# PPCSexRx: Evidence-Based SSTAE Support With Tiered Clinical Safety

## Introduction: Scientific Backbone and Clinical Decision Support

PPCSexRx encodes sub-symptom threshold aerobic exercise (SSTAE) algorithms developed from a systematic review recognised with the 2026 NATA Foundation Best Summary Evidence Research Award (Li, 2026). The peer-reviewed evidence synthesis and CAT logic are archived at OSF (doi:[10.17605/osf.io/kvuf6](https://doi.org/10.17605/osf.io/kvuf6)).

The package is intentionally framed as a clinical decision support system (CDSS), not a black-box calculator: it translates GRADE-rated evidence into executable screening, prescribing, and progress-tracking rules while surfacing certainty, citations, and explicit safety stops at every tier of resource availability.

The intended workflow mirrors bedside practice:

    screen_ppcs()  -->  prescribe_ppcs()  -->  track_progress()

> GRADE disclosure: SSTAE recommendations encoded here carry LOW certainty evidence with a conditional recommendation FOR use in adolescents meeting PPCS definitions (Li, 2026). Licensed clinicians remain accountable for all treatment decisions.

## Case Study 1: The Gold Standard (Well-Equipped Clinic With BCTT)

### Scenario

A 16-year-old athlete presents 35 days after concussion with persistent symptoms consistent with PPCS. Your clinic completed a Buffalo Concussion Treadmill Test (BCTT); symptom-threshold heart rate (HRst) was 145 bpm. There are no active vestibular or cervical contraindications.

This vignette section demonstrates scientific fidelity: when objective exertional testing exists, `prescribe_ppcs()` prefers 80% of HRst as the prescription anchor (Li, 2026, p.11).

### Clinical screen (documentation checkpoint)

    screen_ppcs(
      age              = 16,
      days_post_injury = 35,
      vestibular_symptoms = FALSE,
      cervical_symptoms   = FALSE
    )
    #> ========================================
    #>   PPCSexRx Eligibility Screen
    #>   GRADE: LOW certainty | Li (2026)
    #> ========================================
    #> [OK]  STATUS: ELIGIBLE
    #>
    #> CLINICAL REASON:
    #>  Patient meets PICO eligibility criteria: age 16 years, 35 days post-injury (>= 28), no active contraindications. Proceed to BCTT-guided prescription (Li, 2026).
    #>
    #> NEXT STEP:
    #>  Proceed to prescribe_ppcs(). BCTT preferred for HR target; age-predicted fallback if unavailable.
    #> ========================================
    #> For prescription: prescribe_ppcs()
    #> Evidence: Li G. (2026). NATA Foundation Award.
    #> ========================================

### Prescription anchored to BCTT

    rx_gold <- prescribe_ppcs(
      age              = 16,
      days_post_injury = 35,
      hrst             = 145,
      vestibular_symptoms = FALSE,
      cervical_symptoms   = FALSE
    )
    rx_gold
    #> ========================================
    #>   PPCSexRx Clinical Prescription
    #>   Evidence-Based Protocol | Li (2026)
    #> ========================================
    #> Target HR  : 116 bpm
    #> Duration   : 20 min/session
    #> Frequency  : 5 sessions/week
    #> Method     : BCTT-guided: 80% of symptom threshold HR
    #> ----------------------------------------
    #> CLINICAL NOTE : Maintain current intensity. Monitor weekly for tolerance.
    #> SAFETY        : Clinician supervision required. Stop if symptoms worsen >= 2 PCSS points. See Li (2026), p.14.
    #> EVIDENCE      : GRADE: LOW certainty. Conditional recommendation FOR. See Li (2026), p.11.
    #> ========================================

The computed target HR implements 116 bpm (= 80% x 145 bpm) together with structured disclosures (`method`, `evidence_grade`, `safety_warning`) so auditors can trace every numeric output back to protocol language.

