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HOME CONTENT PREPARATION ANALYSIS DESIGN APPENDICES GLOSSARY
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SECTION II - ANALYSIS
LESSON 6 - FLEXIBILITY LESSON 7 - ENDURANCE LESSON 8 - STRENGTH LESSON 9 - SKILL
LESSON 10 - BODY COMPOSITION LESSON 11 - ENERGY LESSON 12 - NUTRITION
ANALYSIS OF STRENGTH
Muscular Strength and Endurance: Maximum Resistance andRepetitions
Objectives
Upon completion of Lesson 8 you should have knowledge of the following:
v Describe
a muscle fiber and name three ways it can contract.
v Explain
the effect of percentage of 1 repetition maximum (1 RM) and number of
repetitions.
v Describe
the percent of RM and intensity of training, in regard to muscular strength (low
repetitions, 2 RM to 6 RM), muscular power (moderate repetitions, 8 RM to 15 RM),
and muscular endurance (high repetitions 15 RM to 25 RM).
v What
data should you include on a strength training workout record.
v Explain the difference in workouts for muscular strength and muscular endurance.
It is important for an exerciser to know how a muscle fiber functions to gain an understanding of the different ways it can be exercised to improve strength. Additionally, it is important to recognize that there are three kinds of exercises used to improve muscular strength. They are exercises for producing maximum muscular strength, maximum muscular endurance, and muscular power. Each of these categories contributes different effects for sport performance. There are also two basic types of muscle fiber that contribute to how skeletal muscle respond to physical activity. On the average there is an even mix of the muscle fiber types among both male and female. The two basic types of muscle fibers are fast-twitch and slow-twitch. Slow twitch muscle fiber are more suited for endurance activities. Fast twitch muscle fibers enhance power performances. Although both fiber types respond positively to progressive resistance training, the fast-twitch fibers are believed to experience greater increases in size and strength. Consequently, people with a preponderance of fast-twitch muscle fibers may obtain better results from their strength-training program.
Muscular strength refers to the greatest amount of resistance that a person can handle in one attempt or one repetition maximum (1 RM). It is measured by a single instant of work against resistance. Muscular endurance refers to the greatest amount of resistance that can be handled in two or more repetitions. It is measured by the ability to repeat work against resistance; it is symbolized by the maximum number of repetitions completed and RM (For example, 2 RM, 3 RM, 5 RM, or 10 RM). Power refers to work against resistance and the rate of speed in which resistance is handled. It is measured by the ability to, quickly, repeat work against resistance. For instance, an exercise may be done with a specific set of muscles (such as the curling muscles of the upper arm) in two seconds, but to do the same exercise in one second represents and increase in power. When all three types of muscular strength are used to improve sport performance, muscular strength can yield tremendous benefits.
Strength training is the process of exercising with progressively heavier resistance for the purpose of strengthening the musculoskeletal system. Regular strength training results in the following positive adaptations:
1) Increased muscle
fiber size
2) Increased muscle contractile strength,
3) Increased tendon tensile strength,
4) Increased bone strength, and
5) Increased ligament tensile strength.
These changes within the musculoskeletal tissue have a profound influence on physical capacity, metabolic functions, and injury prevention. It is important to note that as strength increases with exercise, the tensile strength of connective tissues (ligaments and tendons) of muscles and the density of bones increase as well.
There are four types of muscle contractions that must be understood to plan for changes in the musculoskeletal system: isometric contraction, isotonic, isokinetic, and plyometrics. When a muscle is signaled to contract, it develops tension and attempts to shorten. The resulting movement or lack of movement of muscle fibers depends on the relationship between muscular forces and resistive forces. If the muscular force is greater than the resistive force, there will be movement (isotonic). If the resistive force is equal to or greater than the muscular force, there will be no movement (isometric). Isokinetic refers to a type of resistance exercise that causes the exercising muscles to generate a maximum amount of force throughout the movement (ROM). The amount of force generated by muscles changes throughout an exercise movement. Plyometrics is also called stretch-shortening cycle exercise because it describes this type of resistance exercise more accurately.
When a muscular force is equal to the resistive force, there is no movement (isometric contraction). For example, if a person can hold 40 pounds at 90 degrees of elbow flexion or bend, his or her effective isometric force output is 40 pounds. When this person moves the 40 pounds through a full range of motion from elbow extension to elbow flexion, the muscle contraction of the muscles responsible for this movement are said to have concentric contraction. In concentric contractions the muscle force is greater than the resistive force and muscles shorten. When the muscular force is less than the resistive force, the muscle lengthens, resulting in an eccentric or negative contraction. So, when the 40 pounds that is curled through a full range of motion is lowered, the muscles responsible for the action creates a muscle force that is less than the resistive force and gradually becomes longer. Concentric and eccentric contraction exercises are classified as isotonic.
Plyometrics or stretch-shortening cycle refers to a natural part of most movements. This process can be demonstrated in walking. During walking, every time a foot hits the ground, the quadriceps muscles go through a stretch-shortening cycle. When the foot hits the ground, the quadriceps muscles contract eccentrically (muscles lengthens), then it contracts isometrically (muscle neither lengthens nor shortens), and finally it concentrically (muscles shorten). If these three actions are performed quickly, the concentric contraction will be more powerful than if no eccentric action was performed. This entire sequence of eccentric, isometric, and concentric actions is called the stretch-shortening cycle (plyometrics).
