Define 'Cross Sectional Area'

i hear all the time about the cross sectional area but I have yet to graps a full knowledge of what exactly it is

I’ve always assumed its where certain muscles attach

Can anyone help me out?

CSA is basically hypertrophy of muscle fibers.

If you cut the muscle transversely, the surface area that is now exposed would be the cross sectional surface.

I’m still confused

Not to take anything away from Myersje, but I’m a little confused about his answer as well. The CSA will show the size of the muscle, but it is usually used to show and describe the makeup of the muscle (the filaments, fibers, etc.).

If you split an apple in two and look at the surface that you have just exposed, you are looking at a cross sectional area of the apple.

Hope this helps.

that helps alot but then why is the CSA so vital to strength gains?

Larger CSA = Larger Muscle Mass = Increased Strength (in theory).

Not necessarily. In theory, the larger the cross sectional area, the greater potential for gains in max strength.

Yes, looking back at my answer, I certainly didn’t communicate my point very well did I. I like your apple analogy.

CSA shows the size of the muscle fibers and, like you said the makeup as well. As a muscle hypertrophies, the CSA will increase and allow for a greater potential for strength gains (generally speaking).

This is absolutely correct. There are two types of hypertrophy; structural and functional. Functional hypertrophy will definitely increase strength because the contractile components of the muscle increase in size and strength. Structural hypertrophy is seen more with bodybuilding training. Here the structural components and the chemical efficiency of the muscles will show changes.

The CSA is not truly VITAL to strength gains, but rather a byproduct of them. I say this because there are methods to increase the components of strength without increasing the mass of the muscle (there is a thread on this subject that was started yesterday).

Totally agree but functional hypertrophy of fast muscle can allow an athlete with say 30/70 percentage muscle percentage in favour of slow fibre to equate to a 70/30 athlete by increasing fast twitch fibres by 2.5x. Also hypertrophy allows more consistency of performance when neural fatigue sets in, since larger CSA will allow more force to be applied in theory. But training for CSA gains all year round is not a good idea.

checkout the following reference:
(page 21)

Read the section on hypertrophy, very interesting. But I have read other research and been in contact with the author. Though most of the info is correct, they found that an increase in hypertophy leads to improvement in top speed (specifically hamstings). Even thoug h hypertophy leads to fast fibre conversion to slow. Interesting stuff. Read it.

Relationship between hip strength and sprint running performance in sprinters


The purposes of this study were 1) to investigate the relationship between sprint running performance and isokinetic hip strength, and 2) to clarify the muscles that are important in sprinting from the standpoint of isokinetic strength and muscle cross-sectional area (CSA). Sixteen male (100 m sprinting time 10.99}0.46 s) and 12 female (12.50}0.44 s) subjects ran 60 m and their sprinting speed was measured from 30 to 60 m. Isokinetic strength of hip and knee flexion and extension (Nm) were measured at 60, 180 and 300 deg/s. Magnetic resonance imaging (MRI) was used to determine the muscle cross-sectional area of the thigh (upper, middle and lower femur) and trunk. In females, there were no significant correlations between sprinting speed and isokinetic strength. In males, there were significant correlations between sprinting speed and hip strength (absolute value) at an angular velocities (r=0.51-0.75, p< 0.05-0.01), except for hip extension at 300 deg/s. Extension at 60 deg/s was significant (r=0.64, p<0.01) only in the male knee. In males, there were significant correlations between the peak torque of hip extension and muscle CSAs of the hamstring and adductor (r=0.50-0.63, p<0.05-0.01), as well as between the peak torque of hip flexion and muscle CSAs of the psoas major and adductor (r=0.59-0.83, p<0.05-0.001). These results suggest that sprint running performance in males is influenced by the strength of hip flexion and extension. In addition, the muscle volume of the hamstring, adductor and psoas major muscles appears to play an important roles during sprint running in males.

(Japan J. Phys. Educ. 45: 520-529, July, 2000)
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That was implied by the “in theory” part. Of course no one should assume that greater CSA will have a direct and necessary correllation with max strength.

Great point. I was not trying to refute the fact that functional hypertrophy increases absolute strength. The point that I was trying to make is two-fold;

1.) Hypertrophy or a greater CSA will not always yeild increases in relative strength, as is the case of structural hypertrophy, and

2.) Strength gains will not always be accomodated by an increase in CSA.

