Transcript Physical Activity & Bone - Western Michigan University

Musculoskeletal & Biomechanical
Adaptations to Training
HPER 6310
Dr. Suzan Ayers
Western Michigan University
Lecture Overview
Effects of Physical Activity on:
 bone
 joints and ROM
 muscle-tendon units
 body size, shape & composition
Biomechanical Adaptations to Training:
 muscular
 neuromuscular
Biomechanical Adaptations to Injury
Physical Activity & Bone
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Disuse results in osteopenia (bone loss)
Genetically determined baseline mass for normal
function (certain level of PA to ↔ bone health)
↓ PA=bone loss, ↑ PA=bone growth (see below)
Weight-bearing PA= bone growth
Too much intense PA problematic; optimal levels
exist for each individual
Physical Activity & Joints/ROM
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Short-term effects of cyclical exercise (bike, run)
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Articular cartilage thickens (improved force dissipation)
2-3x ↑ in volume of synovial fluid in a joint (lubricant)
Evidence supports endurance exercise’s benefits
over sprint training on ligament strength
Degenerative joint disease (osteoarthritis)
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Thinning articular cartilage
Thickening compact bone under articular cartilage
Possible genetic, aging & environmental factors impact DJD dev’t
Regular runners do NOT have > incidence of osteoarthritis
HMMMM…
Physical Activity & Muscle-Tendon Units
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Flexibility: The ability to move a joint through its
complete range of motion (ROM) (ACSM, 2000)
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Laxity: The degree of abnormal motion of a given
joint (Heyward, 2002)
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depends on muscle-tendon units crossing joints
is joint-specific
↑ flexibility related to ↑ extensibility of connective tissue
strength and flexibility training can promote ↑ ROM
↑ injury risk
Hypermobility: Excess ROM at a joint (Heyward,
2002)
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Active
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Passive
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Slow, sustained stretch held for 10-30 sec
Preferred in Physical Education settings
PNF (Proprioceptive Neuromuscular Facilitation)
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Partner provides force of stretch
Static
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Self-stretching
Combo active/passive techniques
NOT for children 6-10 yrs
Ballistic/Dynamic
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Quick movements, bouncing, using momentum
Reserve for those 15+ yrs
Helpful to prepare athletes for competition
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Static stretches should be held to the point of
mild discomfort
“No pain, no gain” is INAPPROPRIATE!
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Training principles
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Frequency: Daily (min 3x/wk)
Intensity: To point of mild discomfort
Time: 10-30 sec
Type: Static, PNF, partner, etc.
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Strength changes
Weeks 6-8 primarily neuromuscular
Weeks 9+ gains due to ↑ fiber size/volume
Long-term benefits
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Tendon Adaptations
Much slower rate of adaptation than muscle
Collagen synthesis ↑
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Fiber changes resulting in improved fatigue-resistance
↑ relative amount of connective tissue
Fibers align more regularly longitudinally
Muscle strains often occur @ junction of tendon
and muscle
Physical Activity’s Effect on Body Size,
Shape & Composition
Endomorph
relaxed, sociable, tolerant, comfort-loving, peaceful, plump,
buxom, developed visceral structure
Mesomorph
active, assertive, vigorous, combative, muscular
Ectomorph
quiet, fragile, restrained, non-assertive, sensitive, lean,
delicate, poor muscles
Dr. William Sheldon’s “somatotypes”
Endomorph
Mesomorph
Ectomorph
Somatotype challenge
In the 1940s, Dr. William Sheldon (1898-1977)
proposed a theory about how certain body types
("somatotypes") are associated with certain
personality characteristics. He claimed that there are
three such somatotypes: endomorphy, mesomorphy,
and ectomorphy. You can rate yourself on each of
these three dimensions using a scale from 1 (low) to
7 (high) with a mean of 4 (average). Therefore, a
person who is a pure mesomorph would have a score
of 1-7-1. A pure endomorph would be 7-1-1. A pure
ectomorph would score a 1-1-7. A mostly average
person who has some endomorphic tendencies
would have a score of 6-4-4 ... etc. Rate the degree
to which you think you possess each of the three
body types.
Endomorphic Body Type
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soft body
underdeveloped muscles
round shaped
over-developed digestive system
Associated personality traits:
 love of food
 tolerant
 evenness of emotions
 love of comfort
 sociable
 good humored
 relaxed
 need for affection
Mesomorphic Body Type
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hard, muscular body
overly mature appearance
rectangular shaped
thick skin
upright posture
Associated personality traits:
 adventurous
 desire for power and dominance
 courageous
 indifference to what others think or want
 assertive, bold
 zest for physical activity
 competitive
 love of risk and chance
Ectomorphic Body Type
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thin
flat chest
delicate build
young appearance
tall
lightly muscled
stoop-shouldered
large brain
Associated personality traits:
 self-conscious
 preference for privacy
 introverted
 inhibited
 socially anxious
 artistic
 mentally intense
Lifestyle Factors
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↑ PA while ↓ caloric intake=fat loss
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Training can make physiological changes at any age
(it’s never too old to teach an old dog new tricks
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Height is genetically predetermined
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Weight can be altered to a given genetic point
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Somatotype can change as strength and endurance
requirements change
Biomechanical Training Adaptations
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Training influences both contractile properties of
muscle (strength, speed) and neural control (coord.)
Strength changes due to
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↑ net neural drive to muscle (motor unit recruitment)
↑ muscle size
both neural and structural changes
Contraction speed changes due to
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Δ in shape of muscle’s force-velocity curve
Δ in value of the intrinsic max shortening velocity
both shape and max shortening velocity changes
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Muscular Training Adaptations
Max force produced depends on length of muscle
during contraction
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Initial strength gains (wk 2-8) primarily neural
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10+ wk gains primarily hypertrophic
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Isokinetic training can change force-velocity curve
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Contraction speed changes also influence forcevelocity curve shape, ergo power
(strength x speed = power)
Neuromuscular Training Adaptations
Incidence of serious knee injury 6x F>M athletes
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Intrinsic risk factors for ACL injury
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Lower extremity malalignment
↓ intercondylar notch width at the knee
↑ knee joint laxity
Hormonal influences (Relaxin)
Extrinsic risk factors for ACL injury
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Imbalanced quad/ham strength
Inadequate neuromuscular control
GOAL: improve stability (balance, coordination),
proprioception, & strength
ACL injury-prevention neuromuscular programs
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Knee stability/function improve with ↑ in postural
equilibrium, intermuscular control & leg muscle strength
Means of ↑ aforementioned factors:
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Stretching
Plyometric exercises (AKA, jump training)
Weight lifting
Evidence supporting neuromuscular training’s role in ↓
incidence of sport-related knee injuries
Ham:Quad strength ratio key to ACL injury prevention
Neuromuscular training can ↑ knee joint stability
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↑ H:Q
Fine-tune neural control over hamstrings