chapter 10

Adaptations to Resistance Training

CHAPTER 10 CHAPTER 10 OverviewOverview

• Resistance training: gains in muscular fitness

• Mechanisms of muscle strength gain

• Muscle soreness

• Resistance training for special populations

Resistance Training: IntroductionResistance Training: Introduction

• Resistance training yields substantial strength gains via neuromuscular changes

• Important for overall fitness and health

• Critical for athletic training programs

Resistance Training: Resistance Training: Gains in Muscular FitnessGains in Muscular Fitness

• After 3 to 6 months of resistance training – 25 to 100% strength gain– Learn to more effectively produce force– Learn to produce true maximal movement

• Strength gains similar as a percent of initial strength– Young men experience greatest absolute gains

versus young women, older men, children– Due to incredible muscle plasticity

Mechanisms of Muscle Strength Gain Mechanisms of Muscle Strength Gain

• Hypertrophy versus atrophy – Muscle size muscle strength

– Muscle size muscle strength– But association more complex than that

• Strength gains result from– Muscle size– Altered neural control

Figure 10.1Figure 10.1aa

Figure 10.1Figure 10.1bb

Figure 10.1Figure 10.1cc

Mechanisms of Muscle Strength Gain:Mechanisms of Muscle Strength Gain:Neural ControlNeural Control

• Strength gain cannot occur without neural adaptations via plasticity– Strength gain can occur without hypertrophy– Property of motor system, not just muscle

• Motor unit recruitment, stimulation frequency, other neural factors essential

Mechanisms of Muscle Strength Gain:Mechanisms of Muscle Strength Gain:Motor Unit Recruitment Motor Unit Recruitment

• Normally motor units recruited asynchronously

• Synchronous recruitment strength gains– Facilitates contraction– May produce more forceful contraction– Improves rate of force development

– Capability to exert steady forces

• Resistance training synchronous recruitment

Mechanisms of Muscle Strength Gain:Mechanisms of Muscle Strength Gain:Motor Unit Recruitment Motor Unit Recruitment

• Strength gains may also result from greater motor unit recruitment– Neural drive during maximal contraction

– Frequency of neural discharge (rate coding)

– Inhibitory impulses

• Likely that some combination of improved motor unit synchronization and motor unit recruitment strength gains

Mechanisms of Muscle Strength Gain:Mechanisms of Muscle Strength Gain:Motor Unit Rate CodingMotor Unit Rate Coding

• Limited evidence suggests rate coding increases with resistance training, especially rapid movement, ballistic-type training

Mechanisms of Muscle Strength Gain:Mechanisms of Muscle Strength Gain:Autogenic InhibitionAutogenic Inhibition

• Normal intrinsic inhibitory mechanisms– Golgi tendon organs– Inhibit muscle contraction if tendon tension too high– Prevent damage to bones and tendons

• Training can inhibitory impulses– Muscle can generate more force– May also explain superhuman feats of strength

Mechanisms of Muscle Strength Gain:Mechanisms of Muscle Strength Gain:Other Neural FactorsOther Neural Factors

• Coactivation of agonists, antagonists– Normally antagonists oppose agonist force– Reduced coactivation may strength gain

• Morphology of neuromuscular junction

Mechanisms of Muscle Strength Gain:Mechanisms of Muscle Strength Gain:Muscle HypertrophyMuscle Hypertrophy

• Hypertrophy: increase in muscle size

• Transient hypertrophy (after exercise bout)– Due to edema formation from plasma fluid– Disappears within hours

• Chronic hypertrophy (long term)– Reflects actual structural change in muscle– Fiber hypertrophy, fiber hyperplasia, or both

Mechanisms of Muscle Strength Gain:Mechanisms of Muscle Strength Gain:Chronic Muscle HypertrophyChronic Muscle Hypertrophy

• Maximized by– High-velocity eccentric training– Disrupts sarcomere Z-lines (protein remodeling)

• Concentric training may limit muscle hypertrophy, strength gains

Mechanisms of Muscle Strength Gain:Mechanisms of Muscle Strength Gain:Fiber HypertrophyFiber Hypertrophy

• More myofibrils

• More actin, myosin filaments

• More sarcoplasm

• More connective tissue

Mechanisms of Muscle Strength Gain:Mechanisms of Muscle Strength Gain:Fiber HypertrophyFiber Hypertrophy

• Resistance training protein synthesis– Muscle protein content always changing– During exercise: synthesis , degradation – After exercise: synthesis , degradation

