Not all miles are equal: understanding training load in runners

Whilst it’s popular to measure training load in distance (mileage), it can often misrepresent training load. For example, a 5km easy run is significantly less stress on the body than a 5km hard run.

In this blog post, we'll explore three popular alternative methods for measuring training load in runners: TRIMP, TSS, and RPE. 

1. Training Impulse (TRIMP):

Training Impulse, or TRIMP, is a method developed by Dr. Eric Banister to quantify the cumulative effect of different training sessions on an athlete's body. TRIMP takes into account the duration & intensity of a workout to calculate a numerical value that represents the overall training stress. It considers heart rate zones, where different zones correspond to different intensities. 

To calculate TRIMP, you multiply the training duration by the intensity factor (IF) and then by a coefficient that corresponds to the heart rate zone. The higher the intensity, the higher the TRIMP score.

Uses heart rate reserve, which considers Resting heart rate & Maximum heart rate, plus a gender-specific weighting factor.

2. Running Training Stress Score (rTSS):

Training Stress Score, or TSS, is a method commonly used by cyclists but can also be applied to running. It was developed by Dr. Andrew Coggan and is based on the principle of Training Stress Balance (TSB). TSS takes into account both duration and intensity, similar to TRIMP, but uses a different algorithm to calculate training stress.

TSS assigns a numerical value to each workout, with the score reflecting the physiological impact of the session. The calculation incorporates factors like heart rate, power output (in cycling), or pace (in running) to estimate the stress on the body. By analyzing the TSS over time, runners can track their overall training stress and adjust their training plans accordingly.

3. Rating of Perceived Exertion (RPE):

While TRIMP and TSS rely on objective data, the Rating of Perceived Exertion (RPE) offers a subjective approach to measuring training load. RPE allows runners to rate their perceived effort during a workout on a scale of 1 to 10, with 1 being very easy and 10 being maximum exertion. This score is then multiplied by the session duration or distance to give a session RPE (sRPE). For example, a session rated as a 4/10 lasting 60 minutes would be assigned 240 units.

Choosing the Right Method:

Wallace et al compared modelling using sRPE, TRIMP & TSS to running performance. (Wallace 2014) The found a slightly better correlation with TSS but all methods were appropriate for quantifying endurance training dose. More recently McLaren et al found that the session-RPE training load score was superior for tracking performance versus heart rate-derived TRIMPs. (McLaren 2018)

All three methods—TRIMP, TSS, and RPE—have their merits, and selecting the most suitable one depends on personal preference and training goals. Some runners may prefer the objectivity of TRIMP and TSS, relying on data-driven metrics to guide their training decisions. Others may find RPE more intuitive, as it reflects their personal experience during workouts.

Conclusion: 

Measuring and managing training load is vital for runners seeking to improve performance while minimizing the risk of injuries. Simply using mileage will frequently underestimate the stress on the body. TRIMP, TSS, and RPE are three popular methods for quantifying training load. TRIMP and TSS utilize objective data to calculate training stress based on duration and intensity, while RPE offers a subjective perspective through perceived effort ratings. 

Understanding the strengths and limitations of these methods can help runners make informed decisions about their training plans, ensuring they strike the right balance between training stimulus and recovery. Remember, every runner is unique, and finding the method or combination of methods that works best for you is key to achieving your goals safely and effectively.