Strength Measurement 

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Strength Measurement

Why Static measurement is the best option

Static procedures provide the only practical and meaningful test of strength

The Dynamic test result is affected by:

1. The force produce by muscular contraction (The true muscular strength)
2. The effect of gravity on the mass of the involved body parts
3. The stored energy
4. The muscular friction
5. The impact forces (The force produced by the test equipment)
6. The variation of number of muscle fibers recruited to produce the force
7. The angular position of the limb
8. The muscle fatigue (Positive tests grossly overstate the loss of fresh strength from exercise, while negative tests understate the true level of fatigue from exercise)

The Static test result is affected by:

1. The force produce by muscular contraction (The true muscular strength)
2. The effect of gravity on the mass of the involved body parts
3. The stored energy
4. The angular position of the limb
5. The muscle fatigue (shows what actually occurred)

Static procedures provide the only meaningful test of strength . . . dynamic tests, regardless of how they are conducted, produce only artifacts; tell nothing about the true level of strength.

Test of positive strength are always an understatement of true strength, reduced by friction in the muscles, while negative tests produce an overstatement of true strength, increased by muscular friction. If the level of friction was known, then perhaps meaningful results could be produced by adding to a test of positive strength, or by subtracting from a negative test . . . but the level of friction, as a percentage of muscular force, changes as a result of two factors, speed of muscular contraction and momentary level of fatigue. 

The actual losses of fresh strength were clearly indicated by the tests of static strength . Positive tests grossly overstate the loss of fresh strength from exercise, while negative tests understate the true level of fatigue from exercise. But static tests will show what actually occurred. The shaded area between the two curves shows static fatigue. Even fresh levels of dynamic strength are biased by muscular friction, but the initial level of friction found in fresh muscles changes as fatigue is produced. When worked to a point where all of the fresh level of positive strength has been lost, the friction has then reached such a high level that it is equal to the force of maximal muscular contraction. Continued positive movement then becomes momentarily impossible; even though the actual level of fresh strength (force of muscular contraction) has been reduced by only fifty percent.

Figure 1: Results of a three-part procedure for testing fresh functional strength of the quadriceps muscles (leg extension). The bar graphs represent static torque in several positions throughout the range of movement, while the highest curve is the coexisting level of eccentric (negative) strength, and the lowest curve shows concentric (positive) strength . . . positive strength is lowest, negative strength is highest, and static strength is midway between the levels of positive and negative strength. In general, when the positive strength is 100 percent, then the negative strength will be 140 (40 percent higher), and static strength will be 120, midway between positive and negative levels. Assuming that you are testing fresh, rested muscles, at any level of strength, and that the dynamic tests are conducted at a relatively slow speed of movement. Fatigued muscles show a far different ratio, and tests conducted at faster speeds during the dynamic portions show a different ratio. But regardless of the level of fatigue, and regardless of the speed during the dynamic testing procedures, static strength will be midway between the positive and negative strength levels

Figure 2 shows the three levels of tested strength, positive, static and negative, after a subject was exercised to the point that his positive strength was totally lost, while only 14 percent of his negative strength was gone, and while his true loss of strength was shown by his remaining level of static strength, reduced by 50 percent from its fresh level.

How to measure

Isolation Muscle Strength (Isolation exercises are movements that are working one particular muscle without much, or any, assistance from other muscles. Most bicep, tricep, and calf exercises are isolation exercises because you'll only be using those muscles to lift the weights for the most part. Other isolation exercises include flyes for the chest, laterals (front, side, or rear) for the shoulders, leg extensions for the quadriceps, and leg curls for the hamstrings. Typically, the motion follows a circular path with respect to a Pivotal Center Point.) The muscle strength is measured by measuring the torque with respect to the Pivotal Center Point at several joint angles along the motion path to generate a Strength Curve.

Compound Muscle Strength (Compound exercises are movements that require you to use more than one muscle to lift the weight. Take the bench press as an example, while the chest is the primary muscle targeted while performing it you'll also be working the front deltoids and triceps to get the weight up. While you squat you'll not only be training the quadricep muscles, but also the hamstrings, glutes, and lower back. Most upper and lower back exercises are compound movements as well because you'll get some assistance from the arm and leg muscles while doing them during your workouts.)

• For Weight Lifting training: The muscle strength is measured by measuring the linear force in vertical direction at several points along the motion path to generate a Strength Curve.
• For Cable Machine training: The muscle strength is measured by measuring the linear force in the cable direction at several points along the motion path to generate a Strength Curve.

How to apply the result to monitor the training progress

The measurement is performed after certain training period such as every two weeks to compare the effectiveness of the training.

How to apply the result to training

For Isokinetic and Isometric training, there is no need to use the Muscle Strength test results for the machine setting since these type of exercise the trainee is encouraged to apply his maximum strength; however, Isotonic and Eccentric training the Muscle Strength test results may be used to set the optimum load setting for maximum training efficiency. The relation between the optimum load setting and the Strength Curve depends on training routine mechanism and the fatigue factor on each type of training; it is a complex empirical procedure, that why Isokinetic training is hailed to be the most efficient.

Muscle Strength vs. Speed

Force-velocity relationship

• there is an inverse relationship between force and velocity of shortening
• V_max is the maximum speed of shortening-occurs when the load is zero
• Po is the maximal force that a muscle can develop-occurs when the muscle is stationary (maximal isometric contraction)
• V_max is thought to reflect the maximal rate of ATP splitting
• force-velocity relationship for eccentric movement is a mirror image of concentric movement-greater velocity of shortening is achieved with greater force as speed of sarcomere shortening increases, the force decreases in exponential fashion (for concentric movements only)
• force-velocity curve is higher for FT fibers than ST fibers

Power-load relationship

• there is an optimal load (~40% of max) which allows for the greatest power development-any load less than or greater than this decreases power output