ISSUE #51                               



-“Muscle Physiology: Type II Fibres”
-“Muscle Physiology: The Fibre Types in Your Muscles”
-“Guest columns: Grip Training & Arm training”





In ISSUE #50 an article discussed the two general types of muscle fibers. This time the article will break down the type II fiber (fast twitch) into its two common subgroups, the IIa fiber and the IIx fiber (note: type IIx has also been referred to as IIb, a long story that isn’t necessary right now). There are a couple of very important points to consider about all fiber types, one being that they exist in a continuum, and two that they are not either “red” or “white”.


In the introduction to muscle fibers (ISSUE #50) it explained that each individual muscle fiber is classified on its composition of myosin protein. Without being too complex, there are at least 3 kinds of myosin (i.e. a Type I fiber, also referred to as a slow fiber, would contain predominately type I myosin, also known as slow myosin).


The reason why all muscle fibers exist along a continuum is because many fibers contain more than one form of myosin, for example, a fiber may contain type IIa and IIx myosin. Therefore this fiber would exist on a continuum between fibers that contain IIa and IIx myosin exclusively. Making things even more complex is the fact that contractile activity (i.e. exercise) can change the type of myosin present in the muscle fiber (another long, long story).


 Next, it is time that training authors cease all references to muscle fibers as red or white. People, muscles are not coloring books! In fact, if the author chooses to refer to red and white fibers, question the author’s understanding of muscle physiology and training. Remember that fibers exist along a continuum, therefore they are not so easily identified simply based on color.


The red and white classification is based on the amount of myoglobin in the fiber, a molecule that functions similar to hemoglobin and binds oxygen. Myoglobin is more prominent in type I (slow-twitch) fibers and adds to the oxidative capacity of the type I fibers. Amongst type II fibers, the IIa subgroup contains a greater amount of myoglobin than the IIx subgroup. The IIa fibers are considered intermediate fibers between type I and type IIx fibers in metabolic and force production capacities.


 The IIx fibers have the fastest speed of contraction and are possibly the strongest fiber type. Both of these characteristics have been measured by testing individual muscle fibers with electrical stimulation. Delicate experiments indeed. Unfortunately, almost any amount of contractile activity can decrease the amount of type IIx fibers in your muscles, and ironically, bed rest or any other type of immobilization (i.e. a cast) may cause an increase in IIx proportions. Not surprisingly, immobilization is a poor method for increasing strength and speed.


 Genetics thus have a great role in determining the fiber make-up of your muscles because there is a huge possible variance in the fiber composition of the same muscle group between people so it is very difficult to make a general statement on one muscle.


Also note that in humans there no muscles are composed exclusively of one fiber type, and although more than 50% of the fibers may be type I, this still does not constitute a “slow-twitch” muscle. Remember that type II fibers grow more in response to training. Therefore, even if you have only 30% type II fibers in a muscle, if they are twice the size of the type I fibers, the total amount of fast myosin will still be greater than the amount of slow myosin. Therefore, many muscles are often given improper designations.




(an excerpt from my thesis literature review)


The quadriceps is a large muscle group composed of the vastus lateralis, vastus medialis, vastus intermedius, and rectus femoris and controls knee extension. The quadriceps is highly active in endurance activities such as cycling (Gollnick et al., 1972) and running (Widrick et al., 1996a) and power activities such as jumping (Häkkinen and Komi, 1986). The vastus lateralis in untrained individuals is characterized by a large proportion of type I fibers (45-59%), a moderate type IIa proportion (30-39%), and a small type IIb proportion (11-15%) (Esbjörnsson et al., 1999; Simoneau and Bouchard, 1989).


However, there is a wide variation between individuals and type I, type IIa, and type IIb proportions have been observed to range between 15-79%, 13-77%, and 0-44%, respectively (Simoneau and Bouchard, 1989). The vastus medialis and the vastus lateralis contain similar percentages of type I fibers, 52.1% (Gollnick et al, 1972) and 51.4% (Kuzon et al., 1990) respectively.

However, as many as 79% of the gastrocnemius fibers (Costill et al., 1976b) and 88% of the soleus fibers (Johnson et al, 1972) may have type I characteristics. The high proportion of type I fibers in the quadriceps, gastrocnemius and soleus is probably due to the fact that these are postural and locomotive muscles that are active for a long duration, but at low contractile forces. In contrast, muscles of the upper body, such as the triceps and biceps, are used for brief forceful contractions and composed of high proportions (60-70%) of type II fibers (Johnson et al, 1972; MacDougall et al, 1982; 1984).

For a full list of references:





First from colleague Matt Jordan, a graduate student at the University of Calgary, and National Speed Skating Coach about grip training.


“Here is a method for training grip strength that I have used with great success:

When performing dead lifts, rowing exercises, pull ups/chin ups use a thicker diameter bar. I know you can purchase dumbbells with oversized grips and we have also bought PVC piping and slid it over top of our Olympic Bars to increase the thickness of our bars.


We have used this type of training with wrestler's, waterpolo players, and other athletes who require a strong grip for their sport. I find that this is a very functional method to train grip strength, as most athletes are required to have powerful grips while performing complex movements. It is amazing how difficult it is to deadlift with a bar that is 1 inch thicker than normal- over a training block, your grip develops very quickly. As far as gains in muscle mass, a few weeks of training with oversized bars, and I have noticed considerable gains in forearm musculature.”


To contact Matt Jordan:


And another note from Mike Zappetelli, as he provides his opinion on a proper schedule for arm training for bodybuilders:


“Anyone trying to grow their arms should know that too much training may have a reverse effect. Remember arms are also used when doing chest, shoulders, and back routines. Doing an arm routine after one of these workouts the day before can impair proper training, proper rest and recovery, and most importantly 'growth'. Here is a routine that I came up with that will allow you to hit every body twice a week, every three days, so that you have plenty of rest time.


Day 1: Bi's and Abs  (light back)

Day 2: Chest and Calves (light tri's)

Day 3: Legs and Abs

Day 4: Back and Calves (light bi's)

Day 5: Shoulders and Tri's (one exercise for chest - flies)

Day 6: Off or Optional (light legs)


**Notice how there is 3 days rest between consecutive body parts.  Day 1 & 4; Day 2 & 5; Day 3 & 6 (all matching body parts).  YOU CAN'T GO WRONG!!!”


To contact Mike for more details:


One important note to add: Although Mike, Matt, and CB are all strength coaches with similar education and certifications, we all have different opinions on the best way to train arms. There is no perfect program. The only “wrong” type of program is one that leads to injury or that does not lead to improvement. Try different approaches if you are not satisfied with your current program and contact Matt or Mike if you like their ideas.


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