04

Force-Time Series

Article 04 · Apr 2026 · [Organization]

Issue 04
THE RISK
SIGNATURE

Two Middle Blockers. Same position. Same match load. Two different mechanical failure modes.

MB·1 · Braking RFD 11,912 N/s · Conversion Failure
MB·2 · L|R Asymmetry 13.29% Elevated · Right limb offloading
MB·1 MB·2 N1 Performance Lab
N1 Performance Lab · The Question Issue 04
Section 01 — Framing the Problem
Most practitioners look for the injury in the clinic.
It was already in the data.

Soft tissue injury in volleyball — patellar tendinopathy, Achilles loading, hip flexor overload — does not arrive without warning. The warning is mechanical. It is written in the force-time curve before the athlete feels it.

The question is not whether the data contains the signal. It does. The question is whether the practitioner is reading it.

Most are not. Most are watching jump height. Jump height is an output. Risk lives in the input — specifically, in how force is applied during the braking phase of the countermovement.

Two metrics drive this analysis: Braking RFD and bilateral asymmetry. One tells you how fast the system loads. The other tells you which limb is carrying the load.

When one limb loads fast and the other does not, soft tissue on the loading limb accumulates stress. The athlete compensates. The compensation is invisible in performance metrics. It is visible in the force-time curve.

First Principle

Soft tissue loading is a function of how force is applied — the rate, the symmetry, the phase sequence. Not how much force. Not the jump height. The curve.

Hawkin Dynamics CMJ · Apr 2026 02 / 10
N1 Performance Lab · Athlete Profiles Issue 04
Section 02 — The Two Signatures
MB·1
178 CM · Middle Blocker · [Organization]
Conversion Failure
Braking RFD 11,912 N/s · ▲ Above SWC
Impulse Ratio 1.66 ▼ Below SWC
L|R Asymmetry 1.95% Symmetric
P1:P2 Ratio 1.44 ▼ Below SWC
L Braking RFD 6,124 N/s · ▲ Above SWC
R Braking RFD 5,788 N/s · ▲ Above SWC

Force is there. Both limbs loading above SWC. Asymmetry within normal range.

Impulse ratio at 1.66 — below SWC — means the propulsive output does not reflect the braking input. The system absorbs force but does not return it.

Clinical risk: patellar tendon and Achilles loading from repeated high-force eccentric absorption without adequate elastic rebound.

MB·2
180 CM · Middle Blocker · [Organization]
Compensatory Loading
Braking RFD 7,062 N/s · ▼ Below SWC
Impulse Ratio 1.64 ▼ Below SWC
L|R Asymmetry 13.29% ⚠ Elevated
P1:P2 Ratio 1.24 ▼ Below SWC
L Braking RFD 4,018 N/s · ▼ Below SWC
R Braking RFD 3,044 N/s · ▲ Above SWC

Force is low. RFD below SWC. Right limb offloading — loading the left limb disproportionately despite a lower overall output.

The 13.29% bilateral asymmetry is the primary flag. Left at 4,018 N/s. Right at 3,044 N/s. A 974 N/s gap per jump cycle.

Clinical risk: stress accumulation on the left limb from compensatory overload. Right limb may be guarding early soft tissue pathology.

Hawkin Dynamics CMJ · Apr 2026 · [Organization] Women's Volleyball 03 / 10
N1 Performance Lab · The Mechanics of Risk Issue 04
Section 03 — Why the Braking Phase is the Risk Phase
Soft tissue does not fail under peak force.
It fails under rate of force.

In a countermovement jump, the braking phase is where the athlete decelerates the downward momentum of the body mass. This requires rapid force production against gravity and inertia. The faster the braking — the higher the Braking RFD — the greater the rate of eccentric loading on the musculotendinous unit.

Tendons are viscoelastic. They tolerate high-magnitude loads over time. What they do not tolerate well is rapid, repeated, asymmetric loading — especially without adequate elastic return.

