Flight time
Time from take-off to landing.
Tests: all. Recorded on every jump and included in exports.
Metrics by test
| Metric | CMJ | SL CMJ | Loaded | Squat | Drop | SL Drop | Hop | SL Hop |
|---|---|---|---|---|---|---|---|---|
| JH (FT) | ● | ● | ● | ● | ● | ● | ● | ● |
| JH (TOV) | ● | ● | ● | – | – | – | – | – |
| Contact time | – | – | – | – | ● | ● | ● | ● |
| Contraction time | ● | ● | ● | – | – | – | – | – |
| CM depth | ● | – | ● | – | – | – | – | – |
| Mean propulsive force | ● | ● | – | – | – | – | – | – |
| Mean landing force | ● | ● | – | – | – | – | – | – |
| RSI (FT/CT) | – | – | – | – | ● | ● | ● | ● |
| RSI (JH/CT) | – | – | – | – | ● | ● | ● | ● |
| RSI-mod | ● | ● | ● | – | – | – | – | – |
| DRI | – | – | – | – | box height | box height | ● | ● |
| EUR | with SJ | – | – | with CMJ | – | – | – | – |
| Fatigue index | 5+ reps | 5+ reps | 2+ reps | 5+ reps | 5+ reps | 5+ reps | 5+ reps | 5+ reps |
| Asymmetry | – | ● | – | – | – | ● | – | ● |
| Load–velocity profile | 0 kg point | – | ● | – | – | – | – | – |
SL = single-leg. Flight time is recorded on every test. Tests marked beta in the app use the same definitions; their accuracy is still being checked against force plates.
Key events
Every timing metric is measured between two of these events.
- Start of movement
- Countermovement jumps only. The last point at which the athlete is standing at body weight before the countermovement begins. This is the start-of-movement definition force-plate software uses for contraction time.
- Take-off
- The first instant the athlete is off the ground.
- Landing
- The first instant of ground contact after a flight (touchdown).
- Initial ground contact
- Drop jumps only. The first contact with the ground after stepping off the box.
- Lowest point
- The bottom of the countermovement, or of the landing, where the centre of mass stops moving down.
Timing metrics
Measured from the timing of the key events. We use the same event definitions as force-plate systems, so the values can be compared with force-plate results. Times are shown in milliseconds; in the formulas, time is in seconds, length in metres and g = 9.81 m/s².
Jump height (flight time)
Jump height calculated from flight time, assuming the athlete lands in the same body position they took off in.
JH = g · t² / 8
t = flight time
Tests: all.
Hops and drop jumps are landed close to the take-off position, so on those tests this value is very close to jump height from take-off velocity. In a countermovement jump most athletes land with more knee bend than they took off with. That lengthens the flight, and flight-time jump height comes out a few centimetres higher.
Contact time
In a drop jump, the time from initial ground contact to take-off. In a hop test, the ground contact before each hop, from the previous landing to that hop’s take-off. The first hop of a bout has no contact time.
Tests: drop jump and hop test, two-leg and single-leg.
Contraction time
Time from the start of movement to take-off, also known as time to take-off.
Tests: countermovement jump, single-leg countermovement jump, loaded jump.
A shorter time is not automatically better; it usually reflects a quicker or shallower countermovement. For that reason Metra shows the average and does not mark a best rep.
Impulse–momentum metrics
On a force plate these are calculated by integrating force over time, so the result depends on the body weight used and on where the integration starts. Software packages handle both differently, so each one is defined as the value the criterion method of Owen et al. (2014) gives on a force plate (see Reference method). Forces are expressed as multiples of body weight (×BW), so body mass isn’t needed.
Jump height (take-off velocity)
The height the centre of mass rises after take-off, calculated from its vertical velocity at take-off. Force plates report this as impulse–momentum jump height. Metra measures take-off velocity from the video and applies the same equation.
JH = v² / (2g)
v = vertical velocity of the centre of mass at take-off
Tests: countermovement jump, single-leg countermovement jump, loaded jump.
Both jump heights are saved for these tests, and Settings controls which one is shown first. Jump height from take-off velocity is not affected by landing posture; flight-time jump height is.
Countermovement depth
How far the centre of mass moves down during the countermovement, from quiet standing to the lowest point, where it changes direction. On a force plate this is the displacement at the lowest point, from integrating twice.
Tests: countermovement jump, loaded jump.
Depth describes how the athlete jumped, so no best value is shown. It is the metric most affected by movement before the dip, because that movement changes the standing position depth is measured from. It isn’t reported for single-leg jumps yet.
Mean propulsive force
The average vertical ground reaction force from the lowest point of the countermovement to take-off (the propulsion phase), as a multiple of body weight. A value of 1.0 equals body weight. Higher values mean the athlete pushed harder into the ground on the way up.
Tests: countermovement jump, single-leg countermovement jump.
Reference: propulsion phase as defined by McMahon et al. (2018). The same metric appears as Average Propulsive Force in Hawkin Dynamics and as Concentric Mean Force in VALD ForceDecks, which reports it in newtons and per kilogram of body mass. Bishop et al. (2026) include it in their recommended metrics for monitoring ACL rehabilitation.
