Protein Slows Digestion? Nope.

By Jordan Feigenbaum MS, Starting Strength Staff, CSCS, HFS, USAW Club Coach

In response to this gem of an article. I answered this on the Starting Strength nutrition forum, but I thought I’d repost it here. The article’s claims are italicized and my responses are in bold. 

The food that we consume is absorbed and its nutrients are subsequently sent to different organs through the blood.

The food that we consume is absorbed and its nutrients are subsequently sent to different organs through the blood. Not really the case literally. Protein and carbohydrates get absorbed as amino acids and monosaccharides through the small intestine’s brush border> into the enterocyte (cell)> into the portal vein> to the liver first before going anywhere else, then they get distributed based on lots of factors.

Fats get absorbed as fatty acids directly into the enterocyte (cell) and packaged into the chylomicron (with cholesterol, phospholipids, etc.)> into the lymphatic system> into the venous circulation and then go to some tissues, but mainly those who express high levels of mitochondria for beta oxidation or peroxisomes for long chain fatty acid oxidation. Principally, these are the liver and skeletal muscle.

However, a slow or sluggish digestive system isn’t able to perform its assigned function effectively. That is why a person experiencing a bout of slow digestion is bound to feel extremely uncomfortable post lunch or dinner. Nausea, bloating and vomiting are the most common symptoms of sluggish digestive system that occur after having meals.

Notice they do not define a normal GI transit time for a mixed meal, a slow GI transit time for a “bad” meal, nor do they distinguish between a pathologically slow state like gastroparesis or ileus or obstruction and a “slow” transit time occurring due to a specific meal composition. Yes, there is a marked difference.

Constipation or common digestive problems like diarrhea and irritable bowel syndrome can make the digestive system sluggish.

Diarrhea is actually the GI contents moving too fast. IBS has physiological symptoms of a combination of diarrhea, constipation, abdominal pain, and abdominal bloating. Seems like it might not make the digestive system sluggish, right? Though if you’re constipated, sure (and fiber and/or some probiotics tend to improve symptoms by increasing motility and osmotic pressure in the intestine to propel the contents)

Although protein is good for health, excessively high amounts of protein in the diet can slow down the digestive health. This is because, the body has to really work to digest protein.

Not the case at all. Proteins are initially broken down via the acidic pH of the stomach (and further in the small intestine by pancreatic enzymes that are all part of our normal physiology) and are absorbed very rapidly into the portal circulation. Whey, for instance- spikes blood plasma levels of amino acids (digestive end products of protein) within 20 minutes of ingestion.

Mixed meals confound the “speed” component, i.e. what is the fat content (slows gastric emptying), fiber content (soluble slows, insoluble speeds), total kCal content (larger is slower), tonicity of the meal (isotonic empties faster than hypo or hyper tonic from the stomach to the small intestine), etc. In addition, the hormonal milieu at the time with respect to previous meals also influence gastric transit time. Ghrelin, for instance- increases when you’re hungry and increases the motility of the gut.

Don’t forget about existing food in the GI tract. See how this is quite complicated to talk about? Let’s not forget about drugs….

At any rate, Carbohydrate rich and protein rich foods empty at about the same rate, but normal gastric emptying following a meal is 2-6 hrs….so yea- perhaps this whole article is a bit silly, eh?

Unlike simple carbohydrates, proteins are heavy, hence are not easy to digest and so when its presence is alarmingly high in everyday meals, the consequence is a slow digestive system.

Now this is easy to see that this is wrong…

People with intestinal problems such as Crohn’s disease tend to have a sluggish digestive system besides bowel dysfunction (diarrhea or constipation), vomiting and stomach pain. In this condition the lining of the small and large intestine are inflamed. However, in most cases, the swelling infiltrates in the inner layers of the bowel tissue. This chronic inflammatory disease considerably slows down digestion as the food tends to move at a very slow pace through the intestine.

Fuark. Crohn’s is, currently, a dysregulation of inflammation in response to bacteria in the walls of the GI tract, which results in proinflammatory substances causing direct mucosal injury.