Muscle fibers respond favorably to progressive resistance training, therefore, each of these three types of muscle contractions may be used to improve strength. However, we have learned that the most appropriate models for training with these methods focus on the type of strength desired (that is strength, endurance, or power). Concentric and eccentric contraction exercises have won out as the most popular models for training for muscular strength and endurance, while plyometrics may be favored for improving muscular power.
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Strength training that is designed to raise the amount of resistance handled in one repetition or to produce maximum strength is achieved by using high amounts of resistance with a low number of repetitions (3 - 5 RM) and long rest periods between sets of repetitions (3 minutes or longer). However, since the neuromuscular system adapts to specific training workloads, it is important to make occasional changes in the resistance/repetitions relationship. For example, if eight repetitions with 80 pounds becomes a strength plateau, perhaps it would be beneficial to complete 12 repetitions with 70 pounds to produce additional strength, because the muscle adapts to gradual increases in exercise. Some experts recommend periodization to enhance the strength-building stimulus. During the first month of training, for example, sets of 8 to 12 repetitions are performed. During the second month, this is reduced to sets of 6 to 8 repetitions, and during the third month, this is further reduced to sets of 4 to eight repetitions. After a week of rest, the three-stage training program is repeated. The main objective for varying the workload and repetitions is to avoid prolonged periods of training with the same weight. The primary goal for this and other methods that may be combined with the first method explained, high load and low repetitions with long rest periods, is to build maximum strength.
There are four types of resistance training equipment: isometric or static equipment is frequently used for testing muscle strength, isotonic, and isokinetic that are used to design equipment for resistance training and the exercises used to create a resistance training program.
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The 2 RM or higher test measures muscular endurance. Strength training that is designed to raise the amount of resistance handled to two or more repetitions or to produce maximum endurance is achieved by using low to moderate amounts of resistance with a high number of repetitions (12 - 15 RM) and moderately long rest periods between sets of repetitions (45 - 90 seconds). Again, it is important to note that the neuromuscular system adapts to specific training workloads. Therefore, it is important to make occasional changes in the resistance/repetitions relationship. Also, the main objective for varying the workload and repetitions is to avoid prolonged periods of training with the same weight. The primary goal for other methods that may be combined with the method of resistance training used to improve muscular endurance or power, is to build maximum strength for 2 or more repetitions (a strength program).
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Strength training that is designed to increase the quickness of ability to work against resistance indicate power. This benefit of resistance training is accomplished by training with low loads and movements that are more rapid than usual. Since repetitions are an important goal for power movements, it is also important to combine power movements with endurance type resistance training. Maximum power and endurance is achieved by using low to moderate amounts of resistance with a high number of repetitions (12 - 15 RM) and long rest periods between sets of repetitions (2 - 3 minutes). However, since the neuromuscular system adapts to specific training workloads, it is important to make occasional changes in the resistance/repetitions relationship. For example, if eight repetitions with 80 pounds becomes a strength plateau, perhaps it would be beneficial to complete 12 repetitions with 70 pounds to produce additional strength. The important criteria to remember for developing power is that rapid movements are required. The primary goal for this and other methods that may be combined with the low to moderate loads and high repetitions and long periods of rest, is to build maximum endurance with power.
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Strength training improves functional capacity to work and exercise, enhances physical appearance, increases metabolic rate, reduces risk of injury, decreases resting blood pressure, builds bone density, and protects against a variety of degenerative problems. To design a safe and effective strength-training program, you must understand the relationship between muscular forces and resistive forces, as well as the factors that affect strength performance. You must also be knowledgeable about the two categories of muscle fibers and how they relate to the three effects that training programs are designed to accomplish.
Every movement we make involves our muscular system, but they must relax to continue functioning. Muscles are unique in their ability to relax, contract and produce force. In addition, this metabolically active tissue is highly responsive to training stimuli. Therefore, with appropriate exercise, muscles become larger and stronger. Without appropriate exercise, muscles become smaller and weaker. Today, strength improving exercises are considered essential for success in sports. The beneficial effects of resistance training have a profound effect on sport performance and general well being.
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Huxley, H. 1969. The Mechanism of Muscular Contraction. Science 164: 1356-21.
Kanehisa, H., and Miyashita, M. 1983. Specificity of Velocity in Strength Training. European Journal of Applied Physiology 52: 104-6.
Komi, P. V., and Karlsson, J. 1978. Skeletal Muscle Fiber Types, Enzymes Activities and Physical Performance in Young Males and Females. International Journal of Sports Medicine 8: 22-29.
Henderson, J. M. 1970. The Effects of Weight Loadings and Repetitions, Frequency, of Exercise, and Knowledge of Theoretical Principles of Weight Training Changes in Muscular Strength. Dissertation Abstracts International 31A: 3320.
Kraemer, W. J., and Fry, A. C. 1995. Strength Testing: Development and evaluation of Methodology. Physiological Assessment of Human Fitness, Eds. P, Maud and C. Foster. Champaign. IL: Human Kinetics.
Fleck, Steven J., and Kraemer, William J. 1997. Designing Resistance Training Programs. Human Kinetics, Champaign, IL.
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