Mean landing force
The average vertical ground reaction force from touchdown until the centre of mass first stops moving down (the landing phase), as a multiple of body weight. During this phase the athlete has to stop all of the downward speed they land with. A softer landing spreads that over a longer time and gives a lower average force.
Tests: countermovement jump, single-leg countermovement jump.
Athletes land faster from higher jumps, so compare landings from jumps of similar height. A higher value means a stiffer, shorter landing. Whether that is good depends on the athlete and the situation, so no best value is shown.
Reference: landing phase as defined by McMahon et al. (2018). Hawkin Dynamics’ Average Landing Force uses the same phase. Bishop et al. (2026) include mean landing force in their recommended metrics for monitoring ACL rehabilitation.
Why we average over the landing phase
Some systems report a mean landing force averaged over a fixed period after touchdown. With a fixed period, the average depends mainly on how fast the athlete was moving at touchdown, which is set by how high they jumped, and it changes very little between a stiff landing and a soft one. Averaging over the landing phase itself reflects how the landing was absorbed. The two metrics have the same name but measure different things, so their values shouldn’t be compared.
Ratios and indexes
Calculated for each rep from the timing metrics, so their accuracy follows from the metrics they are built from. In the formulas, time is in seconds, length in metres and g = 9.81 m/s².
Reactive strength index (FT/CT)
Flight time divided by contact time. A higher value means more time in the air for the time spent on the ground.
RSI = flight time / contact time
Tests: drop jump and hop test, two-leg and single-leg.
Reference: RSI is calculated either as flight time ÷ contact time or as jump height ÷ contact time (Jarvis et al., 2022). Metra shows both, with this one first.
Reactive strength index (JH/CT)
Jump height divided by contact time. A higher value means a higher jump for the time spent on the ground.
RSI (JH/CT) = JH (FT) / contact time
Metra uses flight-time jump height, in metres. Because jump height grows with the square of flight time, a timing difference counts about twice as much here as in RSI (FT/CT).
Tests: drop jump and hop test, two-leg and single-leg.
Reactive strength index modified
Jump height divided by contraction time.
RSI-mod = JH (FT) / contraction time
Metra uses flight-time jump height, in metres. Because contraction time is the denominator, RSI-mod depends on how the start of movement is defined (McMahon et al., 2018).
Tests: countermovement jump, single-leg countermovement jump, loaded jump.
Dynamic rebound index
Combines the height fallen and the height jumped with the contact time. A big rebound from a short contact gives a high DRI.
DRI = (drop height + jump height) / (g · CT²)
In a drop jump, drop height is the box height entered in setup and jump height is flight-time jump height. In a hop test, drop height is the previous hop’s jump height, so the first hop of each bout has no DRI.
Tests: drop jump (when a box height is entered) and hop test, two-leg and single-leg.
Comparisons
Calculated across reps, legs, tests or loads.
Eccentric utilisation ratio
Compares jump height with and without a countermovement. A value above 1.0 means the athlete jumps higher with a countermovement than from a static squat.
EUR = CMJ jump height / squat jump jump height
Both are flight-time jump heights recorded on the same day. Only countermovement jumps done with hands on hips are used, since an arm swing adds height that a squat jump can’t match. The day’s best EUR is the best CMJ divided by the best squat jump; the average EUR divides the averages.
Tests: a countermovement jump and a squat jump on the same day.
Fatigue index
The percentage drop in jump height from the best rep in a set to the last rep. This follows the velocity-loss approach used in resistance training. It is measured from the best rep instead of the first, because the first rep is often not the best.
Fatigue index = (best − last) / best × 100
Only shown when the last rep is lower than the best. Calculated on jump height only; on tests with both jump heights, each gets its own value.
Tests: all, for sets of five reps or more (loaded jumps from two reps).
Asymmetry
The difference between the left and right legs as a percentage of the larger value. Metra also shows which leg is ahead.
Asymmetry = |left − right| / larger value × 100
For contraction time and mean landing force, where a higher value isn’t better, Metra names the leg with the higher value instead.
Tests: single-leg tests, comparing left and right.
Load–velocity profile
Take-off velocity plotted against external load for one day, with a straight line fitted through the points by least squares. Each load contributes either its best rep or its average. The profile reports two numbers from the line: take-off velocity at 0 kg, and the load at which take-off velocity would reach zero.
v = a + b · load
v = take-off velocity, the same velocity jump height (take-off velocity) is calculated from. Only reps that have one are used.
Tests: loaded jump. A hands-on-hips countermovement jump from the same day counts as the 0 kg point. The line needs three or more different loads, and 0 kg counts as one.
Both reported numbers are extrapolations, and the load at zero velocity is a long one, so Metra labels it as projected. It isn’t reported if it falls beyond ten times the heaviest load measured. The chart shows the measured range as a solid line and the projection as a dotted one. Only hands-on-hips countermovement jumps count at 0 kg, because loaded jumps are done without an arm swing.
Reference method for impulse–momentum metrics
A force plate measures force, not motion. To get velocity, the software subtracts body weight, divides by body mass and integrates over time. Integrating a second time gives displacement. Two inputs affect every result: the body weight, and the point where velocity is set to zero and integration begins. An error in either one carries through the whole jump.
