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Metabolic Rate & the Evaluation of Physical Performance in Children
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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
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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
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Average body temperature drops with age SD also drops, indicating better control
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CONTROL IN NEWBORNS
Vasoconstriction well developedCrying increases metabolic rateRestlessness & increased
movementsBrown fat
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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
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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
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Metabolic Rate
Chemical reactions of the body– Reactions = Energy + Heat
Direct Calorimetry– sealed chamber where all inputs
and outputs are monitored
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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
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Respiratory Quotient
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Respiratory Quotient (R.Q.)
CarbohydrateC6H12O6 + 6O2 --> 6CO2 + 6H2O
R = 6CO2 / 6O2 = 1.0
FatC16H32O2 + 23O2 --> 16CO2 + 16H2O
R = 16CO2 / 23O2 = 0.70
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Maximum Oxygen Uptake
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VO2max testing
TreadmillCycle ergometer (15% less)Criteria of max.
– Heart rate above 190– Subjects report– VO2 plateaus
– Blood Lactate– R greater than 1.1
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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
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Units of VO2max
Litres per minute (Absolute)mls per kg of body weight per minute
(Relative)
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Growth of VO2max
Absolute and relative VO2max tell a different story
Occurrence of peak velocity coincident with PHV
Relative VO2max declines prior to PHV
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Physical Work Capacity PWC170
Power output at 170 bts.min-1
Submaximal tests are better tolerated by children
Submax prediction of maximal performance
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Cardiopulmonary Responses to Exercise
Response to a light stress (30W) on cycle ergometer
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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)
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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
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Four Components of Fitness
Body CompositionCardiorespiratoryFlexibilityMuscular Strength, Endurance &
Power
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Health-related Fitness People who possess it
are less likely to suffer disease
Tests– Cardiovascular– Flexibility– Strength– Muscular Endurance– Body Composition
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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
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General Curve– Health-related
Fitness
Neural Curve– Skill-related
Fitness
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What are tests measuring?
Strength tests– Muscle specific
Jumps– Body Weight– Body Composition
Throws– Skill
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Aerobic vs Anaerobic
Muscular Strength & Endurance– Strength and Power not synonymous
Muscular Power (Anaerobic)Cardiorespiratory (Aerobic)
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Muscular Strength
The force or tension a muscle or, more correctly, a muscle group can exert against a resistance in one maximal effort
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Muscular Strength Testing Influence of
tester Cable
Tensiometers Hand Grip
Dynamometers Isokinetic
Devices – (Cybex, Kin-
Com)
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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
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Muscular Endurance
Capacity of a muscle or muscle group to perform repeated contractions over an extended period of time
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Muscular Endurance Testing
Push-upsSit-upsCurl-upsFlexed Arm
Hang
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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’
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Anaerobic – Aerobic Power Ratio
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Muscle Lactate
Muscle lactate concentrations are lower than adult levels for any given level of aerobic activity
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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
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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)
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Total Work Output in 10 secs Cycling
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Muscular Power Testing
Isokinetic Devices
Sargent (Vertical) Jump
Standing Broad Jump
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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
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Force-Velocity Test
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Wingate Anaerobic Test (WAnT)
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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
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