Metabolic Rate & the Evaluation of Physical Performance in Children

HEAT BALANCE & TEMPERATURE REGULATION METABOLISM: CHEMICAL REACTIONS: HEAT & ENERGY HEAT LOSS: – RADIATION, CONDUCTION, CONV ECT ION 70% – EVAPORATION (skin & lungs) 27% – WARMING INSPIRED Al R 2% – URINE & FAECES 1% CONTROL: – H Y P OT H A LAM U S – PERIPHERAL RECEPTORS – Comparison of core and peripheral temperatures

CONTROL IN NEWBORNS Mechanisms of shivering & sweating are poorly developed Sweat glands immature Large S.A./ Wt ratio Thin subcutaneous adipose tissue layer LEADS TO INSTABILITY OF BODY TEMPERATURE

Average body temperature drops with age SD also drops, indicating better control

CONTROL IN NEWBORNS Vasoconstriction well developed Crying increases metabolic rate Restlessness & increased movements Brown fat

Vulnerability of the Adolescent Athlete There have been several deaths of adolescent athletes – Intense prolonged activity – High ambient temperature & humidity – Athletic equipment – Big (small S.A. /Weight ratio) – Lack of water

HEAT STROKE Sweating (Sweat is hypotonic) Water leaves cells to hypertonic exterior Water leaves blood, decrease in blood volume High concentration of electrolytes in blood Excessive water loss, sweating is shut-off Temperature rises rapidly (>40ºC) Heart failure

Metabolic Rate Chemical reactions of the body – Reactions = Energy + Heat Direct Calorimetry – sealed chamber where all inputs and outputs are monitored

Indirect Calorimetry Determination of oxygen uptake Spirometer for oxygen uptake – OK for low levels of oxygen uptake Collection and analysis of expired gases Used as indicator of aerobic fitness

Respiratory Quotient

Respiratory Quotient (R.Q.) Carbohydrate C 6 H 12 O 6 + 6O 2 --> 6CO 2 + 6H 2 O R = 6CO 2 / 6O 2 = 1.0 Fat C 16 H 32 O O 2 --> 16CO H 2 O R = 16CO 2 / 23O 2 = 0.70

Maximum Oxygen Uptake

VO 2 max testing Treadmill Cycle ergometer (15% less) Criteria of max. – Heart rate above 190 – Subjects report – VO 2 plateaus – Blood Lactate – R greater than 1.1

Reliability of VO 2 max (ml.kg -1. min -1 ) in Children and Adolescents SourceSampleTest TypeReliability Coefficient Boileau et al. (1977)21 M, yWalk r =.87 Cunningham et al. (1977)66 M, 10 yWalk/Run r =.56 Cureton (1976)27 M & F, 7-12 yWalk r =.88 Paterson et al. (1981)8 M, yWalk Jog Run R =.47 R =.87 R =.95 Note. r = interclass reliability; R = intraclass reliability (Fitnessgram Reference Guide) Typical R values for Height (0.99) and Skinfold (0.96) measurements

Units of VO 2 max Litres per minute (Absolute) mls per kg of body weight per minute (Relative)

Growth of VO 2 max Absolute and relative VO 2 max tell a different story Occurrence of peak velocity coincident with PHV Relative VO 2 max declines prior to PHV

Physical Work Capacity PWC 170 Power output at 170 bts.min -1 Submaximal tests are better tolerated by children Submax prediction of maximal performance

Cardiopulmonary Responses to Exercise Response to a light stress (30W) on cycle ergometer

Mechanical Efficiency Reliability low below 10 years of age Mechanical efficiency increases with age About 25% for contracting muscle as adult ME = work output / (exercise MR - RMR)

Fitness Tests Should measure an area which extends from severely limited function to high levels of functional capacity Should measure capacities that can be improved with appropriate physical activity Should accurately reflect an individual’s physical fitness status as well as changes in functional capacity by corresponding test scores and changes in these scores

Four Components of Fitness Body Composition Cardiorespiratory Flexibility Muscular Strength, Endurance & Power

Health-related Fitness People who possess it are less likely to suffer disease Tests – Cardiovascular – Flexibility – Strength – Muscular Endurance – Body Composition

Skill-related Fitness People who possess it are likely to be skilled in games and sports as well as vocational skills Tests – Agility – Reaction time – Balance – Co-ordination – Speed

General Curve – Health-related Fitness Neural Curve – Skill-related Fitness

What are tests measuring? Strength tests – Muscle specific Jumps – Body Weight – Body Composition Throws – Skill

Aerobic vs Anaerobic Muscular Strength & Endurance – Strength and Power not synonymous Muscular Power (Anaerobic) Cardiorespiratory (Aerobic)

Muscular Strength The force or tension a muscle or, more correctly, a muscle group can exert against a resistance in one maximal effort

Muscular Strength Testing Influence of tester Cable Tensiometers Hand Grip Dynamometers Isokinetic Devices – (Cybex, Kin- Com)

Effects of Strength Training Prepubertal changes in strength due to resistance training mainly due to neural adaptation No increase in muscle girths concomitant with strength increase – One MRI study showed hypertrophy of muscle fibres with resistance training Any reasonable level of activity is beneficial Can have positive psychosocial benefits

Muscular Endurance Capacity of a muscle or muscle group to perform repeated contractions over an extended period of time

Muscular Endurance Testing Push-ups Sit-ups Curl-ups Flexed Arm Hang

Anaerobic Performance Does not require O 2 to produce ATP However, even when short duration, high intensity there is still an aerobic contribution This aerobic contribution is greater in children than adults However, activities of supramaximal effort and short duration have been termed “anaerobic’

Anaerobic – Aerobic Power Ratio

Muscle Lactate Muscle lactate concentrations are lower than adult levels for any given level of aerobic activity

Tests of Anaerobic Characteristics Metabolic or Biochemical Criteria – Max. O 2 deficit – O 2 debt – Blood lactate Physical performance – Sprinting – Step running – Vertical jump – Monoarticular flexion-extension – Cycling tests – Tests of Mechanical Power

Anaerobic Tests Peak Power – Highest mechanical power generated by a muscle or muscle group in up to 10secs Anaerobic Capacity – Ability to maintain high power over time (15-60secs)

Total Work Output in 10 secs Cycling

Muscular Power Testing Isokinetic Devices Sargent (Vertical) Jump Standing Broad Jump

Margaria Step-Running Test Run up stairs at maximal speed Two steps at a time Few steps run-up Time for four steps Power = Force x Distance / Time Power = mass x 9.81 x height x time -1

Force-Velocity Test

Wingate Anaerobic Test (WAnT)

Wingate Anaerobic Test 30 secs cycling or arm cranking at maximal velocity against an individually determined braking force More relative increase in arms than legs