Performance Testing Protocol · SCI-PT-002
Countermovement Jump
Force-Time Testing & Interpretation
The gold-standard field measure of lower-body SSC-driven explosive power — what the four-component framework reveals, which metrics predict basketball performance, and how to use CMJ data in rehabilitation and seasonal monitoring.
Overview
The countermovement jump (CMJ) is a bilateral lower-body explosive assessment in which the athlete begins from standing, performs a rapid downward countermovement (loading phase), and immediately reverses direction to achieve maximal vertical displacement. It leverages the stretch-shortening cycle (SSC) — the neuromuscular mechanism by which eccentric loading potentiates concentric force production — making it the gold-standard field measure of lower-body SSC-driven explosive power.
On a force plate, the CMJ generates a force-time curve from which dozens of kinetic, kinematic, and temporal metrics can be extracted. García-Ramos et al. identified through principal component analysis (PCA) that 24 reliable CMJ variables reduce to four distinct components explaining 91.8% of overall CMJ variance.1 This four-component model — performance (59%), eccentric (16%), concentric (11%), and strategy (6%) — provides the theoretical framework for how CMJ data should be structured and reported.
Reliability
Jump height and force-based metrics from the eccentric and concentric phases demonstrate excellent reliability. RFD measures — concentric RFD in particular — are essentially not reliable and should not be used as primary monitoring metrics.
| Metric | CV (%) | ICC | Reliability |
|---|---|---|---|
| ECC Mean Force (N) | 0.06 | 0.99 | Excellent |
| CON Mean Force (N) | 2.15 | 0.99 | Excellent |
| CON Impulse (N·s) | 1.62 | 0.98 | Excellent |
| Jump Height (flight time) | 2.92 | 0.97 | Excellent |
| Peak Power (W) | 2.48 | 0.98 | Excellent |
| RSI-modified | 5.81 | 0.91 | Good |
| ECC Braking Impulse | 14.53 | 0.98 | ⚠ Caution (CV > 10%) |
| ECC Braking RFD | 10.86 | 0.87 | ⚠ Caution (CV > 10%) |
| CON RFD (N/s) | 76.45 | 0.57 | ✗ Not reliable |
| Lower Limb Stiffness | 10.21 | 0.35 | ✗ Not reliable |
CON RFD CV = 76.45% — essentially noise. Do not use as a primary monitoring metric. ECC = eccentric; CON = concentric.
Merrigan et al. (2024) compared CMJ metrics across ForceDecks (FD), Hawkin Dynamics (HD), and Sparta Science (SS) in 22 subjects.3 FD and HD agree for jump height and RSImod (CCC ≥ 0.80). Sparta Science systematically overestimates jump height and RSI vs both FD and HD. RFD values are not comparable across any system pairing. Never compare RFD data across different force plate systems or across sessions using different equipment.
Protocol & Setup
Arm condition is the single variable with the greatest impact on CMJ outcomes and must be pre-specified and consistently applied across all sessions. The hands-on-hips protocol is the research standard and most widely used condition in the basketball literature — it maximizes sensitivity to lower-body neuromuscular changes by removing upper-body energy contribution.
| Metric | No Arm Swing | Arm Swing | Direction |
|---|---|---|---|
| Eccentric peak force | Higher | Lower | Favors no arm swing |
| Eccentric braking & decel RFD | Higher | Lower | Favors no arm swing |
| Concentric impulse | Lower | Higher | Favors arm swing |
| Concentric peak power | Lower | Higher | Favors arm swing |
| Jump height | Lower | Higher (~5–7%) | Favors arm swing |
| Contraction time | Shorter | Longer | Arm swing increases duration |
Normative data must match the arm condition used. The Berberet et al. NCAA D-I normative dataset uses hands-on-hips — use this protocol when comparing to those norms.
| Phase | Activity | Intensity | Duration | Rest |
|---|---|---|---|---|
| General | Light jog, leg swings, bodyweight squats, hip hinges | Low | 5–10 min | — |
| Submaximal 1 | CMJ at ~50% perceived max | ~50% | 1 jump | 30 sec |
| Submaximal 2 | CMJ at ~75% perceived max | ~75% | 1 jump | 30 sec |
| Submaximal 3 | CMJ at ~90% perceived max | ~90% | 1 jump | 30–60 sec |
| Maximal trials | Full maximal CMJ | 100% | 3 trials min. | 15–30 sec between |
Minimum 3 maximal-effort trials. Use the best single trial (highest jump height) as the primary outcome — not the mean. Rest 15–30 seconds between trials for monitoring; 60 seconds for performance-maximizing contexts.
