Muscles adapt to increased workloads by becoming larger and stronger and by developing greater endurance. In other words, the muscle must be overloaded. For a muscle to increase in strength, the workload to which it is subjected during exercise must be increased beyond what it normally experiences. The overload principle is the basis for all exercise training programs. These principles are overload, progression, specificity, regularity, recovery, balance, and variety. To have a good exercise program, the seven principles of exercise, described in Chapter 1, must be applied to all muscular endurance and strength training. Actually, a properly designed weight training program with free weights or resistance machines will result in improvements in all three of these categories. The above descriptions are more important to those who assess strength than to average people trying to develop strength and endurance. Each type of contraction has advantages and disadvantages, and each will result in strength gains if done properly. When a muscle is overloaded, whether by isometric, isotonic, or isokinetic contractions, it adapts by becoming stronger. The nature of the eccentric contraction, however, makes the muscle and connective tissue more susceptible to damage, so there is more muscle soreness following eccentric work. This greater overload, in return, may produce greater strength gains. As a result, the muscle may be able to handle more of an overload eccentrically. This is an eccentric (negative) contraction.Ī muscle can control more weight in the eccentric phase of contraction than it can lift concentrically. During the lowering phase of the curl the biceps are lengthening. This is a concentric (positive) contraction. For example, on the upward phase of the biceps curl, the biceps are shortening. In the concentric phase (shortening) the muscle contracts, while in the eccentric phase (elongation) the muscle returns to its normal length. Isotonic and isokinetic contractions have two specific phases - the concentric or “positive” phase and the eccentric or “negative” phase. Some of these devices are classified as pseudo-isokinetic and some as variable-resistance machines. There are other resistance-training machines which, while not precisely controlling the speed of movement, affect it by varying the resistance throughout the range of motion. This requires the use of isokinetic machines. To achieve a constant speed of movement, the load or resistance must change at different joint angles to counter the varying forces produced by the muscle(s) at different angles. Isokinetic contraction causes the angle at the joint to change at a constant rate, for example, at 180 degrees per second. Common examples are push-ups, sit-ups, and the lifting of weights. Isotonic contraction causes a joint to move through a range of motion against a constant resistance. Force is produced with no change in the angle of the joint. Isometric contraction produces contraction but no movement, as when pushing against a wall. Isometric, isotonic, and isokinetic muscular endurance and strength are best produced by regularly doing each specific kind of contraction. Progressively working against resistance will produce gains in both of these components. Muscular endurance is the ability of a muscle or muscle group to do repeated contractions against a less-than-maximum resistance for a given time.Īlthough muscular endurance and strength are separate fitness components, they are closely related. Muscular strength is the greatest amount of force a muscle or muscle group can exert in a single effort. Muscular fitness has two components: muscular strength and muscular endurance. Indeed, survival on the battlefield may, in large part, depend on the muscular endurance and strength of the individual soldier. Infantrymen may need to carry loads exceeding 100 pounds over great distances, while supporting units will deploy and displace many times. For example, based on computer-generated scenarios of an invasion of Western Europe, artillerymen may have to load from 300 to 500, 155mm-howitzer rounds (95-lb rounds) while moving from 6 to 10 times each day over 8 to 12 days. In a single day they may carry injured comrades, move equipment, lift heavy tank or artillery rounds, push stalled vehicles, or do many other strength-related tasks. On today’s battlefield, in addition to cardiorespiratory fitness, soldiers need a high level of muscular endurance and strength.
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