Running Dynamics
Running Dynamics are measures that can provide insight into your running form and economy. These metrics can provide actionable data to improve your running, but I think they function best in the context of an overall running form evaluation. I would highly recommend starting with High Speed Video Analysis, as few runners know what their running form looks like. I found Fredrik Zillen's The Art of Efficient Running Technique well worth the 180 EUR.
The Metrics
Here are the metrics, roughly in order of usefulness. Most of these are available from Garmin devices or Stryd.
- Ground Contact Time Balance. This is the ratio of left and right Ground Contact Time and shows imbalances in the body. If you have a GCT imbalance, it will reduce running economy and likely shows a problem that should be corrected if possible. You can check for weakness or range of motion differences, but you may need a professional evaluation. The imbalance might be in the upper body, so don't just check the legs and hips. (The imbalance could be due to something that can't be fixed, such as a leg bone length difference.)
- Cadence. This is probably the most useful metric in running, and one that's easily understood and changed. If Cadence is too low, running economy is normally lowered.
- Step Speed Loss (SSL). This has been introduced with the Garmin HRM 600 (2025) and shows how much your torso slows down when your foot lands. This is clearly linked to your running economy as the amount you slow down on foot strike has to be offset by pushing harder to accelerate. You can experiment to see how cadence, arm movement, posture, etc., all change your SSL.
- Ground Contact Time (GCT). The Science of Running Economy generally shows that longer Ground Contact Time is correlated with poorer Running Economy. This is mostly because your muscles and tendons have elastic properties, so you can bounce as you run. To get the benefits of the bounce, your contact time must be short enough that the energy stored isn't lost but used to propel you up again. GCT and Cadence are related; try jumping up and down gently using your ankles and lower legs. If your cadence is low, you'll find it much harder than if it's quicker and you're able to bounce. Even running at a slower pace should feel a little bouncy.
- Leg Spring Stiffness (LSS). Efficient running requires your legs to be stiff and bouncy. Stryd calculates a value for LSS, but it's not available in real time.
- Vertical Oscillation. This is how much the torso moves up and down with each stride. It is often believed that less Vertical Oscillation is a better but I suspect that this is an oversimplification. Some are part of your vertical movement happens while your feet are on the ground and can be elastic in nature (the bounce). This movement reflects Leg Spring Stiffness (LSS). You want less VO while your feet are on the ground which comes from higher LSS. However, some of the vertical motion will be while you are airborne (ballistic) and you can't reduce that without spending less time in flight. So be careful evaluating VO and treat it with caution.
- Stride Length. This is computed from your Cadence and your running pace, and its value seems limited, so mostly focus on Cadence. The only exception is in faster running you may find that your stride length is a limiting factor. In that case, you may need to improve range of motion.
- Vertical Ratio. This is Vertical Oscillation to Stride Length ratio, and it's unclear what the value of this metric would be.
Fatigue and Running Dynamics
You can look at how your running form changes as you get fatigued though changes in your running dynamics. You may find your GCT increases as you lose bounce, which will also show up in your LSS. If you are slowing up, how does your cadence/stride length differ from the same speed when you're fresh?
