CHAPTER 4 Muscular Strength and Endurance
Basic Muscle Physiology and the Effects of Strength Training
Muscles are organized in a hierarchical structure: muscle → fascicle → muscle fibers (cells) → myofibrils → sarcomeres (contractile units primarily made of actin and myosin).
Muscle contraction mechanism: myosin heads slide along actin filaments in a ratcheting fashion to shorten the sarcomere and produce force.
Each muscle cell contains multiple nuclei (genes) that control production of enzymes and proteins needed for contraction.
Satellite cells: activated by strength training; provide additional nuclei to muscle fibers to support repair and muscle protein synthesis; effects persist even after intense training declines.
Hypertrophy: increase in size of individual muscle fibers due to strength training; results from enlargement and increased number of myofibrils; begins after about 6–8 weeks of training.
Hyperplasia in humans is not thought to play a significant role in determining muscle size (increase in fiber number); some species show hyperplasia, but not typical in humans.
Reversibility: inactivity leads to a decrease in muscle fiber size (atrophy).
Muscle mass and strength relate to wellness: muscles comprise >40% of body mass and are central to movement, metabolism, injury protection, and overall well‑being.
Muscle Fiber Types and Neural Elements
Slow-twitch (Type I) fibers:
Aerobic/oxidative energy system; fatigue resistant; slower contraction; red in color due to blood supply.
Fast-twitch (Type II) fibers:
Rely more on anaerobic metabolism; contract rapidly and forcefully; fatigue more quickly; typically white/meaty in appearance.
Individuals contain a mix of slow- and fast-twitch fibers, with proportions varying by muscle and person; baseline fiber type distribution is largely set at birth but can adapt somewhat with training.
Endurance activities favor slow-twitch fiber recruitment; strength/power activities favor fast-twitch fiber recruitment.
Motor units: a motor nerve connected to a group of muscle fibers; the number of fibers per motor unit ranges from 2 to hundreds.
Small motor units tend to contain slow-twitch fibers; large motor units contain fast-twitch fibers.
Activation is controlled by the nervous system; building strength also involves improved nerve recruitment and muscle learning, not just muscle size.
Myelin on axons speeds neural conduction; practice can increase myelin along motor pathways, improving speed and accuracy of movement.
Motor programs in the brain store sequences of movements; practice lays down grooves in neural pathways, enabling automatic and precise skilled movements (e.g., typing, cycling).
Motor learning (muscle learning): strength gains can occur before muscle size increases due to improved motor unit recruitment.
Practical implication: technique quality and motor control are foundational for rapid, powerful, and safe lifts.
The Box: Harnessing Motor Control for Improving Skill and Power
The brain stores millions of motor programs and becomes increasingly automatic with practice.
Myelin growth on specific motor nerves strengthens movement speed and efficiency.
Improving motor control emphasizes accurate technique over simply lifting heavier weights.
Strategies:
Focus on accurate technique first; get feedback from a qualified trainer; correct mistakes; practice refined movements.
Move smoothly through whole movements rather than breaking into isolated muscle actions.
Break down complex sequences initially, then progress to whole-body, fluid movements because the brain encodes whole actions, not isolated muscles.
Program motor patterns to increase power and accuracy; training should reinforce reflex-like patterns.
Sex Differences in Muscular Strength
Males are generally larger with a higher proportion of muscle mass, contributing to greater absolute strength.
Relative strength (per unit cross‑sectional area of muscle) is similar between sexes; males may be ~1–2% stronger in the upper body and roughly equal in the lower body.
Testosterone promotes muscle growth; typical male testosterone levels are 5–10× higher than females, aiding upper-body strength gains.
Nervous system factors: males may activate muscles faster, contributing to greater power.
Training results for females: tend to gain muscle and improve body composition without large gains in weight.
Example finding: average females weight-trained 2–3 days/week for 8 weeks gained ~1.75 lb muscle and lost ~3.5 lb fat.
Bottom line: everyone can increase strength through training; pound-for-pound gains can be similar, but absolute gains may differ due to baseline hormonal and body composition differences.
