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 developedCrying increases metabolic rateRestlessness & increased

movementsBrown 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.)

CarbohydrateC6H12O6 + 6O2 --> 6CO2 + 6H2O

R = 6CO2 / 6O2 = 1.0

FatC16H32O2 + 23O2 --> 16CO2 + 16H2O

R = 16CO2 / 23O2 = 0.70

Maximum Oxygen Uptake

VO2max testing

TreadmillCycle ergometer (15% less)Criteria of max.

– Heart rate above 190– Subjects report– VO2 plateaus

– Blood Lactate– R greater than 1.1

Reliability of VO2max (ml.kg-1.min-1)

in Children and Adolescents

Source Sample Test Type Reliability Coefficient

Boileau et al. (1977) 21 M, 11-14 y Walk r = .87

Cunningham et al. (1977) 66 M, 10 y Walk/Run r = .56

Cureton (1976) 27 M & F, 7-12 y Walk r = .88

Paterson et al. (1981) 8 M, 10-12 y WalkJogRun

R = .47R = .87R = .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 VO2max

Litres per minute (Absolute)mls per kg of body weight per minute

(Relative)

Growth of VO2max

Absolute and relative VO2max tell a different story

Occurrence of peak velocity coincident with PHV

Relative VO2max declines prior to PHV

Physical Work Capacity PWC170

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 CompositionCardiorespiratoryFlexibilityMuscular 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-upsSit-upsCurl-upsFlexed Arm

Hang

Anaerobic Performance

Does not require O2 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. O2 deficit– O2 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

MargariaStep-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