1. chapter 9
Adaptations to Resistance Training

2. Learning Objectives
Discover how strength is gained through resistance training
Note changes in the muscles and in the neural mechanisms controlling them that occur as a result of resistance training
Learn what causes muscle soreness and how to prevent it

3. Resistance Training and Gains in Muscular Fitness
Muscle is very plastic, increasing in size and strength with training and decreasing with immobilization
© BananaStock

4. One-Repetition Maximum (1RM)
The maximal weight an individual can lift just once

5. World Records for the Snatch, Clean and Jerk, and Total Weight for Men and Women

6. Neural Control of Strength Gains
Recruitment of motor units
Increased number of motor units recruited from increased neural drive
Synchronicity of motor unit recruitment is improved
Increased frequency of discharge from the a-motor neuron
Decrease in autogenic inhibition
Reduction in the coactivation of agonist and antagonist muscles
Morphological changes in the neuromuscular junction

7. Muscle Hypertrophy
Transient hypertrophy is the increase in muscle size that develops during and immediately following a single exercise bout
Fluid accumulation in the interstitial and intracellular space from the blood plasma
Chronic hypertrophy is the increase in muscle size after long-term resistance training
Changes in both the size of muscle fibers (fiber hypertrophy) and the number of muscle fibers (fiber hyperplasia)

8. Microscopic Views of Muscle Cross Sections Before and After Training
Photos courtesy of Dr. Michael Deschene's laboratory.

9. Fiber Hypertrophy
Net increase in muscle protein synthesis—possibly increasing the number of actin and myosin filaments, and increasing the number of myofibrils
Facilitated by postexercise nutrition
Testosterone plays a role in promoting muscle growth

10. Fiber Hyperplasia
Muscle fibers can split in half with intense weight training (cat research)
Each half then increases to the size of the parent fiber
Conflicting study results may be due to differences in the training load or mode
Satellite cells may also be involved in the generation of new skeletal muscle fibers
Hyperplasia has been clearly shown to occur in animal models; only a few studies suggest this occurs in humans too

11. Heavy Resistance Training in Cats

12. Muscle Fiber Splitting

13. The Satellite Cell Response to Muscle Injury
Reprinted, by permission, from T.J. Hawke and D.J. Garry, 2001, “Myogenic satellite cells: Physiology to molecular biology,” Journal of Applied Physiology 91:

14. Integration of Neural Activation and Fiber Hypertrophy
Early gains in strength appear to be more influenced by neural factors
Long-term strength increases are largely the result of muscle fiber hypertrophy

15. Resistance Training Key Points
Neural adaptations always accompany strength gains
Neural mechanisms leading to strength gains include:
Increased frequency of stimulation
Recruiting more motor units
More synchronous recruitment
Decreased autogenic inhibition
Transient muscle hypertrophy results from edema
(continued)

16. Resistance Training (continued)
Key Points
Chronic muscle hypertrophy reflects actual structural changes in the muscle
Muscle hypertrophy results from an increase in the size of the individual muscle fibers and maybe an increase in the number of muscle fibers

17. Muscle Atrophy and Decreased Strength With Inactivity
Immobilization
Decreased rate of protein synthesis
Decreased strength
Decreased cross-sectional area
Decreased neuromuscular activity
Affects both type I and type II fibers, with a greater effect in type I fibers
Muscles can recover when activity is resumed

18. Muscle Atrophy and Decreased Strength With Inactivity
Cessation of Training
Decreased strength
Little change in fiber cross-sectional area (type II fiber areas tend to decrease)
Maintenance training is important to prevent strength losses

19. Changes in Muscle Strength With Resistance Training in Women
Adapted, by permission, from R.S. Staron et al., 1991, “Strength and skeletal muscle adaptations in heavy-resistance-trained women after detraining and retraining,” Journal of Applied Physiology 70:

20. Changes in Mean Cross-Sectional Areas for the Major Fiber Types With Resistance Training in Women

21. Fiber Type Alterations With Resistance Training
Transition of type IIx to type IIa
Results from cross-innervation or chronic stimulation

22. Muscle Atrophy and Fiber Type Alterations
Key Points
Occurs when the muscle becomes inactive, as with injury, immobilization, or cessation of training
Maintenance programs can prevent atrophy or loss of strength
There is a transition of type IIx to type IIa fibers
One fiber type can be converted to the other fiber type as a result of cross-innervation or chronic stimulation and possibly with training

23. Acute Muscle Soreness
Results from an accumulation of the end products of exercise in the muscles or edema
Usually disappears within minutes or hours after exercise

24. Delayed-Onset Muscle Soreness (DOMS)
Soreness is felt 12 to 48 hours after a strenuous bout of exercise
Results primarily from eccentric muscle activity (e.g., downhill running)
Is associated with:
Structural damage
Impaired calcium homeostasis leading to necrosis
Accumulation of irritants
Increased macrophage activity
May be caused by inflammatory reaction inside damaged muscles

25. Electron Micrograph of a Muscle Sample Taken Immediately After a Marathon
From R.C. Hagerman et al., 1984, "Muscle damage in marathon runners," Physician and Sportsmedicine 12:

26. Electron Micrograph Showing Normal Arrangement of Actin and Myosin Filaments and Z-disk Before and Immediately After a Marathon
From R.C. Hagerman et al., 1984, "Muscle damage in marathon runners," Physician and Sportsmedicine 12:

27. Armstrong’s Sequence of Events in DOMS
Structural damage to the muscle cell and cell membrane
Impaired calcium availability, leading to necrosis
Increased microphage activity and the accumulation of irritants inside the cell, which stimulate free (pain) nerve endings

28. DOMS and Performance
Maximal force-generating capacity is diminished but gradually returns
Loss of strength is due to:
Physical disruption in the muscle
Failure within the excitation–contraction process
Loss of contractile proteins

29. Estimated Contributions of Physical Disruption, Contractile Protein Loss, and Excitation–Contraction Coupling Failure to the Loss of Strength Following Muscle Injury
Reprinted, by permission, from G.L. Warren et al., 2001, “Excitation-contraction uncoupling: Major role in contraction-induced muscle injury,” Exercise and Sport Sciences Reviews 29:

30. The Delayed Response to Eccentric Exercise of Various Physiological Markers
Adapted, by permission, from W.J. Evans and J.G. Cannon, 1991, “The metabolic effects of exercise induced muscle damage,” Exercise and Sport Sciences Reviews 19:

31. Reducing Muscle Soreness
Reduce the eccentric component of muscle action during early training
Start training at a low intensity and gradually increase it
Begin with a high-intensity, exhaustive bout of eccentric-action exercise, which will cause much soreness initially but will decrease future pain

32. Muscle Soreness Key Points
Acute muscle soreness occurs late in an exercise bout and during the immediate recovery period after an exercise bout
Delayed-onset muscle soreness (DOMS) occurs 12 to 48 hours after exercise
Occurs mostly with eccentric muscle action
Causes include structural damage to muscle cells and inflammatory reactions within the muscles
Muscle soreness may be an important part of maximizing the resistance training response

33. Resistance Training in Special Populations
Key Points
Resistance training can benefit almost everyone, regardless of his or her sex, age, or athletic involvement
Most athletes in most sports can benefit from resistance training