## Case Study 2: Resource-Limited Setting with Mandatory Safety Guardrails

### Scenario

A 14-year-old student-athlete is seen at a remote high school without treadmill testing capability 20 days post-injury. Even though HR monitors might be available, the athlete does not yet meet PPCS chronology (fewer than 28 days post-injury are handled outside this SSTAE pathway).

This section demonstrates operational safety: the package refuses to mint an SSTAE prescription when core eligibility gates fail, regardless of whether `hrst` is omitted (resource fallback path).

### Screening surfaces early-phase contraindication

    screen_ppcs(
      age              = 14,
      days_post_injury = 20,
      vestibular_symptoms = FALSE,
      cervical_symptoms   = FALSE
    )
    #> ========================================
    #>   PPCSexRx Eligibility Screen
    #>   GRADE: LOW certainty | Li (2026)
    #> ========================================
    #> [STOP]  STATUS: CONTRAINDICATED
    #>
    #> CLINICAL REASON:
    #>  Symptoms present for only 20 days. PPCS requires >= 28 days post-injury (Li, 2026, p.2). SSTAE is not indicated at this stage.
    #>
    #> NEXT STEP:
    #>  Re-screen when >= 28 days post-injury. Continue standard concussion management.
    #> ========================================
    #> For prescription: prescribe_ppcs()
    #> Evidence: Li G. (2026). NATA Foundation Award.
    #> ========================================

### Hard stop inside `prescribe_ppcs()`

Attempting to prescribe without satisfying PPCS timing triggers an immediate error—there is no silent downgrade to age-based intensities.

    prescribe_ppcs(
      age              = 14,
      days_post_injury = 20,
      vestibular_symptoms = FALSE,
      cervical_symptoms   = FALSE
    )
    #> Error in `prescribe_ppcs()`:
    #> ! Contraindicated: PPCS defined as >=28 days post-injury. See Li (2026), p.2.

Expected safeguard text includes `Contraindicated: PPCS defined as >=28 days post-injury.`, reinforcing that advanced arithmetic never substitutes for foundational eligibility checks.

Together, Case Studies 1 and 2 convey the design thesis demanded by tertiary clinics and resource-constrained outreach programmes: precision where physiology is measured, deterministic refusal where physiology must not yet be stressed.

## Additional Notes for Deployments Beyond These Examples

- `screen_ppcs()` captures referrals for vestibular, cervical, age-out-of-evidence, or vision-risk contexts before exertional planning advances.
- `track_progress()` operationalises session-by-session PCSS deltas with HR titration tied to Li (2026), p.14 progression/stop logic.

Always pair package outputs with local policies, concussion RTP statutes, and supervising physician judgement.

## Evidence Base and Limitations

Key caveats from the underlying CAT:

- Evidence certainty remains LOW; recommendation strength is conditional.
- Included trials employed heterogeneous dosing and outcomes—encoded guardrails intentionally bias toward conservatism when inputs are ambiguous.
- PPCSexRx augments, but never replaces, clinician oversight.

## References

Li G. (2026). Sub-symptom Threshold Aerobic Exercise for Adolescents With Persistent Post-concussion Symptoms (PPCS): A Critically Appraised Topic. Winner, NATA Foundation Best Summary Evidence Research Award. https://doi.org/10.17605/osf.io/kvuf6

Leddy JJ, Haider MN, Ellis MJ, et al. Early Subthreshold Aerobic Exercise for Sport-Related Concussion. JAMA Pediatr. 2019;173(4):319–325.

Kurowski BG, et al. Aerobic Exercise for Adolescents With Prolonged Symptoms After Mild Traumatic Brain Injury. J Head Trauma Rehabil. 2017;32(2):79–89.

Vernau BT, Haider MN, Fleming A, et al. Exercise-Induced Vision Dysfunction Early After Sport-Related Concussion Is Associated With Persistent Postconcussive Symptoms. Clin J Sport Med. 2023;33(4):388–394.