Crohn’s usually presents with diarrhea, fatigue, weight loss, and crampy abdominal pain plus oral ulcerations, perianal fissures, perirectal abscesses, and malabsorption BECAUSE THE FOOD CAN’T BE ABSORBED BECAUSE IT’S MOVING at a normal speed but the mucosa can’t absorb it.

A point to note that although food is digested in the stomach, most of the digestion occurs inside the intestine. Experts say that the intestine is the place where nutrients are observed and eventually circulated in the bloodstream to various parts of the body. However if the food stays for longer time in the stomach, this can affect the digestion process. This condition is known as gastroparesis, in which the stomach takes more time to transfer the ingested food to the intestine. This happens because the stomach muscles that are assigned the task of pushing the food to the intestine, lose their ability to work efficiently. Gastroparesis is the result of malfunctioning of the vagus nerve that regulates movement of muscles lining the stomach wall.

Most common KNOWN causes of gastroparesis:

1) diabetes mellitus
2) idiopathic
3) post-surgical (especially if vagus nerve damaged)

Other causes:

-etoh and tobacco, weed
-infection (mono, chagas, rotavirus)
-CNS injury like a tumor or cerebrovascular event
-PNS pathology (parkinson’s or guillan barre)
-other issues (cancers, hypothyroid, lupus, intestine obstruction, portal hypertension, HIV, stroke and migraines)

So…yea, protein is UNLIKELY to be the cause of “slowed” gi emptying….


Top 10 Mistakes People Following Starting Strength Make

By Jordan Feigenbaum MS, Starting Strength Staff, CSCS, HFS, USAW Club Coach


1) Not reading the book

Seriously, most people who are doing “Starting Strength Novice Progression” have never even read the book. They got the “routine”, replete with rows in place of power cleans, of the Internet and are 100% unprepared for what this program requires. Further, because they have not read the book and thus, are lacking in understanding the rationale- the WHY- behind the program, they do a bunch of inappropriate things as seen in the other 9 items below. Bompa, Issurin, and Zatsiorisky all agree that explaining to an athlete the “why” behind the “what” is important for compliance. If you want to do Starting Strength Novice Progression, you need to read the book. Period.

2) Starting too heavy.

This is usually a result of a failure to read the book, however there are still some people that will start too heavy because the heavier you start the faster you’ll get strong, right? Wrong. What we’re aiming to do is use the smallest effective dose to stimulate the maximum potential response. In lifting terms, we want you starting with a weight that begins to challenge your ability. This can be gauged, roughly, by when the speed of the bar slows down or the technique suffers slightly. If the former happens, then you’ve just done a set of 5 reps that is heavy enough to drive the adaptations we want, i.e. strength, neuromuscular coordination, hypertrophy, etc. If the latter happens, however, we need to back the weight down just a tad in order to preserve proper form (see below).

3) Having poor technique.

This mostly stems from people not doing Step 1, i.e. reading the book, OR not watching all the videos, reading all the articles, etc. on the site, YouTube channel, or various other mediums. Bottom line is, if you’re technique is not good you’re going to see less than optimal results through any training program, period. When compounded by the fact that this program aims to get you as strong as possible in the shortest amount of time, things start to escalate quickly. It would behoove any person to see a Starting Strength Coach within their first week of training just to hammer this all out. If that’s not possible, post a form check on the Q/A the coaches so graciously run.

4) Eating like a bird.

I was thinking about putting this as number one, but alas, I thought the other things were actually more important and, specifically, doing number 1 would take care of this number. Look, if you’re a 16-23 year old male and <165 lbs, you need to gain a significant amount of body weight, like yesterday, in order to be facilitate the fastest rate of strength and muscle size acquisition. This is done through food, like LOTS of it. I’ve already written extensively about this topic in this article, so I suggest checking that out. Look, here’s the simple fact:

You have one chance in your life to put on muscle at an almost unnatural rate. This moment in time also coincides with the ability to gain a tremendous amount of strength, if you’ll only eat to facilitate this process. For 3 months forget about your abs so you can build the ice chest to put the 6-pack in.

