Resistance training (strength training) is a systematic method of exercising against external resistance to improve muscular strength, endurance, power, and hypertrophy.
Foundational Principles
Progressive Overload
The body adapts to a training stimulus only when that stimulus exceeds its current capacity. To continue making gains, the training demand must be progressively increased. Methods of progressive overload include: increasing load (weight) by 2-10% when target repetitions are achieved, increasing volume by adding 1-2 sets per exercise per session, increasing frequency by adding one training day per week, manipulating time under tension by slowing the eccentric phase (2-4 seconds), decreasing rest periods between sets (for endurance), and progressing to more challenging exercise variations.
Specificity (SAID Principle)
Specific Adaptation to Imposed Demands — the body’s adaptations are specific to the type of training performed. Heavy, low-repetition training (1-5 reps) produces strength and neural adaptations. Moderate-repetition training (6-12 reps) produces hypertrophy. High-repetition training (15-25 reps) produces muscular endurance. Isometric training at a specific joint angle produces strength gains primarily at that angle. Exercises should closely mimic the movement patterns of the sport or activity being trained.
Individualization
Training programs must account for individual differences: training status (beginner, intermediate, advanced), age, genetics, recovery capacity, injury history, goals, and available equipment. Beginners typically make rapid gains on almost any program. Advanced individuals require more specific, periodized programming.
Program Variables
Exercise Selection
Exercises are classified as compound (multi-joint) or isolation (single-joint). Compound exercises involve multiple muscle groups and joints simultaneously (squats, deadlifts, bench press, rows, pull-ups, overhead press). They produce greater overall strength and hormonal response, are more time-efficient, and are better for functional strength. Isolation exercises target a single muscle group (bicep curls, tricep extensions, leg extensions, lateral raises). They are useful for targeting weak points, prehab/rehab, and achieving specific hypertrophy goals.
A program should prioritize compound exercises (2-4 per session) with 0-2 isolation exercises as accessories.
Load and Repetitions
Repetition maximum (RM) is the maximum weight that can be lifted for a given number of repetitions. A 1RM is the heaviest weight that can be lifted once. For general strength: 85-100% of 1RM, 1-6 reps, 2-6 sets. For hypertrophy: 67-85% of 1RM, 6-12 reps, 3-6 sets. For muscular endurance: 50-67% of 1RM, 15-25+ reps, 2-4 sets. For power: 80-90% of 1RM (for speed-strength) or 30-60% of 1RM (for explosive movements), 1-5 reps, 3-6 sets.
Volume
Volume is the total amount of work performed: sets × reps × load. For hypertrophy, 10-20 sets per muscle group per week is the general recommendation (with 15-25 sets for advanced individuals). For strength, 5-10 sets per major movement pattern per week. Beginners respond well to lower volumes (5-10 sets per muscle group per week). Volume must be matched to recovery capacity — excessive volume without adequate recovery leads to overtraining.
Rest Periods
For maximal strength (1-5 RM), rest 3-5 minutes between sets to allow full ATP-PCr system recovery. For hypertrophy (6-12 RM), rest 60-90 seconds. For muscular endurance (15-25+ RM), rest 30-60 seconds. For power, rest 2-5 minutes.
Tempo
Tempo describes the speed of each repetition, typically expressed as a four-digit code: eccentric (lowering), pause (at bottom), concentric (lifting), pause (at top). A standard tempo of 2-0-2-0 means 2 seconds lowering, no pause, 2 seconds lifting, no pause. Slower eccentrics (3-4 seconds) increase time under tension and may enhance hypertrophy. Faster concentrics (explosive lifts) enhance strength and power.
Training Frequency
Full-body training (3 days per week) is optimal for beginners and general fitness. Upper-lower split (4 days per week: 2 upper body, 2 lower body) is effective for intermediate individuals. Push-pull-legs split (6 days per week: 2 push, 2 pull, 2 legs) is common for advanced bodybuilders. The total weekly volume per muscle group, not frequency per se, is the primary driver of hypertrophy. Higher frequencies (2-3 times per week per muscle group) may produce slightly better results and allow for higher weekly volume with better recovery.
Physiological Adaptations
Neural adaptations occur first (0-8 weeks): increased motor unit recruitment, improved firing rate, reduced co-contraction of antagonist muscles, and enhanced intermuscular coordination. These adaptations produce strength gains without significant muscle size increase.
Muscle adaptations occur over 8-12+ weeks: increased cross-sectional area (hypertrophy) from increased myofibrillar protein synthesis, increased fiber type II cross-sectional area (especially type IIx converting to IIa), increased connective tissue and tendon stiffness, increased bone mineral density, and improved capillary density in trained muscles.
Hormonal acute responses include transient increases in growth hormone, testosterone, and cortisol immediately post-exercise. These acute responses are not necessary for hypertrophy but may contribute to the adaptive environment.
Summary
Resistance training is programmed using the principles of progressive overload, specificity, and individualization. Key variables include exercise selection (prioritize compound movements), load and repetitions, volume (10-20 sets per muscle group per week), rest periods, and tempo. Neural adaptations precede muscle hypertrophy. A balanced program includes 2-3 sessions per week targeting all major muscle groups through full range of motion with proper form.