Heart Rate Zone Calculator

When I started training for my sub-1:50, I made the classic mistake of running every session at "moderate effort" (around Zone 3). I improved slowly for months.

The breakthrough: Once I learned to actually run at the correct zones, training became much more purposeful. Easy runs became truly easy (Zone 2, conversational pace). Hard intervals hit the right intensity (Zone 4-5). Recovery happened.

Sub 1:50 Key Takeaway: Most of your weekly volume (60-70%) should be in Zone 2. The other 30-40% should be specific Zone 4-5 intervals. If you're always at Zone 3, you'll plateau at sub 1:55 and never break 1:50.

Karvonen vs Fox Formula: Karvonen uses your resting heart rate to give more accurate zones. For someone age 22 with resting HR of 60, Karvonen gives roughly the same result. But for older runners or those with low resting HR, Karvonen is significantly more accurate.