Physiological Changes and Benefits from Strength Training (Table 4.1, summary)
Increased muscle mass and strength; improved body composition; higher resting metabolic rate; improved fuel regulation with aging; improved bone and tendon strength; increased longevity and quality of life.
Neuromuscular adaptations include increased motor unit recruitment and coordination, leading to stronger and more powerful movements.
Hormonal and nervous system influences: testosterone and nervous system efficiency contribute to sex differences in how muscles adapt.
Endurance and speed benefits: improvements in both strength and endurance, plus enhancements in movement coordination and bone health.
Biochemical/metabolic improvements: improved insulin sensitivity, lipid profile, and other metabolic health markers.
Note: genetic and hormonal differences influence magnitude of mass gains, but functional gains (strength) tend to be achieved by all.
Assessing Muscular Strength and Endurance
Muscular strength: assessed by maximum weight that can be lifted in a single effort; 1‑repetition maximum (1RM).
1RM testing guidelines:
Learn proper technique first; base values on a baseline period of training; retest after 6–12 weeks.
Avoid strenuous testing within 48 hours of prior heavy lifting; use direct 1RM testing or estimate via submaximal testing.
See Lab 4.1 for detailed procedures and normative references.
Muscular endurance: assessed by number of repetitions of an exercise or time held (static holds).
Tests include curl-ups, push-ups, squat endurance; Lab 4.2 provides full instructions.
Tests for lower-back endurance exist in Chapter 5.
Creating a Successful Strength Training Program: Key Concepts
Adaptation principle: stress beyond usual loads leads to improvements; the nature of the stress determines adaptation (overload).
Static vs Dynamic strength training:
Static (isometric) contractions: muscle contracts without changing length or joint angle; useful for injured joints and stabilizing the spine; held contractions typically around 6 seconds for max strength gains, 2–10 reps.
Dynamic (isotonic) contractions: muscle contracts with movement; two main types:
Concentric: muscle shortens while producing force (e.g., lifting in a curl).
Eccentric (pliometric): muscle lengthens while producing force (e.g., lowering in a curl); emphasizes eccentric loading.
Constant resistance vs variable resistance:
Constant resistance: fixed load through full range of motion (e.g., free weights).
Variable resistance: load changes to match leverage and strength across range (typical in machines).
Core stability and static work: core muscles stabilize the spine during dynamic movements; static work helps with healing and overcoming weak points.
Training modalities and equipment:
Machines: safer, easier to isolate muscles; require less balance; back support often provided.
Free weights: require balance and coordination; highly functional for real-life movements; preferred by athletes for functional strength.
Body weight: convenient at home; can be scaled with leverage and tempo.
Other tools: resistance bands, stability balls, medicine balls, kettlebells, suspension training (TRX).
Principle: train movements, not just muscles; overload the body in everyday movements for functional gains.
Box: Safety and technique emphasized; use a qualified trainer to learn form; avoid breath-holding; maintain neutral spine; control weight through full ROM.
Static (Isometric) vs Dynamic (Isotonic) Strength Training
Static/isometric:
Contraction without changing muscle length or joint angle.
Useful for stabilizing joints and rehab; can strengthen at weak points in a range of motion.
Dynamic/isotonic:
Contractions with movement; two main forms:
Concentric: shorten muscle; overcome resistance.
Eccentric: lengthen muscle under load; often produces greater force and muscle damage that stimulates adaptation.
Practical distinction: most people use dynamic exercises; static work complements dynamic training for stability and rehab.
Weight Machines, Free Weights, and Body Weight Exercises
Resistance can come from free weights, machines, or body weight.
Machines:
Pros: safety, ease of use, back support, isolation of muscles, no spotter required.
Cons: may provide less functional transfer to real-life movements.
Free weights:
Pros: functional strength, coordination, portability, cost.
Cons: higher risk without supervision, need for proper technique.
Body weight:
Pros: minimal equipment; versatile; good for home workouts; scalable with leverage and tempo.
