Although aerobic activities have been shown to be effective for developing cardiorespiratory fitness, most have little influence on muscular strength or muscular endurance, especially of the upper body. Every activity - including ADL - requires a certain percentage of an individual’s maximal strength and endurance. The maintenance or enhancement of muscular strength and muscular endurance enables an individual to perform such tasks with less physiological stress. The physiological stress induced by lifting or holding a given weight is proportional to the percentage of maximal strength involved.
Resistance training of moderate intensity (i.e., sufficient to develop and maintain muscular fitness and lean body weight) should be an integral part of adult fitness and rehabilitative exercise programs. In addition to the development and maintenance of muscular strength and muscle mass, the physiological benefits of resistance training include increases in bone mass and in the strength of connective tissue. These adaptations are beneficial for middle — age and older adults, and, in particular, postmenopausal women who rapidly lose bone mineral density. Other health benefits which have been ascribed to resistance training include: modest improvements in cardiorespiratory fitness, reductions in body fat, modest reductions in blood pressure, improved glucose tolerance, and improved blood lipid and lipoprotein profiles. These health benefits have been most often associated with circuit weight training, which is a method of resistance training in which a series of exercises are performed in succession with minimal rest between exercises.
Muscular strength and endurance are developed by the overload principle - by increasing the resistance to movement or the frequency or duration of activity to levels above those normally experienced. Muscular strength is best developed by using weights that develop maximal or nearly maximal muscle tension with relatively few repetitions. Muscular endurance is best developed by using lighter weights with a greater number of repetitions. To elicit improvement in both muscular strength and endurance, most experts recommend 8 to 12 repetitions per exercise.
Any overload will result in strength development, but higher intensity effort at or near maximal effort will produce a significantly greater effect. The intensity of resistance training can be manipulated by varying the weight, the number of repetitions, the length of the rest interval between exercises, or the number of sets of exercises completed. Caution is advised for training that emphasizes lengthening (eccentric) contractions, compared to shortening (concentric) or isometric contractions, as the potential for skeletal muscle soreness is accentuated.
Muscular strength and endurance can be developed by means of static or dynamic exercises. Although each type of training has strengths and weaknesses, dynamic resistance exercises are recommended for most adults. Resistance training for the average participant should be rhythmical, performed at a moderate - to - slow speed, involve a full range of motion, and not interfere with normal breathing. Heavy resistance exercise combined with breath - holding can cause a dramatic, acute increase in both systolic and diastolic blood pressure.
