No day should be super hard, and no day should be exceptionally easy.
Some experts believe that power meters and speed and distance devices have made heart rate monitors irrelevant.
The easiest way to monitor your pace and effort has been around for decades—and it doesn't require any gadgets.
Just because your pace remains consistent pace doesn't mean your heart rate will, too.
Not only is it an art, but pacing yourself by feel is also a science.
A recent study by Samuele Marcora suggests this might be the case.
A study suggests your body knows best how hard to run each interval and how long to rest in between.
Get the most bang for your training buck by listening to your body.
There is a performance threshold in running, but it's not the lactate threshold.