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    Home / Todd's Blog / THE DIFFERENCE BETWEEN CARDIAC DRIFT AND CARDIAC SAG
    Mar 21, 2026

    THE DIFFERENCE BETWEEN CARDIAC DRIFT AND CARDIAC SAG

    THE DIFFERENCE BETWEEN CARDIAC DRIFT AND CARDIAC SAG

    HEARTRATES CAN BE SO DUPLICITOUS. With all the fancy ways to measure the all important tickers, one would think we'd have...

    ... perfected interpreting the data.

    But, there's drift.

    And, there's sag.

    Never heard of sag have ya?!

    Well, here's how my climby ride...

    • 7861 ft
    • 47.21 mi
    • 460 Historic Relative Effort

    ... went today.

    The start was spicy.

    First 45 min was pure threshold,
    yielding a few PRs,
    HR 150-160.

    That is what I call Cardiac Sag,
    it's early in the ride and we're romping along...

    ... and our ticker is freshly ho-hum about the effort.

    Two hours later, under a summer-like sun,
    no PRs and power bouncing between endurance and tempo...

    ... with the HR still still in the threshold range.

    That is what is commonly known as Cardiac Drift...

    ... the power plummets while blood pumps along as if a much bigger effort was underway.

    TBH, when I finally met up with my friends who left me for dead...

    ... I lied.

    Told them I'd had mechanical issues and cramping.

    The truth was I found a lone tree,
    finished my last bottle...

    ... sobbing in my helmet.

    Is there anything at all to learn from this?

    Why, yes, there is.

    When we know a challenging day lies ahead,
    keep the power in check early and ignore that lying Cardiac Sag.

    Hours later, if we haven't buried ourselves early, the Cardiac Drift should be minimal...

    ... the power output still strong.

    ===

    164.8
    540 anti-oxidant level
    7.5 hours sleep
    no Upper Body: 75 push ups, 15 pull ups, gripper, heel & toe raises
    no Lower Body: split squats, step ups
    84/104/-20 per Strava

    https://www.strava.com/athletes/10248

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    THE DIFFERENCE BETWEEN CARDIAC DRIFT AND CARDIAC SAG