chapter 7 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. Describe effects of aging on musculoskeletal health and the trainability of older adults. Explain why adaptations to resistance exercise can vary greatly among participants.
Children With the growing interest in youth resistance training, it is important for strength and conditioning professionals to understand the fundamental principles of normal growth and development.
The Growing Child Children 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.
The Growing Child Children 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 rate and 0.8 years after peak weight rate. In girls, peak gains in strength also typically occur after peak height rate, 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 (a) Mesomorph; (b) Endomorph; (c) Ectomorph
Children Youth Resistance Training 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 Responsiveness to resistance training Training-induced gains from a short-duration, lowvolume 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 (8-20 wks) 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 significantly improve their strength above and beyond growth and maturation with resistance training. Neurological factors, as opposed to hypertrophic factors, are primarily responsible for these gains.
Development of Muscular Strength 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.
Resistance Training Myths Related to Youth Females Will Get Big Muscles Since Adolescent Females Generally Have 10-20 Times Lower Levels of Testosterone Than Adolescent Males, Increases in Muscle Size Will be Much Lower in Females Compared to Males Weight Training Will Hinder Growth Lifting Light to Moderate Weight (Sub-Maximal) is not Deleterious to Bone Growth and Development Weight Training Will Build Big Bulky Muscles and Retard Athletic Speed and Performance
Weight Training and Injury Prevention Zaricznyj et al. (AJSM 1980) Found 1576 Youth Injuries in School Related Sports and Activities Over 1 Year Football 19% of Injuries Basketball 15% of Injuries Soccer 2% of Injuries Weight Training < 1% of Injuries
Weight Training and Injury Prevention Hejna et al. (NSCAJ 1982) Studied Male and Female Injury Rates in Athletes 72% of All Injuries Occurred in Athletes Who Did Not Weight Train Only 26% of All Injuries Occurred in Athletes Who Did Weight Train
Weight Training and Rehabilitation Hejna et al. (NSCAJ 1982) Studied Male and Female Rehabilitation Times in Athletes 4.8 Days for Athletes Who Did Not Weight Train Only 2.0 Days For Athletes Who Did Weight Train
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? 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.
Children Youth Resistance Training Guidelines 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 repetitions on a variety of exercises can be performed.
Children Youth Resistance Training Guidelines 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.
Sex Differences Female Athletes 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.
Sex Differences Female Athletes 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 Women can increase their strength at the same rate as men or faster. Female athlete triad Interrelationships between energy availability, menstrual function, and bone mineral density Caused by high training volumes or intensities with inadequate dietary intake Increases the risk for osteoporosis and amenorrhea (the absence of a menstrual cycle for more than three months)
Female Athletes Program Design Considerations for Women Upper body strength development Women tend to have less upper body strength than men, and adding one or two upper body exercises or additional sets may be beneficial for women. The high caloric cost of performing large muscle mass, multijoint, upper body lifts may aid in maintaining a healthy body composition. Be aware of increasing incidence of knee injuries in female athletes in sports such as soccer and basketball where there is a 4-8 times greater rate of ACL injuries in females compared to males, thus a greater emphasis is needed on strengthening the hip abductors and external rotators, plyometric and agility training, and proper running, jumping, and landing mechanics.
Female Athletes How Can Female Athletes Reduce Their Risk of Injury? Begin with a preparticipation screening by a sports medicine physician. 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. Participate in a appropriate year-round conditioning program
Older Adults Age-Related Changes in Musculoskeletal Health Loss of bone and muscle with age (approx 0.5-1% per year) increases the risk for falls, hip fractures, and longterm disability. Bones become fragile with age because of a decrease in bone mineral content that causes an increase in bone porosity (osteoporosis). 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.
Table 7.1
Key Terms osteopenia: A bone mineral density below 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.
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 Age-related changes in neuromotor function Seniors are at increased risk of falling. Factors include decreased muscle strength and power, decreased reaction time, and impaired balance and postural stability. Research shows that physical activity interventions can be effective in improving neuromotor function and preventing falls. (continued)
Older Adults Responsiveness to resistance training in older adults Program design considerations Both aerobic exercise and resistance training are recognized as important components of a well-rounded fitness program for older adults. Attention should be given to preexisting medical ailments, prior training history, and nutritional status before starting a resistance training program. Volume and intensity should be altered throughout the year to prevent overtraining and ensure that progress is made.
Older Adults (continued) Responsiveness to resistance training in older adults Seniors who participate in progressive resistance training programs show significant improvements in Muscular strength and power Muscle mass Bone mineral density Functional capabilities
Key Point 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. Aerobic, resistance, and balance exercise are beneficial for older adults, but only resistance training can increase muscular strength, muscular power, and muscle mass.
RESEARCH RESULTS HIGH INTENSITY TRAINING (70-80%1RM, 3 Ses/wk,LE/UE,M&F) Study # Age Duration Strength Frontera et al,1988 12 60-72 12 wk 107-227% Fiatarone et al,1990 10 90 8 wk 174% Fatouros et al, 2005 20 71±4 24 wk 63-91% Pyka et al,1994 25 68 52 wk 30-97% Taaffe et al,1996 12 65-79 52 wk 59% Taaffe et al,1999 46 65-79 24 wk 37-42% Pratley et al,1994 13 50-65 16 wk 40% Sullivan et al, 2005 19 78±6 12 wk 27-31%
RESEARCH RESULTS LOW INTENSITY TRAINING (40-60% 1RM, 3 Ses/wk, LE, M&F) Study # Age Duration Strength Fatouros et al, 2005 18 71±4 24 wk 42-66% Taaffe et al,1996 12 65-79 52 wk 41% Aniansson et al,1980 12 70 12 wk 9-22% Sullivan et al, 2005 18 78±6 12 wk 18-19% Krebs et al,1998 120 75 25 wk 18% Maiorana et al, 1997 26 60 10 wk 18% Gordon et al, 1996 14 58 8 16% Larsson et al,1982 18 22-65 15 wk 3-7%
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.
Older Adults What Are the Safety Recommendations for Resistance Training for Seniors? 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.