W5 - Scaling for Body Size

Question 1

How would you remove the influence that body size has on the peak VO2 measurement?

Answer 1

Divide peak VO2 by body mass

= peak VO2 is now expressed as mL∙kg-1∙min-1

Question 2

The use of which technique offers a more flexible method for removing the influence of body size?

Answer 2

‘Allometric’ models

Question 3

If you are provided with a significant positive correlation between body mass and VO2, are you able to make a fair interpretation of peak vO2 between boys + girls or across children of different body sizes?

Answer 3

Scaling procedures are needed to make a valid interpretation of sex differences in VO2 max due to the confounding influence of size.

Question 4

The strong linear relationship between peak VO2 and body size makes comparisons between people difficult, which child has the highest level of fitness?

What do you need to do first?

Answer 4

‘normalise’ peak VO2 for body mass to allow a fair comparison

Question 5

What is the point of scaling?

Answer 5

To remove the influence of body size from physiological or performance related measures.

Physiological function or performance can then be interpreted from a qualitative viewpoint as the quantity element has been removed.

Question 6

What does scaling allow us to do?

Answer 6

Compare vs ref values

Make inter-group comparisons

Longitudinal investigations

Explore relationships

Question 7

What is scaling concerned with

Answer 7

Selecting a method to adjust for differences in body size between ind or groups.

Only when this is achieved can researchers make appropriate ‘use’ of data on ind or groups.

Question 8

When is scaling not required

Answer 8

When there is no relationship with body size

Question 9

What is the most common approach to scale for body size

Answer 9

Ratio standard method

Question 10

What does the Ratio standard method do?

Answer 10

Expresses 2 variables as a simple ration i.e X/Y

• Y = Physiological variable (i.e peak VO2)
• X = Body size variable (i.e body mass)

Scaled value is then used in subsequent analyses or comparisons + assumed to be size free

Question 11

What does special circumstance relate to?

Answer 11

Assumed proportionality between Y + X in the ratio standard method.

Question 12

When is the ratio standard method ONLY valid?

Answer 12

When the special circumstance + actual data intersect on the graph.

Question 13

What does distortion from the special circumstance introduce?

Answer 13

Statistical error

Below mean = inflated
Above mean = Deflated

Question 14

How could you check if the ratio standard is valid?

Answer 14

There should be an almost perfect correlation between the variables.

Proportional relationship between the variables (the special circumstance)

No relationship between the scales variables + body size.

Question 15

What if the ratio standard method is NOT valid?

Answer 15

Ind w/ a lower than average body size are advantaged

Those heavier than average are disadvantaged

• Statistical artefact

Question 16

Allometric method

What does the ‘b’ value tell us?

Answer 16

Info about the nature of the relationship between the 2 variables.

Question 17

b>1.0

Answer 17

Y increases at a faster rate than X

Question 18

b=1.0

Answer 18

Y + X are proportional

– Ratio standard method

Question 19

b<1.0

Answer 19

X increases faster than Y

Question 20

How can an allometric relationship between Y + X be derived?

Answer 20

From a log-linear regression

Question 21

What is the ‘b’ value used for?

Answer 21

To modify the equation used for the ratio standard method

Question 22

How is ‘b’ used to create a ‘power function ratio’?

Answer 22

Y / X^b

Question 23

How do you check the log-linear allometric model

Answer 23

Plot the calculates power function ratio against body mass

Y/X^b vs X

Question 24

What does the log-linear allometric model do?

Answer 24

Produces a scaling factor (b) that when used to create a power function ratio, is uncorrelated with body size.

Question 25

Allometric methods and running

Answer 25

Allometric methods may better predict running (treadmill) performance in children + adolescents.

Question 26

What was the strongest predictor of 1-mile performance?

Answer 26

Ratio standard VO2 max.

Question 27

Surface law

Answer 27

b=0.67

Based on the theoretical relationship between body size + metabolic rate. i.e whether you’re standing, sitting, walking…

Question 28

What could explain the changing ‘b’ values

Answer 28

Allometric cascade model

Question 29

What does the allometric cascade model suggest

Answer 29

That the relationship between metabolic rate + body mass is not determined by a ‘1 size fits all’ value.

‘b’ value is determined by the weighting of the ind process involved in energy demand and supply.

The switch from energy demand to energy supply processes from rest to exercise acts to change the b value.

Question 30

Why may body mass not be the most appropriate variable to scale VO2

Answer 30

Confounded by body composition heterogeneity

Body mass scaling factor increases when body fatness is considered

Question 31

How can lean mass be measured?

Answer 31

MRI

DXA

Question 32

‘b’ value for body mass

Answer 32

0.3 to 1.1

Question 33

Why is there large variance in the ‘b’ value

Answer 33

Sample size

Heterogeneity

Body size + composition

Age, sex + maturity status

Physical activity/training status

Question 34

Is there a single unifying ‘b’ to use?

Answer 34

No, the value is dependent on metabolic rate + is supported but the allometric cascade model.