What Determines Muscular Strength | Anatomy & Mechanics Play a Role

Why are some people so much stronger than you - especially when you have about the same body build and train approximately the same? You could say genetics and you would be partially correct.

But what does this mean aside from the simple explanation that we are all born different? What are the exact reasons one person can be so much stronger - or have greater muscle mass? A look into the structure of the muscle and its mechanics may provide the answers.

A typical skeletal muscle is made up of bundles of muscle fibers. Each bundle is made up of units of 100-150 fibers. The bundles are covered with connective tissue, as is the entire muscle. Thus if you were born with a greater number of fibers in each bundle you would have an advantage in strength and muscle mass.

But the muscle and muscle fibers are only part of the answer. The tendons that form the ends of the muscle also play an important role. The tendons are extensions of the connective tissue. And the fibers of the tendon are usually plaided or braided with one another so that tension in any part of the muscle is usually distributed more or less equally to all parts of the attachment to the bone. And the tensile strength of adult tendons is about 4,150 pounds per square inch!

The thickness and strength of the external connective sheath also vary greatly depending upon where the muscle is located. For example, if it's located near the end of a limb, where it might be exposed to blows or abrasions, the sheath will be very heavy for protection. If the muscle is deep in the body, like the psoas (a hip flexor), for example, there is a minimum of connective tissue in the sheaths since it is well protected.

What is most important is that these sheaths form a structural framework for the muscle that is tough and elastic. For example, if it's stretched up to 40% of its length, it will return to its original length. But the relative amount of connective and contractile tissue varies greatly from muscle to muscle. Most people tend to ignore these facts, which leads to great discrepancies when the physical properties of the muscle are examined.

The stronger the tendons and sheaths, the greater your potential strength. The greater your strength, the more you can lift and the greater your mass. But the tendons and connective tissues don't get strong from the usual weight training regimens. As prescribed by the Weider Holistic Training Principle, you must use weights and repetitions that are different from muscle strengthening, i.e., light resistance and high repetitions.

The type of muscle fibers you have in each muscle also determines how much strength and mass you can develop and plays a role in definition as well. There are two main types of muscle fiber structure: the longitudinal, or fusiform, and the penniform. But there are many variations of each type. The simplest and easiest to picture is the longitudinal, in which the fibers run parallel to the length of the muscle. The sartorius muscle in the thigh is an example of the longitudinal arrangement. It consists of a long narrow band of fibers which contract with little force but over a great distance. The intercostal muscle fibers are also parallel but they are very short and contract with great force through a very short distance. Other examples of the longitudinal type arrangement are found in the legs and arms (biceps femoris, biceps brachii).

The penniform muscles, which comprise three quarters of all the muscles in the body, have very different arrangements so that they can contract with greater force. In essence, penniform muscles are arranged like a feather with the tendon as the shaft and the muscle fibers as the feathers. In this arrangement more muscle fibers become involved but the range of motion is decreased. Some of the more common types are:

Unipennate, in which the fibers are on one side of the tendon, for example, the semi membranosus in the hamstring.

Bipennate, in which the fibers are on both sides of a tendon, as for example the rectus femoris in the thigh.

Multipennate, in which the fibers converge to several tendons as for example in the deltoid.

The particular arrangement of the muscle is what determines its definition. And from studying bodybuilders, you can see that the definition is not identical. In addition it determines the strength of the muscle very selectively. The entire muscle does not always contract - only those sections need-ed in the particular movement. For ex-ample, the anterior deltoid in dumbbell flys, the posterior deltoid in reverse dumbbell fives and the middle deltoid in lateral arm raises, with some assistance from the adjacent anterior and posterior portions of the deltoid.

Muscle fibers are also divided into two types - red and white. The red fibers are used more for endurance type activities such as long-distance running and maintaining basic posture. They are adapted to sustained contractions. The white fibers fatigue more easily and are better adapted for fast contractions. The white fibers are served by nerves whose thresholds are lower than those serving the red fibers. For this reason, they are generally more active.

In general the common muscle contains varying amounts of red and white fibers depending upon its task. In the leg, for example, the soleus is predominately red and the gastrocnemius is mixed, along with the tibialis anterior, while the semi tendinosus is white. But it is also known that white fibers can assume the characteristics of red and vice versa - although not to the same extent. It depends upon the kind of training you do!

The muscles of weightlifters appear to be about equally divided between the two types. But the leg muscles of world class long-distance runners contain 75-90% slow-twitch (red) fibers, while those of champion sprinters may be 80-90% fast-twitch (white). However, weightlifters have significantly larger white fibers than do endurance athletes or untrained men, while red fibers are about the same size in all groups.

Thus it appears that both red and white fibers are important for body-builders. Most muscle size, however, comes from the white fibers since they grow larger than the red. Therefore, you should do both high-intensity and speed or explosive type movements to maximally develop these fibers. But the red fibers are also important since they come into play in very slow movements, as when you're struggling to complete a repetition. In addition they are needed for doing sets of 10 or more reps, which brings in the endurance element. Thus you need a varied program for maximum results.

The exact attachment of the origin and insertion of the muscle also plays an important role in determining your strength. The further your muscle inserts from the joint, the stronger you will be. Thus with such an attachment, you can be as strong as someone who has a more developed muscle but a closer attachment.

