1. Muscular Strength: Training Muscles to Become Stronger

2. Learning outcomes
Explain the physiological mechanisms of muscle strength gain
Describe the physiological processes involved in delayed onset muscle soreness and strategies to avoid the occurrence of DOMS
Discuss resistance training principles special populations

3. Resistance Training: Introduction
Resistance training yields substantial strength gains via neuromuscular changes
Important for overall fitness and health
Critical for athletic training programs

4. Assessing Muscular Strength
Cable tensiometry
Dynamometry
One-repetition maximum (1-RM)
Computer-assisted, electromechanical, and isokinetic methods
Isokinetic dynamometer
Resistance-training equipment categories

5. Assessment Considerations
Standardize pretesting instructions
Uniformity of warm-up
Adequate practice
Standardize testing protocol
Body position
Joint angles
Reps
Scoring criteria
Score relative to body size

6. Sex Differences in Muscular Strength
Similar ability to develop strength
Women’s peak 1RM < men’s peak 1RM
Absolute muscle strength
Males 30% higher on lower-body, 50% higher on upper-body lifts
Differences due to muscle size, hormones
Same techniques appropriate for both sexes

7. Sex Differences in Muscular Strength
Relative Strength Differences

8. Types of Contractions Static muscle contraction Isometric
Dynamic muscle action
Concentric action
Muscle shortens
Eccentric action
Muscle lengthens

9. Resistance Training: Gains 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

10. 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

11. Mechanisms of Muscle Strength Gain: Neural 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

12. Mechanisms of Muscle Strength Gain: 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

13. Mechanisms of Muscle Strength Gain: 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

14. Mechanisms of Muscle Strength Gain: Motor Unit Rate Coding
Limited evidence suggests rate coding increases with resistance training, especially rapid movement, ballistic-type training

15. Mechanisms of Muscle Strength Gain: Autogenic 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

16. Mechanisms of Muscle Strength Gain: Other Neural Factors
Coactivation of agonists, antagonists
Normally antagonists oppose agonist force
Reduced coactivation may  strength gain
Morphology of neuromuscular junction

17. Mechanisms of Muscle Strength Gain: Muscle 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

18. Mechanisms of Muscle Strength Gain: Chronic Muscle Hypertrophy
Maximized by
High-velocity eccentric training
Disrupts sarcomere Z-lines (protein remodeling)
Concentric training may limit muscle hypertrophy, strength gains

19. Mechanisms of Muscle Strength Gain: Fiber Hypertrophy
More myofibrils
More actin, myosin filaments
More sarcoplasm
More connective tissue

20. Mechanisms of Muscle Strength Gain: Fiber 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

21. Mechanisms of Muscle Strength Gain: Fiber 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

22. Figure 10.4

23. Mechanisms of Muscle Strength Gain: Fiber Hyperplasia
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

24. Mechanisms of Muscle Strength Gain: Fiber Hyperplasia
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

25. Figure 10.5

26. Mechanisms of Muscle Strength Gain: Neural 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

27. Mechanisms of Muscle Strength Gain: Atrophy and Inactivity
Reduction or cessation of activity  major change in muscle structure and function
Limb immobilization studies
Detraining studies

28. Mechanisms of Muscle Strength Gain: Immobilization
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

29. Mechanisms of Muscle Strength Gain: Detraining
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

30. Mechanisms of Muscle Strength Gain: Fiber 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

31. Mechanisms of Muscle Strength Gain: Fiber 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

32. Muscle 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

33. Muscle Soreness: Acute 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

34. Muscle Soreness: DOMS 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

35. Muscle Soreness: DOMS 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

36. Muscle Soreness: DOMS 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

37. Muscle Soreness: DOMS 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

38. Muscle Soreness: Sequence 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)

39. Muscle Soreness: 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

40. Muscle Soreness: Sequence 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

41. Muscle Soreness: DOMS 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

42. Muscle Soreness: DOMS 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

43. Muscle Soreness: Reducing 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)