• Testosterone facilitates fiber hypertrophy– Natural anabolic steroid hormone– Synthetic anabolic steroids large increases in

muscle mass

Mechanisms of Muscle Strength Gain:Mechanisms of Muscle Strength Gain:Fiber HyperplasiaFiber Hyperplasia

• Cats– Intense strength training fiber splitting– Each half grows to size of parent fiber

• Chickens, mice, rats– Intense strength training only fiber hypertrophy– But difference may be due to training regimen

Figure 10.3Figure 10.3


• Humans– Most hypertrophy due to fiber hypertrophy– Fiber hyperplasia also contributes – Fiber hypertrophy versus fiber hyperplasia may

depend on resistance training intensity/load– Higher intensity (type II) fiber hypertrophy

• Fiber hyperplasia may only occur in certain individuals under certain conditions


• Can occur through fiber splitting

• Also occurs through satellite cells– Myogenic stem cells– Involved in skeletal muscle regeneration– Activated by stretch, injury– After activation, cells proliferate, migrate, fuse

Mechanisms of Muscle Strength Gain:Mechanisms of Muscle Strength Gain:Neural Activation + HypertrophyNeural Activation + Hypertrophy

• Short-term in muscle strength– Substantial in 1RM– Due to voluntary neural activation– Neural factors critical in first 8 to 10 weeks

• Long-term in muscle strength– Associated with significant fiber hypertrophy– Net protein synthesis takes time to occur– Hypertrophy major factor after first 10 weeks

Mechanisms of Muscle Strength Gain:Mechanisms of Muscle Strength Gain:Atrophy and InactivityAtrophy and Inactivity

• Reduction or cessation of activity major change in muscle structure and function

• Limb immobilization studies

• Detraining studies

Mechanisms of Muscle Strength Gain:Mechanisms of Muscle Strength Gain:ImmobilizationImmobilization

• Major changes after 6 h– Lack of muscle use reduced rate of protein

synthesis– Initiates process of muscle atrophy

• First week: strength loss of 3 to 4% per day– Size/atrophy

– Neuromuscular activity

• (Reversible) effects on types I and II fibers– Cross-sectional area cell contents degenerate– Type I affected more than type II

Mechanisms of Muscle Strength Gain:Mechanisms of Muscle Strength Gain:DetrainingDetraining

• Leads to in 1RM– Strength losses can be regained (~6 weeks)– New 1RM matches or exceeds old 1RM

• Once training goal met, maintenance resistance program prevents detraining– Maintain strength and 1RM – Reduce training frequency

Figure 10.6Figure 10.6cc

Mechanisms of Muscle Strength Gain:Mechanisms of Muscle Strength Gain:Fiber Type AlterationsFiber Type Alterations

• Training regimen may not outright change fiber type, but– Type II fibers become more oxidative with aerobic

training– Type I fibers become more anaerobic with

anaerobic training

• Fiber type conversion possible under certain conditions– Cross-innervation– Chronic low-frequency stimulation– High-intensity treadmill or resistance training

Mechanisms of Muscle Strength Gain:Mechanisms of Muscle Strength Gain:Fiber Type AlterationsFiber Type Alterations

• Type IIx type IIa transition common

• 20 weeks of heavy resistance training program showed– Static strength, cross-sectional area – Percent type IIx , percent type IIa

• Other studies show type I type IIa with high-intensity resistance work + short-interval speed work

Muscle SorenessMuscle Soreness

• From exhaustive or high-intensity exercise, especially the first time performing a new exercise

• Can be felt anytime– Acute soreness during, immediately after exercise– Delayed-onset soreness one to two days later

Muscle Soreness:Muscle Soreness:Acute Muscle SorenessAcute Muscle Soreness

• During, immediately after exercise bout– Accumulation of metabolic by-products (H+)– Tissue edema (plasma fluid into interstitial space)– Edema acute muscle swelling

• Disappears within minutes to hours

Muscle Soreness:Muscle Soreness:DOMSDOMS

• DOMS: delayed-onset muscle soreness– 1 to 2 days after exercise bout– Type 1 muscle strain– Ranges from stiffness to severe, restrictive pain

• Major cause: eccentric contractions– Example: Level run pain < downhill run pain– Not caused by blood lactate concentrations

Muscle Soreness:Muscle Soreness:DOMS Structural DamageDOMS Structural Damage

• Indicated by muscle enzymes in blood– Suggests structural damage to muscle membrane– Concentrations 2 to 10 times after heavy training– Index of degree of muscle breakdown

• Onset of muscle soreness parallels onset of muscle enzymes in blood

Muscle Soreness:Muscle Soreness:DOMS Structural DamageDOMS Structural Damage

• Sarcomere Z-disks: anchoring points of contact for contractile proteins– Transmit force when muscle fibers contract– Z-disk, myofilament damage after eccentric work

• Physical muscle damage DOMS pain– Fiber damage and blood enzyme changes may occur

without causing pain– Muscle damage also precipitates muscle hypertrophy

Muscle Soreness:Muscle Soreness:DOMS and InflammationDOMS and Inflammation

• White blood cells defend body against foreign materials and pathogens– White blood cell count as soreness – Connection between inflammation and soreness?

