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Biomechanics of Resistance Exercise

By Tony Matthews,2014-05-08 20:54
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Biomechanics of Resistance Exercise

    Age- and Sex-Related Differences and Their Implications for Resistance Exercise Chapter Objectives

    Evaluate evidence regarding the safety and effectiveness of resistance exercise for children.

    Discuss sex-related differences in muscular function and their implications for female athletes.

    (continued)

    Chapter Objectives (continued)

    Describe effects of aging on musculoskeletal health and the trainability of older adults.

    Explain why adaptations to resistance exercise can vary greatly among partici-pants.

    Section Outline

    Children

    The Growing Child

    Chronological Age Versus Biological Age

    Muscle and Bone Growth

    Developmental Changes in Muscular Strength

    Youth Resistance Training

    Trainability of Children

    Potential Benefits

    Potential Risks and Concerns

    Program Design Considerations for Children

    Children

    With the growing interest in youth resist-ance training, it is important for strength and conditioning professionals to understand the fundamental principles of normal growth and development.

    Children

    The Growing Child

    Chronological Age Versus Biological Age

    Puberty refers to a period of time in which secondary sex characteristics develop and a child is transformed into a young adult.

    During puberty, changes also occur in body composition and the performance of physical skills.

    Children do not grow at a constant rate, and there are substantial inter-individual differences in physical development at any given chronological age. Children

    The Growing Child

    Muscle and Bone Growth

    Muscle mass steadily increases throughout the developing years.

    During puberty, a 10-fold increase in testosterone production in boys results in a marked increase in muscle mass, whereas in girls an increase in estrogen production causes increased body fat deposition, breast development, and widening of the hips. When the epiphyseal plate becomes completely ossified, the long bones stop growing.

Key Point

    Growth cartilage in children is located at

    the epiphyseal plate, the joint surface, and the apophyseal insertions. Damage to the growth cartilage may impair the growth and development of the affected bone. Children

    The Growing Child

    Developmental Changes in Muscular Strength

    In boys, peak gains in strength typically occur about 1.2 years after peak height velocity and 0.8 years after peak weight velocity.

    In girls, peak gains in strength also typically occur after peak height velocity, although there is more individual variation in the relationship of strength to height and body weight.

    On average, peak strength is usually attained by age 20 in untrained women and between the ages of 20 and 30 in untrained men.

    General Body Types

    Figure 7.1 (next slide)

    (a) Mesomorph

    (b) Endomorph

    (c) Ectomorph

    Figure 7.1

    Children

    Youth Resistance Training

    Despite previous concerns that children would not benefit from resistance exercise or that the risk of injury was too great, clinicians, coaches, and exercise scientists now agree that resistance exercise can be a safe and effective method of conditioning for children.

    Children

    Youth Resistance Training

    Trainability of Children

    Training-induced gains from a short-duration, low-volume training program are not distinguishable from gains attributable to normal growth and maturation. Strength gains of roughly 30% to 40% have been typically observed in untrained preadolescent children following short-term resistance training programs. Similar to adults, continuous training is needed to maintain the strength advantage of exercise-induced adaptations in children.

    Key Point

    Preadolescent boys and girls can signifi-cantly improve their strength with resistance training. Neurological factors,

    as opposed to hypertrophic factors, are primarily responsible for these gains. Development of Muscular Strength

    Figure 7.2 (next slide)

    Theoretical interactive model for the integration of developmental factors related to the potential for muscular strength adaptations and performance Figure 7.2

    Children

Youth Resistance Training

    Potential Benefits

    Participation in a youth resistance training program can influence many health- and fitness-related measures.

    Potential Risks and Concerns

    Appropriately prescribed youth resistance training programs are relatively safe. Program Design Considerations for Children

    Consider quality of instruction and rate of progression.

    Focus on skill improvement, personal successes, and having fun. Children

    How Can We Reduce the Risk of Overuse Injuries in Youth?

    Prior to sport participation, young athletes should be evaluated by a sports medicine physician.

    Parents should be educated about the benefits and risks of competitive sports. Parents should understand the importance of preparatory conditioning. Children and adolescents should be encouraged to participate in year-round physical activity.

     (continued)

    Children

    How Can We Reduce the Risk of Overuse Injuries in Youth? (continued)

    Youth coaches should implement well-planned recovery strategies. The nutritional status of young athletes should be monitored. Youth sport coaches should participate in educational programs. Boys and girls should be encouraged to participate in a variety of sports and activities.

    Children

    Youth Resistance Training Guidelines

    Each child should understand the benefits and risks associated with resistance training.

    Competent and caring fitness professionals should supervise training sessions. The exercise environment should be safe and free of hazards.

