Principles of Resistance Training

The principles of exercise intensity, duration, frequency, overload, progression, and specificity apply to resistance training as well as aerobic training.

Intensity and Duration

For muscular development and health enhancement, the intensity of resistance training may be set by selecting a weight that can be lifted at least 8 times but no more than 12 times. This weight probably represents 70% to 80% of a maximum effort. Each of these lifts is called a repetition. The duration of resistance training is determined by the number of repetitions of each exercise and the number of sets completed; 8 to 12 repetitions of an exercise constitutes one set of that exercise. If the development of strength is the primary goal, you may select the appropriate resistance for each exercise by determining, through trial and error, the amount of weight needed to perform 6 repetitions maximum (RM). This means that you are strong enough to perform 6 repetitions but not 7. This is the basis of progressive resistance exercise. For example, if the RM for the bench press is 120 Ib, you should perform 3 sets of this exercise in the following manner -

The intensity level for resistance exercise varies according to the system used. The intensity level for isometric exercise usually ranges from a minimum of two thirds maximum force to maximum force. The duration of exercise is the total of the time it takes to devote 30 seconds of muscle contraction to each of the exercises. The muscles should be stressed for 30 seconds at several joint angles in the range of motion.

Frequency

Isometrics can be performed every day because muscle soreness does not occur. However, for physiological and psychological reasons, you should designate 2 to 3 days of rest throughout the week.

The new ACSM guidelines for resistance training for healthy adults include the following:
  • The program should consist of 8 to 10 exercises designed to stress the major muscle groups.
  • The exercise program should be repeated a minimum of twice weekly.
  • The exercise program should consist of a minimum of one set of 8 to 12 repetitions to near fatigue.
These must be regarded as minimum standards that will produce approximately 75% of the gain documented with resistance programs featuring three sets of each exercise 3 days per week. Resistance programs following the ACSM guidelines do not produce optimal results but are excellent adjuncts to the cardiorespiratory component and are appropriate when time is a limiting factor. Except for very advanced participants, resistance exercises should be performed no more than every other day.

Overload and Progression

The principle used to gain strength is straight forward the muscles must be subjected periodically to greater resistance as they adapt to the previous resistance. This exemplifies the overload principle, which applies to all muscles regardless of the system of training.

Overload may be applied by progressively increasing the amount of weight lifted or the number of repetitions performed or by decreasing rest time between sets. An increase in the number of repetitions leads to increases in muscle endurance, an increase in the amount of weight lifted leads to an increase in muscle strength, and a decrease in rest time increases muscular and aerobic endurance.

Calisthenics are not as effective as weight training in the development of strength because overload is more difficult to apply. In calisthenic type exercises the body weight is the resistance, and this can not be conveniently changed as participants become stronger. Calisthenics lose their effectiveness in developing strength rather quickly and become more associated with promoting muscle endurance.

The principle of progression relates to the application of overload or, more precisely, how much and when an increase in resistance should occur. In a progressive resistance system of 6 RM, overload is applied by adding more weight when the exerciser can perform more than 6 repetitions on more than one occasion with the current weight. When 6 RM is surpassed with the new weight, it is time to add again.

Specificity

The principle of specificity reflects the body’s response to exercise. The type of training dictates the type of muscle development. Training programs that emphasize high resistance and low repetitions increase muscle strength and size. The gains are the result of
  • Muscle hypertrophy, which is an increase in the diameter of muscle fibers.
  • The recruitment of more motor units.
Training programs that emphasize low resistance and a high number of repetitions develop muscle endurance. The high volume of work increases the blood and oxygen supply to the muscles by increasing capillary density and muscle myoglobin concentration. Myoglobin is similar to hemoglobin: it is an oxygen carrying protein that makes oxygen available to the muscle for contraction.

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