This can be explained here in a very simplified way by using a formula from biomechanics: R x Ra = F x Fa, where R is the resistance you are overcoming, Ra the resistance arm (the distance from the resistance to the axis (joint), F the amount of force you are applying by the muscle contraction and Fa the distance from the point where your muscle (tendon) attaches the bone to the joint. Let us use an easy example to illustrate. The resistance is 100 pounds and the resistance arm is 15 inches (1.25 feet) and the force arm is 1 inch (0.083 feet). Thus: 0.083 F = 100 x 1.25 F = 1,506 foot-pounds But if we change the force arm (point of muscle insertion) from 1 inch to 2, we get 0.166 F = 125 or F = 753 foot-pounds. Thus the amount of force needed to lift the weight would be cut in half! But even an insertion change of one-eighth or one-quarter of an inch would make a tremendous difference in how much you could lift. Thus where your muscle inserts plays a critical role in how much weight you can handle.

The type of lever system also plays a role in how much you can lift. This relates to where the muscle (tendon) is inserted on the bone, where the resistance is applied and where the axis of rotation (the joint) is located. There are three basic types of lever system, but only one is predominant in the body. This is the third-class lever.

In this arrangement the muscle insertion is between the joint (axis) and the resistance. In general, the muscle inserts close to the axis (fulcrum) and the resistance (weight) is held at the distal end of the extremity. This relationship is best seen in the drawing; where point A is the axis, point B is the muscle insertion or where the Force is applied, and point C is where the resistance is.

In this arrangement it takes a great amount of muscle force to lift a weight. The reason for this is that the point of application of Force (B) is close to the axis, which produces a short force arm (the distance from point A to point B). In addition there is a long resistance arm (distance from point A to point C). Thus the shorter the force arm (AB) or the longer the resistance arm (AC), the greater the force you must apply to lift the weight. Conversely the longer the force arm and the shorter the resistance arm, the less force needed to move the weight.

To illustrate this point we can use the example of the biceps curl. The elbow is the axis (point A), the insertion of the muscle is point B (W2-2 inches from the axis) and point C is the weight. The resistance arm (the distance from elbow to hand) is 12-16 inches in length and the force arm is \xh-2 inches. In this case the resistance arm is long and the force arm is short. Thus if you have a short forearm (12 inches or less) you can lift more than a person with a long forearm (13 or more inches) with the force arms equal. If you have a longer force arm (2 inches or more) you will be able to curl more weight than the person with a short force arm (under 2 inches). And if you have both a long force arm and a short resistance arm you will have an even greater advantage for lifting heavier weights.

However, what you lose in force is gained in speed. For example, if you have a short force arm and a long resistance arm you will be able to accelerate the weight greatly. This is why you see most throwers with long arms and most weightlifters with short arms. The same holds true with the legs. Most short-legged persons make better squatters, while long-legged individuals make better runners.

The second-class lever is ideal for the production of force. However, there are very few joints in our body that are constructed for this result. Probably the best example of this lever system is the ankle joint when you do calf raises. In this arrangement the weight is located between the point of application of force and the axis, where A = axis, B = resistance and C = point of application of force.

In the calf raise your bodyweight falls between the ball of the foot (the axis) and the heel bone (point of attachment of the gastrocnemius and soleus muscles). Because of this set-up you are able to lift very heavy weights in addition to your bodyweight. An-other example of this lever system is the wheelbarrow. The axis is the wheel, the weight is in the tub and the handles are where the force is applied.

In the first-class lever the fulcrum (axis) is located between the resistance and force (similar to a seesaw); A = point of application of force, B = axis and C = resistance.

A typical example of this lever system in the body is the triceps muscle. The elbow is the axis (fulcrum), the point of application of force is the attachment of the triceps on the ulna bone about 1 inch from the joint, and the resistance is the weight you hold in your hand. In this case as in other examples in the body the force arm is very short and the resistance arm is long. Thus this arrangement is best suited for the production of speed - not force. But if you have a longer force arm or a shorter forearm you will have an advantage for the production of force.

Also playing a role in the production of force is the angle of muscle pull. The angle of pull is related to the angle the muscle makes with the bone it's moving. For example, if when you are doing a biceps curl the angle of pull of the muscle is very small when you are in the starting position (Figure A). With the arms straight, most of the pull of the muscle is straight up into the joint and it is not directed in a way that it turns the forearm upward. Because of this it is called a nonrotatory component. It pulls the forearm into the joint for stabilization, which is an important safety factor - keep in mind that the weight is pulling the joint apart! Also because the direction of force is straight up, it makes the exercise very difficult. This is why you have to apply so much force at the beginning to get the weight moving.

After you apply sufficient force the forearm begins to rotate upward and the angle of pull changes. Thus if the angle at the beginning was 10 degrees, it increases to 20-30 degrees and more. And as the angle increases the pull becomes easier since the rotatory component increases and the non rotatory (stabilizing) component decreases. This is why the exercise be-comes easier to do. Also, this is why many bodybuilders cheat when doing this exercise. They try to get a greater angle to make the starting easier.

When the angle reaches 90 degrees, all your force is directed to rotating the forearm, i.e., all the force raises the weight and none goes into the joint. This is why in a flexion-type movement when the angle of pull is 90 degrees, you are strongest. And you can handle the greatest amount of weight at this angle. The amount of weight is much more than you could handle at the beginning of the exercise. Because of this, if you want maximum development of the muscle you must use more weight and work in a shortened range, for example, 45-90 degrees. But keep in mind that if you do this you will lose flexibility, so do repetitions through the full range also.

In an extension-type movement the angle at which you can apply the greatest force is about 145 degrees (180 degrees is a straight limb). Thus if you want maximum development of the muscle you should do some short-range exercises (120-180 degrees). But as in the flexion type movement you must also do full-range repetitions to maintain flexibility, good posture and proper appearance.

Many factors play a role in strength and in the development of muscle mass. Some are genetically determined while others are determined by the mechanics of lifting. All are important. By paying greater attention to all these factors you will be able to develop your body to its fullest.