The older, heavier, or more female you get away from this “ideal Starting Strength candidate” the less extra food you need to drive these processes. Again, see the article linked above “To Be a Beast” for more discussion on this topic.

5) Not resting long enough between sets.

After 3 minutes, approximately 80% of your muscle’s ATP has been replenished, at 5 minutes, approximately 95% is back in the game, and at 8 minutes ~ 100% is there. Don’t try to hit PR’s, which happen everyday on this program, with 80% of your muscles’ energy available.

6) Adding in too much bullshit.

Remember that we’re using the minimum effective dose to get the maximum response here. Adding in a bunch of extra stuff dilutes the “effective dose” AND spreads the body’s available resources for adaptation to the “dose” too thin for optimal results for a novice trainee. Of course, as you become more “trained” and thus, can tolerate more volume, frequency, and intensity, you’ll be able to add more exercises, sets, reps, etc. 

If, on the other hand, you add too much tomfoolery TOO SOON in your training career, you run a very serious risk of attenuating (diminishing) your adaptive responses to training, thus blunting your progress.

The take home, keep it simple Santa (K.I.S.S.- I don’t like calling people stupid, normally). The big five, squat, bench press, press, deadlift, powerclean plus chins, curls, and back extensions will work beautifully for your dedicated novice progression. Read the book to see implementation, or this excellent article on Fitocracy by Michael Wolf.

7) Resetting a million times.

Sometimes you just have to call a spade a spade and realize it’s time to move on. Whether it’s due to not enough food, not enough recovery, or poor technique, etc. you just need to either get some help or move on. If you’re not progressing every training session, you’re no longer on the Novice Progression anyway, so don’t be married to it if it’s not working for you (and you’re doing all the necessary things to make it work).

That being said, having a training program that revolves around the big 5 and some HIIT (if necessary) is the best base template you could hope for, with rep ranges, total volume, and frequency all reflecting an individual’s needs and goals. Put simply, you could do a lot worse than to keep resetting over and over again, but do you really want to stay weak? Figure out the limiting reagent and nip it in the bud. Grow. Progress. Profit.

8) Missing workouts (and not adjusting accordingly).

Simple enough, right? If you miss a workout on this program you are, by default, failing to provide a stimulus for your body to adapt to. This adaptation response is what is used to drive the next training day’s progress. Thus, if you miss a day you shouldn’t be expecting to “go up” in weight the next training day, although in the beginning this is more feasible. Moreover, novices tend to de-train more quickly than advanced trainees, as they’ve had less cumulative exposure to the lifts, progression, etc. and thus, it’s not unusual to see some of these detraining or deconditioning effects if a person misses a workout.

So, what do you do if you miss a workout? Simply repeat the last workout you did and start from there. If you miss a series of workouts and are a true novice, you’ll just start all over again. I really shouldn’t have to say this, but how about just not missing workouts?

9) Reading too much bullshit.

Bro 1: “Hey man, did you see that new exercise on today?”

Bro 2: “Nah, bro. What was it?”

Bro 1: “It’s like this weird lunge thing with kettlebells. All the Russians used to use it and that’s why their legs are so jacked. I heard Klokov invented it!”

Bro 2: “Dude, this is awesome. We don’t have to do squats today then. Let’s do like 40 minutes of mobility, to make sure we activate all our muscles during training, then do Klokov lunges with kettlebells.”

Bro 1: “Yea, squats are so old-school. said these were better for hypertrophy anyway. I don’t care about being strong, I just want to LOOK strong.”

Sadly, this sort of crap happens everyday in gyms (CrossFit and black-iron gyms are not exempt from this either) across the country. People mistake “new” or “proprietary” with “better” and try to reinvent the wheel. Look boys and girls, barbells are the most efficient way to load the human musculoskeletal system and stress the body. Because it’s the most efficient*  way to stress the body, it’s the most efficient at causing the body to adapt and these adaptations are more robust than any other silly shit your “guru” is pushing.

