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7
Age- and SexRelated 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.
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 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.
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
– 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.