tension developed and therefore more force can be produced leading to increased levels of fibre damage (4). Muscle fibres do not obey Hooke’s Law of Elasticity, they will exert proportionally more tension the greater the force applied under stretch! (4). This is why pre-stretching the long triceps head and both biceps is effective in French presses and incline dumbbell curls respectively. Also when you lower the weight, it requires more force than needed to raise it, therefore developing more tension even as the fibres continue to lengthen. This is where the most muscle fibre damage occurs (5, 7).

Sarcomeres are the contractile units within the myofibrils which in bundles form muscle fibres, and these contain the actin and myosin proteins responsible for the "sliding filament" contraction (4, 5). During the eccentric lowering of the weight, these proteins are under greater tension since external resistance is greater than muscular force, and their component parts actually break because of this (5, 7). Each rep, more sarcomeres will "break", some on the concentric lift but most on the eccentric. Once you have completed your workout, thousands of sarcomeres at different points along the fibre will have been broken. If you continue to workout after this, you can easily pull your muscle, which occurs because certain muscle fibres have too many broken sarcomeres along their length and the tension delivered by the rest of the muscle is high enough to tear the whole muscle fibre which could not cope because of its weakened state.

These principles applied to chest development

If you bench press with a narrower rather than wider grip, your elbows will naturally remain close to your torso. On either grip though you are getting more or less the same fibre recruitment (2). However, the wider grip allows a greater stretch in the fibres at the bottom of the rep which means more force can be developed (3). The fibres also contract horizontally in the direction that they run across the chest, which creates maximal levels of force in the fibres by removing the angular element of the contraction (mechanics in a straight line is always superior to angular mechanics) (6). This is why the benchpress will yield more mechanical force than a dip for exactly the same muscular activity, not that you can tell because it is far more complicated than that.

If you think about how much the fibres contract though, obviously with a wider grip you have a lower range of motion at the top of the movement because of hand spacing, which does limit fibre shortening. This effect is conteracted though, by the greater stretch at the bottom of the rep because the elbows are flared out to the sides and you have a wide grip. Consequently, between a narrower and wider grip there is probably a similar level of overall fibre contraction. Contraction however is just a general term, because the wider grip will be allowing a greater stretch and the narrower grip allows more shortening at the top of the press. This greater shortening of the pecs at the top of a narrow press is sometimes associated with actually working the "inner" portion of the pec, which doesn’t exist. This theory of localised shortening of fibres is not correct because the myofibrils of the fibres contract uniformly during concentric actions in response to a massive diffusion of calcium ions from the nerve ending down the fibre (1, 4). The myofibrils are not intelligent, they must obey the calcium ions, which gives rise to the sliding filament theory. The sarcomeres contract like a zipper down a coat only it is almost instantaneous. When you zip up your coat, you can't miss out some of the metal links, and this is how muscle fibres work. Either the fibre contracts along the whole length, or it isn't recruited on that rep at all.

There is something else to consider though! An increase in R.O.M. is equal to an increase in distance travelled, which in turn increases time under tension. Increased time under tension will result in greater muscle damage and is believed to be more important than even the total contractile distance regardless of time. So the narrower grip would give a marginally greater TUT if performed at the same pace as a wider grip, because of its greater R.O.M which could in turn cause more damage. I don’t believe this is that significant though.

So to conclude, the greater stretch of the wider grip will increase force production and therefore damage, and the narrower grip will develop both less force because of no stretch and also because of maximum fibre contraction at the top of the press (due to interference of the myosin cross bridges and a reduction in tension). The triceps and anterior deltoids are also strong synergists in the movement which further reduces the stress across the chest. This makes the wider grip better for force development and damage. This is an obvious conclusion, but these are the reasons why.

As for non-uniform, localised fibre contraction, if you consider the pecs, glutes, lats and traps, these are all large muscles that cover a huge area. The traps consist of lower, mid and upper fibres, and all perform different tasks and yet it is still just one muscle. Does this apply to the pectorals? I think no is the answer since the origins of the clavicular and sternocostal heads are far closer and the mechanics are very similar for any chest movement. The traps have many more motor units and nerve endings which are sent different messages from the brain based on the different insertion and origin points of the fibres. The neural coordination of the pecs is complex too, if only because of the huge range of motion over which they work. I believe based on my research though, that the pecs always contract as one.

Thank you for taking the time to read my work, it took some time to research, draw my own conclusions and write it up. I am currently working on another article about the mechanics of the elbow flexors and the influence on fibre recruitment, this may be ready soon. Right, time to go and work that chest and those triceps!

References

1. Adds, J., Larkhom, K. & Miller, R. 2001. Respiration and Coordination. (Revised Edition). Nelson Thornes.

2. Clemons & Aaron. 1997. Effect of grip width on the myoelectric activity of the prime movers in the bench press. J. Strength Conditioning.

3. Hall. 1995. Basic biomechanics. Mosby

4. Lamb, J.F., Ingram, C.G., Johnston, I.A. & Pitman, R.M. 1991. Essentials of Physiology. Third Edition. Blackwell Scientific.

5. McArdle, Katch, Katch. 1994. Essentials of Exercise Physiology. Lea & Febiger.

6. Nigg, B.M. 1995. Biomechanics as applied to sports. Oxford Textbook of Sports & Medicine. Edited by: Harries, M., Williams, C., Stanish, W.D. & Micheli, L.J. Oxford.

7. Wilmore, J.H., & Costill, D.L. 1994. Physiology of Sport and & Exercise. Human Kinetics

[peroxadic]

ima print this and read it during lunch at work, thnx

[iForce Dave]

there is still a lot of debate on working upper chest. what are your thoughts and suggestions on this topic?

can it be isolated (not completely but you know what i mean)?
exercise reccommendation for upper pec thickness?

[paulmh]

I only ever train upper chest with incline flys that is isollating the upper chest.. But i only train upper chest maybe 2-3times a month..

[ProjectCG]

Well lookin at your pic man^ youve just got some good genetics for your chest. When i started my upper chest was relatively nonexistent. Whats worked for me is for thickness is dumbbell incline and the most isolated for me is the hammer strength incline press.