This is where MB·1's profile becomes clinically significant. The RFD is high (11,912 N/s). The impulse ratio is low (1.66). The tendon is absorbing a large, fast load — and not returning it. That energy is not stored and reused. It is dissipated as structural stress. Over a season of twice-daily training, this accumulates.

MB·2's profile is mechanically different but equally concerning. The RFD is low (7,062 N/s) — but asymmetric (13.29%). The left limb is overloading. The right limb may be protecting a site of early pathology. The system is compensating. Compensation at this scale is not a behavioral choice. It is a structural one.

The tendon does not read the athlete's pain scale. It reads the rate of loading.
Hawkin Dynamics CMJ · Apr 2026 04 / 10
N1 Performance Lab · The Asymmetry Threshold Issue 04
Section 04 — Reading the Asymmetry Index

Bilateral Braking RFD — L vs R Limb

Bilateral Asymmetry Index · Hawkin formula: (L − R) / (L + R) × 100

MB·1
1.95%
10% Flag
Acceptable
MB·2
13.29%
10% Flag
⚠ Elevated

The clinical concern threshold for Braking RFD asymmetry is 10%. At 10–15%, the asymmetry is flagged for monitoring. Above 15%, clinical intervention is indicated — reduced unilateral loading, asymmetry-targeted drills, soft tissue assessment.

MB·2 sits at 13.29%. That is not a threshold violation requiring immediate removal. It is a directional signal requiring immediate attention. Left limb at 4,018 N/s. Right at 3,044 N/s. A 974 N/s gap. Each jump cycle, the left limb absorbs disproportionate braking load.

MB·1 at 1.95% is symmetric. That is not the risk signal. The risk signal is the impulse ratio — and the P1:P2 ratio. Symmetry without elastic return is not safety. It is stored injury.

Hawkin Dynamics CMJ · Apr 2026 05 / 10
N1 Performance Lab · Full Data Issue 04
Section 05 — Metric Summary · Apr 2026
Metric MB·1 MB·2 SWC Direction Clinical Note
Braking RFD (N/s) 11,912 7,062 ↑ MB·1 ▲ above · MB·2 ▼ below MB·1 loading faster — higher eccentric stress rate
L Braking RFD (N/s) 6,124 ▲ 4,018 ▼ Both left limbs dominant Left dominant in both athletes
R Braking RFD (N/s) 5,788 ▲ 3,044 ▲ MB·2 right limb below average Right limb offloading in MB·2
L|R Asymmetry (%) 1.95% 13.29% ⚠ Threshold: 10% flag MB·2 above monitoring threshold
Impulse Ratio 1.66 ▼ 1.64 ▼ Both below SWC Braking input not converting to propulsive output
P1:P2 Ratio 1.44 ▼ 1.24 ▼ Both below SWC Early propulsive phase underpowered — elastic return deficit
Overall Flag ⚠ Monitor ⚠ Monitor — Both flagged for different mechanical reasons
Risk Signature Conversion Failure Compensatory Loading — Different failure modes — different interventions

Important

Both athletes flagged ⚠ Monitor. Neither is cleared. The failure modes differ — which means the interventions differ. Treating both athletes with the same protocol would address one risk and miss the other.

Hawkin Dynamics CMJ · Apr 2026 · [Organization] Women's Volleyball 06 / 10
N1 Performance Lab · Intervention Issue 04
Section 06 — What the Data Triggers

MB·1 · Conversion Failure

Load Management
+ Elastic Return Work

The force is present. The return is not. Intervention targets the tendon's ability to store and release elastic energy — not to increase braking force, which is already above SWC.

Plyometric Load Reduction

Cap maximum-intensity jump volume. Monitor impulse ratio as the readiness signal — not jump height. Target: ratio above 1.80 before returning to full bilateral plyometric load.

Elastic Return Protocol

Isometric holds at 90° knee flexion, 3 × 45s. Tendon loading without high-rate deceleration. Transition to slow eccentric-concentric cycles before reintroducing fast braking.

Retest Trigger

Retest CMJ at 72-hour intervals. Cleared when: Impulse Ratio ≥ 1.80 AND P1:P2 ≥ 1.60 for two consecutive sessions.

