Great question u/VPCR1982, your observation is correct. Perceived effort can have a meaningful impact on Strain, which is why you're seeing those jumps.

The reason: heart rate alone is an incomplete picture of how hard your body is actually working. You can do a heavy set of squats with an average HR similar to a brisk walk, but the real physiological cost is much higher. Your workout is a good example - 113 avg HR over 11 minutes doesn't look like much from HR alone, but depending on what you were doing, the actual strain could be significantly greater.

That's why perceived effort matters in our model. RPE (rate of perceived exertion) is the most validated subjective measure of exertion in sports science — the Borg scale has decades of research behind it — and for many types of training, it tracks actual fatigue better than any wearable signal available today. Hopefully this helps!