Guides · ForceDecks · 9 min read
How to read a ForceDecks report: every metric, what a good number looks like, and when to worry
A practitioner's guide to ForceDecks CMJ metrics — jump height, RSI-modified, peak power, asymmetry, eccentric and concentric phases — and how to turn them into decisions.
By Vikas Kashyap · Updated 25 September 2026
A ForceDecks countermovement jump produces well over a hundred metrics. Almost nobody needs more than a dozen. The rest of this guide is the dozen — what each one measures, what tends to move it, and the mistake practitioners most often make when reading it. It assumes you are running a standard CMJ (hands on hips, self-selected depth, 3–5 trials) on dual plates.
Start with the output metrics
Output metrics describe what the jump achieved. They are the easiest to explain to a coach and the ones most likely to be over-interpreted on their own.
| Metric | What it is | How to read it |
|---|---|---|
| Jump height (impulse-momentum) | Height calculated from take-off velocity, itself derived from the net impulse during the propulsive phase. | Prefer this over flight-time height: flight time is inflated by landing with bent knees. Track the athlete against their own rolling baseline, not the squad average. |
| Jump height (flight time) | Height from the time between take-off and landing. | Useful for comparing with jump-mat history. Otherwise treat as secondary. |
| Peak power (W and W/kg) | Highest instantaneous product of force and velocity during propulsion. | Relative (W/kg) for comparing athletes; absolute for tracking one athlete through a mass change. |
| RSI-modified | Jump height divided by time to take-off (from the start of the countermovement to leaving the plate). | The single best 'how efficiently did they jump' number. It drops when an athlete is fatigued even when height holds, because they take longer to produce the same jump. |
Then the strategy metrics — the ones that explain the output
Two athletes can reach the same jump height by completely different routes. Strategy metrics show the route, and it is the route that changes first under fatigue, after injury, or during a training block.
| Metric | What it is | What a change usually means |
|---|---|---|
| Countermovement depth | How far the centre of mass drops before the jump. | Deeper depth with the same height often signals the athlete compensating with more range to make up for less force. Shallower after a strength block is common. |
| Eccentric (braking) duration | Time spent decelerating the downward movement. | Lengthens with neuromuscular fatigue. One of the more sensitive fatigue markers in the literature. |
| Concentric (propulsive) duration | Time from the bottom of the countermovement to take-off. | Lengthens when force production is impaired. Read together with RSI-mod. |
| Braking and propulsive impulse | Force × time in each phase. | The propulsive impulse is what physically produces the jump. If height drops, check whether impulse dropped or contact time changed. |
| Peak braking and propulsive force | Highest force in each phase, often reported relative to body mass. | Strength-side markers. A drop in peak propulsive force with an unchanged jump height means the athlete is compensating through time. |
Asymmetry: the metric everyone reports and few read carefully
Dual plates give a left–right split of every force and impulse metric. ForceDecks expresses asymmetry as a percentage relative to the stronger limb, and it is tempting to apply a single cut-off to all of them. Three points keep this honest.
- Asymmetry is metric-specific. A 12% asymmetry in propulsive impulse and a 12% asymmetry in peak landing force are not the same finding. Decide which two or three asymmetry metrics matter for your context and ignore the rest.
- The commonly used 10–15% threshold comes from return-to-play work, mostly after ACL reconstruction, where limb symmetry index is the outcome of interest. In a healthy squad, asymmetries of that size are common and often stable. Treat a change from the athlete's own baseline as more informative than the absolute number.
- Check the direction. An asymmetry that flips side between sessions is usually noise or a technique effect. One that grows in the same direction across three sessions is worth a conversation.
Read the trend, not the session
A single CMJ session has typical error of a few percent on most metrics. That means a 3% drop in jump height on Monday is not a finding; it is within noise. The reading that matters is where today sits against the athlete's own history, and whether the change is bigger than the noise.
- Establish a baseline: the mean and standard deviation of each key metric over the athlete's last 6–10 sessions in a non-fatigued state.
- Express today as a z-score against that baseline. A z of −1 or worse on RSI-mod or eccentric duration is the usual point to look closer; −1.5 to −2 across two metrics is a flag.
- Use the smallest worthwhile change (commonly 0.2 × the between-athlete SD, or a metric-specific typical error × 1.5) to decide whether a change is real before you decide whether it matters.
What 'good' looks like
Norms exist for jump height, RSI-mod and relative peak power by sport, sex and level, and VALD publishes its own reference ranges inside VALD Hub. They are useful for one question: is this athlete unusually low or high for their population? They are not useful for the question you ask every week, which is whether this athlete has changed. Use norms once, at profiling; use the athlete's own baseline every session.
A checklist for reading one athlete's CMJ
- Jump height (impulse-momentum) and RSI-mod versus the athlete's baseline — as z-scores, not raw numbers.
- Eccentric and concentric duration — lengthening?
- Countermovement depth — changed strategy?
- Propulsive impulse asymmetry and peak braking force asymmetry — direction and trend across three sessions.
- Relative peak power — for the coach's report.
- One sentence that says what changed and what you recommend.
How Kinexis handles this
Kinexis reads every ForceDecks session against the athlete's own rolling baseline, calculates the z-scores and the smallest worthwhile change, and writes the sentence — 'RSI-mod −1.4 SD with eccentric duration lengthening over three sessions, jump height stable; recommend a loading review' — so the interpretation above happens for every athlete in the squad in minutes, alongside their NordBord, ForceFrame and speed data.