Fitness Fundamentals: The Science of Physical Adaptation
The Core Principle: Stress → Adaptation
Your body is a survival machine. It adapts specifically to the demands you place on it:
- Lift heavy things → Muscles grow stronger
- Run frequently → Cardiovascular system becomes efficient
- Stretch regularly → Tissues become more pliable
- Do nothing → Systems atrophy (use it or lose it)
This is the SAID Principle: Specific Adaptation to Imposed Demands.
The Three Training Variables
Every training program manipulates these:
1. Volume (How Much)
- Sets × Reps × Weight = Total volume
- Primary driver of muscle growth (hypertrophy)
- More isn't always better — there's a recoverable dose
2. Intensity (How Hard)
- Percentage of your maximum capacity
- For strength: heavier weight, fewer reps (1-5 reps at 85%+ of max)
- For hypertrophy: moderate weight, more reps (6-12 reps at 65-80%)
- For endurance: lighter weight, high reps (15+ reps at <65%)
3. Frequency (How Often)
- How many times per week you train a movement/muscle
- Research shows 2-3x per week per muscle group is optimal for most
- Allows adequate volume while permitting recovery
Progressive Overload: The Non-Negotiable Law
Your body only adapts when forced to.
If you do the same thing repeatedly, your body has no reason to change. You must progressively increase demands:
| Method | Example |
|---|---|
| Add weight | 100kg → 102.5kg |
| Add reps | 8 reps → 10 reps |
| Add sets | 3 sets → 4 sets |
| Decrease rest | 90 sec → 75 sec |
| Increase range of motion | Half squat → Full squat |
| Slow the tempo | 2 sec down → 4 sec down |
The principle: Do slightly more than last time. Small increments compound into massive changes over months and years.
The Fundamental Movement Patterns
All human movement reduces to these patterns. A complete program trains all of them:
| Pattern | Examples | Primary Muscles |
|---|---|---|
| Hinge | Deadlift, kettlebell swing, good morning | Hamstrings, glutes, lower back |
| Squat | Back squat, front squat, goblet squat | Quads, glutes, core |
| Push (Horizontal) | Bench press, push-up | Chest, front delts, triceps |
| Push (Vertical) | Overhead press, pike push-up | Shoulders, triceps, upper chest |
| Pull (Horizontal) | Barbell row, cable row | Lats, rhomboids, biceps |
| Pull (Vertical) | Pull-up, lat pulldown | Lats, biceps, rear delts |
| Carry/Core | Farmer's walk, planks, pallof press | Core stabilizers, grip |
| Locomotion | Walking, running, sprinting | Cardiovascular system, legs |
A balanced week hits all patterns. Imbalances (e.g., lots of pushing, little pulling) lead to postural issues and injury.
Training Splits: Organizing Your Week
Full Body (3x/week)
Mon: Full body Wed: Full body Fri: Full body
- Best for: Beginners, those with limited time
- Advantage: High frequency per muscle, fewer sessions
- Example session: Squat, Bench, Row, Hinge, Carry
Upper/Lower (4x/week)
Mon: Upper Tue: Lower Thu: Upper Fri: Lower
- Best for: Intermediate lifters, balanced approach
- Advantage: Good volume and frequency balance
Push/Pull/Legs (6x/week or 3x/week)
Mon: Push Tue: Pull Wed: Legs (repeat or rest)
- Best for: Advanced lifters wanting high volume
- Advantage: Maximum volume per muscle group
The Evidence
Research by Schoenfeld et al. shows that training each muscle 2x per week produces superior hypertrophy compared to 1x per week, even when volume is equated. Frequency matters.
Rep Ranges and Their Effects
| Rep Range | Primary Adaptation | Mechanism |
|---|---|---|
| 1-5 reps | Strength (neural) | Teaches nervous system to recruit more fibers |
| 6-12 reps | Hypertrophy (muscle size) | Metabolic stress + mechanical tension |
| 12-20 reps | Muscular endurance | Mitochondrial density, capillary growth |
| 20+ reps | Endurance, conditioning | Aerobic adaptations |
The truth: There's significant overlap. You can build muscle in any range if taken close to failure. But the 6-12 range is most efficient for hypertrophy — enough load to create tension, enough reps to accumulate volume.