*ef·fi·cien·cy: noun, plural ef·fi·cien·cies.

1. the state or quality of being efficient; competency in performance.
2. accomplishment of or ability to accomplish a job with a minimum expenditure of time and effort: The squat is increasing Christy’s exercise efficiency by working all the muscles of her legs and trunk instead of wasting hours doing isolation/activation bullshit.
3. the ratio of the work done or energy developed by a machine, engine, etc., to the energy supplied to it, usually expressed as a percentage.

10) Being a p*ssy.

Any program that’s designed to add weight to the bar 3x a week is going to be hard, make no bones about it. If you want it to be easy or, more commonly, easier week to week you need an attitude check.

“It never get’s easier, you just go faster”- Greg LeMond

The “New” Mayo Clinic Diet??

By Jordan Feigenbaum MS, CSCS, HFS,  USAW CC, Starting Strength Coach
First order of business today: I’m teaching a Starting Strength pulling camp at Crystal Coast Strength and Conditioning. You can check it out on Facebook here, and register for it ($150.00) here. It’s being held February 9th from 1-5pm and we’ll cover the mechanics, anatomy, coaching, etc. of the deadlift and powerclean in the classroom and on the platform. If you’re looking to check out one of the best gyms in the country, improve your own lifting or coaching, or just learn more about training in general, don’t miss out on this!!
Okay, now let’s talk about the “New Mayo Clinic Diet“, which you can check out in the picture below or here.     
Screen shot 2013-01-21 at 4.11.23 PM
So what do I think about it???
The gist of the diet:
They are trying to push a low-ish carb, low calorie diet with the idea that since they’re including satiating fats and proteins at each meal that they’ll improve compliance by: a) people not being  hungry, b) not be too low calorie (which reduces REE and performance very quickly), and c) not being too restrictive  with classically “unhealthy” foods* like bacon, seasoning, butter, etc.
*Unhealthy in the “appeal to authority”, sheep-like conventional wisdom that people who should know better, like physicians, RD’s, etc., fail to rebuke.
The criticisms:
Of course this diet “could” work if it improves compliance for someone while also reducing their caloric intake to the appropriate level, which obviously varies based on diet composition, i.e. is it a high carb, low carb, high fat, low fat, high/low/moderate protein diet, etc?
On the other hand, I think it’s deficient in protein, which has been shown to improve body composition in isocaloric diets, i.e. diets with the same calories but different macros (pro/carb/fat). Pro-tip 1: Bump up the protein
It also may or may not be low in fats for a long term intervention depending on how much a person was using at their meals to cook or put on salads. You definitely need some help with the essential fatty acids, so I’d supplement with either fish or cod liver oil. Pro-tip 2: Either eat fish or supplement with fish oil.
The grapefruit thing has a little backing behind it as the flavonoid “naringin” does alter the cytochrome P450 liver detox pathway which is used to clear, among other things, caffeine. By combining this with coffee or tea, the half life of caffeine is extended which theoretically increases lipolysis rate. The unsweetened juice, unless it’s grapefruit juice, does not contain significant amounts of this enzyme so that’s pretty pointless.Pro-tip 3: Grapefruit would be the fruit to choose if trying to maximize caffeine’s activity.
Now let’s pick apart the “instructions” one by one:
 1. At any meal you may eat until you are full, and you can not eat anymore. You must eat the minimum listed listed at each meal.

Without any sort of way to keep accountable this could, over time, result in a spontaneous increase in calorie intake just like any other diet thereby preventing any weight or fat loss. On the other hand, most carbohydrate restricted diets do result in a spontaneous reduction in calories due to both palatability/mouth-feel of the foods changing (decreasing in palatability, food-reward) and increased satiation. Overall, I don’t have a super big problem with the claim you can eat ad libitum on this diet, although it is technically inaccurate.

2. Do not eliminate anything from the diet, especially don’t skip the bacon at breakfast or omit salads. It is the combination of foods that burn the fat.