Reject and repeat if any of the following are observed:
- Forward or backward lean causing foot to shift position on the plate
- Hands detach from hips during the jump (hands-on-hips condition)
- Athlete does not fully land on the plates after the jump
- Visible squat-and-pause — the countermovement must be one continuous fluid motion
- Excessive lateral weight shift (dual-plate asymmetry > 60% to one side during quiet standing)
Cueing Strategy
The cueing strategy directly affects both jump height achieved and the movement strategy used. Height cues maximize jump height and concentric peak velocity — the standard for performance testing. Speed/fast cues reduce time-to-takeoff and maximize RSImod, relevant for reactive strength testing contexts.
- "Step onto the force plates with feet shoulder-width apart, toes slightly out."
- "Hands on hips — do not move your arms during the jump."
- "Stand tall and completely still until I tell you to go."
- Quiet period: 1–2 seconds — confirm stable force trace at bodyweight before cueing
- "Ready... JUMP as HIGH as you can!"
- "Stay on the plates after landing until the trial is saved."
For RSImod-specific profiling use speed cues: "Jump as FAST as you can — ground contact is lava." Lock cue language at the start of a monitoring window and reproduce verbatim across all sessions.
Force-Time Metrics & Four-Component Framework
The CMJ force-time curve is divided into five phases: unweighting, braking (eccentric), deceleration (eccentric), concentric (propulsive), and landing. PCA of 24 reliable CMJ variables identifies four components that together explain 91.8% of total CMJ variance.1 Monitoring only jump height captures only 59% of the available information.
| Priority | Metric | Component | Reliability | Why It Matters |
|---|---|---|---|---|
| 1st | Jump Height (flight time) | Performance | Excellent (ICC 0.97) | Most published normative data; highest reliability across all devices |
| 2nd | RSI-modified (JH ÷ TTT) | Performance | Good (ICC 0.91) | Captures jump height AND SSC efficiency; detects fatigue before JH changes |
| 3rd | Concentric Impulse / Peak Power | Performance / CON | Excellent (ICC 0.97–0.98) | Direct determinant of jump height; primary RTS kinetic criterion |
| 4th | ECC Mean Power / ECC Peak Force | Eccentric | Good (ICC 0.93–0.97) | Only CMJ metrics significantly correlated with basketball playing time and efficiency12 |
| 5th | Countermovement Depth / FT:CT ratio | Strategy | Good (CV ~7–8%) | Strategy changes before outcome changes — early fatigue sentinel |
| ⚠ Caution | CON RFD (all forms) | All | Poor (CV 76%, ICC 0.57) | Essentially noise — do not use as primary monitoring metric |
RSI-Modified
RSImod quantifies how efficiently an athlete converts available time into vertical displacement. It is derived from the CMJ (unlike traditional RSI which requires a drop jump) and is more sensitive to training-induced SSC adaptations than jump height alone.
RSImod = Jump Height (m) ÷ Time to Takeoff (seconds)
- Higher RSImod = more efficient SSC utilization — rapid eccentric loading followed by explosive concentric output
- RSImod decreases when JH is stable = increasing time-to-takeoff signals fatigue or compensatory strategy — early warning before outcome metrics change
- Height cues (standard testing) maximize JH; speed cues maximize RSImod — specify which before monitoring and do not change
- McMahon et al. demonstrated RSImod distinguishes levels of play in rugby league (large effect) — superior athletes achieve similar JH in significantly less time9,25
Basketball-Specific Applications
| Finding | Guards (n=55) | Forwards (n=37) | Significance |
|---|---|---|---|
| Body mass | 87.0 ± 7.0 kg | 103.7 ± 10.4 kg | Significant |
| Metrics with significant differences | 18 of 40 metrics (45%) | 14 with d > 0.50 | |
| Relative jump height | Higher (lighter athletes) | Lower | Favors guards |
| Absolute force metrics | Lower | Higher | Favors forwards |
| Normative tool | Percentile 3rd–97th (traffic light system) | Position-matched | |
Position-matched normative comparisons are required for meaningful benchmarking. Guards and forwards cannot be compared on absolute force metrics without accounting for body mass and position-specific demands.
