UMVA has learned that the Garmin Forerunner 970 hides a powerful duo of metrics—running economy and step speed loss—behind a price‑tagged accessory.
These numbers promise a glimpse into how efficiently you turn oxygen into forward motion, but unlocking them requires the $170 HRM‑600 heart‑rate monitor. To decide if the extra cost earns its keep, I strapped the sensor on countless runs, including a half‑marathon in early May, and uncovered what the data really reveals.
Running economy, in scientific terms, measures the oxygen you consume at a given pace. In everyday running talk, it translates to how little energy you waste while holding a speed. Garmin distills this into a single score by blending heart‑rate, speed, and dynamic stride data, all of which hinge on a key input: step speed loss.
Step speed loss (SSL) captures the tiny braking moment when your foot first strikes the ground and your forward velocity dips before rebounding. Measured in centimeters per second, a lower SSL means each stride glides more like a smooth wheel, while a higher SSL signals you’re fighting against your own momentum.
Why does SSL matter? Imagine a runner who repeatedly hits the brakes with each step—energy drains, fatigue spikes, and speed stalls. Conversely, a low SSL indicates a light, quick footfall directly beneath the hips, minimizing drag and maximizing propulsion.
Factors that inflate SSL include a sluggish cadence, overstriding, or a heavy, stomping footfall. The antidote is a shorter, quicker stride that lands beneath the center of mass, turning each step into a seamless push forward.
During my half‑marathon, the Forerunner recorded an average SSL of 8.2 cm/s, or 2.85 % of my forward speed lost each step. The metric held steady through the latter half of the race, suggesting my form resisted fatigue, and the brief spikes aligned with downhill sections where my stride naturally altered.
Cadence hovered at 181 steps per minute, flirting with the oft‑cited “optimal” 180 spm benchmark. Yet my vertical ratio—a measure of how much vertical oscillation bites into stride length—settled at 8.5 %, placing me below the average runner.
Garmin’s running economy score landed at 214, slotting me into the “Trained” tier. The platform warns that progress at this level will be gradual, requiring careful ramps in intensity and volume. Still, the score offers a concrete target: push the number into higher percentile bands and watch efficiency blossom.
The real test is whether the HRM‑600’s cost justifies the insight. For data‑driven athletes hungry for granular feedback, continuous SSL tracking becomes a real‑time form‑check, nudging you to shorten overlong strides or adjust cadence on the fly.
For the casual runner, the obsession may feel excessive. Percentile rankings are fun, but the true value lies in trend direction—are you consistently lowering SSL, or does it creep upward as fatigue sets in?
Bottom line: if you already extract maximum value from the Forerunner 970 and crave the next layer of precision, the accessory can transform vague effort into measurable efficiency. If you’re still mastering basic consistency, channel that $170 into more miles on the road and let the data catch up later.
