HKIN 103 - 5 Physiologic changes at Puberty

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HKIN 103 - 5Physiologic changes at Puberty

• Exercise Physiology through the teens, and
  ramifications for training.

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• Unless otherwise noted, the information contained
  in this section of the course is from
• Rowlands, T.W., Childrens Exercise Physiology,
  2nd Ed.,Human Kinetics, Windsor ON, 2005

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Outline

• Effects of Growth factors on Exercise
• Effects of Exercise on Growth
• Pubertal effects on fitness
• Training effects
• Aerobic fitness
• Anaerobic fitness
• Muscle strength
• Responses to Physical Training

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Effects of Growth factors on Exercise

• GH/IGF-1 axis
• GHRH (hypothalamus)- GH (Pituitary)- IGF-1
  (liver) - peripheral tissue growth.
• Insulin.
• Effects of increased body size
• Biological age vs chronological age
• Gene expression.

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Effects of Exercise on Growth

• Is it a positive or negative relationship?
• Caloric stealing!
• No increase in serum IGF-1 levels from Xs.
• ve Correlation between VO2 max and IGF-1 levels.
• Rate and timing of peak height velocity
• Conclusion

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Effects of Puberty on Fitness.

• Increase in VO2 max throughout childhood.
  (Lmin-1)
• Big difference in genders during after puberty
• There is a gender difference if we look at
  relative VO2 max. Females decline steadily from
  age 8. Males stable.
• Increases mediated by increases in heart and
  muscle size.
• Increases in Aerobic endurance due to training
  are only significant during after puberty.

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Training effects on puberty

• Intensive exercise causes increase in sex hormone
  levels - principle of diminishing returns!
• Intensive exercise appears to cause
  hypoestrogenemia through inhibition of H-P-G axis

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Baer J.T., Endocrine parameters in amenorrheic
and eumenorrheic adolescent female runners. Int.
J. Sports Med. 14 191-195, 1993

• Group Estradiol level
• Amenorrheic runners 113 mmoles L-1
• Eumenorrheic runners 247 mmolesL-1
• Eumenorrheic sedentary 251 mmoleL-1

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Training and Puberty

• Intensive training can cause delayed menarche of
  two years.
• Usually in conjunction with hyponutritional
  status.
• Generally, there is no evidence of pubertal delay
  from physical activity
• Again, the tall slender hips, thin athletic
  phenotype is typically a late maturer - Natural
  selection rather than causative by activity.

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Aerobic fitness

• Glycogen stores are lower in children and
  increase with age.
• Little data to show increases in enzymatic levels
  from training, but Ericksson .
• Prepubertal athletes show large increases in
  lactate tolerance (56incr)

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Aerobic fitness

• In general, aerobic metabolism declines as
  children age, with an increase in anaerobic
  glycolysis.
• Much of the improvements in fitness are
  tolerance to increasing lactate levels and
  running economy.
• At puberty, there is a sudden increase in
  endurance training response to aerobic
  metabolism.
• RHR response is similar to adults (69/81 bpm)

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Anaerobic fitness

• Increases of 3.4 - 3.7 on wingate test
• Increases of 20 in treadmill run to exhaustion
  (7mph_at_18) 10-11 yrs, 12 weeks, but no
  improvement in 40 m. sprint time. (Mosher et al,
  1985)
• Generally, anaerobic training yields small
  improvements, if any.

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Strengthchanges in Lean Body Mass (LBM)

• age males females
• 11yrs 11 kg 11 kg
• 17 yrs 35 kg 22 kg

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Strength

• age males females
• 11 yrs 42 41
• 17 yrs 53 42
• Lean muscle mass as a percentage of total body
  weight

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Strength

• Does strength mirror increases in body height?
• Does strength mirror increases in muscle mass?
• Does strength mirror an increase in number of
  muscle fibers?
• Do nerves work better? (faster conduction
  velocities)
• Does female strength parallel males in children?

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Strength

• May be related to angle of pennation
• Changes in central inhibition (golgi tendon
  organs?
• Neural recruitment and conduction velocity are
  likely reasons.

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Strength

• Unpennated
• Unipennate
• Bipennated

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Response to Strength training

• Increases of 30 - 40 over 8-12 weeks (subjects
  were U18)
• Increases of 22.6 - 27.8 were accompanied by
  16.8 increase in EMG
• Males 9-11 yrs, increases of 35(bench press)
  22 (leg press)

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Thermoregulation in prepubertals

• Same as adults when ambient temp does not exceed
  7 degrees above skin temp.
• Prepubertals do not tolerate heat as well as
  adults greater dizziness, headaches, nausea and
  inability to persist.

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fluid balance

• Water repletion is necessary during exercise
  bouts in excess of 60 minutes.
• Repletion is generally voluntarily stopped at
  about 70 of fluid losses.
• Smaller circulatory volume of children can be
  impacted to a greater degree than the adult.
  Must drink after satiation.