You may already understand this, but you cannot change a slow twitch fiber into a fast twitch fiber, and vice versa. They can, however, adapt through stimulation of myosin isoforms to form a hybrid muscle fiber. These hybrids will resemble the original fiber type with varied contractile properties. In other words, the slow twitch fiber can adapt to contract with a quicker rate of force developement, but it will retain some of it’s fatigue resistance. There are many combinations of hybrid fiber types, and this topic is still considered a little controversial.

This is an interesting absract, but one thing compromises the study. Isokinetics, although easy to extract scientific data, are a poor indicator of strength components. Isokinetic actions are rarely seen in sporting movements outside of water sports (rowing or swimming). An Isokinetic action will not stimulate the muscles enough to produce absoluteor max strength, but rather measure the max torque applied to the machine. The acceleration phase of the muscle contraction is virtually eliminated, as is the deceleration phase. Other than this, the idea and theory of the abstract are sound. I do agree with the findings as well.

perhaps the hypertrophy inducing method plays a significant role here; is there any info on that?

(sorry, but the .pdf link didn’t work for me; perhaps there is some info there…)

You will not benefit from greater hypertrophy only if you do not go through a phase of max strength training after. Check out Tudor Bompa’s “Periodisation training for sports” or read in full the PDF reference above or do a search on Prof Schmidtbleicher to gain a greater insite into adv’s and disadv’s

No a fast twitch fiber will not turn into a slow twitch fiber but you can make a fiber behave less like its intended function in terms of velocity. Contractile velocity decreases whilst contractile force increases after strength training. The point is, slow fibre can generate high contractile forces also but fast fibres have velocity making them more powerful. Strength training whether hypertrophy methods or Max strength decrease contractility (velocity) of fast fibre Leading to an increase in relaxation time. (Sprint training increases contractile velocity which is a good thing and what we want).

This disadvantage of strength training is overcome if you consider that the impulse developed in 90ms by a muscle with contractile time of 180ms will be the same as that of a muscle half as strong cinsisting only of type iib fibres.

Increasing the CSA of muscle indiscriminately leads to weight gain which may be a major disadvantage for many athletes.

Bompa’s work on this subject is questionable. Right up there with the whole time under tension debate. It depends on what type of hypertrophy you are developing. Sarcoplasmic hypertrophy refers to growth of the fluid surrounding the myofibrils and noncontractile proteins that do not affect force production; Myofibrillar hypertrophy refers to the hypertrophy of the muscle fibers as it gains more myofibrils and more myosin and actin filaments immediately improving force production capability[Zatsiorsky. Science and Practice of Strength Training]. In short, hypertrophy training can bring gains in maximum strength without a max strength phase. And max strength training can bring hypertrophy without a hypertrophy training phase as well. It’s dependent on the individual and training variables.

Yes you are right but. Schmidtbleicher and Tidow, Staron, Klitgaard, Diffee and others are not dubious sources to name a few who back what Bompa is saying. Yes both types of training cause hypertrophy. But I know very few athletes who could train at 90-95% of max strength for 8-12 weeks (in order to gain hypertophy with max strength) without burn-out, decreased testosterone, adrenal function CNS propagation decriment. Yes hypertrophy training can bring max strength gains without a max strength phase but you leave it to a hit or miss outcome without being thorough. In fact schmidtbleicher has shown that a hypertrophy phase followed by plyometrics can lead to max strength and explosive strength improvements.

Hence loading and un-loading. And myofibrillar hypertrophy does not require 90-95% training. Training as low of an intensity as 80% will still bring about the required change in some athletes. The principle is individualization And I don’t think that we were talking about avoiding max strength, I think the discussion was on CSA. In elite weightlifters, I believe above 90% intensity training [in the competitive season] only makes up about 10-12% of training. I think we’re getting into a different discussion, that is linear training vs. alternating periodization.

No, but it depends on your classification of max stength. With 80% intensity that is hypertrophy training or sub max strength NOT max strength training.

The bottom line is hypertophy training is more efficient/optimal at increasing CSA than max strength but it has the disadvantage of contractility decrements. Max stength is more effective at recruiting and synchronising the new grown fibre but is less optimal for hypertrophy whether myofibrillar or sacroplasmic check out other sources apart from zatriovsky he does not have a monopoly on this subject. Schmidtbleicher is the leading light.

Absolutely not. It is max strength training. What definition are you going by? By bompa’s definition, anything above 70% is max. strength training. According to King + Poliquin, training between 80-88% brings the best compromise between relative/max-strength and hypertrophy gains. I would define max-strength training separately than I would maximum strength. Max-strength training would be any lifting performed that improves your maximum strength directly, while maximum strength is the athletes maximum capacity for strength.