Hyrox Endurance Physiology & Gastrointestinal Stress Simulator

Race Variables & Countermeasures

1km Run Intensity (% HR Max) 85%

Pacing across all eight 1,000m running splits.

Sled Push / Station Exertion 92%

Anaerobic spikes during Sled Push, Burpee Jumps, & Lunges.

Hydration Ingestion Rate 600 ml/hr

Fluid volume intake; excessive cold fluids cause gastric distension.

Caffeine Bolus Intake 200 mg

Stimulates colonic motor activity and sphincter relaxation.

Athlete Body Mass 75 kg

Influences metabolic heat accumulation and dissipation area.

Target Finish Duration 70 min

Elite Hyrox finishing time (Pro average: 58-75 min).

Intra-Race Splanchnic Blood Shunt & Core Hyperthermia

Visceral Blood Flow (%)

Core Temp (°C)

Gastric Emptying (ml/min)

Hyrox 8-Station Physiological Strain Progression Station 2: Sled Push (Peak Sympathetic Surge)

1. SkiErg1000m

2. Sled Push4x12.5m

3. Sled Pull4x12.5m

4. Burpees80m Broad

5. Rowing1000m

6. Farmers200m Carry

7. Lunges100m Sandbag

8. Wall Balls75-100 Reps

Splanchnic Hypoperfusion

During extreme hybrid exertion (85-95% VO₂ max), the autonomic nervous system shunts up to 80% of mesenteric blood flow away from the intestines and stomach into working quadriceps and skin for heat dissipation. This causes acute ischemic mucosal damage and cellular leakage.

Thermal & Mechanical Stress

Core temperatures exceeding 39.0°C loosen intestinal epithelial tight junctions, releasing endotoxins into circulation. High impact from 8km of running combined with intense abdominal intra-cavity pressures from heavy sleds induces severe involuntary defecation.