What is Garmin’s metric “Step Speed Loss”?
Garmin’s Step Speed Loss (SSL) is a new running gait metric introduced in May 2025, measured on the HRM 600 and displayed on compatible watches like the Forerunner 970. It measures how much you slow down when your foot hits the ground and is specifically defined as the difference between your forward speed when you first hit the ground and your minimum forward speed during that step’s stance phase. SSL is measured at the chest using a heart rate monitor in units of cm/s, and the lower the figure, the better.
TL;DR – It is a measure of braking in each step
SSL is influenced by running form; lower cadence or overstriding is bad and tends to increase SSL. A higher SSL indicates that you perform more propulsive work to regain speed after ground contact. Running techniques which achieve a smooth, light stride or reduce step length will improve SSL.
SSL accounts for the effect of gravity when running on hills, where the watch’s barometer provides grade as an adjustment factor. SSL is invariably lower when running uphill due to gravity and higher when running downhill. It also requires steady forward movement and may not be continuously calculated; thus, it may not appear during turns or on variable surfaces like technical trails.
TIP: Hill adjustments are not applied for treadmills and are not computed when walking. Just use it for running.
SSL generally increases at faster speeds. To normalise SSL, Garmin provides a related metric called Step Speed Loss Percent (SSL%), which removes the effect of speed. Like SSL, a lower SSL% is good. You can view SSL% on your watches or in Garmin Connect.
TIP: If you are going to look at these braking metrics, use SSL%
How similar is Step Speed Loss to STRYD’s Leg Spring Stiffness and Impact Loading Rate measures?
In a previous article, a reader asked if SSL was the same as any of the Stryd running Pod metrics or Fourth Frontier X2. The short answer is: No.
However, there are similarities to Stryd’s Leg Spring Stiffness (LSS) and Impact Loading Rate (ILR), which are related to braking. Similarly, Fourth Frontier’s Body Shock (BS) considers the body’s physiological reaction to braking via continuous ECG.
- Step Speed Loss (SSL): Measures forward (horizontal) speed loss during the ground contact phase. It is a measure of horizontal deceleration or braking during the stride.
- Leg Spring Stiffness (LSS): Defined by Stryd as a model representing the leg as a spring, calculated from the maximum vertical force generated and the vertical displacement during ground contact. The general concept of “leg stiffness” or “Kleg” is discussed elsewhere in biomechanics.
- Impact Loading Rate (ILR): Stryd defines the initial rate of increase in vertical force as the foot contacts the ground. ILR focuses specifically on how quickly the vertical force is applied at the beginning of the stance phase.
Thus, these three metrics all relate to distinct physical characteristics of the ground contact phase of running:
- SSL focuses on horizontal braking and forward speed changes.
- LSS focuses on the leg system’s overall vertical stiffness and energy return capacity during stance.
- ILR focuses on the initial rate of vertical force application (impact) at foot strike.
What Watches Are compatible?
At launch, only the Forerunner 970 is compatible and not the FR570. Thus, Garmin sees this as a premium running metric, and I would expect Fenix 8 models to get the metric soon, but certainly not Instinct 3 nor Fenix E.
An HRM 600 chest strap is also required.
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What Metrics Can I Display?
Eight related metrics are available when this feature launches.
| Metric | Description |
| Step Speed Loss Gauge | A colour gauge showing your current step speed loss while running. |
| Step Speed Loss% Gauge | A colour gauge showing your average step speed loss per cent. |
| Average Step Speed Loss | The average measure of step speed loss for the current activity. |
| Avg. Step Speed Loss Percent | The average ratio of step speed loss over speed for the current activity. |
| Lap Step Speed Loss | The average step speed loss for the current lap. |
| Lap Step Speed Loss Percent | The average ratio of step speed loss over speed for the current lap. |
| Step Speed Loss | The measure of step speed loss in centimetres per second while running. |
| Step Speed Loss Percent | The ratio of step speed loss to speed while running. |
What is a Good Step Speed loss range?
In this chart, the purple range is the best and red the worst.
What other metrics are impacted?
Step Speed Loss is a key input into Garmin’s latest Running Economy metric, which includes heart rate, speed, and other running dynamics such as stride length, ground contact time, and vertical oscillation.
Take Out
Perhaps some biomechanicists can chime in here. I’m not an expert on this by a long way.
SSL seems like a sensible metric that is made better by removing the effect of speed. However, Garmin doesn’t adequately answer, “What is a good SSL?”, other than to say “lower is better”. Nor does Garmin say how we can improve this metric or, indeed, if it is possible for you. An understanding of peer group values would be helpful. If yours is twice that of everyone else at your running level, then there’s a decent chance you can improve it.
Often, gait metrics can be improved by ‘running faster’; however, that appears not to be the case here (which is good). I’ll probably test this by alternating between heel, mid-foot, and forefoot striking at different speeds, and I expect the metric to improve with forefoot striking. That will probably quantify the obvious and focus us on how to tweak our style rather than fundamentally change it.
I suspect this metric is not crucial for most people to understand or obsess over. However, it is a vital input in Garmin’s Running Economy metric, which is an important metric (if correctly calculated).
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For me at least, the Fenix peaked at around the 6 where we had full offline navigation, grade adjusted pacepro (great for ultras), training load broken down by intensity and auto-generated workout recommendations.
Everything after this was just icing as far as I’m concerned and didn’t add anything that would fundamentally impact training.
Perhaps we’ll end up seeing highly specific training recommendations in time (ie I’m a rock climber and a runner, so I’d love to see a workout strategy that maximised all of these) but this will likely end up behind a Connect+ pay wall if it is ever released.
Garmin has significantly lost innovative power in recent years and gained a ‘business winner-takes-all’ attitude. This will continue to drive EBITDA thanks to a broad mass of the athletic ‘middle class’, but it’s like a tanker that missed its departure. At some point, the flexibility for innovation will be lost. Since the introduction of HRV, SpO2, payment, and some navigation features, nothing significant has been added. Significant is here defined as a metric that opens up a course of action. ‚SSL‘, as an example, is the opposite. The metric has no biomechanical or physiological relevance and does not open up any new course of action. Knowing it is probably as valuable as knowing the outside temperature in Togo during a run through Boston… The competition is different: eg Stryd provides values that attempt to open up new biomechanical/physical or physiological insights for possible changes. Or detrended fluctuation analysis of heart rate variability—a very interesting new concept. On top of that, Garmin’s design is becoming increasingly playful, lacking in technical, functional design clarity, and looking like the interior of a Western Chinese restaurant in the 1990s.
This new metric is the first interesting thing I’ve seen Garmin come out with in the last two years. They’d be crazy not to port it back to older watch models, since i think the boost from new HRM sales would trump whatever losses in new watch sales they think they’d have if they did. Plus it would help them mute some of the recent public outcry that Garmin has recently abandoned adding new features to older watches. Seems like a win-win for them. Which means they probably won’t, lol
That’s true. I would probably buy hrm600 if the measurements went to my F7XSS.
agreed. the running economy are tolerance both seem good and useful as well.
backporting: could go either wya. it requires a new HRM so it might get backported to boost the sales of that
I would gamble that Garmin feels pretty comfortable that the HRM 600 offers enough purchase incentive w/o this feature and so they’ll hold it back as a watch incentive.