Athlete Profiling: Custom Training Design

A 2016 landmark study by Samozino et al. established that individualizing training toward an athlete's dominant mechanical deficit — either force deficit or velocity deficit as revealed by the force-velocity profile — produced 15% greater power output improvements compared to non-individualized training of equal volume and duration. That finding has since been replicated in team sport, individual sport, and rehabilitation contexts, establishing athlete profiling as the most evidence-supported method for designing training programs that produce maximal performance returns.

This guide explains what an athlete profiling process looks like in practice: which tests to run, how to interpret the data, and how to translate profile results into specific training modifications that address each athlete's unique mechanical gaps.

What Athlete Profiling Actually Means

Athlete profiling, in the sports science context, refers to the systematic collection of objective performance data across multiple physical qualities to identify each athlete's individual strengths, deficits, and mechanical characteristics — and to use that information to design more targeted training programs.

It is not the same as general fitness testing. A fitness test tells you where an athlete ranks on population norms. Athlete profiling tells you why they perform the way they do and which specific physical quality, if developed, would produce the greatest performance improvement for that individual.

The profile typically covers four domains:

• Mechanical profile: The force-velocity (F-V) curve, which characterizes whether an athlete's power deficit is driven by insufficient force capacity (force-deficit athlete) or insufficient velocity capacity (velocity-deficit athlete).
• Jump and explosive power: Countermovement jump height, reactive strength index, and broad jump for lower-body power and elastic energy utilization.
• Asymmetry: Bilateral force or velocity imbalances between limbs, which predict injury risk and impair sport performance in directional tasks.
• Sport-specific capacities: Sprint mechanics, change-of-direction speed, or sport-specific power outputs depending on the athlete's primary sport demands.

Building a Force-Velocity Profile

The force-velocity (F-V) profile quantifies the linear inverse relationship between force production and movement velocity across the full continuum from maximal strength to maximal velocity. Developed and validated by Samozino et al. (2012, 2016), it provides a single diagnostic framework that identifies whether to prioritize strength (heavy resistance) or speed (light/ballistic) training for maximum power gain.

Field Protocol for Lower-Body F-V Profiling

The jump squat-based F-V protocol is the most accessible field method:

1. Perform maximal-effort squat jumps (no countermovement) at 5 progressively heavier loads: typically 0% (bodyweight), 20%, 40%, 60%, and 80% of squat 1RM.
2. At each load, record mean or peak concentric velocity using an IMU sensor.
3. Plot force (estimated from load + body weight) on the Y-axis against velocity on the X-axis for each condition.
4. Fit a linear regression — the slope defines the F-V slope, intercept on the force axis is theoretical maximum force (F0), and intercept on the velocity axis is theoretical maximum velocity (V0).
5. Calculate the Slope Factor (SF) = the actual F-V slope normalized to the theoretically optimal slope for maximum power. SF <1 indicates force deficit; SF >1 indicates velocity deficit.

The entire profiling session adds only 20–25 minutes to a standard training day and requires no specialized equipment beyond an IMU sensor.

Jump and Power Testing Battery

A comprehensive athlete profile supplements the F-V curve with a jump and power testing battery that captures elastic energy utilization, rate of force development, and single-leg symmetry:

The CMJ/SJ ratio is particularly diagnostic. A ratio below 1.06 indicates impaired stretch-shortening cycle (SSC) function — the athlete cannot efficiently use the eccentric phase energy stored during the countermovement. This pattern, often seen in athletes returning from lower-limb injuries or during periods of high fatigue accumulation, specifically flags the need for plyometric and reactive training to restore SSC efficiency (Bosco et al., 1983).

Asymmetry Screening and Injury Risk

Bilateral asymmetry — meaningful force or velocity differences between the dominant and non-dominant limb — is both a performance limitation and an injury risk factor. Research by Hewett et al. (2016) found that athletes with single-leg CMJ limb symmetry indices (LSI) below 85% had 2.6× higher ACL injury rates than those with LSI above 90% during a prospective two-year follow-up.

