--- id: sra_curve name: SRA Curve aliases: [Stimulus-Recovery-Adaptation, SRA cycle, supercompensation] category: principle applies_to: [all_systems] related: [progressive_overload, periodization, deload, volume_landmarks] sources: - title: "Scientific Principles of Hypertrophy Training" author: "Israetel, M., Hoffmann, J., Davis, M., Feather, J." year: 2019 publisher: "Renaissance Periodization" credibility: expert_consensus - title: "The General Adaptation Syndrome: Potential misapplications to resistance exercise" author: "Buckner, S. L., Mouser, J. G., Dankel, S. J., Jessee, M. B., Mattocks, K. T., Loenneke, J. P." year: 2017 journal: "Journal of Science and Medicine in Sport" volume: 20 issue: 11 pages: "1015-1019" doi: "10.1016/j.jsams.2017.02.012" pmid: "28377133" credibility: rct - title: "The General Adaptation Syndrome: A Foundation for the Concept of Periodization" author: "Cunanan, A. J., DeWeese, B. H., Wagle, J. P., Carroll, K. M., Sausaman, R., Hornsby, W. G., Haff, G. G., Triplett, N. T., Stone, M. H." year: 2018 journal: "Sports Medicine" volume: 48 issue: 4 pages: "787-797" doi: "10.1007/s40279-017-0855-3" pmid: "29214418" credibility: expert_consensus --- # SRA Curve The SRA (Stimulus–Recovery–Adaptation) curve describes the fatigue, recovery, and supercompensation a body goes through after a single training stimulus. It is the mechanistic foundation of why all periodized programs work — and why programs that ignore recovery timing produce stagnation or overtraining. ## Historical Context: GAS vs. SRA Early periodization theory borrowed Hans Selye's **General Adaptation Syndrome (GAS)** as its conceptual foundation. Selye's original work, however, was based on systemic, lethal-level pharmacological stressors — not the localized, sub-maximal mechanical stress of resistance training. Buckner et al. (2017) demonstrated that GAS models systemic non-specific responses poorly suited to the localized tissue microtrauma and neuromuscular adaptations that resistance training induces. The SRA framework (derived from GAS but applied correctly) addresses this by modeling **localized depletion and supercompensation** of specific tissues — muscle fiber proteins, glycogen stores, connective tissue — rather than a systemic alarm response. Cunanan et al. (2018) formalized the connection: the Alarm, Resistance, and Exhaustion stages of GAS correspond broadly to the Stimulus, Recovery, and (if training load exceeds recoverable capacity) Overtraining phases of SRA — but the practical application requires treating each muscle group's SRA curve as independent. ## Core Definition Training lowers functional performance in the moment (fatigue phase), which then rebounds during recovery and, in the supercompensation phase, rises above the original baseline. The best time for the next session falls at the **peak of supercompensation** — not while fatigue is still present, and not after supercompensation has decayed back to baseline. Miss the window too early: training on residual fatigue accumulates damage faster than adaptation. Miss it too late: the supercompensation decays and each session returns to baseline rather than building on a higher floor. ## Three Phases 1. **Stimulus** — training causes muscular microtrauma and metabolic stress; performance temporarily drops below baseline; the alarm phase in GAS terms 2. **Recovery** — nutrition and sleep drive repair; inflammatory resolution clears the acute damage signal; performance rebounds toward baseline 3. **Adaptation** — supercompensation sets a new baseline slightly above the previous one; this is when the fitness gain is expressed A fourth state — **exhaustion** (GAS) / **non-functional overreaching** or **overtraining** (sports science) — occurs when repeated stimuli are applied without adequate recovery, driving performance below baseline for weeks or months. ## Curve Length and Training Volume The SRA cycle length is determined by the magnitude of the stimulus: | Stimulus magnitude | Approximate SRA cycle | Example | |-------------------|----------------------|---------| | Low (single small-muscle isolation) | 24–36 h | Cable curl, lateral raise | | Moderate (compound moderate volume) | 48–72 h | Moderate-volume squat session | | High (high-volume large-muscle compound) | 72–96 h or more | Heavy high-volume deadlift session | These ranges are approximate and vary significantly by training status. Novices have longer SRA cycles because their damage response is proportionally greater relative to their recovery capacity. Advanced athletes have shorter cycles because their recovery infrastructure (hormonal environment, local tissue resilience) is more developed. This directly determines **training frequency design**: a muscle group trained with high volume requires more days before the next stimulus than one trained with low volume. Frequency and volume are co-determined by the SRA curve, not independently set. ## Interaction with Volume Landmarks Volume accumulation across a mesocycle gradually extends the SRA curve because cumulative fatigue adds to the acute fatigue of each session. This is why performance often declines in the final weeks of a hard training block even when per-session stimulus is unchanged — the accumulated fatigue layer lengthens effective SRA cycle duration beyond the available recovery window. A deload resets this accumulated fatigue, allowing supercompensation to be expressed. ## How Systems Differ Each system arranges different stimulus density and recovery intervals to suit its goals. Those differences are recorded in each system's `index.md`; this entry defines only the principle itself. - **Powerlifting**: Frequency is calibrated so that the next heavy session falls at or near supercompensation peak for the competition lifts. This typically means 2–3x/week per lift at submaximal loads, with the highest-intensity session occurring when fatigue from prior sessions has fully cleared. - **Bodybuilding**: Higher volume per session extends SRA cycles. Training frequency is typically 1–2x/week per muscle group, with the second session placed when soreness and performance have returned to baseline. - **Olympic Weightlifting**: Daily or twice-daily training is possible because session volumes are often low per movement; the SRA curve for a single lift at low volume resolves in 24 hours, allowing high frequency. - **CrossFit**: The mixed-modal structure makes SRA modeling complex; glycogen SRA and muscular SRA operate on different timescales. A 48-hour recovery window between high-intensity sessions is the minimum practical rule.