Fitness Facts: Muscles can't push

This is a basic physiology lesson for all of you out there who are wondering what muscles to use for which moves. The principles outlined here will is useful for weightlifting, running, walking, yoga, cycling, martial arts…any kind of fitness pursuit, any kind of movement. Of course, the info here will be extremely useful for belly dancers.

Here is the lesson, summed up in three words: muscles cannot push.

Muscles are comprised of a large number of fibres whose job it is to contract. Contraction = pulling. Muscles pull. This contracting/pulling action has more than one purpose; in terms of muscular physiology, the term 'contraction' refers to the creation of tension in the muscle fibres, and that tension can be used to achieve different ends. When you are lifting something heavy, the muscles doing the work are shortening (contracting) to generate power. When you are lowering something slowly, your muscles are contracting in order to resist lengthening, thereby controlling how quickly they stretch. When your muscles are generating force to keep something in place, they contract and then hold that contraction to keep it constant.

There are three different kinds of muscle contractions, where the muscle is actually working:

Concentric contraction – muscle actively shortening - this is the muscle contraction that is usually occurring when people are thinking about muscles working. The fibres of the muscle are actively contracting so that they shorten, generating the sort of power required to lift a weight, or to flex your bicep (ooh la la).

Eccentric contraction – muscle actively lengthening - this muscle contraction isn’t used to lift or hoist, but instead to control movement and resist lengthening. The muscle fibres are engaged in order to control the speed and rate at which they are lengthening, resisting the outside force (it could be as gentle as gravity or as violent as gravity plus 40 pounds of groceries) acting on it. Grab something heavy and lower it in the most controlled manner possible – that’s an eccentric contraction. The muscle fibres are still contracting, in order to control the rate at which they release and relax.

Isometric contraction – muscle actively held at a fixed length - the purpose of this contraction is to maintain a constant force in the muscle to hold something in place. If you are holding a dumbbell straight out in front of you, your muscles have contracted with tension that allows neither lengthening (eccentric contraction) nor shortening (concentric contraction). Spending some time holding the plank position gives a great lesson on the strength and importance of isometric contractions.

The above information came primarily from this website, which has great info on the workings of muscles:

Muscle Physiology Home Page: Types of Contractions

Another fun site with interactive, animated info about how muscles work on a cellular level is Thomson Brooks/Cole study resources: Muscle Contraction

I was hesitant to post the following article because of the taint of unreliability that Wikipedia has acquired, but it is a good, solid explanation of muscle contraction and is consistent with the information in my print resources:
Muscle Contraction.

This sort of info is extremely useful to have on hand. I find that having a basic understanding of how muscles function, and which ones would be contracting and relaxing during a given move make moves easier to understand and execute. It doesn’t mean that I execute them correctly, of course, just that I get what they are in theory and hope that eventually my limbs will agree with my brain.

Body composition tests - measuring the fat

The results are in! I took my urine-filled jugs and 12-hour fasted self to the nutrition lab, laid under the DEXA x-ray machine for five minutes, and got to see a shiny print-out of my body composition.

The verdict is that I am 23% fat. If I recall correctly, the chart I looked at after my scan stated that the average Canadian woman is about 32% (don’t quote me on that – I don’t have the print out in front of me, and I won’t get my copies until they give me the results package in a week or so, which will include the analysis by a qualified nutritionist). According to the Body Composition Clinic, who also uses DEXA scans to measure body composition, this puts me in the “fitness” category of body types. Their classification table is:

Classification
Athletes - Women: 14-20%, Men: 5-13%
Fitness - Women: 21-24%, Men: 14-17%
Acceptable - Women: 25-31%, Men: 18-25%
Obese - Women: 32%+, Men: 26%+

The Body Composition Clinic also gives a good description of necessary and storage body fat, DEXA scans, and why body fat is important. Browsing their information is highly recommended.
The body composition study folks also weighed and measured me, and at just under 5’9” and exactly 134 pounds, I think that I could stand to put on a few pounds of lean muscle. As I work out quite a bit and include strength training along with my dance and cardio, I believe the next steps to take are to add a few more calories of protein to my diet. 134 is a bit on the skinny side, but I don’t want to gain weight in fat and after doing a double take at my diet diary, I realized that it was pretty damn meager. It could be that by averaging 1,800 calories a day and going through my various workouts and generally active lifestyle, I’m not feeding my muscles enough to allow them to build up more lean tissue.