• Muscle damage inflammation pain– Damaged muscle cells attract neutrophils– Neutrophils release attractant chemicals, radicals– Released substances stimulate pain nerves– Macrophages remove cell debris

Muscle Soreness:Muscle Soreness:Sequence of Events in DOMSSequence of Events in DOMS

1. High tension in muscle structural damage to muscle, cell membrane

2. Membrane damage disturbs Ca2+ homeostasis in injured fiber

– Inhibits cellular respiration– Activates enzymes that degrade Z-disks

(continued)

Muscle Soreness:Muscle Soreness:Sequence of Events in DOMS (continued)Sequence of Events in DOMS (continued)

3. After few hours, circulating neutrophils

4. Products of macrophage activity, intracellular contents accumulate

– Histamine, kinins, K+

– Stimulate pain in free nerve endings– Worse with eccentric exercise

Muscle Soreness:Muscle Soreness:Sequence of Events in DOMSSequence of Events in DOMS

• Damage to muscle fiber, plasmalemma sets up chain of events– Release of intracellular proteins– Increase in muscle protein turnover

• Damage and repair processes involve buildup of intra- and extracellular molecules

• Precise causes of skeletal muscle damage and repair still poorly understood

Muscle Soreness:Muscle Soreness:DOMS and PerformanceDOMS and Performance

• DOMS muscle force generation

• Loss of strength from three factors– Physical disruption of muscle (see figures 10.8,

10.9)– Failure in excitation-contraction coupling (appears to

be most important)– Loss of contractile protein

Muscle Soreness:Muscle Soreness:DOMS and PerformanceDOMS and Performance

• Muscle damage glycogen resynthesis

• Slows/stops as muscle repairs itself

• Limits fuel-storage capacity of muscle

• Other long-term effects of DOMS: weakness, ultrastructural damage, 3-ME excretion

Muscle Soreness:Muscle Soreness:Reducing DOMSReducing DOMS

• Must reduce DOMS for effective training

• Three strategies to reduce DOMS– Minimize eccentric work early in training– Start with low intensity and gradually increase– Or start with high-intensity, exhaustive training

(soreness bad at first, much less later on)

Muscle Soreness:Muscle Soreness:Exercise-Induced Muscle CrampsExercise-Induced Muscle Cramps

• Frustrating to athletes– Occur even in highly fit athletes– Occur during competition, after, or at rest

• Frustrating to researchers– Multiple unknown causes– Little information on treatment and prevention

• EAMCs versus nocturnal cramps


• EAMC type 1: muscle overload/fatigue– Excite muscle spindle, inhibit Golgi tendon organ

abnormal -motor neuron control– Localized to overworked muscle– Risks: age, poor stretching, history, high intensity

• EAMC type 2: electrolyte deficits– Excessive sweating Na+, Cl- disturbances– To account for ion loss, fluid shifts– Neuromuscular junction becomes hyperexcitable


• Treatment depends on type of cramp

• Fatigue-related cramps– Rest– Passive stretching

• Electrolyte-related (heat) cramps– Prompt ingestion of high-salt solution, fluids– Massage– Ice

Resistance Training for Special Resistance Training for Special Populations: Women Populations: Women

• Have same ability to develop strength

• Women’s peak 1RM < men’s peak 1RM

• Differences due to muscle size, hormones

• Same techniques appropriate for both sexes

Resistance Training for Special Resistance Training for Special Populations: AgePopulations: Age

• Children and adolescents– Myth: resistance training unsafe due to growth plate,

hormonal changes– Truth: safe with proper safeguards– Children can gain both strength and muscle mass

• Elderly– Helps restore age-related loss of muscle mass– Improves quality of life and health– Helps prevent falls

Resistance Training for SportResistance Training for Sport

• Training beyond basic strength, power, and endurance needs of the sport not worth it

• Training costs valuable time

• Training results should be tested with sport-specific performance metric

chapter 10

Documents

muscle hypertrophyhypertrophy

strength gainlearn

neural controlstrength

plasticitystrength gain

overviewresistance training

musclemotor unit recruitment

months of resistance

motor units