This is BS. The “combination” of foods most certainly does not burn fat, the decreased energy intake and slight benefit in hormonal function burns fat. There’s nothing special about eggs, grapefruit, bacon (ok well maybe bacon) etc. At the end of the day, it will come down to the 3 C’s, calories, compliance, carbs :-).
3.The grapefruit is important because it acts as a catalyst that starts the burning process.
No. As discussed above, this has a mild, if any, effect on lipolysis whereas caffeine and coffee are the real deal. You still will occasionally see “naringin” included in fat burners because it excites the bro-scientists.
4.Cut down on coffee, it affects the insulin balance that hinders the burning process. Try to limit to one cup each meal.
No. Coffee (regular and decaf) is perhaps the strongest appetite suppressant out there (except for maybe nicotine). It doesn’t negatively affect insulin balance or insulin sensitivity in the long term and in fact, can preferentially help shuttle glucose into skeletal muscle, which would be very nice (Borat voice) post workout. It also improves lipolysis, which is another obvious plus. I’d skip it at dinner if it kept me awake tho and opt for decaf then.
5. Don’t eat between meals, if you eat the combination of food suggested, you will not get hungry.
This doesn’t really matter. 6 meals a day vs 3 vs 1 meal a day, it doesn’t matter. There is no “stoking” the metabolism with more meals. Use the frequency that makes you most compliant, prevents hypoglycemic and ravenous feeding episodes, etc. Eating too frequently though may prevent significant lipolysis from occurring if too many cals/carbs are taken in too frequently, thereby precluding fatty acids from being burned for fuel.
6. The diet may eliminate sugars and starches. Fat does not form fat, it helps burn it, so you can fry food in butter and use butter generously on vegetables.
Fat most definitely forms fat and does so  easier than carbohydrates and much easier than protein because it does not need to be modified as much to form, you guessed it, fat. That being said, increased intake of dietary fat also improves beta oxidation, the metabolism of fatty acids for fuel. If a diet is lacking in fat, then the enzymes responsible for this process decrease, which may lead to decreased satiety (not being able to access your own body’s fat stores for fuel between meals making you hungry) and decreased vitamin and sex steroid status. Fat intake can be “high” or “low” depending on the type of diet being used and in this instance, a low carb diet, it should be higher obviously. On the other hand, if it’s too high, the calories may or may not be conducive to bodyfat loss just like if carbs or protein were too high.
7. Do not eat desserts, breads and white vegetables of sweet potatoes. You may double or triple helpings of meat, salads or vegetables. Eat till you are stuffed. The more you eat the more weight you will lose.
In a word, No. You will not lose more weight the more you eat. If eating a bit more meat/fat keeps you more compliant and improves your adaptation to ketosis then you’ll see an uptick, but overall you’ll still have to be calorically restricted with your hormones/metabolism functioning correctly. God I sound like a broken record.
8. There may be no weight loss in the first 4 days, but you may lose 5 pounds on the 5th day. You may lose 1 and 1/2 pounds every two days until you reach your goal.
If you don’t lose any weight on this diet on day 1, you’re doing it wrong. The diuresis (water loss) from cutting the carbohydrates should be significant within the first day.
At a minimum.
Other comments:
Citrus fruits vs berries debate: actually, blueberries (7.3)/strawberries (8.0)/blackberries (8.1) have more sugar than grapefruit (6.3)- although you’re correct if we were talking about apples (13.3) or grapes (18.1). All amounts per 100g.I like your recommendation for oil/vinegar dressing, too. The trans fats, lecithins, soybean oils, and other “sh!t” in the dressings are something I like people to avoid.

