Bone and Resistance Training

Anatomical/Physiological Aspects

u  Bone is a connective tissue

–   sensitive to changes in forces

u  weight-bearing

u  mechanical

–   bending, compressive, torsional, pulling from muscle contraction

Bone Metabolism

u   2 important processes involved:

 

–  Breaking down bone

u  when bones become worn, uneven, or aged, osteoclasts clean out surface

 

–  Building up bone

u  when bones need to be rebuilt, osteoblasts migrate to the surface where strain occurred. These cells initiate the bone matrix needed to re-build or strength bone

Adaptations of Bone to Resistance Training

1. Response to mechanical loading occurs at

     different rates in:

–       Axial skeleton

u      Skull/cranium, vertebral column, ribs, sternum

–     Vertebral column contains ~ 70% trabecular (softer) bone
u     Trabecular bone is more metabolically responsive to mechanical stress/exercise than cortical bone

–       Appendicular skeleton

u      Shoulder bones, pelvis, long bones of upper and lower extremities

–     Ends of long bones contain more trabecular bone
–     Cortical (hard) bone composes compact outer shell

Adaptations of Bone to Resistance Training

u  Response Time to Mechanical Stress/Exercise

u  1st Step

u  Deposition of new collagen fibers in vertebral bones occur after 8-12 weeks of mechanical stress/exercise

u 2nd Step

u  Mineralization of new collagen fiber matrix requires several weeks to months for full strength attainment

 

Adaptations of Bone to Resistance Training

2. Strength of bones increase provided

    resistance is above minimal

    essential strain (MES) threshold

u Signal is sent to have osteoblasts move to bone layer and lay down a matrix of proteins

u MES believed to be at a stress level which is 1/10 of the force needed to fracture the bone

Adaptations of Bone to Resistance Training

3. A decrease in activity or immobilization of body part will decrease bone density

u  bone loss occurs at a faster rate than formation

u  can maintain vertebral bone mass by 3 hours of standing per day

Adaptations of Bone to Resistance Training

4. Resistance/weight training may influence bone mass, area, and width more than density

u  Resistance training should focus on:

–  Specificity of loading
–  Exercise selection of needed areas of structure, i.e. vertebral column
–  Progressive Overload
u  Incorporate weight training and weight bearing activity early in life to achieve peak bone mass
–  Vary exercise selection

Adaptations of Bone to Resistance Training

5. Essential components of mechanical loading influence rate of adaptations. These components include:

u Intensity

u Speed

u Direction of forces

u Volume of loading

Adaptations of Bone to Resistance Training

6. Prescriptive (Rx) guidelines for stimulating bone growth:

u  Load – range of 1 to 10 RM

u  Volume – 3-6 sets up to 10 repetitions

u  Rest – 1 to 4 minutes between sets

u  Variation – utilize periodization schemes

u  Exercise Selection – incorporate structural exercises which would include: e.g.

–  Squats, cleans, deadlifts, bench presses, shoulder presses

Adaptations of Bone to Resistance Training

u          Untrained or aged people

–        Adaptations can occur but may be a slower process

u        Approach:

1. Perform assessment
–       Obtain patient history, physical exam, analysis of joint stability, flexibility and muscle strength
2. Teach proper exercise technique; use “active” ROM in initial stages
3. Start with low resistance and work up to structural exercises

Muscle Considerations to Resistance Training

1. Muscle growth occurs by hypertrophy (↑ cross-sectional area of existing fibers)

u        Due to:

–       ↑  actin and myosin protein
–       ↑  # of myofibrils within muscle fiber (increased layering)

 

2.  Training Programs should have focus:

u        If training for strength

 - use high intensity, low reps, full recovery periods

u        If training for muscle size

        - use moderate loads, high volume, short to moderate rest periods

u        If training for muscular endurance

        - use low intensity, high volume, little recovery

Muscle Considerations to Resistance Training

3. Subcellular adaptations to muscular endurance:

       - ↑ # and size of mitochondria

       - ↑ myoglobin

       - ↑ aerobic enzymes

       - ↑ glycogen and triglyceride

               stores

 

Connective Tissue Considerations to Resistance Training

1. Resistance training improves the quantity and quality of tendons, ligaments, fascia, and cartilage

       - major structural component is

         collagen

       - sites of increased strength

u      Junctions between tendon and bone surface
u      Within body of tendon or ligament
u      In network of fascia within skeletal muscle                         

Connective Tissue Considerations to Resistance Training

2.  If rupture of connective tissue occurs:

u       Tends to occur at tendon-bone junction in untrained individuals

u       Tends to occur within body of tendon or ligament in trained individuals

 

3.  Turnover rate is slower than muscle

u       Due to poor vascularity and circulation              

Connective Tissue Considerations to Resistance Training

4. Strength of connective tissue improves via:

u      ↑ collagen fibril diameter

u      ↑ cross-links of fibrils

u      ↑ # collagen fibrils

u      ↑ density of fibrils            

Connective Tissue Considerations to Resistance Training

5. Low- to moderate-exercise intensity doesn’t affect collagen content

 

 

6. High-intensity loading does increase growth of collagen

Cartilage Considerations to Resistance Training

1. Weight-bearing forces and complete ROM are essential in maintaining tissue viability

 

2. Moderate aerobic exercise:

     ↑ cartilage thickness

     ↑ # of cells and total ground substance

          in articular cartilage

Cartilage Considerations to Resistance Training

3.  Strenuous exercise

u      ↓   cartilage thickness and proteoglycan content

u      Can cause indentation stiffness

u      Can stimulate remodeling of subcondral bone

u      Not specifically linked to degenerative joint disease