Anecdotally, I experience somewhat higher perceived effort at a given (moderate) heart rate when better trained. For example, my resting and max heart rates have been nearly constant at 36-40 and 170-175 since about 18 (I&#x27;m 32 now). During that time, I&#x27;ve been a top-10 NCAA nordic skier, alpinist, and a casual runner (2y in Chicago; &#x27;nuff said).<p>I try to avoid &quot;junk&quot; time in the 128-142 zone because the intensity is too high for recovery&#x2F;endurance benefits, but not high enough to target aerobic threshold or VO2max.  When in mediocre shape and trying to do a lower intensity workout, I accidentally end up in that range more easily than when in racing shape.  Meanwhile, threshold and VO2max intensities are easier to sustain when better trained, though I can hit similar max heart rates either way.  I interpret this as the lactic acid versus heart rate curves have different profiles even with similar endpoints.<p>I&#x27;ve also seen acute short-term effects.  For example, I did a 160-mile backcountry race after a competitive nordic ski season.  For about a week after the race, I couldn&#x27;t get my heart rate above 145 (30 beats below my normal max).  During that week, I did VO2max-intensity intervals with a well-matched regular training partner and could match a pace that would normally require me to be at 160 while I was at just 140.  The pace felt more comfortable than expected (probably &quot;felt like 150&quot;), but there was no headroom to go faster.