Exercise Physiology & Biomechanics

ExPhys fundamentals: understanding how the human body adapts to physical stress through structured TR programs. The core principle is progressive OVL — systematically increasing training stimulus to drive physiological ADP.

Energy Systems & Metabolism

Three primary ES power human movement: ATP-PC (phosphocreatine, ~10s max effort), GLYC (anaerobic glycolysis, 30s-2min), and OXP (aerobic oxidative phosphorylation, sustained effort). Training specificity dictates which ES dominates. Sprint athletes primarily train ATP-PC and GLYC pathways, while endurance athletes target OXP capacity through elevated MVO2 (maximal oxygen uptake).

MVO2 represents the ceiling of aerobic performance. Elite endurance athletes achieve 70-85 ml/kg/min. Key determinants: cardiac output (HR x stroke volume), arteriovenous O2 difference, and mitochondrial density. HIIT protocols (4x4min at 90-95% HRmax) produce significant MVO2 improvements within 8-12 weeks. LT (lactate threshold) training at 75-85% MVO2 improves the fractional utilization — the percentage of MVO2 sustainable for prolonged effort.

Muscular Physiology & Fiber Types

Skeletal muscle contains two primary FT categories: Type I (slow-twitch, oxidative, fatigue-resistant) and Type II (fast-twitch, subdivided into IIa and IIx). Type I fibers dominate endurance activities with high MITO density and capillary supply. Type IIx fibers generate peak force but fatigue rapidly. Type IIa fibers are intermediate and highly trainable — they shift characteristics based on TR stimulus.

MFH (muscle fiber hypertrophy) occurs through two mechanisms: myofibrillar HYP (adding contractile proteins, increasing force production) and sarcoplasmic HYP (increasing fluid and glycogen stores, increasing muscle volume). Resistance TR at 65-85% 1RM with 6-12 reps primarily drives myofibrillar HYP. Higher rep ranges (15-25) with shorter rest periods emphasize metabolic stress and sarcoplasmic changes.

The SRA curve (stimulus-recovery-adaptation) governs training frequency. After a TR session, muscle performance temporarily decreases (fatigue), then recovers to baseline, then briefly surpasses baseline (supercompensation). Optimal subsequent training occurs at peak supercompensation — typically 48-72h for moderate sessions, 72-120h for high-intensity sessions.

Biomechanics Principles

BMX analysis examines forces, torques, and movement patterns during human motion. Key concepts: GRF (ground reaction forces), measured via force plates, reveal how athletes interact with terrain. During running, peak GRF reaches 2.5-3x BW at foot strike. Elite sprinters generate higher horizontal GRF components, which correlates with velocity.

Joint KIN (kinematics) describes motion without reference to forces — angular displacement, velocity, acceleration. Joint KNT (kinetics) examines the forces causing motion — joint moments, power, work. The inverse dynamics approach uses KIN data plus anthropometric measurements to calculate net joint moments.

The SSC (stretch-shortening cycle) is fundamental to explosive movement. An eccentric pre-stretch of muscle-tendon unit stores elastic energy and triggers the stretch reflex, enhancing subsequent concentric force production. Plyometric TR specifically targets SSC efficiency. Depth jumps from 30-60cm heights with minimal ground contact time (<200ms) develop reactive strength index (RSI = jump height / contact time).

RFD (rate of force development) measures how quickly force is produced — critical for sprinting, jumping, throwing. Peak RFD occurs within first 50-100ms of contraction. Heavy resistance TR (>85% 1RM) and ballistic exercises improve RFD. The force-velocity relationship shows inverse proportionality: as contraction velocity increases, force capacity decreases. Power output (force x velocity) is maximized at approximately 30-60% 1RM depending on exercise.

Periodization & Programming

PRZ structures long-term TR into phases targeting different physiological qualities. Classical linear PRZ progresses from high-volume/low-intensity to low-volume/high-intensity across mesocycles (3-6 week blocks). Undulating PRZ varies intensity within microcycles (weekly). Block PRZ concentrates training loads into sequential blocks emphasizing one quality (accumulation → transmutation → realization).

Recovery & Adaptation

REC quality determines adaptation rate. Sleep is the primary REC modality — 7-9 hours with emphasis on SWS (slow-wave sleep) for GH release and tissue repair, and REM for neural consolidation. Nutrition timing matters: 0.3-0.5g/kg protein within 2h post-TR maximizes MPS (muscle protein synthesis). CHO replenishment at 1-1.2g/kg/h restores muscle GLY stores.

HRV (heart rate variability) provides objective autonomic nervous system monitoring. High HRV indicates parasympathetic dominance and readiness to train. Chronically suppressed HRV signals OTS (overtraining syndrome) risk. Weekly training load monitoring using RPE x duration (session RPE method) or TRIMP (training impulse) helps manage fatigue accumulation.

Neuromuscular Considerations

MU (motor unit) recruitment follows Henneman's size principle: smaller Type I MUs recruit first, larger Type II MUs recruit only at higher force demands. Maximum voluntary contraction requires full MU recruitment plus optimal firing rate (rate coding). TR increases both recruitment capacity and firing rate synchronization.

The bilateral deficit phenomenon shows that unilateral force production exceeds 50% of bilateral — important for sport-specific TR design. Cross-education effect: unilateral TR produces strength gains in the contralateral untrained limb (10-15%), mediated by neural adaptations.

Intermuscular coordination — the timing and magnitude of agonist, antagonist, synergist, and stabilizer activation — improves with practice specificity. This is why general strength does not automatically transfer to sport performance without movement-specific TR.

Thermoregulation & Environmental Physiology

Exercise in heat challenges cardiovascular and thermoregulatory systems simultaneously. Core temp >39.5C impairs performance; >40C risks EHS (exertional heat stroke). Heat ACC (acclimatization) over 10-14 days improves sweat rate, reduces sweat sodium concentration, expands plasma volume, and lowers resting core temperature.

Altitude exposure reduces PIO2 (partial pressure of inspired O2). At 2500m, PIO2 drops ~25%. EPO (erythropoietin) secretion increases within hours, stimulating red blood cell production over 2-3 weeks. The live-high-train-low model (sleep at 2000-2500m, train at <1500m) optimizes hematological ADP while maintaining training intensity.

Applied Assessment Methods

PRF testing battery should include: body composition (DEXA or skinfold), aerobic capacity (graded exercise test for MVO2 and LT), anaerobic power (Wingate 30s test), maximal strength (1RM or predicted), power output (countermovement jump, force plate), and sport-specific movement quality screens. Longitudinal tracking against individual baselines reveals training effectiveness better than normative comparisons.