The starting point is the more common problem. If integration begins after the athlete has already moved, for example after rising onto the toes or lifting the arms before the dip, take-off velocity, jump height and especially countermovement depth will be wrong. A systematic review of force-plate jump height equations notes that differences in method may explain large differences between published results (Eythorsdottir et al., 2024).
The Owen et al. (2014) criterion
Metra’s impulse–momentum metrics are defined as the values this method gives on a force plate:
- Body weight is the mean force over one second of quiet standing immediately before the jump. It is measured separately for each jump, on the platform or platforms the athlete is standing on.
- Movement onset is the first point where force moves more than five standard deviations (of that one-second window) away from body weight, in either direction.
- Integration starts 30 ms before the onset, with velocity and displacement set to zero.
Why we use it
It is a published and fully described method. McMahon et al. (2018) refer to it as the most recent criterion method for the countermovement jump. Adlou et al. (2026), who analysed 32,952 countermovement jumps, describe its five-standard-deviation rule as the canonical one.
It copes with athletes who rise before they dip. Owen et al. looked for movement in both directions because roughly half of jumpers raise their centre of mass first. Since integration starts from quiet standing, before any movement, the rise is included in the calculation. Methods that search backwards from the dip for the last moment near body weight can start after the rise, when the body is already moving. In our own force-plate recordings of jumps with a rise, that approach under-read jump height by about 5 cm and over-read depth by about 15 cm on average. The Owen criterion did not.
Body weight is measured for every jump. It comes from the second of standing before each jump, on the platform carrying the athlete, so it doesn’t rely on a single weigh-in or on two platforms reading identically. This matters most for single-leg jumps.
When the athlete starts still, it agrees with the other common methods. The results only differ when the athlete moved before the dip, and that is where those methods have problems.
Testing protocol
These metrics are only well defined if the athlete starts still, and that is as true on a force plate as it is in Metra. For results that compare with a force plate:
- Stand still for 2–3 seconds before and after each jump.
- Keep hands on hips. This makes it less likely the athlete rises before the dip.
Processing details. When a force-plate trial contains several jumps, the one-second weighing window is the steadiest second (lowest standard deviation) in the four seconds before each jump, using the sliding minimum-standard-deviation window of Adlou et al. (2026). If the standard deviation of force in that second is above 10 N, the jump has no criterion value and is left out of comparisons. Force is integrated unfiltered, with the zero offset corrected from the flight phase. Take-off is the first sample below 20 N. Timing metrics keep the standard start-of-movement definition; the Owen onset is used only for impulse–momentum metrics.
Metrics we don’t report
The following are left out because we can’t yet measure them reliably from video.
- Peak landing force, loading rate and landing stiffness
- All three depend on the impact peak in the first few tens of milliseconds after touchdown. The peak is too brief to measure reliably from video, and it varies a lot between landings even on a force plate.
- Mean braking force
- Not yet reliable enough from video.
- Countermovement depth in single-leg jumps
- Not yet reliable enough from video. Depth is reported for two-leg jumps.
References
- Adlou B, Goodlett MD, Wilburn C, Weimar W (2026). A multivariable decision rule for weight-rocking-driven onset detection method bias on bilateral force plates across 32,952 countermovement jump trials. Sensors 26(16):5043. doi:10.3390/s26165043
- Bishop C, Maestroni L, Bettariga F, Jordan M, Read P, Turner A (2026). Beyond jump height: monitoring countermovement jump metrics across the anterior cruciate ligament rehabilitation journey. Physiotherapy Theory and Practice. doi:10.1080/09593985.2026.2738832
- Eythorsdottir I, Gløersen Ø, Rice H, Werkhausen A, Ettema G, Mentzoni F, Solberg P, Lindberg K, Paulsen G (2024). The battle of the equations: a systematic review of jump height calculations using force platforms. Sports Medicine 54:2771–2791. doi:10.1007/s40279-024-02098-x
- Hawkin Dynamics. Metric Database: Average Landing Force, Average Propulsive Force, Landing Phase. hawkindynamics.com/hawkin-metric-database, accessed 26 September 2026.
- Jarvis P, Turner A, Read P, Bishop C (2022). Reactive strength index and its associations with measures of physical and sports performance: a systematic review with meta-analysis. Sports Medicine 52:301–330. doi:10.1007/s40279-021-01566-y
- McMahon JJ, Suchomel TJ, Lake JP, Comfort P (2018). Understanding the key phases of the countermovement jump force-time curve. Strength and Conditioning Journal 40(4):96–106. doi:10.1519/SSC.0000000000000375
- Owen NJ, Watkins J, Kilduff LP, Bevan HR, Bennett MA (2014). Development of a criterion method to determine peak mechanical power output in a countermovement jump. Journal of Strength and Conditioning Research 28(6):1552–1558. doi:10.1519/JSC.0000000000000311
- VALD Performance (2024). ForceDecks Technical Glossary, version 2.0.
Hawkin Dynamics and VALD ForceDecks are named only to identify equivalent metric definitions. Metra is not affiliated with either.