Explaining Acute on Chronic Workload Ratio (ACWR)
ACWR is a training load metric. Most training load metrics just use extrinsic load, measured in distance or duration completed. Some also use heart rate to guess the intrinsic loads being placed on your body.
The unique part of ACWR is that it includes both extrinsic loads and intrinsic loads, without relying on the accuracy of your heart rate monitor (most are inaccurate). This is done by recording your RPE (see below).
ACWR shows you how much you have done recently compared to chronically. It helps you know how much load you're placing on your body currently compared to what it is used to.
Our bodies take time to adapt to an increase in loading stimulus. Monitoring ACWR can help you make adjustments to help you avoid doing too much, too soon & therefore increasing your injury risk.
While you can fully customize the definition of acute and chronic in the ‘advanced analytics’ tab, the standard ACWR = 7 day total / 7 day average of last 28 days.
Examples:
Extrinsic factors only:
Distance
Numerator is the sum of last 7 days total distance
48 miles ran over last 7 days
Denominator is the 7-day average of the last 28 days
If my last 4 weeks of mileage is:
48 miles
40 miles
32 miles
40 miles
Then my 7-day average is 40 miles
To calculate the ratio:
Take 48/40 = 1.2 ACWR (distance) score for today.
Duration
Same as distance but using minutes instead of miles
Extrinsic Factors * Intrinsic Factors (most accurate representation of training load):
*DistanceRpe (or DurationRpe) - most accurate
Every day’s data takes the miles completed, and multiples that by your RPE (relative perceived exertion) rating (1-10) for the activity.
Every day then gets a total load score, and these scores are what is used to calculate the acute 7 day total load score (numerator) and the chronic 7 day average of the last 28 days load score (denominator).
Distance Example:
10 miles at 5/10 RPE = activity load score of 50.
Duration Example:
30 minutes at 9/10 RPE = activity load score of 270.
Do this for every activity, every day to calculate the total load score for the last 7 days, and the 7 day average load score for the last 28 days.
The DistanceRPE and DurationRPE training load scores are the most accurate, because you as the athlete are selecting how challenging the activity felt and not relying on your heart rate monitor to be accurate and your heart rate adequately reflecting the actual difficulty.
With practice, you will always be better at understanding how your body feels than your watch.
Incorporating RPE allows you to account for intrinsic factors, such as your fueling status, hydration status, mental fatigue & stress, altitude & weather adjustments, injury & illness symptoms, etc. None of this is picked up in an extrinsic-load-only metric.
DistanceHeartRate (or DurationHeartRate)
While RPE is better than heart rate for the above reasons, we recognize that not everyone is going to stay consistent with answering a post-activity RPE score for every activity.
While it may be less accurate, using heart rate instead of RPE can be a nice way to automate incorporating some intrinsic load factors. Worse recovery status in theory should show up as a higher heart rate at the same training pace.
To calculate, we use your average activity heart rate and convert it to an RPE number, 1-10, based on your max heart rate and estimated heart rate zones.
It is then calculated like the RPE ACWR metrics (above), where every day’s data takes the distance/duration completed, and multiplies that by the auto-selected RPE.
