Bone, Muscle

1
Bone, Muscle Connective Tissue Adaptations to
Physical Activity

• Strength Conditioning
• University of Massachusetts Boston
• Timothy R. Morgan, DC

2
Adaptation of Bone to Exercise

• Exercise creates mechanical forces that cause
  deformation of specific regions of the skeleton
• In response to these mechanical forces, bone
  cells (osteoblasts) migrate to the site where the
  strain was applied
• These bone cells manufacture and deposit collagen
  molecules, which form into fibers to form a bone
  matrix
• This bone matrix becomes mineralized in time
  resulting in greater rigidity

3
Mineralization of Bone
Normal Bone

• Bone mineralization occurs both on the dense,
  outer surface of bone (periosteum) and in the
  thin, internal, porous trabecular bone resulting
  in thickening of the bone and internal
  strengthening
• Trabecular bone responds more rapidly than does
  cortical bone
• Trabecular bone is found within the ends of long
  bones and vertebral bodies whereas cortical bone
  forms the compact outer shell of all bones
• Collagen deposition can be realized after 8-12
  weeks of mechanical loading, with mineralization
  occurring more slowly
• Osteoporosis a disease marked by critically low
  BMD

Osteoporotic Bone
4
Bone StrengtheningExercise Program Design

• Programs designed to stimulate new bone formation
  should incorporate
• Specificity of loading
• Proper exercise selection
• Progressive overload
• Program variation
• Structural exercises
• Weight bearing exercises

5
Exercise Specificity

• Specificity of Loading employing exercises that
  directly load a particular area exercises are
  prescribed depending on the desired effect
• Program Variation prescribed exercises must
  apply multi-directional loads to all regions of
  the body and should be varied in order to
  constantly provide a unique stimulus for new bone
  formation
• i.e. walking/running may increase BMD of the
  femur, but not the wrist
• i.e. overhead dumbell presses in the seated
  position can increase BMD at the shoulders,
  wrists potentially within the spine, but the
  hips and femur are not significantly loaded

6
Exercise Selection and BMD

• BMD is optimally built during the early adult
  years, corresponding to the time in life when
  the individual is in the anabolic phase of life,
  and when higher impact activities are better
  tolerated by the body
• Loading the skeleton at sites (hips, spine,
  wrists) where osteoporosis is particularly
  consequential is very important
• Structural Exercises exercises which allow
  greater absolute loads to be used in training,
  involve many muscle groups and joints, and direct
  mechanical force through the spine and hips

7
Progressive Overload

• Progressive Overload progressively placing
  greater-than-normal demands on the body
  specifically to the muscles, bones and connective
  tissues
• Minimal Essential Strain (MES) the threshold
  stimulus that initiates a beneficial growth
  response from muscles, bones and connective
  tissues
• MES is created by activities that create forces
  that exceed the intensity of normal daily
  activities (forces that exceed those which the
  body is accustomed)
• The MES for young, healthy individuals is greater
  than that of older individuals therefore,
  exercise stimulus must be greater in order to
  return the same benefits
• Conversely, the MES for weakened tissue (i.e.
  injury or age-related decline) is less and
  therefore requires less stimuli to return
  benefits

8
Progressive Overload and MES (cont.)

• Regardless of the age, training level and/or
  physical state of the individual, the physical
  activities chosen need to be weight bearing
• MES is believed to represent 1/10th the force
  required to fracture the bone
• Through a training program, increases in the
  force production capacity of muscle directly
  results in a proportional increase in the
  strength of bone and connective tissue
• Periods of inactivity, immobilization or lack of
  weight bearing exercise see a more rapid loss of
  Bone Mineral Density (BMD) than bone formation
• Preservation of BMD can be easily attained
  through the prescription and performance of
  exercises specific to the individuals need

Forces that reach or exceed a threshold stimulus
initiate new bone formation in the area
experiencing the mechanical strain.
9
Exercise Selection (cont.)

• Isolation Exercises exercises which isolate a
  single muscle group these types of exercises
  should be de-emphasized as they rely on body
  positioning and equipment supports to isolate the
  agonist rather than encouraging the coordination
  of agonist, antagonist, synergist, stabilizer and
  neutralizer muscles
• As a consequence to their design, isolation
  exercises prevent the beneficial transmission of
  mechanical forces to other regions of the body

10
Progressive Overload Injury

• Regardless of the desired training effect, a
  properly designed exercise program employs the
  systematic and progressive application of forces
  to the body
• Applying forces with an intensity and/or volume
  that exceed the tissues ability to handle them
  will result in injury
• Instantaneous tissue damage can occur as a result
  of a single episode of excessive force intensity
• Chronic tissue damage can occur as a result of
  high volume training with inappropriate rest and
  recovery between exercise bouts