MB·2 · Compensatory Loading

Asymmetry Correction
+ Right Limb Assessment

The asymmetry is the lead signal. Intervention prioritizes the right limb — specifically, determining whether the right is guarded (early pathology) or simply undertrained relative to the left.

Clinical Soft Tissue Screen

Refer for palpation and load testing on right Achilles, patellar tendon, and hip flexor complex within 48 hours. Do not prescribe unilateral loading before screening.

Unilateral Braking Work

Single-leg landing absorptions on right limb — submaximal (60% effort), emphasis on deceleration control. Target: right limb RFD within 8% of left before returning to bilateral load.

Retest Trigger

Retest at 48-hour intervals tracking L|R asymmetry exclusively. Cleared when: asymmetry ≤ 8% for two consecutive sessions and clinical screen negative.

Hawkin Dynamics CMJ · Apr 2026 07 / 10
N1 Performance Lab · Physiology Issue 04
Section 07 — The Soft Tissue Mechanism
Why the tendon fails — and what the impulse ratio is actually measuring.

The Achilles and patellar tendons function as energy storage and return systems. In jumping, they operate on the stretch-shortening cycle (SSC): the eccentric phase (braking) stretches the tendon, storing elastic strain energy. The concentric phase (propulsion) releases that energy, augmenting muscular output.

This cycle is efficient when the rate of loading is matched by the rate of return. High Braking RFD with high Impulse Ratio indicates a well-functioning SSC. High Braking RFD with low Impulse Ratio — MB·1's profile — indicates the tendon is loading fast but not returning efficiently. The elastic energy is being lost, not released.

At the cellular level, this pattern activates repetitive collagen micro-damage. Individual loading events are below the threshold of structural failure. But cumulative, asymmetric loading at the rates seen in pre-season volleyball (100+ maximal jumps per session) accumulates faster than collagen turnover can repair. Tendinopathy onset is not an event — it is a process. The curve captures the process.

For MB·2, the bilateral asymmetry adds a different mechanism: shear loading. When one limb contributes 13% more deceleration force than the other, the loading limb also bears an off-axis component. This shear stress is less tolerated by tendinous tissue than axial compression. It is associated with higher rates of insertional Achilles pathology in high-volume jump sports.

Clinical Reference

Bilateral asymmetry indices >10% in Braking RFD are associated with elevated injury risk in jump-sport athletes (Cook et al., 2016; Docking & Cook, 2019). The 15% threshold is used as a clinical intervention marker in several elite volleyball programs.

Hawkin Dynamics CMJ · Apr 2026 08 / 10
VERDICT

Section 08 — What the Data Says

Two athletes.
Two risk signatures.
One protocol solves nothing.

Both athletes were identified not through clinical presentation — no pain, no performance decline. Routine CMJ testing. April 17, 2026.

Not a performance number.
A readiness signal.

Hawkin Dynamics CMJ · Apr 2026 · [Organization]  ·  09 / 10

Clearance Thresholds

1.80

MB·1 — Impulse Ratio Target

Cleared when Impulse Ratio ≥ 1.80 AND P1:P2 ≥ 1.60 for two consecutive sessions. No additional eccentric work until then.

≤8%

MB·2 — Asymmetry Clearance

Clinical screen first. Then L|R asymmetry ≤ 8% for two consecutive sessions before returning to bilateral load.

48h

Next Test — Both Athletes

MB·2 prioritized. Asymmetry tracking at 48-hour intervals. MB·1 at 72-hour intervals monitoring impulse ratio exclusively.

N1 Performance Lab Issue 04
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Force-Time CMJ Series · A01–A04

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Series continues with Article 05

Force-Velocity Profiling — Which MB Profile is Faster?

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A01 — Positional Forensics · Published A02 — Braking RFD · Published A03 — Good vs Poor Curve · Published A04 — Risk Signature · Current

Athlete identities and institutional affiliations protected across all published outputs
Data source: Hawkin Dynamics CMJ · Metrics averaged across three trials · SWC = Smallest Worthwhile Change
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