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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

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

Evidence Base and Limitations

Key caveats from the underlying CAT:

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.

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