Core principle: plan should include major muscle groups with 8–10 exercises in a full-body routine; choose modality based on goals, access, and safety.
Other Dynamic Exercise Techniques and Equipment
Eccentric loading/negatives: emphasize lengthening phase to overload muscle.
Plyometrics: rapid eccentric loading followed by a fast concentric contraction; enhances explosive strength and supports bone density.
Speed loading: move loads as fast as possible to train neuromuscular speed and power.
Isokinetic training: constant movement speed with accommodating resistance; useful for strength and endurance development.
Kettlebell training: ballistic movements with fast, pendulum-like motions; emphasizes posterior chain and core control.
Suspension training (TRX), stones, carrying exercises: functional, whole-body conditioning; focus on core and posture.
Stability balls: develop core stabilization; adds balance challenge; caution due to instability risk.
Blood flow restriction (KAATSU/BFR): increases metabolic stress; may aid hypertrophy with low loads but risk of injury; not universally superior to traditional training.
The FITT Principle: Selecting Exercises and Building a Program
FITT: Frequency, Intensity, Time, Type.
Frequency: general guideline is at least 2 nonconsecutive days per week; allow 1 day of rest between workouts; some evidence for training same muscle 3 days/week or split routines.
Intensity (amount of resistance): choose weights that fatigue muscles with proper form; to build strength, use around 80% of 1RM for ~8–10 reps; for endurance, use lighter loads (40–60% 1RM) for more reps (15–20).
Time (reps and sets): continuous effort to fatigue; typical program aims for 8–12 reps per exercise; 1–3 sets for general wellness; heavier loads may require 3–5 minutes rest between sets; older/frail individuals may benefit from 10–15 reps with lighter loads.
Type: 8–10 exercises targeting major muscle groups; consider sport-specific muscles; ensure both agonist and antagonist muscle groups are trained; plan for balanced development.
Volume and progression:
Volume = Frequency × Intensity × Time; adjust across workouts to promote progress and prevent plateaus.
Progression: add weight or sets as strength increases; vary load and repetitions; maintain form; after achieving goals, maintain with 1–3 sessions/week.
Warm-up and cool-down: essential before and after any weight training session; gradual aerobic activity followed by warm-up sets; cool-down with light cardio and optional stretching.
Example progression: start with 1 set of 8–12 reps, then progress to 2–3 sets; increase weight when you can complete 12 reps with good form; if reps drop or form suffers, reduce weight.
Order of exercises: train large muscle groups before small ones; alternate pushing and pulling movements; train opposing muscle groups in sequence.
Warm-up example: bench press warm-up with light weight before working up to working weight; use sets to gradually increase load.
Program Design Details: Getting Started and Progression
Beginners should focus on learning movements, building technique, and gradually increasing resistance.
When adding resistance, if you can still complete 12 reps with good form, you’re progressing; if you can only perform 4–6 reps, you may have added too much weight.
Larger muscle groups (e.g., squats, bench press) can tolerate greater weight increases than smaller muscle groups (e.g., lateral raises).
Provide rest between exercises; 1–2 minutes between exercises is common for general fitness; longer rests (3–5 minutes) for high-load strength sets.
Advanced training approaches include cycle/periodization where volume and intensity vary across weeks or cycles to maximize progression and minimize overuse.
Warm-Up, Cool-Down, and Injury Prevention
Warm-up: 5–10 minutes of light cardio plus movement-specific warm-up sets.
Cool-down: 5–10 minutes of low-intensity activity; gentle stretches may help with flexibility post-workout.
Safe Weight Training: follow guidelines to prevent injuries; learn proper technique from a trainer; use spotters and collars for free weights when necessary; never hold breath during lifting (exhale on exertion, inhale on reset).
Common equipment safety: ensure collars are secure; inspect equipment for wear; avoid training through pain; address injuries with R-I-C-E (Rest, Ice, Compression, Elevation).
Spotting and safety strategies: use spotters for lifts crossing the face/head, overhead presses, squats; use power racks for heavy squats; communicate signals with spotters before lifts.