| CMJ Metric | r value | Outcome | p-value |
|---|---|---|---|
| Eccentric mean power | r = 0.464 | Playing time | p = 0.022 |
| Eccentric mean power / BM | r = 0.406 | Playing time | p = 0.049 |
| Eccentric mean power | r = 0.522 | Playing efficiency | p = 0.009 |
| Eccentric peak power | r = 0.406 | Playing efficiency | p = 0.047 |
| Eccentric mean force | r = 0.410 | Playing efficiency | p = 0.046 |
| Jump height | — | Both outcomes | Not significant |
Jump height was NOT significantly correlated with playing time or efficiency at the professional level. Practitioners who monitor only jump height may be missing the metric most relevant to court performance prediction.
Cabarkapa et al. found that eccentric peak velocity, force, and power showed moderate decreases post-game (Cohen's g = 0.509–0.627) even without reaching statistical significance — the eccentric phase detects neuromuscular fatigue before changes are visible in jump height.14 Jump height and RSImod showed no pre/post-game difference. If practitioners collect only jump height pre/post-game, they will consistently fail to detect acute neuromuscular fatigue from competition.
Seasonal Monitoring
Cabarkapa et al. tracked CMJ changes across a full NCAA D-I men's basketball season (n = 12 players; 219 total screenings) across pre-season, non-conference, conference, and post-season periods.13
| Metric | Status | Key Finding |
|---|---|---|
| Jump height | Stable | No significant changes across four seasonal periods — not sensitive to within-season adaptation |
| RSI-modified | Stable | No significant changes — mirrors jump height in seasonal stability |
| Concentric peak force | Changed | Significantly larger during non-conference, conference, and post-season vs pre-season |
| ECC mean deceleration force | Changed | Significantly larger in non-conference, conference, and post-season vs pre-season |
| Countermovement depth | Changed | Shallower during non-conference vs pre-season — strategy adaptation without outcome change |
| Braking and concentric duration | Changed | Shorter in non-conference vs pre-season — more efficient SSC utilization |
| CON/ECC impulse | Stable | No significant changes — energy transfer stable even as force and strategy shift |
Jump height stability across a season should be interpreted as a positive sign — not as the test failing to detect change. Monitoring only jump height will fail to detect meaningful neuromuscular adaptations occurring in force production and movement strategy.
Implement weekly or biweekly CMJ monitoring during the competitive season. Establish individual baseline values during preseason — use these as the reference for within-athlete change assessment, not population norms. When strategy metrics change (deeper countermovement, longer braking duration) without corresponding outcome changes, investigate training load, sleep, and recovery status before altering programming.
Rehabilitation & Return-to-Sport
Kotsifaki et al. evaluated jumping performance in 126 ACLR athletes versus 532 healthy controls at the time of return to sport.19 Despite having passed physician-approved traditional discharge criteria, ACLR athletes still showed significant asymmetries — concentric impulse symmetry was the most consistently impaired metric across all jump tests.
| Metric | ACLR LSI (%) | Control LSI (%) | p-value | Effect Size |
|---|---|---|---|---|
| vGRF LSI | 85.9 ± 9.6 | 94.9 ± 5.3 | < 0.001 | d = −0.64 — Significantly impaired |
| Max Power LSI | 84.9 ± 8.4 | 95.6 ± 4.2 | < 0.001 | d = −0.78 — Significantly impaired |
| Deceleration RFD LSI | 68.0 ± 23.1 | 76.7 ± 17.2 | 0.081 | d = −0.19 — Largest absolute deficit |
Stojanovic et al. (2026) demonstrated that deceleration LSI was significantly lower than knee extensor strength LSI (p = 0.001; d = 2.09) in 44 professional athletes post-ACLR — standard isokinetic strength testing substantially overestimates readiness when deceleration capacity is assessed separately.21
- Concentric impulse asymmetry — consistently the most impaired metric across all CMJ test variants (bilateral and unilateral)
- Peak landing force asymmetry — significantly greater in ACLR vs controls; reflects load absorption deficit; use bilateral force plate system
- Eccentric deceleration metrics — most sensitive to between-limb differences; more discriminating than strength tests alone
- Single-leg CMJ jump height — more sensitive than horizontal hop distance for detecting residual impairment at RTS22
The traditional ≥ 90% LSI threshold is the most commonly applied RTS criterion — but at RTS clearance, ACLR athletes with ≥ 90% quadriceps strength LSI still demonstrate vertical jump LSIs of 77–83%.19 Deceleration LSI of 68% was observed in athletes who had passed conventional RTS criteria.20 No current LSI threshold has been validated as predictive of re-injury risk. Use CMJ LSI as one component of a multi-criterion RTS decision framework — not as a standalone clearance measure.
