Download continued - Human Kinetics

chapter
16
Development
of Strength
and Flexibility
Strength
• Strength is the ability to exert force.
• Strength enhances performance of sport
and dance skills, as well as daily living
activities.
• Give examples where lack of strength acts
as a rate-limiting constraint to performance
of a skill.
Muscle Mass and Strength
• Muscle mass growth follows sigmoid
pattern.
• In part, the force a muscle can exert
depends on its cross-sectional area.
• Neurological factors are also involved.
• Strength does not always change in parallel
with muscle size.
Developmental Changes in Strength
• Strength increases as children grow.
• Boys and girls are similar in strength levels
until age 13 years.
• Peak strength increases follow peak muscle
increases.
(continued)
Developmental Changes
in Strength (continued)
• Among same-size children of different ages,
more mature children are stronger.
• Endocrine function probably influences
strength.
• Neural factors likely exert influence
(including improved motor unit activation
with maturation).
Strength Increases Steadily
as Children Grow
Implications
What are the implications of the link between
strength and maturation for youth sport
programs?
Strength in Adolescence
and Young Adulthood
• Males add more muscle mass in
adolescence.
• Males are generally stronger, especially in
the arms and shoulders.
(continued)
Strength in Adolescence
and Young Adulthood (continued)
• Size does not account for all gender
differences.
– Cultural norms can affect motivation.
– Cultural norms can affect habitual activity levels.
• After growth ceases, increases in muscle
mass are associated with resistance
training.
Strength in Middle
and Older Adulthood
• Strength generally declines gradually after
the 30s.
• Muscle mass declines in the average older
adult.
• Loss of strength may be greater than loss of
muscle mass (possibly due to changes in
fiber types, nervous system, vascular
system).
(continued)
Strength in Middle
and Older Adulthood (continued)
• Muscular coordination factors might be
involved in declining strength.
• Some older adults do not lose strength.
• Loss of strength is greatly affected by
exercise and activity levels.
Strength Training
• Prepubescents can increase strength with
training.
– Improved neuromuscular coordination plays a role.
– Youths should be monitored to avoid injuries.
• Adolescents and adults can increase
strength and muscle mass with appropriate
resistance training.
– Muscle mass can be increased with training over time.
– Those with cardiovascular disease should be
monitored.
Percentage Increase
in Strength With Training
Strength Training Implications
• Does increased muscle size due to training
occur in prepubescent children? Why or
why not?
• What about the growth of the skeletal and
muscle systems might dictate a cautious
approach to strength training in children?
• What are the differences, if any, between the
results achieved by adult men and adult
women who train for strength?
Development of Strength: Summary
• Childhood is a period of steady increase in
strength.
• Adolescent girls continue a steady increase.
• Adolescent boys experience a spurt of
growth in strength.
• Strength levels are stable in young
adulthood.
(continued)
Development of Strength:
Summary (continued)
• Strength declines in older adulthood,
gradually at first.
• Training can improve strength throughout
the life span.
• Strength is related to muscle mass and
neurological factors.
Assessment of Strength
• Force is exerted against resistance.
– Isotonic or isokinetic strength if limbs move
– Isometric if exerted against immovable resistance
• Must specify muscle group, movement,
speed of movement, and joint angle.
(continued)
Assessment of Strength (continued)
• Common isotonic tests use 1-repetition
maximum.
• Common isometric tests use dynamometer
or cable tensiometer.
• Functional strength tests include chin-ups,
flexed arm hang, and rope climbing.
Flexibility
• Flexibility is the ability to move joints
through a full range of motion.
• It can benefit sport and dance performance.
• Limited flexibility can be a factor in injury.
• Flexibility is specific to each particular joint.
Developmental Changes in Flexibility
• Infants and toddlers are very flexible; in
what positions have you seen babies
illustrate this fact?
• Studies show that declines in flexibility start
in childhood.
• Flexible individuals can maintain or improve
levels.
(continued)
Developmental Changes
in Flexibility (continued)
• Girls as a group are more flexible than boys.
– Flexibility exercises are socially “acceptable” for
girls.
– Girls participate in activities stressing flexibility.
– What are some of these activities?
• In adolescence, flexibility is variable; some
individuals lose a significant degree.
Changes in Sit-and-Reach
Test Performance
Flexibility in Adulthood
• Adults gradually lose flexibility, especially
in little-used joints and after age 50.
• Adults who maintain training for flexibility
maintain their levels.
Flexibility Training
• Training can maintain range of motion in
those with full range.
• Training can improve range of motion in
those with limited range.
Development of Flexibility: Summary
• Range of motion probably reflects activity
and training more than age.
• Flexibility declines over the life span with
limited use (exercise).
• Flexibility training can restore lost mobility.
• Arthritis can affect individuals of any age,
but treatment must be age appropriate.
Assessment of Flexibility
• Since flexibility is joint specific, it must be
measured for each joint you wish to assess.
• A goniometer is often used.
– Axis is placed over joint center.
– Instrument arm is aligned with limb at extremes of
movement range.
• Sit-and-reach test is a common measure but
has disadvantages.