Muscular strength is generally defined as the ability to generate force at a given velocity of movement. One of the five primary components of physical fitness — along with muscular endurance, flexibility, cardiovascular fitness and body composition — muscular strength typically is developed using resistance training. This type of training typically aims to stimulate increased strength on various physiological levels. Strength can be an indicator of overall health or a measure of progress during resistance or rehabilitation training programs. There are several methods for testing physical strength, including the use of certain devices or determining how much weight can be used during certain exercises.
The Purpose of Muscle
The fundamental purpose of skeletal muscle is the generation of force, either to stabilize and balance the skeleton or to produce movement. Muscular force is produced by a complex series of interactions between neurons, nucleotides, ions and protein complexes within the muscle. The level of force generated can vary not only between muscles and muscle groups but also within the range of motion of each particular muscle. Factors that can affect muscular strength include age, sex and level of physical conditioning. From day to day, strength levels can be influenced by nutrition, sleep, one's state of mind and even the time of day.
Types of Strength
Muscular strength can refer to either isometric strength or dynamic strength. Isometric strength is a measure of how much force can be exerted against an immovable object or fixed resistance. Standing in a doorway and pressing one's hands outward against the frame is an example of using isometric strength. This type of strength training typically is used more often in rehabilitation clinics than in fitness centers, because it can help prevent atrophy of an immobilized limb. In a sports setting, isometric training is most often used to overcome weaknesses at a particular angle of a limb's range of motion.
Concentric and Eccentric Movements
Dynamic strength can be further divided into concentric movements and eccentric movements. Concentric movements are those in which the muscle shortens as it moves, such as the biceps muscle when the arm goes from being extended to being fully bent at the elbow. Eccentric movement is when the muscle is lengthening as it moves, such as the biceps when the arm goes from being bent to being fully extended. In a rested muscle, eccentric strength can be as much as 40% greater than concentric strength.
Measuring Strength
A device called a cable tensiometer can be used to measure isometric strength. It originally was designed to measure the strength of aircraft cables. Another device, called a dynamometer, can test muscular strength by assessing the amount of force used to squeeze the instrument with the hand or legs. From these measurements, overall muscular strength can be roughly estimated. More highly technological devices involving computers and electroconductive materials also can be used.
In the interest of simplicity and ease of access, the most popular method of muscular strength testing usually is the one-repetition maximum test. This test measures the greatest amount of weight that a person can move during one repetition of a specific exercise. Although this usually is a reasonably accurate assessment of muscular strength, it should be carried out only with extreme caution. Performed improperly or without appropriate assistance, if necessary, this type of test can pose a risk of significant injury.
