How to Test Explosive Strength with IMU: 5 Validated Protocols

McGuigan (2004) defined explosive strength as the total force expressed per unit time, and reported that 0-100ms RFD (Rate of Force Development) is one of the strongest predictors of sport performance. Direct RFD measurement traditionally required a force plate, but an 800Hz IMU now resolves acceleration at 0.00125 second intervals and correlates with force-plate output at r=0.94. This guide walks through five field-validated explosive strength protocols developed by the PoinT GO Sports Science Lab. The five axes (CMJ flight time, squat jump RFD, medicine ball slam power, barbell acceleration, rotational power) jointly profile an athlete's explosive capacity, and the entire battery completes in under 30 minutes. Pair this protocol with our athlete testing battery guide to systematize pre- and post-season comparisons.

Explosive strength is not raw maximal force; it is the rate at which force is produced. Academically it decomposes into RFD (slope of the force-time curve) and impulse (area under the curve). Behm et al. (2016) distinguish neural RFD over 0-50ms from contractile RFD over 100-200ms.

An IMU measures acceleration directly. Multiplying by mass yields force, and differentiating versus time yields RFD. At 800Hz the inter-sample interval is 1.25ms, so the 0-50ms window contains roughly 40 samples, well above the 30-sample minimum recommended for reliable RFD estimation.

Combining the five axes into an Explosive Force Index (EFI) provides a powerful longitudinal tracking variable.

The countermovement jump (CMJ) is the most common explosive strength benchmark. Procedure: (1) standardized 8-10 minute warm-up with dynamic stretching, (2) attach the IMU at the sacrum using a sport belt, (3) hands fixed on hips, perform 3 jumps with 60 seconds rest, (4) record both the mean and best of three.

An 800Hz IMU detects takeoff (vertical acceleration drops below 1g) and landing (acceleration exceeds 1g) automatically. Jump height is computed from flight time t as h = (g·t²)/8. With 1.25ms time resolution, height error is roughly ±0.5cm.

Common pitfalls: hands leaving hips inflate flight time and overestimate height; bending knees on landing shortens flight time and underestimates height. Standardized form is non-negotiable. See our CMJ technique guide for cues.

The squat jump (SJ) removes the stretch-shortening cycle (SSC) contribution and isolates concentric explosive strength. Athletes hold a 90-degree knee flexion for two seconds, then jump without any countermovement. SJ height is normally 5-15% lower than CMJ; that gap quantifies SSC utilization.

To extract RFD from the IMU: identify t0 as the first instant acceleration crosses 0.5 m/s² above baseline, then compute cumulative impulse at t0+50ms, t0+100ms, and t0+200ms. Normalizing by body mass yields a comparable RFD value.

In Helms's (2014) autoregulation framework, an SJ RFD drop of 5% or more in-season signals neural fatigue accumulation. A weekly SJ measurement can thus pre-empt injury risk. The CMJ-SJ ratio (Eccentric Utilization Ratio, EUR) above 1.10 indicates strong SSC use; below 1.05 calls for plyometric reinforcement.

The medicine ball slam evaluates upper-body explosive output and core energy transfer simultaneously. Use a medicine ball with embedded IMU (or attach one) and perform five consecutive slams at 5kg.

Procedure: (1) shoulder-width stance, raise the ball overhead, (2) sequenced extension of hip-trunk-shoulder drives the ball into the floor, (3) the IMU records peak velocity at release plus impulse (area under acceleration curve), (4) compute power as P = F·v in watts.

Reference: 800-1200W for male athletes, 1200W+ marks elite, 500-800W for female athletes. If the power drop from rep 1 to rep 5 exceeds 15%, anaerobic endurance is limited; under 5% indicates excellent explosive endurance. Combine this with the Reactive Strength Index (RSI) for a comprehensive profile.

Protocol 4 measures barbell acceleration. With 30% 1RM on the bench press or back squat, the athlete performs one set of 5 reps with maximal intent. The IMU outputs both peak and mean acceleration over the first 100ms. Sánchez-Medina (2010) showed that 100ms barbell acceleration at 30% 1RM is one of the strongest predictors of full 1RM.

Protocol 5 captures rotational power. Holding a 3kg medicine ball at chest level, the athlete rotates 90 degrees laterally and throws against a wall or partner. The gyroscope tracks angular velocity (ω); combined with linear acceleration, the IMU yields rotational power. This is essential for baseball, golf, tennis, and combat athletes.

Together the five protocols build a four-axis profile: lower-body explosive (CMJ, SJ), upper-body integrated explosive (med ball slam), loaded explosive (barbell acceleration), and rotational explosive (rotational throw). Tested at season start and re-tested every two weeks, this profile supports both training-effect tracking and early injury-risk detection. Cross-reference outputs with the threshold tables in our autoregulated velocity guide for fast decisions. Run all protocols at the same time of day (ideally 10am-12pm) following an identical warm-up to keep longitudinal data comparable.