Belts and bracing: weight belts are not universally protective and can enable lifting beyond safe form; use them cautiously if at all.
Safety Guidelines in Practice: Weight Training Boxes and Tips
Safe Weight Training General Guidelines: learn technique; lift from a stabilized position; protect your back; avoid holding breath; breathe smoothly; use proper form; inspect equipment; don’t train through illness or injury.
Free Weights: ensure even loading; lift with a neutral spine; hinge at the hips; avoid bouncing; keep weights controlled.
Spotters: use appropriate spotting based on exercise; coordinate with lifter on signals.
Weight Increments: aim for roughly 5% increases per progression (about +0.5 lb for every 10 lbs lifted).
Progress Tracking: keep a workout card to monitor loads, sets, reps; sample layout provided in the book.
The Weight Training Exercises: Overview of Major Muscle Groups and Sample Movements
The program covers major muscle groups: neck/back, shoulders, arms, chest, abdomen, lower back, hips, thighs, calves, glutes.
Example exercise families by modality:
Body weight: air squats, push-ups, planks, side bridges, bird dogs, etc. (progressions like stir-the-pot on stability ball).
Free weights: bench press, pull-ups (assisted if needed), shoulder press, upright rows, biceps curls, lateral raises, squats, heel raises, leg extensions, leg curls, etc.
Weight machines: bench press, lat pull, leg press, leg extension, leg curl, pullover, triceps extensions, etc.
The text emphasizes a balanced, full-body routine with 8–10 exercises for major muscle groups.
The Labs (4.1–4.3) guide assessment and program design:
Lab 4.1: Assess current strength (1RM tests and functional lower-body movement tests); use results to set goals.
Lab 4.2: Assess current muscular endurance (curl-ups, push-ups, squat endurance, etc.).
Lab 4.3: Design and monitor a strength program using the FITT framework; includes a sample program plan and a workout card.
Lab 4.3 emphasizes the use of apps or tools (Beast Sensor, Strong, Stronger) to track progress; monitoring helps with progression and accountability.
Supplements and Ergogenic Aids in Strength Training
Creatine monohydrate:
Popular supplement; increases muscle phosphocreatine content by ~20 ext{%}; supports ATP regeneration and high-intensity performance; may improve training capacity and hypertrophy with long-term use; long-term safety unclear.
Protein and amino acids:
Protein intake generally 0.8–1.5 g/kg body weight per day for active individuals; timing around workouts (pre/post) can enhance amino acid delivery and protein synthesis; supplements can be convenient but are not superior to whole foods.
Carbohydrate beverages and recovery: can aid glycogen replenishment after intense training.
Other supplements (e.g., DHEA, testosterone boosters, anabolic steroids, growth hormone, diuretics, etc.): potential benefits are often overstated and risks include liver toxicity, hormonal disturbances, cardiovascular issues, immune changes, cancer risk, and legal/safety concerns. Most are not proven to be safe or effective for athletic performance.
Caffeine:
CNS stimulant; can enhance endurance, strength, and power at moderate doses; higher doses may cause arrhythmias and insomnia.
The text emphasizes that dietary supplements are not regulated as rigorously as drugs; the primary strategy should be a balanced diet, with caution around ergogenic aids.
Common Questions and Practical Guidance
Will I gain weight from resistance training?
If using a general fitness program (8–10 exercises, 8–12 reps, 2 nonconsecutive days/week), you may not see a large weight change, but fat loss and muscle gain can offset to leave similar body weight; body composition often improves.
Do I need more protein when training with weights?
Generally no; most people meet protein needs with a normal diet; timing around workouts can help but protein bars/shakes are not mandatory; high-protein strategies may help in combination with caloric control and resistance training.
What causes muscle soreness after training?
Delayed-onset muscle soreness results from micro-damage and inflammation; not lactic acid buildup; protective proteins develop after training to reduce soreness with subsequent workouts.
Will strength training automatically improve sports performance?
Not automatically; skill and technique are required; improved strength supports performance when integrated with sport-specific training and motor skills practice.
Should I train every day?