11
Stress Fractures
12
Essential Components of Mechanical Loading

• Components of Mechanical Load that stimulate
  bone growth include
• Magnitude of the load (intensity)
• Rate (speed) of loading
• Direction of the forces
• Volume of loading (number of repetitions)

• The stimulus for bone growth increases as
• The magnitude of the load increases
• The rate of contraction increases (high power
  output)
• The bond loading pattern is varied
• If the magnitude and rate of the load applied is
  sufficient, the volume of repetitions can be
  limited to a total of 30-35

13
l
Exercise Prescription Guidelines for
Stimulating Bone Growth
From Conroy Earle, ESTC 2000
14
Adaptation of Muscle to Exercise

• Hypertrophy muscular enlargement that happens
  from resistance training occurs primarily due to
  an increase in the cross-sectional area of the
  existing muscular fibers
• Increase in the synthesis of Actin Myosin
  contractile proteins
• Increase in the number of myofibrils within a
  muscle fiber
• New myofilaments (contain A M) are added to the
  external layers of the myofibril, increasing its
  diameter
• Hyperplasia a theory holding that muscular
  fibers undergo longitudinal splitting in response
  to resistance training effectively creating new
  muscle fibers
• This theory is not widely accepted, but cannot be
  discounted as a possibility
• Specificity of Training the type or mode of
  exercise (Strength, Size, Endurance) dictates the
  changes in the muscle or other connective tissues

15
Training Programs for Strength, Size Endurance

16
Strength, Size, Endurance (cont.)

• Strength Training increases cross sectional
  area of muscles used Type II fibers recruited
  more readily, and therefore undergo more
  hypertrophy than Type I fibers in response to
  this type of training
• Hypertrophy (Size) Training exercise reps
  limited within the range of 6-12, but load must
  be great enough to elicit either concentric or
  eccentric contraction failure .
• Bodybuilders will often perform up to 12-20 sets
  of an exercise targeting a particular muscle or
  muscle group
• Hypertrophy training may result in a Type I fiber
  predominance, much like endurance training
• Bodybuilders exhibit a larger amount of collagen
  connective tissue deposition within the muscle,
  contributing to increased cross sectional area
• Endurance Training Increases the aerobic
  capacity of both Type I and Type II fibers
  however because Type I fibers have a much higher
  aerobic potential than Type II fibers, most of
  the gains in aerobic capacity attributable to
  endurance training is a result of the increase in
  Type I fiber aerobic potential
• Endurance Training may result in a conversion of
  Type IIb fibers to Type IIa
• There is little evidence that suggests that Type
  II fibers undergo a conversion to Type 1 fibers

17
Adaptation of Connective Tissue to Exercise

• Connective Tissues (CT) are essentially the
  structural glue that holds the body together
• Exercise training can strengthen the quantity and
  quality of CT
• Changes in CT health and integrity can have a
  positive or negative effect on athletic
  performance
• Healthy, responsive CT adaptations results in a
  stronger musculoskeletal system whereas
  weakened, injured CT can serve as the weak link
  within the kinetic or kinematic chain

18
Collagen Response to Training

• Collagen is the primary structural component that
  gives strength and integrity to all CTs,
  including ligaments, tendons, fascia and bone
• Collagen fibers are arranged in manners which
  support the demands of the particular CT in which
  they are found
• i.e. longitudinally in ligaments, tendons or in
  multi-directional sheets in bone and fascia
• As with bone, mechanical loading of CT results in
  a specific and directional strengthening of the
  CT due to synthesis and re-arrangement of
  collagen fibers
• As bone growth occurs in response to mechanical
  loading, the tendon or ligament insertion becomes
  buried in the layers of expanding bone

19
Connective Tissue Adaptation (cont.)

• The force of muscular force is transmitted to the
  endomysium, perimysium, to the epimysium and
  eventually to the tendon and bone
• A strengthened and more extensive CT network is
  necessary to withstand the increased muscular
  force generation capacity seen strength and
  hypertrophy training programs
• Clinical Note It is thought that one
  detrimental effect of anabolic steroid use is the
  inadequate growth and strengthening of CTs in
  response to the rapid, prolific growth of
  muscular tissue the enhanced force generating
  capacity of the muscle may cause CT injuries,
  particularly to the intramuscular CT, fascia and
  tendons

Healthy people undergoing strenuous exercise
training experience changes in the
force-generating capabilities of muscle,
resulting in a coordinated and proportional
increase in the load-bearing capacity of bone and
other connective tissues.
20
References

• Baechle, TR. Earle, RW. Essentials of Strength
  Training and Conditioning, 2nd Ed. 2000. Human
  Kinetics.

References