- Bilateral CMJ provides global neuromuscular monitoring — appropriate for weekly tracking throughout rehabilitation
- Unilateral CMJ is required for limb-specific asymmetry quantification — bilateral will mask deficits where the non-injured limb compensates
- Conduct both bilateral and single-leg CMJ at key rehabilitation milestones and at formal RTS assessment
- Kinetic metric asymmetries (concentric impulse, landing force) detected in bilateral CMJ are not captured by standard clinical criteria — bilateral force plate testing is required, not just flight-time-based height measurement
Device Validity
| Device | Jump Height | RSImod | Phase Metrics | Notes |
|---|---|---|---|---|
| Dual force plate (ForceDecks, Hawkin Dynamics) | Gold standard | Gold standard | Full metrics | FD and HD agree for JH and RSImod; cross-system RFD not comparable3 |
| Optojump / Output Capture | Valid (ICC ≥ 0.80) | Valid with correction | Not available | No phase-level data26 |
| My Jump Lab (smartphone) | Excellent (r = 0.98) | Valid with correction | Not available | Time to takeoff correction required for RSImod27 |
| IMU (Output V2) | Valid (r ≥ 0.983) | Valid | Not available | Good-to-excellent test-retest (CV ≤ 2.3%); cost-effective field option |
| Contact mat (SmartJump) | Acceptable | Not available | Not available | Valid for JH only; no force-time data |
Only force plate systems provide the full four-component metric profile. For phase metrics critical to rehabilitation (eccentric impulse, landing force, concentric impulse asymmetry), force plates are non-negotiable.
Key Takeaways
- Monitor all four components, not just jump height. Jump height captures only 59% of CMJ variance. Eccentric, concentric, and strategy metrics change across a season and with fatigue even when jump height remains stable.1,13
- Eccentric mean power predicts basketball playing time and efficiency. Jump height does not. Practitioners monitoring only jump height are missing the most sport-relevant CMJ metric at the professional level.12
- RSImod detects fatigue before jump height changes. A decrease in RSImod with stable jump height signals increased time-to-takeoff — early fatigue or compensatory strategy before outcome metrics are affected.9
- Arm condition must be pre-specified and fixed. Hands-on-hips is the research standard for basketball. Never change arm condition across sessions or compare data collected under different conditions.6
- CON RFD is essentially not reliable (CV 76%). Do not use as a primary monitoring metric. RFD values are also not comparable across different force plate systems.2,3
- ACLR athletes who pass conventional RTS criteria still have significant CMJ deficits. Vertical jump LSI of 77–83% and deceleration LSI of 68% observed in athletes who cleared standard strength criteria. CMJ force plates, not just flight time, are required for RTS assessment.19,20,21
- Concentric impulse and landing force asymmetry are the primary kinetic RTS criteria. Not jump height LSI alone. Include single-leg CMJ for limb-specific deficit quantification at formal RTS milestones.19
The CMJ is the most information-dense single test available in applied sport science. Used well — with a force plate, standardized arm condition, and metrics drawn from all four components of the four-component framework — it provides a real-time window into explosive power output, SSC efficiency, loading strategy, fatigue state, and limb symmetry from a single 30-second effort.
Its most common misuse is reduction to jump height alone. Jump height does not predict basketball playing time or efficiency, does not change meaningfully across a season, and does not detect acute game-induced fatigue. The eccentric phase — particularly eccentric mean power — is where the basketball-relevant signal lives. The concentric phase is where the RTS-relevant signal lives. Jump height is the entry metric; it should never be the only metric.
- García-Ramos A, Cabarkapa D, Janicijevic D, et al. Assessment of countermovement jump: what should we report? Life. 2023;13(1):190.
- Merrigan JJ, Stone JD, Hornsby WG, Hagen JA. Identifying reliable and relatable force-time metrics in athletes: considerations for the IMTP and CMJ. Sports. 2021;9(1):4.
- Merrigan JJ, Strang AJ, Eckerle J, et al. Countermovement jump force-time curve analyses: reliability and comparability across force plate systems. J Strength Cond Res. 2024;38(1):30-37.
