Ground Contact Time in Plyometric Training Part 1: Why Shorter Isn't Always Better
If you think an athlete has a ground contact of 150 milliseconds is good, so 120 milliseconds must be better.
Right?
A more informed question is:
What's it better for?
From what I have seen the topic of ground contact time has become an increasingly common metric in plyometric training.
There is a specific reason for this.
The amount of time we see that an athlete takes when contacting the ground during a plyometric movement gives feedback about the way the athlete is producing force in the time they have.
However, there is a glaring issue.
Coaches and athletes can start to use this as a score, rather than a piece of data for guidance and direction of athletic development.
What I can see is that in an absolute form
Shorter becomes good.
Longer becomes bad.
And suddenly the objective of every plyometric becomes:
"Get off the ground as quickly as possible."
In my experience the problem with that thinking is that where you have a bound, a pogo hop, a hurdle jump, or a change of direction.
They are all being covered under the same blanket metric.
So before trying to reduce ground contact time, we first need to understand what produced it.
Don't optimise the metric until you understand the demand.
What Is Ground Contact Time in Plyometric Training?
Ground contact time describes the period between initial ground contact and the athlete subsequently leaving the ground again.
If an athlete lands and takes off 0.18 seconds later, their contact time for that interaction is approximately 180 milliseconds.
Simple enough.
What the number actually means is more complicated.
Ground contact time tells us:
How long the athlete was interacting with the ground.
It does not independently tell us:
How much force the athlete produced;
The direction in which force was applied;
How much displacement they achieved;
Whether they used the intended movement strategy;
Or whether the exercise successfully trained the quality we wanted.
Research examining drop jumping has demonstrated this problem for decades.
Bobbert, Huijing and van Ingen Schenau (1987) showed that altering drop-jump technique changed the biomechanics of the movement, despite the athlete still performing what we would broadly call a drop jump.
This gives us an important starting point:
The exercise name does not tell you everything about the stimulus.
In Part 2 of this 6 part series we will cover
Why Ground Contact Time Shouldn't Be Used as a Score
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