A good way to monitor how hard you are running is the "talk test." If you can't carry on a conversation while running, you are likely pushing too hard. Of course, this doesn't apply to those speed days on the track when you are hammering it.
But, in a normal training run, if you can't carry on a conversation with your partner, you are running too hard.
Run within yourself except for those speed days.
Kenneth Williams, @MarathonKoach.
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