- Lonergan B, Cohen DD, Williams S, et al. Inter-day reliability of CMJ metrics in elite academy soccer players. Int J Strength Cond. 2025;5(1).
- Bianco A, Palma A, Paoli A, et al. A review of countermovement and squat jump testing methods in adolescence. Front Physiol. 2019;10:1384.
- Cabarkapa D, Philipp NM, Cabarkapa DV, Eserhaut DA, Fry AC. Comparison of CMJ force-time metrics with and without arm swing in professional basketball. Int J Strength Cond. 2023;3(1).
- Heishman AD, Brown BS, Daub BD, et al. CMJ inter-limb asymmetries in collegiate basketball players. Sports. 2019;7(5):103.
- Heishman AD, Brown BS, Daub BD, et al. Influence of CMJ protocol on RSImod and FT:CT in collegiate basketball players. Sports. 2019;7(2):37.
- McMahon JJ, Jones PA, Suchomel TJ, Lake J, Comfort P. Influence of RSImod on force- and power-time curves. Int J Sports Physiol Perform. 2018;13(4):501-510.
- McMahon JJ, Rej SJE, Comfort P. Sex differences in CMJ phase characteristics. Sports. 2017;5(1):8.
- Berberet D, Petway A, Bell K, et al. Force plate-derived CMJ normative reference values from seven NCAA D-I Power Five men's basketball teams. Int J Strength Cond. 2024;4(1).
- Cabarkapa D, Cabarkapa DV, Aleksic J, Scott A, Fry AC. Relationship between vertical jump performance and playing time and efficiency in professional male basketball. Front Sports Act Living. 2024;6:1399399.
- Cabarkapa D, Philipp NM, Nijem RM, Fry AC. Changes in CMJ force-time characteristics across a basketball season. PLoS ONE. 2023;18(9):e0286581.
- Cabarkapa D, Cabarkapa DV, Aleksic J, Mihajlovic F, Fry AC. Impact of Basketball Champions League game on lower-body neuromuscular performance. J Strength Cond Res. 2024;38(10):e595-e599.
- Cabarkapa D, Cabarkapa DV, Aleksic J, Philipp NM, Fry AC. CMJ differences between starting and non-starting professional male basketball players. Front Sports Act Living. 2023;5:1327379.
- Cabarkapa D, Cabarkapa DV, Philipp NM, Fry AC. Position-specific CMJ differences in professional male basketball players. Front Sports Act Living. 2023;5:1218234.
- Alvarez-Yates T, Serrano-Gomez V, de Pedro-Munez A, Garcia-Garcia O. Intraseason changes in vertical jumps of male professional basketball players. Int J Environ Res Public Health. 2023;20(6):5030.
- Berberet D, Petway A, Bell K, et al. CMJ Rebound normative reference values from seven NCAA D-I Power Five men's basketball teams. Int J Strength Cond. 2025;5(1).
- Kotsifaki R, Sideris V, King E, Bahr R, Whiteley R. Performance and symmetry measures during vertical jump testing at RTS after ACLR. Br J Sports Med. 2023;57(13):817-824.
- Forelli F, Moiroux-Sahraoui A, Nekhouf B, et al. Is deceleration the key element in vertical jump performance to RTS after ACLR with hamstring graft? Int J Sports Phys Ther. 2025;20(9).
- Stojanovic MDM, Andric N, Jezdimirovic Stojanovic T, Versic S, Calleja Gonzalez J. Limb strength and power asymmetries in professional athletes at RTS following ACLR. Medicina. 2026;62(4):654.
- Kotsifaki A, Jonkers I, Bahr R, et al. Single leg vertical jump identifies knee function deficits at RTS after ACLR. Br J Sports Med. 2022;56(17):994-1001.
- Nishiumi D, Saito H, Hirose N, et al. Associations of eccentric force variables during jumping with vertical jump performance: a systematic review. PLoS ONE. 2023;18(8):e0289631.
- Kaya E, Kucuk H, Ceylan L, et al. Associations between single-leg CMJ force-time metrics, agility, and sprint in youth male basketball players. Children. 2023;10(3):427.
- McMahon JJ, Jones PA, Comfort P. Comparison of CMJ-derived RSImod between super league and championship rugby league players. J Strength Cond Res. 2022;36(1):226-231.