What is Garmin’s metric “Running Tolerance”?

Garmin’s Running Tolerance (RT) is designed to help runners recognise and avoid training patterns that might lead to injury. Its primary goal is to give ranges for safe training so that mileage can be maintained or increased safely. It balances the risk of injury with the potential for performance gains.

Many of us are familiar with training load (TL), which quantifies the load on our body by modelling either heart rate or power data. Running Tolerance approaches this differently and attempts to quantify Impact Load (IL). IL consider the biomechanical load, which impacts muscles, joints, and tendons, and accumulates stride by stride. This impact varies based on a complex combination of factors. Simplistically, a single step whilst sprinting downhill will have a greater IL than a single step whilst running in Z2 up a gentle incline.

With that in mind, we can see how generally accepted advice about ‘increasing mileage’ is simplistic – for example, what type of mileage should be increased?

Compatible Garmin devices use algorithms to quantify runs in terms of their total impact on your body. Key inputs like weight, speed, and intensity are combined with running dynamics such as cadence and ground contact time. Uphill and downhill efforts receive special consideration based on steepness and so on. The device continuously analyses performance and impact load, which is then shared with you as an equivalent mileage.

Consider: IMPACT Load as being similar to TSS or TRIMP. It can be added to quantify the Impact Load of any workout, then averaged over time to determine your normal range. just like Training Load, keep your short-term average inside the range. More importantly, you can determine what the impact of your upcoming workout needs to be to stay in range and hence injury free.

Thus, the equivalent mileage approach quantifies how harder, faster running produces higher ground reaction forces and causes more wear and tear than easy jogging. Walking segments during a run produce only half the impact of basic endurance running, while a downhill effort might have up to three times the effect of the same speed on level ground. This insight helps in planning weekly mileage targets. Furthermore, you can review your impact load after a run on your watch or in the Garmin Connect app to see how different parts of the run had different impacts.

Beyond individual runs, Garmin Running Tolerance considers the bigger picture of cumulative impact using two related metrics:

1. Acute Impact Load: This is a weighted sum to reflect the cumulative and residual impact of your recently recorded runs. The full impact load of a new run is added directly, and its influence gradually diminishes over time. It indicates your capacity to run within your weekly running tolerance on a given day. The accumulation of Acute Impact Load, particularly from efforts like long runs or excessive downhill running, can also extend recovery time recommendations. (Similar to Acute Training Load)
2. Tolerance: This metric reflects the maximum acute load your body can manage based on your running history. It is personalised and adjusted weekly based on a science-based interpretation of your recent and long-term running history.

Understanding these two metrics helps your load management. If your acute impact load exceeds your tolerance, you should evaluate your immediate training and proceed with care. Consistently pushing beyond this limit will likely be a hazardous training pattern, risking injury.

The training week screen (glance) on your Garmin shows recent changes to your running tolerance. Consistently challenging training will gradually increase your running tolerance, and the converse is true – mathematically, a higher daily load increases the moving average and upper range (tolerance!).

Science: Bowser (2018) – Tibial shock is correlated with loading rates, which supports the idea that metrics derived from device-based measurement can be a proxy for lab equivalents.

Garmin Metrics

Key RT data is accessed via the Running Tolerance GLANCE, typically by the up/down buttons on the left. Glances can be manually added and removed.

• Acute Impact Load (distance) by day and week
• Tolerance distance/week, in total and trended by day for a week
• Actual weekly distance and actual daily distance

Running Tolerance – Supported Watches

Some of the raw data for Running Tolerance is only captured (at launch) by the HRM 600 chest strap and only displayed on the Forerunner 970.

The RT metric will likely be quickly passed to Fenix 8 owners who buy the strap.

It’s unclear if Garmin will roll this back to older watches or include it in the Connect+ subscription for older watches, which would be a decent idea from Garmin’s perspective. After all, many older watches give all the other running dynamics metrics based on a strap, RD POD or from the wrist. The watch hardware is capable of supporting RT with an HRM 600.

Take Out – Running Tolerance.

Initially, this seemed like ‘yet another metric’ and is certainly not a fancy, neon coloured one you can brag about to your friends. (VO2max, we’re thinking of you here).

RT is a helpful addition to the Garmin stable. It’s not a metric you will probably regularly look at. However, when training hard and you think you might be getting close to some limit, it’s perhaps worth monitoring Running Tolerance to see if that ties with how you feel, perhaps telling you to back off for the next few runs – or even to do the planned distance but on a less phsically stressful route.

I also suspect, from experience of training by ‘feel’, that this metric might be able to latch onto a problem before you realise or feel it exists.

Garmin Forerunner 970

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