18 Days Out…

Keeping it rolling with some more gift ideas for the serious (or soon-to-be serious) trainee on you holiday list…

1) Best Belts Lifting Belt– 78.00-88.00

The Prime Cut belt

The Prime Cut belt

Belts have gotten a bad rap in recent times. Some (uninformed) people contend that lifting without a belt is somehow superior than to utilizing one of the oldest tools in a lifters’ arsenal. The fact of the matter is, a belt allows a lifter to actually contract their abs harder by giving them a surface to contract against Once this tactile cue is used by the lifter, his or her abdominal contraction without a belt is also increased since they now know how to really contract their abs. Additionally, for anyone who has ever dealt with a back issue, a belt is just a smart precaution and should be used for almost every set of every barbell exercise. The belt just offers that tactile cue for keeping tight, the abs engaged, and back from moving under load. There are many belts to choose from and you’ll want to get the right one for your recipient. Women will likely be better suited to a 3″ belt, general strength trainees will likely appreciate a 4″ single prong belt that’s 10mm thick, and the most competitive lifters will want the 13mm single prong belt that’s 4″ wide all the way around. Tapered belts aren’t too useful except in some Olympic lifting populations and some people prefer them for bench press only. If you’re in this for the long run or someone on your holiday list is, give them the gift of belt!

2) Deadlift Loading Ramps– 129.99

DEADZONE Ramps 3One of the biggest hassles when training is loading the deadlift with progressively more and more weight ( you are using more weight, right?) and having to partially lift the whole barbell and plates off the floor on one side to get another plate on the bar. This can be potentially stressful and injurious to the person doing the loading since it’s hard to get into a good position to do this. Enter the deadlift loading ramp. These cast aluminum ramps allow the lifter to roll the barbell and plates onto the ramp, load the additional plates without having to scoot them against the floor, and then roll the barbell and plates off. No muss, no fuss. Check out the video!


Dynamic Fitness Coach Preview – Muscle A & P

What follows is both an excerpt from my upcoming e-book Practical Training Handbook and a Dynamic Fitness Coach preview. Head over to my other website and sign up for your free 1 week trial!


Muscles are made up of cells and each cell is between a few micrometers to a few centimeters in length. An actual muscle is comprised of thousands muscle cells that are organized at multiple different levels. The following picture is a good reference about this organization:

Fig. 1: Skeletal muscle organization. Many hundreds (if not thousands) of muscle cells make up each individual muscle fiber and a sheath of connective tissue called endomyosium surrounds each muscle fiber. A muscle fiber, or myofibril, is a series of repeated sarcomeres, which are the functional units of a muscle.

Fig. 2: A myofibril and sarcomere

Sarcomeres are overlapping thick and thin filaments that form cross bridges during muscle contraction. Without getting into too much detail here, we can simply state that each myofibril is a series of sarcomeres that contract simultaneously, thus shortening the muscle fiber as unit. When many myofibrils contract in unison, large-scale muscular movements can occur.

Muscle fibers (myofibrils) are grouped together as fascicles, which in Latin means, “little bundle of sticks.” Each muscle contains multiple fascicles that are each individually covered by another connective tissue sheath called perimysium. The entire muscle is additionally covered by yet another connective tissue sheath called epimysium, which blends into the muscle’s tendons at its origin and insertion. Muscular contractions are transmitted between the specific muscle’s origin and insertion, where the insertion is pulled, rotated, or otherwise moved towards the origin. In this manner, the origin remains relatively stable, whereas the insertion is the actively moving end of the contraction.

The skeletal muscle’s origin is the more proximal (closer to the axial skeleton-ribs, vertebrae, skull, etc.) connection to the skeleton and the insertion is more distal, or further away. Each skeletal muscle has its own innervation by a motor nerve, which receives signals from the central nervous system (CNS), i.e. the brain and spinal cord. A motor neuron, or nerve that provides innervation to a skeletal muscle, ends at what is known as a motor end plate (MEP). The motor end plate represents the junction of the CNS and the skeletal muscle, whereby through a series of events- excitatory or inhibitory signals are transmitted to the muscle fibers. The motor unit is the basic unit of the innervated skeletal muscle. It is defined as the motor nerve and all of the muscle fibers (myofibrils) that it innervates. Moreover, when the nerve sends an excitatory signal to the muscle (i.e. contract) then all of the muscle fibers of that motor unit contract. Similarly, all muscle fibers of a single motor unit are of the same type, i.e. either fast twitch or slow twitch.

