Force-Velocity Imbalance Explained: Diagnose Weakness with an 800Hz IMU

Two athletes can post the exact same vertical jump height through completely different internal structures — one pushing slowly with massive force (force-dominant), the other firing rapidly with light loads (velocity-dominant). Samozino et al. (2014) formalized this with the F-V profile and introduced the Force-Velocity Imbalance (FVi) as the percentage deviation from each individual’s optimal profile. Follow-up RCTs (Jiménez-Reyes et al., 2017) showed that FVi-matched prescriptions yielded +9% greater jump improvement than generic ones over 12 weeks. To jump higher, then, the answer is not “more jumping” but “the right training for your weakness.” An 800Hz IMU now produces a full F-V profile from a 5-load jump series in 5–10 minutes — what used to require a force plate lab. This guide covers (1) the core of Samozino’s theory, (2) the 800Hz IMU measurement protocol, (3) FVi interpretation and four profile classifications, and (4) a profile-specific 12-week prescription matrix. Combine it with our CMJ protocol for sharper diagnostics.

Add external load to a jump and average force rises while average velocity falls. Plot the loaded jumps and the relationship is essentially linear — that line is the Force-Velocity Profile. Three parameters define it: F₀ (theoretical maximum force at zero velocity), V₀ (theoretical maximum velocity at zero force), and P_max = F₀ × V₀ / 4.

Samozino et al. (2014) proved mathematically that jump height depends on both P_max and the balance between F₀ and V₀. Two athletes with identical P_max can differ in jump height by 7–12% if their balance is different. FVi is computed as (actual slope − optimal slope) / optimal slope × 100; absolute values above 10% are classified as imbalance. Negative values indicate force-deficient athletes, positive values indicate velocity-deficient athletes.

Classical F-V profiling required a force plate and 6–8 loaded jumps over an hour. The 800Hz IMU compresses that to 5–10 minutes. The validated PoinT GO protocol is below.

Step 1 — Placement. One IMU at S2. Jump height comes from flight time and 800Hz resolves take-off and landing to within 1.25 ms.

Step 2 — Jump series. CMJ at five loads — 0, 20%, 40%, 60%, and 80% bodyweight — two reps each, with two minutes between sets. Heavy loads use a barbell or weighted vest.

Step 3 — Automatic calculation. The PoinT GO app fits the load–jump-height regression, derives F₀, V₀, and P_max, compares to the individual’s optimal profile, and outputs FVi. The test–retest ICC is 0.91, statistically equivalent to force plates at 0.94 (García-Ramos et al., 2018).

Two cautions: (1) loads must increase linearly across the series, and (2) every jump must be performed with maximal intent — a relaxed jump underestimates V₀. Pairing FVi with the reactive strength index adds a SSC dimension to the diagnosis.

FVi outputs sort athletes into four buckets.

Typical distribution (Jiménez-Reyes et al., 2017, n=84): 32% balanced, 41% force-deficient, 27% velocity-deficient. More than half are imbalanced and most of those need more strength — a useful corrective to the typical jump-and-plyometric-heavy training culture.

The bigger the FVi, the bigger the jump-improvement potential. Severely force-deficient athletes on a strength-led 12-week plan often gain 12–18% in jump height, far ahead of the 3–5% balanced athletes typically see. Weakness, properly diagnosed, becomes the fastest path forward.

Each profile gets its own 12-week matrix.

Force-deficient (severe). 70% of training volume on 80–90% 1RM squats and deadlifts; 30% on jumps and plyometrics. Four sessions per week. Re-test every four weeks; once FVi recovers above −15% transition to the balanced template.

Force-deficient (mild). 60% strength, 40% velocity. 75–85% 1RM lifts plus CMJs and box jumps. Three to four sessions per week.

Velocity-deficient (mild). 40% strength, 60% velocity. 30–50% 1RM jump squats, depth jumps, ballistic push variations. Three sessions per week.

Velocity-deficient (severe). 80% velocity-led. 20–40% 1RM ballistic work, medicine ball slams, and jump series. Four sessions per week. Strength volume drops to maintenance.

Balanced. Push P_max overall — 50/50 strength and velocity, anchored by the load–velocity profile. See our autoregulated training guide.

The Jiménez-Reyes et al. (2017) RCT found that FVi-matched prescription beat generic prescription by +9.0% in jump height and +5.4% in sprint over 12 weeks. The principle is simple — train your weakness — and the 800Hz IMU finally makes that diagnosis available to every coach and athlete. You cannot prescribe what you cannot measure, and you cannot progress what you cannot prescribe.