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.
Strenua implements a block periodization model organized into mesocycles — typically 3-6 week training blocks. Each mesocycle progresses through three phases:
Accumulation
The volume-building phase. Training volume (sets per muscle group per week) increases progressively from your Minimum Effective Volume toward your Maximum Adaptive Volume. Intensity is moderate — typically working at 2-4 RIR (Reps in Reserve). The goal is to accumulate mechanical tension and metabolic stress to drive hypertrophy and strength adaptation.
Intensification
The intensity-building phase. Training loads increase while volume is maintained or slightly reduced. You work closer to failure — 1-2 RIR — to express the fitness built during accumulation. This phase tests the limits of your current strength and exposes you to heavier loads that drive neural adaptation.
Deload
The recovery phase. Both volume and intensity are reduced to approximately 80% of normal levels. This allows accumulated fatigue to dissipate while maintaining the training stimulus needed to preserve adaptations. Deloads are not optional — they are a critical component of long-term progression.
Volume Landmarks
Volume — measured as the number of challenging sets per muscle group per week — is the primary driver of hypertrophy. But not all volume is equal, and more is not always better. Research by Dr. Mike Israetel and others has identified three critical thresholds that define the productive training zone:
MEV — Minimum Effective Volume
The minimum number of sets per muscle group per week required to make progress. Below MEV, you are not providing enough stimulus to drive adaptation. For most muscle groups in trained individuals, this is approximately 6-10 sets per week. Beginners can make progress with fewer sets.
MAV — Maximum Adaptive Volume
The volume range that produces the highest rate of adaptation. This is the "sweet spot" — enough stimulus to maximize growth, but not so much that fatigue management becomes the limiting factor. Typically 12-20 sets per muscle group per week, depending on training age, recovery capacity, and the specific muscle group.
MRV — Maximum Recoverable Volume
The absolute ceiling of volume from which you can still recover. Training beyond MRV leads to accumulated fatigue that outpaces recovery, resulting in stagnation or regression. Strenua's intelligent system monitors your training load to ensure you stay below this threshold — and programs deloads when you approach it.
Strenua tracks volume landmarks per muscle group and adjusts programming accordingly. During accumulation phases, volume progresses from MEV toward MAV. Strenua will never program volume above MRV, and will trigger a deload phase when cumulative fatigue indicators suggest you are approaching your recoverable limit.
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 in Strenua, the system uses your reported RIR along with the weight and reps performed to estimate your current 1RM. This estimate is then used to calibrate loads for your next session. The result is a program that automatically adjusts to your daily readiness without manual intervention.
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
Weight increases are calculated from estimated 1RM changes and capped at 7% per session to prevent injury from excessive jumps. The system uses both the Brzycki formula (for sets of 15 reps or fewer) and the Epley formula (for higher rep ranges) to estimate maxes from training data.
Volume Progression
Set count increases progressively within mesocycles, starting at MEV and building toward MAV. Volume increments are typically 1-2 sets per muscle group per week, added every 1-2 weeks depending on recovery status.
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
The system enforces minimum weight increments based on equipment type. Barbell movements progress in 2.5 kg (5 lb) increments, dumbbell exercises in 2 kg (5 lb) jumps, and cable/machine exercises in the smallest available increment. Strenua never prescribes a weight below the equipment minimum.
Recovery Modeling
Training is only half the equation. Adaptation occurs during recovery — specifically during the supercompensation window, the period after training where the body rebuilds muscle tissue stronger than before. Train too soon and you interrupt recovery. Wait too long and the window closes.
Strenua models recovery on a per-muscle-group basis using a supercompensation curve that factors in:
- Base recovery time — each muscle group has a different baseline recovery period (e.g., quadriceps: 72-96 hours, biceps: 48-72 hours)
- Training volume — higher set counts extend recovery time, with a volume factor capped at 2.0x to prevent unrealistic estimates
- Training intensity — sets closer to failure (lower RIR) create more fatigue and require longer recovery
- Training frequency — the model accounts for sessions per week, adjusting recovery expectations for high-frequency training
- Time since last stimulus — a decay function tracks how recovered each muscle group is at any given time
When Strenua generates your next workout, it queries the recovery model for each potential muscle group. Muscles that haven't fully recovered are deprioritized or excluded. Muscles that are in their supercompensation window are targeted for optimal timing of the next stimulus.
On-Device Processing
All of the algorithms described above run locally on your iPhone using Apple's CoreML framework and the Neural Engine. This architectural decision has several implications:
Complete Privacy
Your workout data, body measurements, and performance metrics never leave your device. There is no cloud server storing your personal records.
Offline Operation
Strenua works without an internet connection. Generate workouts, log sessions, and track progress anywhere — the gym, outdoors, or underground.
Instant Response
No server latency. Workout generation, 1RM estimates, and recovery calculations happen in milliseconds on the Neural Engine.
Hardware Security
Your training data is protected by the same hardware encryption that secures Face ID and Apple Pay. iOS data protection applies automatically.
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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