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Types of Muscle Contraction
Muscle Contractions can be divided into:
- Isotonic (meaning same tension)
- Isometric (meaning same distance or not moving)
- Isokinetic (meaning same speed)
Isotonic contractions maintain constant tension in the muscle as the muscle changes length. This can occur only when a muscle's maximal force of contraction exceeds the total load on the muscle.
There are two types of Isotonic contraction:
Concentric contractions are those which cause the muscle to shorten as it contracts. An example is bending the elbow from straight to fully flexed, causing a concentric contraction of the Biceps Brachii muscle. Concentric contractions are the most common type of muscle contraction and occur frequently in daily and sporting activities.
Eccentric contractions are the opposite of concentric and occur when the muscle lengthens as it contracts. This is less common and usually involves the control or deceleration of a movement being initiated by the eccentric muscles agonist.
For example, when kicking a football, the Quadriceps muscle contracts concentrically to straighten the knee and the Hamstrings contract eccentrically to decelerate the motion of the lower limb. This type on contraction puts a lot of strain through the muscle and is commonly involved in muscle injuries.
In contrast to isotonic contractions, isometric contractions generate force without changing the length of the muscle . This is typical of muscles found in the hands and forearm: the muscles do not change length, and joints are not moved, so force for grip is sufficient. An example is when the muscles of the hand and forearm grip an object; the joints of the hand do not move, but muscles generate sufficient force to prevent the object from being dropped.
Isokinetic contractions are similar to isotonic in that the muscle changes length during the contraction, where they differ is that Isokinetic contractions produce movements of a constant speed. Examples of using isokinetic contractions in day-to-day and sporting activites are rare.
Principles of Conditioning
This article addresses the principles of conditioning and how these fundamental principles can be appropriately incorporated into school-based physical education. The components of health-related fitness discussed in the overview are muscular strength, muscular endurance, and aerobic endurance as conditioning principles directly apply to each of these components. The principle of overload and the FITT principles are discussed as they relate to resistance training, which develops muscular strength and muscular endurance, and aerobic conditioning, which develops aerobic enduranc
Principles of conditioning are those tenets of exercise science that address the physiological processes by which individuals improve their muscular strength, muscular endurance, aerobic and anaerobic capacity, and flexibility. The scientific theories and tenets that these principles are based upon are addressed in the fields of exercise and muscle physiology. For the purpose of this article, the specific physiological processes that occur during physical activity will not be discussed; rather the focus will be to provide a synopsis of the principles of conditioning based on how they are relevant to physical education. Principles of conditioning, within the context of physical education, involve the application of physiological principles to the learning objectives and teaching methods that are employed in the classroom in order to design activities and curricula in a manner to enhance the students' level of physical fitness and knowledge and understanding of conditioning concepts.
The National Association for Sport and Physical Education (NASPE) has set forth recommended content standards for teaching and learning in physical education (NASPE, 2007). The six national standards provide a framework to guide state and local school administration in the development of physical education curricula and also demonstrate the purpose of physical education and its academic merit and value as a component of education (NASPE, 2007). The third and the fourth standards state that students should engage in regular physical activity and demonstrate or achieve and maintain a level of physical fitness that enhances health (NASPE, 2007). With the number of obese and overweight youth having increased dramatically over the last few decades, it has become increasingly important for physical educators to focus on achieving these standards by incorporating physical activity and health-related fitness education into the physical education curriculum (Greer & Gilbert, 2006). A 2010 position statement by NASPE, "Appropriate Uses of Fitness Measurement," affirms these standards and the NASPE's position that fitness measurement should be used to improve student health and physical activity programs, and should focus on the process of achieving fitness rather focusing on individual achieved outcomes to assign student grades or teacher effectiveness ratings. Physical education can also play an important role in a student?s general education, addressing measures such as problem-solving and personal growth, as argued by Thorburn and MacAllister (2013).
Physical fitness is defined as the ability to perform physical activity (Casperson, Powell, & Christenson, 1985). Health-related fitness is a term that is used to indicate physical activity that aims to promote good health and wellness as opposed to conditioning that is specifically designed with performance as the focus. Performance-focused training is called skill-related fitness and focuses on the development of speed, power, reaction time, balance, coordination and agility, which are related to enhancing performance and/or sport skill development (Corbin, 2004). Health-related fitness, which is applicable to the physical education setting, encompasses five components: 1) muscular strength, 2) muscular endurance, 3) aerobic endurance, 4) flexibility, and 5) body composition (Maina, Griffin, Ryan, & Schlegel Maina, 2001).
Muscular strength, muscular endurance, and aerobic endurance are the health-related fitness components that are directly related to physical conditioning in the physical education setting. Muscular strength is defined as the force that a muscle can produce or exert in a one time maximal effort or the greatest amount of weight or resistance a muscle can move or lift for one repetition only, also known as a "one rep max" (Maina et al., 2001). Muscular endurance is defined as the ability for a muscle group to perform, or contract, repeatedly at a resistance below the maximum resistance that the muscle can move (Maina et al., 2001). Aerobic endurance is defined as the body's ability to engage in activity over a prolonged period of time and utilizes oxygen in the process of energy generation (Universal Fitness Tester, 2007).
Resistance training, or weight training, is a mode of exercise that aims to increase muscular strength and endurance through the process of overloading the muscles. The conditioning principle of overload requires that the body must undergo a level of stress that is greater than the norm in order for the body to undergo physiological adaptations that increase muscular strength and endurance. Resistance training as a form of conditioning for youth has been investigated to determine whether or not this type of exercise is appropriate for children and adolescents and what benefits result (Kraemer, Fry, Frykman, Conroy, & Hoffman, 1989). Research has shown that resistance training is appropriate for youth when programming is dynamic and individualized. Resistance training has been shown to improve body composition, prevent injury, and improve blood lipid profiles in youth (Kraemer et al., 1989)
It is recommended that prior to starting a resistance training program with a child the teacher should be sure that the child has medical clearance, an understanding of the purpose of the program, a willingness to try the program, and an understanding that strength training is a lifetime pursuit. Resistance training programs for children need to take into account physiological and psychological factors.
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