Mechanical resistance exercise is any form of exercise in which resistance (the exercise load) is applied by means of some type of exercise equipment. Frequently used terms that denote the use of mechanical resistance are resistance training, weight training, and strength training.
Mechanical resistance exercise is an integral component of rehabilitation and conditioning programs for individuals of all ages. However, use of mechanical resistance in an exercise program has some advantages and disadvantages. The positive and negative qualities of specific types of exercise equipment are described in the last section of this chapter.
Advantages
• Establishes a quantitative baseline measurement of muscle performance against which improvement can be judged.
• Most appropriate during intermediate and advanced phases of rehabilitation when muscle strength is 4/5 or greater or when the strength of the patient exceeds the therapist’s strength.
• Heavy exercise loads, far beyond that which can be applied manually by a therapist, can be used to induce a training effect for already strong muscle groups.
• Increases in level of resistance can be incrementally and quantitatively documented.
• Quantitative improvement is an effective source of motivation for the patient.
• Useful for improving dynamic or static muscular strength.
• Adds variety to a resistance training program.
• Practical for improving muscular endurance.
• Some equipment provides variable resistance through the ROM.
• High-velocity resistance training is possible and safe with some forms of mechanical resistance (hydraulic and pneumatic variable resistance machines, isokinetic units, elastic resistance). Potentially better carryover to functional activities than relatively slow-velocity manual resistance exercises.
• Appropriate for independent exercise in a home program after careful patient education and a period of supervision.
Disadvantages
• Not appropriate when muscles are very weak or soft tissues are in the very early stages of healing, with the exception of some equipment that provides assistance, support, or control against gravity.
• Equipment that provides constant external resistance maximally loads the muscle at only one point in the ROM.
• No accommodation for a painful arc (except with hydraulic, pneumatic, or isokinetic equipment).
• Expense for purchase and maintenance of equipment.
• With free weights and weight machines, gradation in resistance is dependent on the manufacturer’s increments of resistance.
Mechanical resistance exercise is commonly implemented in rehabilitation programs to eliminate or reduce deficits in muscular strength, power, and endurance caused by an array of pathological conditions and to restore or improve functional abilities.
Use in Conditioning Programs
There is a growing awareness through health promotion and disease prevention campaigns that training with weights or other forms of mechanical resistance is an important component of comprehensive conditioning programs to improve or maintain physical fitness and health throughout most of the life span. As in rehabilitation programs, resistance training complements aerobic training and flexibility exercises in conditioning programs. Guidelines for a balanced resistance training program for the healthy, but untrained adult (less than 50 to 60 years of age) recommended by the American College of Sports Medicine and other resources are summarized below.
Special Considerations for Children and Older Adults
As noted previously, children and older adults often wish to, or may find it necessary to, engage in resistance training in a conditioning program to improve physical fitness, reduce health-related risk factors, or enhance physical performance. Resistance training can be safe and effective if exercise guidelines are modified to meet the unique needs of these two groups.
Summary of Guidelines for Resistance Training in Conditioning Programs for Healthy Adults (< 50-60 years old)
• Prior to resistance training, perform warm-up activities followed by flexibility exercises.
• Perform dynamic exercises that target the major muscle groups of the body (approximately 8-10 muscle groups of the upper and lower extremities and trunk) for total body muscular fitness.
• Balance flexion-dominant (pulling) exercises with extension-dominant (pushing) exercises.
• Move through the full, available, and pain-free ROM.
• Include both concentric (lifting) and eccentric (lowering) muscle actions.
• Use moderate-intensity exercises: at least 8 to 12 repetitions per set.
• Perform 1 to 3 sets of each exercise for 8 to 12 repetitions per set.
• Use slow to moderate speeds of movement.
• Use rhythmic, controlled, nonballistic movements.
• Exercises should not interfere with normal breathing.
• Include rest intervals of 2 to 3 minutes between sets. While resting one muscle group, exercise a different muscle group.
• Frequency: two to three times per week.
• Increase intensity gradually (increments of approximately 5%) to progress the program as strength and muscular endurance improve.
• Whenever possible, train with a partner for feedback and assistance.
• Cool down after completion of exercises.
• After a layoff of more than 1 to 2 weeks, reduce the resistance and volume when reinitiating weight training.
