The Science Behind Strenua
Every workout Strenua generates is built on decades of exercise science research. This page explains the principles and algorithms that drive your programming.
Periodization Theory
Periodization is the systematic planning of athletic training into distinct phases, each with specific goals for volume, intensity, and exercise selection. The concept originated in Soviet sports science during the 1960s and has since become the foundation of evidence-based strength training.
For trained strength and hypertrophy users, Strenua uses a four-week cycle. The phase is resolved before a workout is generated, so the third week reaches its planned target, the fourth week deloads, and the following cycle resets before its first session.
Accumulation
Early work establishes and progresses the planned set range while keeping effort targets conservative. The engine allocates all exercises against one shared muscle ledger rather than making independent per-exercise volume decisions.
Intensification
Later work shifts rep ranges, sets, and effort targets for the current goal. Phase changes never apply a multiplier directly to the previous weight; load progression remains anchored to valid logged performance.
Deload
The fourth week reduces work sets and increases the intended effort reserve. Deload performance is not used as the next cycle's progression anchor, preventing a lighter week from resetting normal training loads.
Planned Set Ranges
Resistance-training volume has diminishing returns and varies by person. Strenua therefore uses transparent planning ranges and your completed-volume history rather than presenting universal biological thresholds as precise.
Direct Work
A completed set counts fully toward its primary muscle. All exercises in a generated session draw from the same remaining weekly budget, so later selections cannot ignore earlier allocations.
Secondary Work
Muscles that assist a movement receive fractional set credit. The same direct-plus-secondary accounting is used during live logging, imports, relaunch rebuilding, and future workout generation.
Duration Boundaries
A shorter requested session may remove exercises or sets. Duration scaling is not allowed to add work beyond the shared allocation or restore an exercise excluded by equipment or health restrictions.
These are planning controls, not guarantees of adaptation or recovery. Users can compare planned work with their own completed history and adjust training when performance or wellbeing changes.
RIR-Based Autoregulation
Traditional programs prescribe fixed percentages of your one-rep max (e.g., "4 sets of 8 at 75% 1RM"). The problem: your true 1RM fluctuates daily based on sleep, stress, nutrition, and accumulated fatigue. A weight that represents 75% on Monday might feel like 80% on Thursday.
Reps in Reserve (RIR) solves this by prescribing effort instead of absolute load. Instead of "bench 185 lbs for 8 reps," Strenua might prescribe "bench for 8 reps at 2 RIR" — meaning you should stop the set when you have approximately 2 reps left in the tank.
When you log a set, Strenua keeps the weight, repetitions, and optional RIR as performance evidence. Readiness is handled separately through the pain, soreness, fatigue, and sleep check-in rather than inferred from load alone.
Progressive Overload Algorithms
Progressive overload — systematically increasing the demands placed on the body — is the fundamental mechanism of strength adaptation. Strenua implements progressive overload through multiple variables, not just adding weight to the bar:
Load Progression
New or untrusted exercises begin with guided calibration and no guessed starting weight. A later increase is exactly one valid equipment increment and only occurs after the applicable logged-performance conditions.
Volume Progression
Planned set ranges change across the cycle while the shared ledger counts direct and fractional secondary contributions. Duration adjustments may remove work but cannot exceed the remaining allocation.
Effort Progression
RIR targets decrease across a mesocycle — early weeks might prescribe 3 RIR while later weeks push to 1 RIR. This gradually increases the proximity to failure, which is a key driver of both strength and hypertrophy adaptations.
Equipment-Aware Floors
Each canonical equipment definition supplies its valid load mode and increment. Unknown equipment does not match automatically, and an exercise is eligible only when one complete equipment option is available.
Readiness Decision Support
Training decisions should reflect how you feel today without pretending that an app can predict injury. Strenua uses a short check-in to produce one of three decision-support bands:
- Ready — no current pain and normal or mild soreness, fatigue, and sleep responses
- Caution — a skipped check-in or moderate response reduces affected volume and removes high-effort grouped work
- Rest — current pain or severe adverse responses exclude affected work and offer unaffected training or rest
Training recency and personal workload history remain visible context. They are not displayed as recovery percentages, medical conclusions, or injury-risk predictions.
On-Device Processing
Workout generation and training calculations run locally on the device. Optional services are separated clearly:
Optional Cloud Backup
Signed-in users can store selected profile and training data in Firebase for account sync, backup, and restore. Health restrictions stay local unless the user separately opts in to their cloud sync.
Offline Operation
Core planning, workout generation, logging, and history work without an internet connection. Sign-in, cloud backup and restore, and subscription services require connectivity.
Instant Response
Workout generation does not wait for a remote AI response. The local engine uses versioned exercise, equipment, muscle, movement-pattern, and category identifiers.
Hardware Security
Apple platform data protection secures local app storage. Firebase Authentication, owner-only Firestore rules, TLS, and App Check protect the optional account and cloud-backup path.
Science meets your pocket.
Every principle on this page is implemented in the app. No marketing fluff, no "proprietary algorithms" — just transparent, evidence-based programming running on your device.
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