Key Concepts about Estimating VO2 Max
When analyzing other types of NHANES data, you may want to create new variables for you analysis. Analyses for cardiovascular fitness are different in that NHANES has already calculated the variable of interest, which is estimated VO2 max. Here, we show you how NHANES calculated this variable.
Because the relation between heart rate and oxygen consumption is linear during exercise, we can estimate V02 max by measuring the heart rate response to known levels of submaximal work. This relation can be summed up by the equation for a line: y = mx + b, where y is heart rate, m is slope, x is V02, and b is the intercept. By rearranging these terms, we can derive the following equation:
Estimated VO2 max = PMHR - Intercept
Slope
PMHR = Predicted Maximal Heart Rate
Slope = Change in Heart Rate/Change in VO2 consumption between Stage 1 and 2 of Assigned Protocol
Intercept = Y#-(Slope)*X#
Y# = mean of End of Stage 1 Heart Rate and End of Stage 2 Heart Rate
X# = mean of End of Stage 1 VO2 and End of Stage 2 VO2
Submaximal VO2 max values at stages 1 and 2 vary by protocol and can be found in the table below, which is taken from Appendix H of the NHANES Cardiovascular Fitness Procedures Manual.
| Exercise Protocol Number | Warmup Predicted VO2 max (ml/kg/min) | Warmup Speed (mph) | Warmup Grade (%) | Warmup % predicted VO2 Max |
Stage 1 Speed (mph) | Stage 1 Grade (%) | Stage 1 % predicted VO2 Max (ml/kg/min) |
Stage 2 Speed (mph) | Stage 2 Grade (%) | Stage 2 % predicted VO2 Max (ml/kg/min) |
Recovery Speed (mph) | Recovery Grade (%) | Recovery % predicted VO2 Max (ml/kg/min) |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| 1 | <20 | 1.7 | 0 | 45(8.1) | 2.1 | 0.5 | 55%(9.6) | 2.1 | 4.5% | 76(13.6) | 2.0 | 0 | 49(8.9) |
| 2 | 20-24 | 2.0 | 1 | 45(10) | 2.3 | 2.0 | 55(11.9) | 2.3 | 6.5% | 75(16.9) | 2.0 | 0 | 41(8.9) |
| 3 | 25-29 | 2.2 | 2 | 45(11.5) | 2.7 | 3.0 | 55(14.6) | 2.7 | 7.5% | 75(20.6) | 2.0 | 0 | 33(8.9) |
| 4 | 30-34 | 2.7 | 2 | 45(13.3) | 3.1 | 4.0 | 55(17.8) | 3.1 | 8.5% | 75(24.4) | 2.0 | 0 | 28(8.9) |
| 5 | 35-39 | 3.0 | 3 | 45(16) | 3.7 | 4.0 | 55(20.6) | 3.7 | 8.0% | 75(27.8) | 2.0 | 0 | 24(8.9) |
| 6 | 40-44 | 3.1 | 3.5 | 45(17) | 3.7 | 5.5 | 55 (23.3) | 3.7 | 10% | 75(31.4) | 2.0 | 0 | 21(8.9) |
| 7 | 45-49 | 3.2 | 5 | 45(19.8) | 3.7 | 7.0 | 55(26.0) | 3.7 | 12.5% | 75(35.9) | 2.0 | 0 | 19(8.9) |
| 8 | >50 | 3.6 | 5 | 45(21.8) | 3.7 | 8.5 | 55(28.7) | 3.7 | 14.5% | 75(39.5) | 2.0 | 0 | 17(8.9) |
- Protocol Number
- number to identify protocol being used (see table)
- Speed
- miles per hour
- Grade
- percent incline
- % predicted VO2 max
- predicted VO2 max as % (submaximal VO2 in ml/kg/min in parenthesis)
Example: A man age 40 years was assigned to Protocol 6. Looking in Appendix H, we see that the corresponding submax V02 values for Stages 1 and 2 are 23.3 and 31.4 ml/kg/min, respectively. His heart rate at the end of Stage 1 is 120 and at the end of Stage 2 is 140 beats/min, respectively. Plugging these
numbers into the formulas above, the equation is solved as follows:
Estimated V02 max = 180 – 62.47 = 47.6 ml/kg/min
2.469
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