Chapter 4Detraining, Bedrest

1
Chapter 4-Detraining, Bedrest Bone Health

• Bone is much more dynamic than most of us would
  believe. Active turnover of tissue through
  osteoclast/osteoblast balance
• Remove physical activity or weight bearing
  activities bone mineral content (BMC)
  decreases
• Inactivity tends to either increase resorption
  (osteoclasts) activity only or increase it more
  than osteoblast changes.

2
Bone Health

• Loss or removal or mechanical loads on bone also
  cause increased release of calcium which raises
  serum calcium levels and stimulates parathyroid
  hormone to release Ca on urine.
• change in trabecular bone volume and bone mineral
  density with various "bone unloading events.
  0.07-0.11 per week.

3
Bone Health Detraining

• Lower limb bone appears more susceptible than
  upper limbs-trabecular (Cancellous) more so than
  cortical
• Architecture of bone may change, reducing
  fracture point, whereas overall bone mineral mass
  may not decrease significantly.
• Rate of regaining lost BMC varies-may take years
  with prolonged bedrest exposure.

4
Chapter 4- Deconditioning Retention of
Endurance Training

• Majority of cardiorespiratory gains one makes due
  to endurance training may evaporate with several
  months of inactivity.
• Time-course of loss of function likely depends
  upon magnitude of gains.
• Some loss of function is likely due to other
  extrinsic factors (Fig. 22.3 22.4).

5
Energy Metabolism of Muscle

• Significant drop in oxidative capacity of
  skeletal muscle, but not glycolytic capacity
  Table 22.2
• Capillary density decreases.
• Ability to retain function with reduced training
  frequency At least one intense session/week
  maintains VO2max heart function.
• Does it take longer to regain what was originally
  lost with inactivity? Unknown,

6
NM response to detraining

• Atrophy, Atrophy, Atrophy-sarcopenia-loss of mass
  plus strength with aging.
• Appears all fibers atrophy equally
• Migration from Type IIa to type IIb with
  detraining
• Lose efficiency of muscle-easier to reach
  fatigue
• Loss of oxidative capacity as noted earlier
• Loss of force primarily due to atrophy, although
  some loss occurs due to loss of activation
  inability to recruit high threshold motor units
• Need greater activation of muscle mass to perform
  same submaximal force.
• More susceptible to muscle damage, especially
  during eccentric loading.

7
Bone health (cont)

• Loss or removal or mechanical loads on bone also
  cause increased release of calcium which raises
  serum calcium levels and stimulates parathyroid
  hormone to release Ca on urine.
• Change in trabecular bone volume and bone mineral
  density with various "bone unloading
  events.0.07-0.11 per week.
• Lower limb bone appears more susceptible than
  upper limbs-trabecular (Cancellous) more so than
  cortical
• Architecture of bone may change, reducing
  fracture point, whereas overall bone mineral mass
  may not decrease significantly.
• Rate of regaining lost BMC varies-may take years
  with prolonged bedrest exposure