Strength. Endurance. Recovery. Periodization. The physiology and the practice of training a human body to do more than it could yesterday.
Stress a tissue beyond its comfort. Recover. The tissue rebuilds slightly stronger. This is the principle of supercompensation — the engine of every training program ever written.
Hans Selye described the General Adaptation Syndrome in 1936: alarm, resistance, exhaustion. Apply too little stress and nothing changes; apply too much without recovery and you regress or break. The art of programming is finding the dose that produces adaptation without destruction.
ATP-PCr / phosphagen — the ten-second sprint
Anaerobic glycolysis — burns under fatigue
Oxidative — long, slow, with oxygen
Every effort is fueled by some mix of these three. Sprinters live on the first two; marathoners almost exclusively on the third. Most field sports oscillate. Knowing which system a sport demands tells you how to train it.
Strength is the maximal force a muscle (or system) can produce. It depends on muscle cross-sectional area, neural drive (the brain's ability to recruit motor units), and lever mechanics.
Resistance training adapts both: hypertrophy (muscle growth) and neural efficiency (better recruitment). Beginners gain mostly via the latter for the first ~6 weeks. Hypertrophy compounds slowly — perhaps 0.5 kg of muscle per month under good conditions.
Per major muscle, 10–20 weekly sets at 60–85% 1RM, taken close to failure, drives ~95% of available adaptation in trained lifters. More volume yields diminishing returns and rising injury risk.
Endurance is the capacity to sustain submaximal output. The headline metric is VO₂ max — the maximum rate of oxygen consumption, measured in mL/kg/min. Elite male endurance athletes hit 75–85; sedentary adults sit around 30–40. VO₂ max is among the strongest predictors of all-cause mortality.
The Norwegian double-threshold model and Stephen Seiler's polarized 80/20 framework dominate modern endurance practice: most volume easy (Zone 2), a smaller share at threshold or VO₂ max.
Periodization is the structured variation of training over time to peak when it matters and avoid overtraining. Originating with Russian sport science (Matveyev, 1965), it now appears in three flavors:
| Model | Structure | Best for |
|---|---|---|
| Linear | Volume high → intensity high (over months) | Beginners, single peak |
| Block | Concentrated phases (hypertrophy → strength → power) | Strength athletes |
| Undulating (DUP) | Daily/weekly variation in load and reps | Multi-quality, in-season |
All models share a deload — a planned reduction in volume every 3–6 weeks to allow accumulated fatigue to dissipate.
Static stretching held for >30s before strength or sprint work transiently reduces force output. Dynamic warm-ups outperform static ones for performance preparation. Yoga, mobility flows, and joint-specific drills retain value for movement quality and injury reduction.
The much-cited claim that stretching prevents injury is not strongly supported. What does reduce injury: progressive load, sleep, and well-built strength in the relevant ranges.
Adaptation happens between sessions, not within them. The hierarchy of recovery levers, ordered by effect size:
| Zone | %HRmax | Feel | Adaptation |
|---|---|---|---|
| Z1 — recovery | 50–60% | Conversational, light | Active recovery |
| Z2 — aerobic base | 60–70% | Steady, full sentences | Mitochondria, fat oxidation |
| Z3 — tempo | 70–80% | Comfortably hard | Aerobic capacity |
| Z4 — threshold | 80–90% | Hard, short sentences | Lactate clearance |
| Z5 — VO₂ max | 90–100% | All-out, gasping | Cardiac output, VO₂ max |
A common adult-fitness prescription: 150 minutes/week Zone 2 + 1–2 short Zone 4–5 sessions. WHO recommends 150–300 min moderate or 75–150 min vigorous activity weekly, plus two strength sessions.
annual all-cause mortality reduction per 1 MET of fitness
risk of several cancer types in physically active adults vs. sedentary
daily protein for trained adults in calorie deficit
weekly volume increase ceiling — past which injury rises
The training adaptations described here are the same in elite and recreational athletes — only the dose differs. Elite athletes are not biologically distinct; they are people who can absorb more training and have done so for longer.
Andy Galpin, PhD exercise physiology, on the science of strength, endurance, and recovery — a six-episode deep dive on the Huberman Lab.
"Train. Eat. Sleep. Repeat. The basics, executed for years, beat the gimmick every time."
Strength and endurance physiology are well-established. Programming details (optimal frequency, set count, rest interval) have moderate evidence with substantial individual variation. Many supplement claims (BCAAs, fat burners, "test boosters") have weak or null evidence. Three supplements with credible support: creatine monohydrate, caffeine, protein powder when dietary protein is insufficient.
Educational content. Consult a physician before starting a training program if you have cardiovascular, metabolic, or musculoskeletal disease, or are pregnant.