The Concept of Proximity to Failure
RIR = Reps In Reserve (how many more reps could you have done)
| RIR | Effort Level | Use Case |
|---|---|---|
| 4+ | Warm-up, technique work | Learning movements |
| 2-3 | Productive training | Most working sets |
| 1 | Hard set | Key sets, strength work |
| 0 | Failure | Sparingly, final sets |
Research shows: Sets taken to 0-3 RIR produce similar hypertrophy. Going to failure every set increases fatigue without proportional benefit. Train hard, not maximal.
Cardiovascular Training: The Continuum
| Type | Heart Rate Zone | Duration | Adaptations |
|---|---|---|---|
| Zone 2 (Aerobic base) | 60-70% max HR | 30-90 min | Mitochondrial density, fat oxidation, recovery |
| Threshold | 80-85% max HR | 20-40 min | Lactate clearance, aerobic power |
| HIIT | 85-95% max HR | 10-25 min | VO2max, anaerobic capacity |
| Sprint | 95-100% max HR | 5-15 min total | Power, neuromuscular efficiency |
The overlooked foundation: Most people do too much high-intensity cardio and not enough Zone 2. Elite endurance athletes spend 80% of their training in Zone 2. It builds the aerobic base that supports everything else.
Minimum effective dose for health:
- 150 min/week moderate activity, OR
- 75 min/week vigorous activity
- Plus 2x/week resistance training
Recovery: Where Adaptation Actually Happens
Training is the stimulus. Recovery is when you actually get stronger.
The Recovery Hierarchy
-
Sleep (non-negotiable)
- Growth hormone peaks during deep sleep
- Muscle protein synthesis elevated during sleep
- 7-9 hours for most adults
-
Nutrition (covered previously)
- Protein for repair
- Carbs to replenish glycogen
- Adequate calories to support adaptation
-
Stress Management
- Cortisol (stress hormone) is catabolic when chronic
- Training is a stressor — life stress adds to training stress
- High life stress = reduce training volume
-
Active Recovery
- Light movement increases blood flow
- Walking, swimming, mobility work
- Better than complete rest for most
Signs of Under-Recovery
- Plateau or regression in performance
- Persistent fatigue
- Elevated resting heart rate
- Mood disturbances, irritability
- Frequent illness
- Loss of motivation
Periodization: The Long Game
You can't push maximally forever. Training should wave between periods of:
- Accumulation: Higher volume, moderate intensity (building capacity)
- Intensification: Lower volume, higher intensity (expressing strength)
- Deload: Reduced volume and intensity (recovery week every 4-6 weeks)
Simple linear periodization for beginners:
- Week 1: 3×8 at RPE 7
- Week 2: 3×8 at RPE 8
- Week 3: 4×8 at RPE 8
- Week 4: Deload — 2×8 at RPE 6
- Week 5: Add weight, restart
Practical Programming Template
Beginner Full Body (3x/week)
A1. Squat variation 3×8
A2. Horizontal push 3×8
B1. Hinge variation 3×8
B2. Horizontal pull 3×8
C1. Vertical push or pull 2×10
C2. Core work 2×10
D. Carry or conditioning 5-10 min
Intermediate Upper/Lower (4x/week)
Upper A:
Bench Press 4×6
Barbell Row 4×6
Overhead Press 3×10
Pull-ups 3×8
Tricep/Bicep work 2×12 each
Lower A:
Squat 4×6
Romanian Deadlift 3×10
Leg Press 3×12
Leg Curl 3×12
Calf Raises 3×15
Upper B & Lower B: Similar structure, different exercises
The Principles That Matter Most
- Consistency beats perfection — showing up 3x/week for years beats 6x/week for 2 months
- Progressive overload is mandatory — do more over time
- Recovery is part of training — not optional
- Train movements, not muscles — compound lifts are the foundation
- Specificity matters — train for your goals
- Minimum effective dose — more isn't better, better is better
- Patience — meaningful physical change takes months to years
Summary
| Principle | Application |
|---|---|
| SAID Principle | Your body adapts to what you do |
| Progressive Overload | Increase demands over time |
| Movement Patterns | Train all 7 patterns weekly |
| Rep Ranges | Match reps to goals |
| Frequency | 2-3x per muscle per week |
| Recovery | Sleep, nutrition, stress management |
| Periodization | Wave intensity and volume |
Document created: December 2024 Part of the Wellness Guide Series