Exercise Physiology Across the Lifespan: Children and Older Adults

Exercise Physiology Across the Lifespan: Children and Adolescents

• Discusses the relevant physiological considerations for children across various body systems.
• Covers metabolic, respiratory, cardiovascular, and neuromuscular characteristics.
• Addresses environmental factors, particularly heat.

Energy Systems in Children

• Children can oxidize fat at a higher intensity than adults.
• The crossover point (fat vs. carb utilization) is shifted to the right, indicating better fat utilization.
• Children have a higher phosphocreatine ratio and faster recovery rate.
• Children have a lower glycolytic capacity and lactate accumulation.
• Lactate threshold is higher in children due to better fat mobilization.
• Relative peak power is lower in children because of lower glycolytic capacity and smaller muscle fiber size.

Aerobic Characteristics

• Children have a lower running economy, meaning they are less efficient aerobically.
• Reasons for lower running economy:
  • Higher basal metabolic rate.
  • Larger surface area to mass ratio.
  • Immature running mechanics.
  • Less efficient ventilation.
  • Decreased anaerobic capacity.
• Prepubertal children have a significantly lower running economy compared to adults.

Respiratory System Characteristics

• Children have a lower tidal volume and a higher respiratory rate.
• Minute ventilation is higher at submaximal intensities but lower at maximal intensity.
• AVO2 difference (arterial-venous oxygen difference) is higher at submaximal intensities due to:
  • Greater vasodilatory effect of arterioles irrigating active muscles.
  • Increased heat production per unit of muscle.
• AVO2 difference is lower at maximal capacity, indicating less oxygen available in the blood.
• No sex differences in respiratory characteristics in prepubertal children.

Cardiovascular System Characteristics

• Children have a higher heart rate at rest and during exercise.
• Stroke volume is lower due to smaller heart size.
• Cardiac output at rest is comparable to adults, but lower at maximal intensity.
• Cardiac output can double from age 12 to young adulthood.
• Cardiovascular drift phenomenon occurs similarly in children and adults.
• VO2 max (maximal oxygen consumption) is lower in children.

Muscular System Characteristics

• Boys and young men (post-pubescent) have greater increases in strength.
• Children have comparative muscle fiber percentages to adults.
• Muscle fiber number is comparable, but fiber size is smaller in children.
• Children have comparable strength relative to their cross-sectional area.
• Children exhibit lower force kinetics and a lower force-velocity relationship.
• Children have a significantly lower ability to generate torque compared to adult counterparts.

Environmental Considerations

• Children are at a higher risk of heat-related illnesses due to:
  • Morphological differences limiting heat dissipation.
  • Physiological differences in cutaneous vessel control and sweating capacity.
  • Mechanically inefficient movement.
• Decreased sweat gland output causes less evaporative heat loss.
• Risk Reduction Strategies:
  • Adjust rest periods, especially in prolonged activities.
  • Acclimatize children to extreme environments.
  • Ensure proper hydration (100-250ml every 20 minutes).
  • Wear breathable light-colored clothing.
  • Educate children and adults on signs and symptoms of heat illnesses.
• Concerns for the future include less activity, increased obesity rates, type 2 diabetes, dyslipidemia, weather extremes, air pollution, and UV exposure.
• Recognize that children are not mini adults; they have different physiological responses.

Exercise Physiology Across the Lifespan: Older Adults

• Covers exercise physiology for individuals 60 years or older.
• Addresses metabolic, respiratory, cardiovascular, and neuromuscular responses.
• Discusses risks in hot and humid environments.

Aerobic and Anaerobic Characteristics

• Anaerobic power significantly decreases with age (linear decline).
• Reduction in ATP-PC stores and less efficient use of those stores.
• Higher lactate accumulation during exercise.
• Basal metabolic rate slows down (lower BMR).
• Lower energy intake and reduced fat oxidation capacity.

Respiratory System

• Total lung capacity remains unchanged, but expiratory reserve volume decreases.
• Vital capacity lowers, residual volume increases, and functional residual capacity increases.
• Forced vital capacity, forced expiratory volume, and peak expiratory flow decrease.
• Minute ventilation decreases as respiratory muscles steal oxygen from locomotor muscles.
• Ventilatory work is harder for same output.
• Decline starts as structural (less elastic tissue), leading to functional limitations (reduced FEV1), and neural decline (slower regulatory mechanisms).

Cardiovascular System

• Overall decline in cardiovascular capacity at rest and during exercise.
• Modest decrease in heart rate.
• Significant decrease in stroke volume.
• Modest increase in blood pressure (arterial stiffness, atherosclerosis).
• Significant increase in total peripheral resistance.
• Noticeable decrease in cardiac output (product of heart rate and stroke volume).
• VO2 max declines roughly 10% per decade.
  • Cardiac output is the biggest contributor.
  • Fat-free mass mitigates reductions in aerobic capacity.
  • Arterial stiffness plays a role.

Muscular System

• Steady decline in the total number of muscle fibers with age.
• Reduction in muscle cross-sectional area.
• Steady decline in number of push-ups (upper body strength) and leg lifts (lower body strength) for both men and women with age.
• Reduced number and size of muscle fibers.
• Decrease in functional motor units which results in reduced muscle strength.
• Sarcopenia (loss of muscle mass) is a big concern:
  • Muscle is replaced by fat (metabolically inert).
  • Higher prevalence of type II muscle fibers lost (impacts balance).
  • Perform power based activity to help with balance maintenance.
• Significant reduction in muscle cross-sectional area across lower body and trunk muscles.

Flexibility

• Decent flexibility maintained until about 65 years of age.
• Steady decline in lateral trunk flexion (side to side).
• If you train, you retain.
• Strength increases are possible even for frail elderly with training.

Aging and Performance

• Decreased anaerobic capacity, respiratory function, cardiovascular characteristics, reduced strength and cross-sectional area.
• Endurance performance (aerobic) decreases with age with a number of contributing factors.
• Decreased maximal heart rate, stroke volume, and AVO2 difference.
• Training volume and intensity are often reduced which furthers the issue.

Environmental Considerations

• Older adults at increased risk of thermal strain, heat illness, cardiovascular risks, thermoregulatory risks, and fluid regulation risks.
• Significant electrolyte imbalances and then acute kidney injuries or strain significantly more prevalent in older adults.
• Age is the highest contributor toward heat vulnerability.
• Ninety percent of heat wave-associated mortality attributable to cardiovascular events.
• Training at a higher volume and intensity can worsen this issue. An increase in training volume and intensity can actually exacerbate the decrease in stroke volume, decrease in heart rate and decrease in sweat rate, which further amplifies that problem.
• Is it really beneficial to put the body through that much physical stress that far into life?
• An acute bout of exercise could be considered a transient bout of aging (potentially and conceptually), because of how closely they line up together.