    All equipment should be in good repair and properly sized to fit each child. Dynamic warm-up exercises should be performed before resistance training.

     (continued)

    Children

    Youth Resistance Training Guidelines (continued)

    Static stretching exercises should be performed after resistance training. Carefully monitor each child's tolerance to the exercise stress. Begin with light loads.

    Increase the resistance gradually (e.g., 5% to 10%) as strength improves. Depending on needs and goals, 1 to 3 sets of 6 to 15 repeti-tions on a variety of exercises can be performed.

     (continued)

    Children

    Youth Resistance Training Guidelines (continued)

    Advanced multijoint exercises may be incorporated into the program if appropriate loads are used and the focus remains on proper form. Two or three nonconsecutive training sessions per week are recommended. Adult spotters should be nearby to actively assist the child. The resistance training program should be systematically varied throughout the year.

    Children should be encouraged to drink plenty of water before, during, and after exercise.

    Section Outline

    Female Athletes

    Sex Differences

    Body Size and Composition

    Strength and Power Output

    Resistance Training for Female Athletes

    Trainability of Women

    Program Design Considerations for Women

    Female Athletes

    Sex Differences

    Body Size and Composition

    Before puberty there are essentially no differences in height, weight, and body size between boys and girls.

    Adult women tend to have more body fat and less muscle and bone than adult males.

    Women tend to be lighter in total body weight than men.

    Female Athletes

    Sex Differences

    Strength and Power Output

    In terms of absolute strength, women generally have about two-thirds the strength of men.

    If comparisons are made relative to fat-free mass or muscle cross-sectional area, differences in strength between men and women tend to disappear. Key Point

    In terms of absolute strength, women are generally weaker than men because of their lower quantity of muscle. Relative to muscle cross-sectional area, no differences in strength exist between the sexes, which indicates that muscle quality is not sex specific.

    Female Athletes

    Resistance Training for Female Athletes

    Trainability of Women

    Women can increase their strength at the same rate as men or faster. Program Design Considerations for Women

    It is important for strength and conditioning professionals

    to be aware of the increasing incidence of knee injuries in female athletes, particularly in sports such as soccer and basketball.

    Female Athletes

    How Can Female Athletes Reduce Their Risk of Injury?

    Begin with a preparticipation screening by a sports medicine physician. Participate in a year-round conditioning program that includes resistance training, plyometric training, agility training, and flexibility training.

(continued)

    Female Athletes

    How Can Female Athletes Reduce Their Risk of Injury? (continued)

    Every exercise session should be preceded by a general dynamic warm-up and a specific warm-up using movements that resemble those involved in the activity. Athletes should wear appropriate clothing and footwear during practice and games.

    Athletes should be encouraged to maximize their athletic potential by optimizing their dietary intake.

    Section Outline

    Older Adults

    Age-Related Changes in Musculoskeletal Health

    Resistance Training for Older Adults

    Trainability of Older Adults

    Program Design Considerations for Older Adults

    Older Adults

    Age-Related Changes in Musculoskeletal Health

    Loss of bone and muscle with age increases the risk for falls, hip fractures, and long-term disability.

    Bones become fragile with age because of a decrease in bone mineral content that causes an increase in bone porosity.

    After age 30 there is a decrease in the cross-sectional areas of individual muscles, along with a decrease in muscle density and an increase in intramuscular fat. Key Terms

    osteopenia: A bone mineral density between ?1 and ?2.5 standard deviations (SD)

    of the young adult mean.

    osteoporosis: A bone mineral density below ?2.5 SD of the young adult mean.

    Table 7.1

    Key Point

    Advancing age is associated with a loss of muscle mass, which is due to physical inactivity and the selective loss of Type II (fast-twitch) muscle fibers. A direct result of the reduction in muscle mass is a loss of muscular strength and power. Older Adults

    Resistance Training for Older Adults

    Trainability of Older Adults

    Though aging is associated with a number of undesirable changes in body composition, older men and women maintain their ability to make significant improvements in strength and functional ability.

    Both aerobic and resistance exercise are beneficial for older adults, but only resistance training can increase muscular strength and muscle mass. Older Adults

What Are the Safety Recommendations

    for Resistance Training for Seniors?

    All participants should be prescreened.

    Warm up for 5 to 10 minutes before each exercise session. Perform static stretching exercises before or after, or both before and after, each resistance training session. Use a resistance that does not overtax the musculoskeletal system. (continued)

    Older Adults

    What Are the Safety Recommendations

    for Resistance Training for Seniors? (continued)

    Avoid performing the Valsalva maneuver.

    Allow 48 to 72 hours of recovery between exercise sessions. Perform all exercises within a range of motion that is pain free.

    Receive exercise instruction from qualified instructors.

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