Asymmetry screening should be included in every profiling battery for athletes in cutting sports (basketball, football, soccer, tennis). Key asymmetry metrics:

• Single-leg CMJ height LSI: Most sensitive to neuromuscular asymmetry. A drop in LSI from one profile to the next can signal developing injury risk before symptoms appear.
• Single-leg landing force (qualitative): Observe and score landing mechanics on a 3-point scale (0 = valgus collapse, 1 = neutral, 2 = varus-stable). Athletes scoring 0 bilaterally have significantly elevated ACL risk.
• Velocity asymmetry in barbell exercises: Mean concentric velocity difference between left and right phases in split exercises (Bulgarian split squat, rear-foot elevated split squat) provides a strength-specific asymmetry measure independent of CNS coordination effects.

The practical threshold for intervention is an LSI below 90% on any single-leg test, or a change of more than 5 percentage points in LSI from one profiling session to the next.

Interpreting Profile Results

Profile interpretation requires integrating data across domains rather than treating each metric independently. The most common profile patterns and their training implications:

• Force-deficit / high CMJ / poor RSI: The athlete is strong but stiff and lacks reactive leg spring. Training priority: plyometrics, depth drops, and reactive landing drills. Reduce heavy strength work to maintenance.
• Velocity-deficit / low CMJ / high SJ: The athlete has strength but poor explosive expression — a common pattern in powerlifters transitioning to team sport. Training priority: ballistic training at 30–50% 1RM, loaded jumps, and contrast methods.
• Force-deficit AND velocity-deficit (low overall power): Rare in well-trained athletes but common in deconditioned or young athletes. General strength and jump training address both deficits simultaneously.
• High asymmetry (>15% LSI) with normal bilateral values: The athlete has sufficient bilateral capacity but distributes load unevenly. Training priority: unilateral corrective exercises targeting the weaker limb, plus asymmetry monitoring to confirm improvement.

Translating Profile Data to Training Prescription

The Samozino et al. (2016) framework provides quantitative training prescription from the F-V profile:

• Force-deficit athlete (SF <1): Increase training load emphasis toward the force side of the F-V curve. Specifically, 60–70% of weekly resistance training volume at loads >75% 1RM. Reduce jump and sprint volume to maintenance levels (1–2 sessions per week).
• Velocity-deficit athlete (SF >1): Shift training emphasis toward the velocity side. 60–70% of weekly resistance training volume at loads <50% 1RM with maximal velocity intent, including loaded jumps, throw variations, and short sprints. Heavy resistance work remains for maintenance (1–2 sessions per week).
• Balanced profile (SF ≈ 1.0): The athlete is at or near the theoretically optimal F-V balance. Maintain current training emphasis but introduce novel stimuli to continue adaptation.

Block length for targeted profiling work is typically 6–8 weeks — long enough to shift the F-V slope measurably but short enough to re-profile before over-correcting in one direction. After each block, re-measure and adjust.

When and How to Re-Profile

Athlete profiles change with training, injury, seasonal stress, and physical maturation in younger athletes. Re-profiling is necessary to keep training prescriptions aligned with current physical characteristics.

Recommended re-profiling schedule:

• Every 6–8 weeks during a training block: F-V profile re-testing confirms whether the targeted deficit is responding to training and whether the prescription should continue, pivot, or maintain.
• After injury: Asymmetry and LSI testing every 2 weeks during rehabilitation, with return-to-sport clearance requiring LSI >90% across all profile tests.
• Pre-season: Full baseline profile establishes starting points for seasonal monitoring. Compare pre-season to end-of-season profile to quantify accumulated fatigue and identify structural changes from the competitive year.
• Post-deload/off-season: Re-profile after a 2-week deload to confirm full recovery before starting a new training block. F-V profile metrics often improve 3–5% after a structured deload, and a new prescription should be based on post-deload values.

Athletes under 18 should be re-profiled every 4–6 weeks during growth-intensive periods because physical maturation can shift the F-V profile substantially — both through height/mass changes and through neural development — requiring more frequent prescription updates than adult athletes.