But that is a topic for another day. Namely, that is a topic that will be addressed when I get my results back and receive the promised info from the body composition study’s nutritionist! When I get the results back, I’ll also go deeper into reporting the actual results chart. It should be quite interesting!

Body composition tests - collecting data

Today is an interesting day in my quest for healthy living!

As several of my cronies know, I am a sucker for participating in medical studies. I’ve been a healthy control subject for a PMS study, I’ve had my brain photographed with MRI scanners for a variety of reasons, I’ve given blood samples, and I’ve carried out psychological tests. I find these studies quite fun and interesting. It is a way to donate some of my time and capabilities (being a relatively healthy person) to good scientific and educational causes. As a very welcome bonus, I often receive procedures or information that would otherwise be very expensive to obtain, and I often get paid for my troubles!*

The study I’m participating in right now is of particular interest because it is to improve ways to measure body composition. The oncologists at our local cancer institute are hoping that they can find a way to use body fluids to determine muscle/fat ratios. The standard they are measuring their study against is the Dual Energy X-ray Absorbtiometry (DEXA) scan, which is a low-radiation scan that measures regional body fat and also lean tissue mass with ridiculous accuracy. Skin fold calipers be gone! Electric pulse scales move aside! Water displacement shove over! The DEXA scan is the most accurate measure of your percent of lean muscle tissue and percent fat available. It’s painless and non-invasive. It is also very expensive, which is why they’d like to find a different way of achieving the same accurate measurements.

I’m not getting paid for this study, but I am getting a full DEXA scan, will be told my body composition, and get a short consultation for a nutritionist based on my test results and my diet diary.

So aside from sitting on an x-ray slab for five minutes, what else do I have go do?

-Record my diet for one day (and it has to be a truthful record of my normal diet, no cheating about measurements or fibbing about treats, but I’ve done this before and have no problems being truthful).

-Get a fasting blood sample, which means that I can’t eat for 12 hours before my 9:40 am blood test. THAT is going to be the tricky bit – I’ll do the fast, but I won’t like it. I usually have some tea before bed or a small snack after my evening dance classes, and I’m a monster without my breakfast. Unless I eat within about fifteen minutes of actually getting out of bed, I’m a wreck. This is why I take my thyroid meds so early in the morning, a full hour before I actually get out of bed.

-Do a 24 hour urine collection. That means that I’ve had the privilege of peeing into one of these:



all day (no that is not the actual jug. My jug was opaque orange with a white cap, had a wide opening, and can hold 2 litres of fluid).

I’m thoroughly keen on seeing what the results of my test are. A couple other girls from the dance studio are also participating. How often do you get the chance of finding out your exact body fat/lean muscle composition with an incredibly accurate and expensive test FOR FREE?

Once the results of the tests come in, I’ll let you know what the verdict is. Too fat? Too thin? Just right? It will all be revealed!

Seeing as we are on the subject of body composition and food and whatnot, I would like to share the link that Stacey sent my way:
Drop 10 Pounds by Snacking

The article certainly reinforces why it is a bad idea to habitually chug back calorically dense drinks (juice, pop, wine, etc) without being mindful of how much we are actually drinking. Personally, I tend to stick with drinking water at meals and only drink water or herbal teas that don’t require milk or sugar while at work. My downfall is chocolate milk. Honestly, I can slam back a jug of chocolate milk in the blink of an eye. We rarely have it in the house, though, and when we do get it as the odd treat I usually pour it into either very small glasses or into wine glasses that are filled with ice.

*Trust me, the pay isn’t much and not all of the studies have the budget to fork over for their research subjects. But I do get a little bit of pocket money every now and then, which is always fun.

**Peeing into the jug is much easier than I initially thought it would be. Actually, peeing into a cup is more difficult than voiding into that sucker. But it definitely is not pleasant. Besides, I’ve had to tote around a big soft-sided beer cooler filled with ice packs and pee jugs around my office all day. I’m certain that people are wondering what the heck is going on, but happily they are too polite to inquire. I’ve never been so grateful for single toilet bathrooms with lockable doors.