CMJ Force–Time Metrics: A Sensitive Lens for Neuromuscular Fatigue Monitoring

CMJ Force–Time Metrics: A Sensitive Lens for Neuromuscular Fatigue. Why Jump Height is No Longer Enough.

Using Jump Height in the CMJ Test to assess fatigue in football players can be deceiving. The latest research, led by Marques et al. (2026), highlights how professional athletes are capable of maintaining consistent performance in terms of centimeters even when fatigued, by simply altering their movement strategy. To identify the true state of recovery, we must shift our focus to movement quality and analyze what happens across the entire Force-Time curve.

Note: If you want to download our CMJ Test Analysis Dashboard, scroll to the bottom of the post for the download link.

Why looking only at Jump Height can lead to errors ?

When an athlete is fresh, they execute the Countermovement Jump (CMJ) quickly and efficiently: they drop rapidly into the eccentric phase and rise just as fast, maximizing the Stretch-Shortening Cycle (SSC).

However, when neuromuscular fatigue sets in, the athlete can no longer produce the same amount of force in such a short window. To compensate for this loss of reactivity and still reach the same flight height, the athlete extends the duration of the movement:

• Increased Braking Phase Time: They take longer to decelerate or "brake" during the countermovement.

• Increased Total Contraction Time: The overall time to take-off becomes dilated.

In practice, the athlete applies less force but over a longer period. From a physics standpoint, the total impulse (force x time) remains similar, resulting in an almost unchanged jump height. Yet, the neuromuscular cost and the coordinative strategy are profoundly different.

In the study conducted on professional football players, 48 hours after a match, jump height showed no noteworthy variations (with negligible changes ranging between -0.12 and +0.11 standard deviations), even in players who had played more than 70 minutes. Conversely, metrics based on the force-time curve recorded significant drops.

Which parameters are truly effective for assessing player recovery?

According to research, if you want to know if an athlete has truly recovered, you must stop looking at height alone and start monitoring Force-Time metrics. Here are the most reliable ones:

1. RSImod (Modified Reactive Strength Index)

This is the ratio between jump height and time to take-off. It is the most sensitive indicator: if the athlete jumps as high as they did yesterday but takes longer to do so, their RSImod drops. The study found sharp declines in this metric 48 hours post-match.

For a good recovery, this ratio must indicate efficiency:

• High Height + Low Time: A sign of freshness. The athlete "explodes" rapidly.

• Low Height + High Time: A sign of acute fatigue (typical 24h post-match).

• High Height + High Time: A sign of chronic fatigue or compensation (the athlete jumps as high as before but has become "slow"). This does not represent a full recovery.

2. Contraction Time (Time to Take-off)

Fatigue makes the athlete "slow" at expressing force. An increase in the total time spent jumping is an unmistakable red flag for residual neuromuscular fatigue.

3. Braking Phase Time

The eccentric phase is the first to suffer. If the time required to decelerate during the countermovement increases, the athlete is not yet ready for high-intensity loads.

4. Concentric Impulse (0-100 ms)

The ability to generate explosive force in the very first moments of the push. This metric reflects changes in physical form throughout the various quarters of the season better than any other.

Comparative Analysis: CMJ Test 48h Post-Match (vs. Athlete Baseline)

In this table, the percentage represents the deviation from the athlete's historical baseline (0% = standard performance).

• The "False Positive" (Athlete 5): Notice how his jump height is actually slightly above average (+1%), yet his contraction time has skyrocketed by +35%. Without Force–Time metrics, this athlete would be considered "at his peak," while in reality, he is the one at the highest risk.

• The Critical Threshold: The study by Marques et al. (2026) suggests that negative deviations in RSImod greater than 10–15% indicate neuromuscular fatigue that requires attention, even when the jump height remains unchanged.

• The Sensitivity of the Eccentric Phase: Look at Athlete 2. While his height drops by only 1%, the duration of his braking phase increases by 40%. This is exactly where the hidden fatigue that leads to injuries resides.

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Do you want to discover how to correctly evaluate your team's performance and create individual profiles using CMJ Test data? Check out the link below to download the Power BI Dashboard and start analyzing your data like a pro.

CMJ Test Analysis with VALD Force Plate: Power BI Dashboard Insights

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📚 Bibliography

The following scientific study was consulted for the creation of this post:

• Marques, J. B., Sideris, V., Rabelo, F., Maria, T. S., Marques, L., & Buchheit, M. (2026). Beyond Jump Height: CMJ Force–Time Metrics Reveal Hidden Neuromuscular Responses in Elite Football. Science Performance and Science Reports, 293, v1.