The beauty of the Training Stress Score (TSS) is that it’s versatile, and you can use any performance metric for which you have a known, sustainable one-hour maximum, also known as your threshold. This could be pace, heart rate (HR), or power. Let’s explore using both HR and Power as examples.
TSS is calculated using the following formula:
TSS = duration (in hours) * normalized intensity factor (IF) * normalized intensity factor (IF) * 100
Normalized Intensity Factor (IF) is the intensity of your workout, expressed as a ratio of your actual exercise metric (HR, power, etc.) to your threshold metric.
- Let’s first calculate using Threshold Heart Rate (HR):
For instance, suppose you have a workout where you run for 1 hour at an intensity that is 90% of your Threshold HR.
- Duration = 1 hour
- IF = 0.9 (as you’re working at 90% of your Threshold HR)
Plugging these numbers into the formula:
TSS (HR) = 1 * 0.9 * 0.9 * 100 = 81
- Now, let’s calculate using Threshold Power:
If you were to perform the same 1-hour workout at 90% of your Threshold Power:
- Duration = 1 hour
- IF = 0.9 (as you’re working at 90% of your Threshold Power)
Plugging these numbers into the formula:
TSS (Power) = 1 * 0.9 * 0.9 * 100 = 81
This means that the workout has a TSS of 81, whether we calculate it using HR or Power.
TSS quantifies the physiological stress of a workout based on its intensity and duration. Having accurate measures of your Threshold HR or Power will make your TSS calculation more precise, help you optimize your training plan, and track improvements over time.