Children and Resistance Training
Until the past decade or two, health professionals have been reluctant to support preadolescent youth participation in resistance training as a part of fitness programs because of concerns about possible adverse stress and injury to the immature musculoskeletal system, in particular, growth-plate injuries and avulsion fractures. Furthermore, a common assumption was that the benefits of resistance training were questionable in children.
There is now a growing body of evidence that demonstrates that children do achieve health-related benefits from resistance training and can safely engage in closely supervised weight-training programs. Use of body weight as a source of resistance and equipment specifically designed to fit a child contributes to program safety. Training-induced strength gains in prepubescent children have been documented, but sports related injury prevention remains of questionable benefit. As with adults, information on the impact of strength training on the enhancement of functional motor skills is limited.
Focus on Evidence
Research has shown that, although some acute and chronic responses of children to exercise are similar to those of adults, other responses are quite different. For example, children dissipate body heat less easily, fatigue more quickly, and may need more time to recover from exercise than young adults. Such differences in response to resistance exercise must be addressed when designing and implementing strength training programs for children.
Accordingly, the American Academy of Pediatrics, the American College of Sports Medicine, and many health professionals support youth involvement in resistance training—but only if a number of special guidelines and precautions are consistently followed.
Although the risk of injury from resistance training is quite low, exercise-induced soft tissue or growth-plate injuries have been noted if guidelines and precautions are not followed. Special guidelines are summarized below. Consistent with adult guidelines, a balanced program of dynamic exercise for major muscle groups includes warm-up and cool-down periods.
Older Adults and Resistance Training
It is well known that muscle performance diminishes with age, and deficits in muscle strength, power, and endurance are associated with a higher incidence of functional limitations and disability. The extent to which decreasing muscle strength is caused by the normal aging process versus a sedentary lifestyle or an increasing incidence of age-related diseases, such as hypertension and osteoarthritis, is not clear.
Resistance Training for Children: Special Guidelines and Special Considerations
• No formal resistance training for children less than 6 to 7 years of age.
• At age 6 to 7, introduce the concept of an exercise session initially using exercises without weights, then with light (only 1- or 2-pound) weights.
• Maintain close and continuous supervision by trained personnel or a parent who has received instruction.
• Focus on proper form, exercise technique, and safety (alignment, stabilization, controlled motion).
• Emphasize low intensity throughout childhood to avoid potential injury to a child’s growing skeletal system and to joints and supportive soft tissues.
• Emphasize a variety of short-duration, play-oriented exercises to prevent boredom, overheating, and muscle fatigue.
• Perform warm-up activities for at least 5 to 10 minutes before initiating resistance exercises.
• Select low exercise loads that allow a minimum of 8 to 12 or 12 to 15 repetitions. Emphasize multijoint, combined movements.
• Perform only one to two sets of each exercise; rest at least 3 minutes between sets of exercises.
• Initially progress resistance training by increasing repetitions, not resistance, or by increasing the total number of exercises. Later, increase weight by no more than 5% at a time.
• Limit the frequency to two sessions per week.
• Use properly fitting equipment that is designed or can be adapted for a child’s size. Many weight machines cannot be adequately adjusted to fit a child’s stature.
A major goal of resistance training in older adults is to maintain or improve their levels of functional independence and reduce the risk of age-related diseases. As with young and middle-aged adults, older adults (less than age 60 to 65) benefit from regular exercise that includes aerobic activity, flexibility exercises, and resistance training. Even in previously sedentary older adults or frail elderly patients, a program of weight training has resulted in training-induced gains in muscle strength – and improvements in a number of parameters of physical function, such as balance, speed of walking, and the ability to rise from a chair. It also has been suggested that strength training in the elderly population may minimize the incidence of falls.
Although many of the guidelines for resistance training that apply to young and middle-aged adults are applicable to healthy older adults, in general, resistance training for older adults should be more closely supervised and initially less rigorous than for younger populations of adults. Accordingly, impaired balance, age-related postural changes, and poor vision that can compromise safety must be addressed if present. Also, because of age-related changes in connective tissue, there is a higher incidence of DOMS and greater muscle fiber damage in older versus young adults after heavy-resistance, high-volume strength training.
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