A distinctive feature of Crickles is that it will estimate your Cardiac Stress even when you’re exercising without monitoring your heart rate with a chest strap or sports watch. This is critical if you want to track your Fitness, Fatigue and Form since these are cumulative measures and if you leave out chunks of your exercise regime they’ll be wrong. Herein lies a weakness of  most  of the non-Crickles sites that claim to show you this. For example, when you can get it to work, Strava’s intensity metric (Relative Effort) has improved (and thus become a little more like the Crickles CSS) over the last couple of years since it replaced Strava’s Suffer Score. Although there is very little consistency between Relative Effort and Power, you can now at least combine them on Strava’s Fitness & Freshness chart. However, if you go for a swim during which you don’t measure your heart rate, or you do a run or a bike ride without a HR monitor or a power meter, then those activities have absolutely no impact on Strava’s fitness and fatigue curves.

Crickles does not have this flaw. Moreover our Cardiac Stress Score tracks as well to the standard Training Stress Score derived from a power meter as you would expect it to. For example, if you do a triathlon with no heart rate measurement on the swim, a power meter on the bike leg and a heart rate monitor on the run you’ll get a sensible Cardiac Stress Score for each leg of the event and they will feed into your Fit-Fat curves.

From this weekend, the estimation of cardiac stress when you have neither a heart rate monitor nor a power meter is significantly improved in Crickles. This has been achieved in two ways:

  1. For (non-virtual) bike rides and runs, we have a sophisticated new statistical model for estimating Intensity in the absence of heart rate data. You can now see this explicitly for each ride or run on the Activities tab of the Navigator in the Intensity column.
  2. For all other activities, the current model has been improved and re-calibrated using the very large amount of data that Crickles athletes have made available to us over time. Rather than giving an Intensity reading for each activity, this generates a Cardiac Stress Score for each activity. CSS for these activities is now shown on the Activities tab. It can also be inferred on the Timeline, where the y-axis position indicates CSS. You can also see the daily sum of CSS values in the hover tips on the Fit-Fat curves where it is called Stress Load.

Historical activities have all been re-calculated according to the improved model. If you always use a heart rate monitor you won’t notice any change. However, to the extent that non-measured activities make up a meaningful portion of your overall exercise load, you may notice. None of the metrics should be hugely different as the prior model wasn’t terrible! In my personal case, I’ve been doing swims and pilates regularly over the past several weeks alongside cycling and running with a heart rate monitor. I can see that the new model assigns a lower CSS to the swims and the pilates than the old one and so my Fitness and Fatigue levels are now marginally lower than they were before the change.

Please do get in touch if you have any comments.



  1. Hi, If I exercise on an E-Bike with no HR monitor does crickles account for this in a reasonable way? Regards Nick


    1. Hi Nick, Crickles will be more reasonable than other sites in that it won’t assume your exercise load is zero! However, the more sophisticated modelling that I just introduced has only so far been calibrated for non-virtual rides on non-electric bikes. The pre-improvement estimate is reasonable, especially if this comprises only a portion of your exercise regime. Best, Ian

Leave a Reply

%d bloggers like this: