19 October 1993

Dear BIOMCH-L Readers,

We have just completed a study of the energy requirements

of the Canadian Aerobic Fitness Test (CAFT). This is a

cadence-controlled, bench-stepping test of fitness where

the participant ascends two 20.3cm steps forwards and

descends the two steps backwards. There are 6-steps per

ascent-descent cycle. Our study involved testing a

group of younger females (< 35 yrs) and older females

(>65 yrs) at Level 1 (11 cycles per minute), The CAFT

predicts aerobic fitness on the basis of regression

equations. Recently, Shephard has calculated that

the efficiency of a person performing the CAFT is

approximately 14%. He calculated this using (a) the

so-called 'net' metabolic power (subtracting baseline);

and (b) estimating mechanical power based on a point-

mass model.

Our study involved collecting O2 data along with kinematics

of a 12-segment sagittal plane 2D model of the subjects.

Mechanical power was calculated in several ways:

1. Mechanical power assuming that energy can be exchanged

within and between segments

2. Mechanical power assuming only energy exchanges within

segments

3. Mechanical power assuming no exchanges of energy of any

kind

[The above are adapted from Pierrynowski et al. (1980)]

4. Mechanical power of the centre of mass assuming that an

exchange of energy types can occur (KE PE)

5 Mechanical power of the centre of mass assuming no exchanges

of energy types

6 Mechanical power calculated by the following simple equation:

(Mass x (2 x 0.203m) x 9.81)/ time of one cycle

[This is basically Shephard's method]

We also have the metabolic power data in both gross and net

formats.

>From the above 6 mechanical power values (numerator) and 2

metabolic power values (denominators), we can calculate

12 efficiency values (Oh no, not the dreaded "E" word!). We

believe that our "best" estimate of the efficiency of the

CAFT uses #1 above as our mechanical power and the gross

metabolic power, for an efficiency of about 28%. The data

look something like this:

Mechanical Power Gross O2 Power Net O2 Power

Wwb (#1 above) 28% 35%

Ww (#2) 30% 40%

Wn (#3) 38% 50%

CG-exchange not available yet not available yet

CG-no exchange not available yet not available yet

CG-simple calculation 12% 22%

After all this, our query to our learned colleagues is this:

In the absence of any gold standard that we can ascertain, what

is the concensus about the best way to calculate efficiency?

We believe we have something quite valuable to add to the body

of literature in this area. Our data refutes Shephard's assumptions

about the efficiency of the CAFT, and probably has implications for

other activities. However, we would appreciate the input of others

with more experience in this area.

We will be happy to post a synopsis of the responses we receive.

Thank you.

Drew Smith PhD Elaine Aimone MSc LYNDHURST HOSPITAL

Scott Thomas PhD Sara McConnell MSc UNIVERSITY OF TORONTO

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* Andrew (Drew) Smith, Ph.D. | INTERNET: awsmith@utcc.utoronto.ca *

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