HKIN 103 - 5Physiologic changes at

Puberty

Exercise Physiology through the teens, and ramifications for

training.

Unless otherwise noted, the information contained in this section of the course is from:

Rowlands, T.W., Children’s Exercise Physiology, 2nd Ed.,Human Kinetics, Windsor ON, 2005

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

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.

Effects of Exercise on Growth

1. Is it a positive or negative relationship?2. Caloric stealing!3. No increase in serum IGF-1 levels from X’s.

4. +ve Correlation between VO2 max and IGF-1 levels.

5. Rate and timing of peak height velocity6. Conclusion

Effects of Puberty on Fitness.

Increase in VO2 max throughout childhood. (L*min-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.

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

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

Group Estradiol level

1. Amenorrheic runners 113 mmoles * L-1

2. Eumenorrheic runners 247 mmoles*L-1

3. Eumenorrheic sedentary 251 mmole*L-1

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 activityAgain, the tall slender hips, thin athletic phenotype is typically a late maturer - Natural selection rather than causative by activity.

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 (56%incr)

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)

Anaerobic fitness

Increases of 3.4 - 3.7 % on wingate testIncreases of 20% in treadmill run to exhaustion (7mph@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.

Strengthchanges in Lean Body Mass (LBM)

age males females

11yrs 11 kg 11 kg

17 yrs 35 kg 22 kg

Strength

age males females

11 yrs 42% 41%

17 yrs 53% 42%

Lean muscle mass as a percentage of total body weight

StrengthDoes 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?

Strength

May be related to angle of pennation

Changes in central inhibition (golgi tendon organs?

Neural recruitment and conduction velocity are likely reasons.

Strength

Unpennated

Unipennate

Bipennated

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)

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.

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.