Data Processing From Indirect Calorimetry: Recommendations and Guidelines
Robert A. Robergs, Ph.D., FASEP, EPC
Exercise Physiology Laboratories, Exercise Science Program, University of New Mexico
Maximal Oxygen Consumption (VO2max)
Time or Intensity
VO2
VO2max
Cardiorespiratory limitations
A.V. Hill
VE
FEO2
FECO2
• No universally recommended procedures for processing VO2 data
from breath-by-breath indirect calorimetry, or from time averaged systems.
• No standardized criteria or recommended methods for detecting either of a VO2 plateau, the maximal rate of oxygen consumption
(VO2max), or a peak VO2 in the absence of a VO2 plateau
(VO2peak).
• Increasing use of breath-by-breath indirect calorimetry in education, research and professional practice
• The lack of any objective criteria to follow when processing decreases the validity of measurement.
Background
Challenges• How do researchers in exercise physiology currently collect and process data?
• What causes the “noise” in breath-by-breath VO2 data?
• Should this “noise” be reduced?
• How should this “noise” be reduced?
• What is a VO2 plateau?
• How can a VO2 plateau be objectively determined?
• What is VO2max?
• What is VO2peak?
• How can VO2max and VO2peak be objectively determined?
How do researchers in exercise physiology currently collect and process data?
• Survey conducted over internet
• International sport science email discussion list (www.sportsci.org)
• n = 75
• Breath-by-breath = 48%
• Time averaged mixing chamber = 25%
• Either depending on purpose = 27%
• Data processing = 30 s (38%), 60 s (18%), 20 s (11%), a moving average of 5-11 breaths (10%), 15 s (8%) and the middle 5 of 7 breaths (7%), other (8%)
• Check for VO2 plateau = 93%
• VO2 Plateau criteria
• < 150 mL/min (34%)
• < 2 mL/kg/min (27%)
• subjective visual (18%)
• other (19%)
• Secondary criteria = attainment of age predicted HRmax (53%), RER > 1.10 (49%) or RER > 1.15 (27%), RPE > 17, 18 or 19 (20%)
• Why these methods used? = own beliefs (32%), what they were taught (26%), what they read in research articles (22%), tradition (13%) and the influence of their colleagues (7%)
• No distinction between VO2max or VO2peak = 76%
1.01.52.02.53.03.5
VO
2 (
L/m
in)
What causes the “noise” in breath-by-breath VO2 data?
2.17 0.3 L/min, with a range of 1.4 – 3.3 L/min
10
25
40
55
70
VE
ST
PD
(L/m
in)
0 2 4 6 8 10 12 14
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
MeasuredPredicted
Time (min)
VO
2 (
L/m
in)
0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.00.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0 Pred VO2 = 0.9572(Meas VO2) + 0.0898
R2 = 0.9572SEE = 0.059 L/min)
Measured VO2 (L/min)
Pre
dic
ted
VO
2 (
L/m
in)
Variability 96 % explained by a two-factor model of VE and FEO2
0 2 4 6 8 10 12 140.0
0.5
1.0
1.5
2.0
2.5
5%error
Time (min)
VO
2 (
L/m
in)
Should this “noise” be reduced?
SIM
How should this “noise” be reduced?
0 5 10 15 200.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5a=bb
Time (min)
VO
2 (
L/m
in)
0 5 10 15 200
1
2
3
4b=15 s
Time (min)V
O2 (
L/m
in)
0 5 10 15 200
1
2
3
4c=30 s
Time (min)
VO
2 (
L/m
in)
0 5 10 15 200
1
2
3
4d=60 s
Time (min)
VO
2 (
L/m
in)
0 5 10 15 200
10
20
30
40
15 s
30 s
60 s
e
Time (min)
Bre
ath
s
Time Averaging
0 5 10 15 200.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5a=bb
Time (min)
VO
2 (
L/m
in)
0 5 10 15 200
1
2
3
4
5b=5 breaths
Time (min)V
O2 (
L/m
in)
0 5 10 15 200
1
2
3
4c=11 breaths
Time (min)
VO
2 (
L/m
in)
0 5 10 15 200
1
2
3
4d=21 breaths
Time (min)
VO
2 (
L/m
in)
0 5 10 15 200.00
0.25
0.50
0.75
1.00
1.25
1.50
1.75
21 breaths
11 breaths
5 breaths
bb
Time (min)
Tim
e In
terv
al (
min
)
Breath Averaging
0
1
2
3
4a
VO
2 (
L/m
in)
0
1
2
3
4d
VO
2 (
L/m
in)
0
1
2
3
4b
VO
2 (
L/m
in)
0 50 100 150 200 2500
1
2
3
4e
Data Points
VO
2 (
L/m
in)
0 50 100 150 200 2500
1
2
3
4c
Data Points
VO
2 (
L/m
in)
muscle
cardiovascular
ventilation
Digital Filtering
0 2 4 6 8 10 12 14 16 180
500
1000
1500
2000
2500
3000
3500
4000
rest exercise
Time (min)
VO
2 (
mL
/min
)
linear regression
initial deviation from linearity
VO2 plateau at VO2max
12 13 14 15 16 17 182750
3000
3250
3500
3750
Time (min)V
O2
(mL
/min
)
What is a VO2 plateau?
What is VO2max or VO2peak?
0 2 4 6 8 10 12 14 16 180
1
2
3
4
5
Time (min)
VO
2 (
L/m
in)
Data Example
10 11 12 13 14 152000
2400
2800
3200
3600
4000treadmill running
Time (min)
VO
2 (
mL
/min
)
Custom Programming Example
Conclusions
• Clear rationale for processing breath-by-breath VO2 data to decrease “noise”.
• Processing best done by digital filtering
• Still formulating and debating criteria and methods to quantify VO2 plateau, VO2max, VO2peak
• In the absence of a VO2 plateau, what are valid criteria to use to verify a “true” VO2max?
Thank you