Generally no; recovery is essential; overtraining can hinder progress; vary frequency, volume, and intensity; consider planned rest days and progressive overload.
Do I turn my muscle into fat if I stop training?
Muscle and fat are different tissue types; inactivity leads to muscle atrophy and potential fat gain if energy balance shifts, but fat does not turn into muscle.
Advanced Strength Training Concepts
More advanced programs: higher volume with lighter loads (3–5 sets of 4–6 reps), explosive lifting, and periodization to vary loads, sets, and exercises over cycles to maximize gains and reduce injury risk.
Getting started and progression: start with 1 set of 8–12 reps, rest 1–2 minutes; gradually add sets and weight; maintain good form; adjust progression based on rate of improvement.
Progression criteria: if you can perform 12 reps with good form, increase weight; if you can’t reach 12 reps, stay at current weight until you can.
Labs and Practice Summary (Labs 4.1–4.3)
Lab 4.1: Assessing current muscular strength using 1RM methods and functional lower-body movement tests; establish baseline and set goals.
Lab 4.2: Assessing muscular endurance through curl-ups, push-ups, and squat endurance tests; gauge abdominal, upper-body, and lower-body endurance; translate results into goals.
Lab 4.3: Designing and monitoring a strength program using the FITT framework; includes a sample program, a workout card, and guidance on goal setting, frequency, intensity, time, and volume; emphasizes tracking progress with apps or devices for motivation and data.
At-Home and Digital Wellness Options
Wellness in the Digital Age: virtual workouts, online classes, personal trainers, and connected equipment offer flexible options for home training.
Options include live virtual sessions, pre-recorded classes, and smart devices that provide real-time feedback on technique and form.
Safety considerations: ensure proper instruction, space, and equipment; start with familiar exercises and gradually progress; consider professional guidance when transitioning from machines to free weights.
Practical Exercises: Quick Reference (Sample Exercises by Modality)
Body weight: air squats, lunges, planks, side bridges, push-ups, burpees, single-leg step-ups, chair squats.
Free weights: bench press, barbell squats, overhead press, bent-over rows, biceps curls, triceps extensions, lateral raises, goblet squats.
Machines: leg press, leg extension, leg curl, lat pull, seated row, chest press, overhead press.
Core and balance: stability ball exercises, front plank, side plank, bird dog, stir-the-pot.
Quick Formulas and Key Numbers to Remember
1RM estimation (Brzycki):
1RM = \frac{\text{weight}}{1.0278 - 0.0278 \times n}
where n = number of repetitions performed.Percentage guidance for program planning:
Strength focus: weight ≈ 0.8 × 1RM for 8–10 reps (high-intensity, lower reps).
Endurance focus: weight ≈ 0.4–0.6 × 1RM for 15–20 reps.
Volume (general guideline):
\text{Volume} = \text{Frequency} \times \text{Intensity} \times \text{Time}Intensity guidance examples:
Heavier loads: 70–80% of 1RM for 8–12 reps.
Lighter loads for endurance: 40–60% of 1RM for 15–20 reps.
Training frequency: minimum 2 nonconsecutive days per week; rest 1–3 days between sessions depending on load and goals.
Rest between sets:
Moderate/strength: 1–3 minutes between sets.
Heavier strength: 3–5 minutes between sets.
Summary Takeaways
Strength training improves muscle size, strength, endurance, metabolic health, and longevity; benefits extend to bones, tendons, and ligaments.
Muscle size increases via hypertrophy; hyperplasia is not a major contributor in humans.
Training should emphasize motor control and technique; neural adaptations contribute to strength gains even before substantial hypertrophy.
The FITT framework provides a practical structure for designing and adjusting a program; progression should be gradual and systematic to avoid plateaus.
Safety, technique, and consistency are more important than chasing rapid increases in weight; use proper spotting, equipment checks, and rest.
Supplements can offer limited benefits and carry risks; prioritize a balanced diet and evidence-supported approaches.
Labs and home programs provide practical methods to assess and design a personalized plan; aim for a sustainable, enjoyable routine that fits your goals and environment.