Sources & Methodology
Last updated: May 20, 2026
Not medical advice. Coach Orion and Orion Coach provide general fitness, training, and educational information only. They are not a medical device and do not provide medical advice, diagnosis, or treatment. Consult a qualified healthcare professional before starting any exercise program, and stop and seek care if you experience pain, dizziness, shortness of breath, or other unusual symptoms.
The calculations and recommendations Coach Orion makes are grounded in established exercise-science research and standard public-health references. The sources for each are listed below.
Coach Orion may also mention other general health figures, like body-fat or calorie estimates. Those are educational gauges based on the same kind of standard references, not medical advice. For any health decision, check with your doctor.
Body Mass Index (BMI)
When asked, Coach Orion computes BMI as weight in kilograms divided by height in metres squared (kg/m²). BMI is a population-level screening tool and does not distinguish muscle from fat, so for someone training for muscle it is a blunt measure — body-composition and strength trends are more informative.
Sources:
- World Health Organization — Obesity and overweight (fact sheet)
- Centers for Disease Control and Prevention — About Adult BMI
- National Heart, Lung, and Blood Institute (NIH) — BMI Calculator
Estimated one-rep max (1RM)
Coach Orion estimates your one-rep max from the weight and reps you log: the Epley formula for sets of 10 reps or fewer, and the Brzycki formula above 10 reps. The estimate is computed at display time from your raw logged sets.
Sources:
- Epley B. (1985). Poundage Chart. Boyd Epley Workout. Lincoln, NE.
- Brzycki M. (1993). Strength testing — predicting a one-rep max from reps-to-fatigue. JOPERD, 64(1), 88–90.
- Validation literature on 1RM prediction equations (PubMed)
Reps in Reserve (RIR) & perceived exertion
Coach Orion uses Reps in Reserve — how many reps you had left in the tank — to gauge effort and decide when to add load or reps. It never prescribes training to failure (RIR 0) as a target.
Sources:
- Zourdos M.C. et al. (2016). Novel resistance training-specific RPE scale measuring repetitions in reserve. J Strength Cond Res, 30(1), 267–275.
- Helms E.R. et al. (2016). Application of the RIR-based RPE scale for resistance training. Strength Cond J, 38(4), 42–49.
- Find on PubMed
Weekly training volume per muscle
Coach Orion targets a weekly number of working sets per muscle group and titrates it up or down based on your recovery and soreness. The target band reflects the dose-response research on training volume and muscle growth.
Sources:
- Schoenfeld B.J., Ogborn D., Krieger J.W. (2017). Dose-response relationship between weekly resistance training volume and increases in muscle mass. J Sports Sci, 35(11), 1073–1082.
- Find on PubMed
Recovery & heart-rate-variability-guided training
When you connect Apple Health, Coach Orion reads HRV, sleep, and resting heart rate to estimate your recovery and adjust each session's volume. Heart-rate variability is a well-studied marker of nervous-system recovery.
Sources:
- Plews D.J. et al. (2013). Training adaptation and heart rate variability in elite endurance athletes. Sports Med, 43(9), 773–781.
- Buchheit M. (2014). Monitoring training status with HR measures. Front Physiol, 5, 73.
- Find on PubMed
Exercise prescription & periodization
The structure of Orion Coach's programs (progressive overload, training blocks, and rest weeks) follows established guidelines for resistance-exercise prescription.
Sources:
- American College of Sports Medicine. ACSM's Guidelines for Exercise Testing and Prescription (11th ed.). — acsm.org
Questions about a specific recommendation? Ask Coach Orion in the app, or reach us via Support. For medical concerns, consult a healthcare provider.