Fig. 3: Muscle fiber type characteristics

Skeletal muscles are organized by what myosin heavy chain they possess and their oxidative phosphorylation ability of fuel (e.g. carbohydrates, fats, and protein metabolites). The two main categories are Type I (slow-twitch) and Type II (fast-twitch). There are many differences between these two types of fibers and in principal, we care pare the discrepancies down to the following three things: time to exhaustion, contraction strength, and size. Type I fibers, in general, take longer to fatigue, provide less strength when they contract (but can contract for long periods of time), and are small. These types of fibers are present in motor units, whose functions include maintaining posture, locomotion, and similar long-term tasks. Because they are resistant to fatigue, they must have high concentrations of mitochondria, which make energy for the muscle. They also are rich in capillaries and other vasculature, which allows them to remove metabolic byproducts that cause fatigue like hydrogen ions, for instance. Finally, these fibers tend to be smaller than their type-II counterparts, thus they are the first motor units to contract. Type II fibers come in a variety of flavors depending on the text used to describe them, but in general they are less resistant to fatigue, have the potential to generate high levels of force, and are larger than slow-twitch muscle fibers. Motor units are summoned to be active based on the needs of the muscular contractile force. That is, the higher the force, the more motor units are required to be active. Additionally, they are recruited from smallest to largest to produce the contraction and furthermore, as less and less force is needed the largest (read high threshold) motor units become less and less activated. So for a simple task like picking up a pencil off a desk, it is likely that only slow-twitch motor units are functioning, since there is a low force requirement for successful completion of this task. In a task like a limit squat or deadlift however, more motor units are required to complete this task, if it is possible to do so, and so the higher threshold motor units that are larger and more difficult to activate, must be summoned to contract. It would be appropriate to call slow-twitch muscle fibers “low threshold” and classify fast-twitch muscle fibers as “high threshold”. Imagine a muscle group like the quadriceps muscle. Whilst standing, walking, or kneeling there is certainly some low level activity by the low-threshold motor units, i.e. the slow-twitch (type I) fibers at all times to maintain posture, provide contraction for locomotive movements, and balance. Then during a squat, these motor units’ contractile strength are not sufficient to complete the task, thus other motor units of this muscle group must be called upon to help in providing contraction of the muscles during the movement. The heavier the weight or the quicker the movement requires incrementally more extensive motor unit recruitment. Thus, to effectively train more muscle, more motor units, and subsequently stress the muscle in a more complete fashion, there exists a certain intensity (weight and/or speed) that the load must represent of that individual’s particular ability.

This generalized distinction between the two main types of muscle fibers provides us with a framework for how muscles adapt to specific stressors we impart upon them during training. We will soon compare and contrast two different modalities of training, endurance exercise via running long distances and strength training via barbell exercise in order to showcase how the different fibers respond differently based on their own individual properties listed in Figure 3.

In summary, skeletal muscle fibers are organized at various different levels with the sarcomere representing the most basic unit of a fiber. Muscles receive nervous innervation from the CNS and are grouped together as motor units. Motor units can contain anywhere from 10-10,000+ muscle fibers, which is dependent on the amount of fine motor control necessary in the area. For instance, the motor units of the muscles of the hand are much smaller than those of the back or legs, as the back and legs do not require very fine movements, whereas the hands and fingers do. Motor units consist of only a single type of muscle fiber and each type of muscle fiber has specific properties that characterize its function in movement of the skeleton. Furthermore, muscles can either contract or relax from excitation or inhibition stemming from the nervous system. When they contract, they exert force between their origins and insertions to produce movement about the insertion. These movements are known as the actions of a muscle and they are only produced about the joint or series of joints that the muscle crosses. In short, if a muscle does not cross a joint it does not act upon that joint.


To complete this aerial overview of skeletal muscle anatomy and function we must briefly describe some anatomical terms so that all further explanations are clear. When we talk about anatomy, we do so with normal anatomical position in mind. Normal anatomical position looks like Figure 4.

 Fig. 4-Standard anatomical position

Check out the rest of this excerpt at Dynamic Fitness Coach. Sign up for your free 1 week trial!