Post Run Analysis Metrics
For most of these metrics we are about to discuss we are looking at changes in them throughout the session. A negative change indicates a drop in running form and / or an increase in fatigue levels. A positive change means the athlete is coping well with the session and form is actually improving. So the numbers give us good objective data on how the athlete is handling a session which helps us decide win to make the session harder or easier next time. I’ll give some examples once we have gone through the various metrics.
Ground contact time ( stance time )
This is a measure of how long one’s foot stays on the ground. It’s linked to both a runner’s speed and their running economy. The more efficient they are the shorter their ground contact time .
In terms of absolute numbers, we see elite sprinters with contact time less than 100ms and elite marathoners around 150-180ms, whereas running at a slower paces would be more like 220-270ms. Much over that could indicate its something to work on ( although will depend on the running speed – if they are running at 8 min ks then it may be ok, if running at 5 min ks it needs work ! )
The quicker the ground contact time the better the use of elastic energy and hence the better the running economy. To understand this picture two elastic bands – one thick one thin, the thick band needs much less stretch before releasing compared to the thin one. The time taken to stretch the elastic band is equivalent to the stretch the Calf and Achilles undergo during ground contact time when running.
When analysing our athletes’ data, there is no specific ground contact time they should be aiming for at a particular pace , it’s very much dependent on the athletes’ running biomechanics. Stance time will usually be longer on trails and uphills at slower paces. However, over time you might see ground contact time reducing for a given pace, indicating running economy has improved.
It’s also useful to look at how ground contact time changes throughout a speed or hard hill session. An increase in ground contact time often suggests the Calf–Achilles complex ( and to a lessor degree hips ) is becoming less efficient at storing and releasing elastic energy. When your foot stays on the ground longer, more of that potential energy leaks into the ground instead of being returned to you. As a result, you get less elastic rebound to drive you forward, and your muscles have to pick up the slack. Even if speed is consistent, this would indicate the runner is feeling fatigued as running economy is deteriorating.
Vertical Oscillation VO
This refers to the amount of up-and-down movement of your pelvis, centre of mass, or chest (depending on the device you’re using and how it measures it) throughout your running gait.
The amount of vertical oscillation you produce depends on both your running speed and your individual biomechanics. When you run faster and stride length increases , you need slightly more vertical lift to create the extra airtime needed for the longer strides.
Runners with a higher cadence and shorter stride length will usually have lower vertical oscillation than someone running at the same speed with a lower cadence and longer stride length.
There are two parts to vertical oscillation: how high you rise during the flight phase, and how much you drop during the stance phase (which depends on how much your ankle, knee, and hips bend). Too much of either is inefficient. You don’t want to waste energy pushing yourself too high off the ground, and you also don’t want to sink too low in the stance phase. Too low in stance phase and your ground contact time increases causing a loss of elastic energy
Unfortunately, you cant tell from the data if there is too much oscillation in the flight phase or stance phase so some detective work is needed ( such as looking at other metrics such as ground contact time and leg spring stiffness )
VO is usually in the range of 5-10 cm and will be lower at slower paces.
I find the best use of vertical oscillation is to divide it by stride length. This gives a number that reflects the balance between vertical and horizontal movement. The lower the number, the better, as it indicates more forward motion relative to upward motion. While it depends on speed, you can track it throughout a session to gauge fatigue even if pace remains the same. For example, if VO/stride length increases during a session, it suggests the runner is using more energy moving upward rather than forward.
I will typically see VO/SL to be less than 6.0 for efficient runners . Note that uphill it will be higher as you need to climb as well as move forward.
For example recently a set of hill reps and then a few days later the same session on the flat – VO/SL was 6.5-5.5 on the hill session ( I got quicker each rep ) and 5.2- 4.5 on the flat ( also got quicker each rep)
Another factor to consider when comparing vertical oscillation between athletes is that different watches and foot pods calculate it differently. Comparisons can be misleading unless you know both devices measure it in the same way.”