Calculating Target Heart Rate During Exercise Testing
The target heart rate during exercise testing is calculated as 80-90% of the predicted maximum heart rate using the formula: 220 minus age in years, and this formula applies equally to both males and females. 1
The Standard Formula
The American Thoracic Society guidelines establish that predicted maximum heart rate is calculated as:
Predicted Maximum HR = 220 - age (in years) 1
Target Heart Rate = 80-90% of Predicted Maximum HR 1
This formula is not sex-specific in the ATS guidelines for exercise challenge testing, meaning the same calculation applies to both males and females. 1
Practical Application
For a 40-year-old patient (male or female): Predicted max HR = 220 - 40 = 180 bpm, so target range = 144-162 bpm 1
Exercise duration: The target heart rate should be maintained for at least 4 minutes, with total exercise duration of 6-8 minutes (6 minutes for children <12 years, 8 minutes for older children and adults) 1
Progressive approach: Start at low speed/grade and progressively advance during the first 2-3 minutes until reaching the target heart rate of 80-90% of predicted maximum 1
Alternative Monitoring Method
Ventilation can be used instead of heart rate to monitor exercise intensity, with a target of 40-60% of predicted maximum voluntary ventilation (MVV, estimated as FEV1 × 35) 1
Important Caveats About the 220-Age Formula
While the ATS guidelines use 220-age as the standard, this formula has significant limitations:
High variability: There is ±10-15 bpm variability within any age group 1
Underestimates in older adults: The 220-age formula tends to underestimate maximum heart rate in older individuals 1, 2
Alternative formulas exist: Research suggests 208 - (0.7 × age) 2 or sex-specific formulas [197 - (0.8 × age) for women and 204 - (0.9 × age) for men] 3 may be more accurate, but these are not incorporated into current ATS exercise testing guidelines
Not a strict endpoint: Achievement of 85% of age-predicted maximum heart rate should not be used in isolation as a termination criterion, as it has limited validity 1
Factors Affecting Heart Rate Response
Beta-blockers and other cardiovascular medications will lower both the incremental rise and maximum heart rate achieved, limiting interpretation of cardiac response 1
Physical fitness level strongly influences the grade and speed necessary to obtain the desired heart rate, with fitter individuals requiring higher workloads 1
Body weight also influences the heart rate response to exercise, with heavier individuals potentially reaching target heart rates at different workloads 1
Safety Monitoring
A licensed physician or experienced technician must observe the patient during exercise and recovery, monitoring for severe wheezing, chest pain, lack of coordination, ECG abnormalities, falling blood pressure, or severe oxygen desaturation 1
Heart rate monitoring should use at minimum a three-lead ECG configuration, with 12-lead ECG advisable for those at higher risk for coronary artery disease 1