kinesiology
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Kenney7E_PP_chap101.pptxAdaptations to Resistance Training
Chapter 10
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CHAPTER 10 Overview
Resistance training and gains in muscular fitness
Mechanisms of gains in muscle strength
Interaction between resistance training and diet
Resistance training for special populations
Resistance Training: Introduction
Substantial strength gains via neuromuscular changes
Important for overall fitness and health
Critical for athletic training programs
Resistance Training: Gains in Muscular Fitness
After 3 to 6 months of resistance training
25% to 100% strength gain
Better force production
Ability to produce true maximal movement
Similar strength gains as percent of initial strength
But greater absolute gains for young men than for young women, older men, or children
Due to incredible muscle plasticity
Mechanisms of Muscle Strength Gain
Hypertrophy versus atrophy
– muscle size muscle strength
– muscle size muscle strength
But association more complex than that
Sources of strength gains
– muscle size
Altered neural control
Figure 10.1a
Figure 10.1b
Figure 10.1c
Mechanisms of Muscle Strength Gain: Neural Control
Strength gain cannot occur without neural adaptations via plasticity.
Strength gain can occur without hypertrophy.
Strength is a property of the motor system, not just of muscle.
Essential elements include motor unit recruitment, stimulation frequency, and other neural factors.
Mechanisms of Muscle Strength Gain: Motor Unit Recruitment
Motor units normally recruited asynchronously
Synchronous recruitment strength gains
Facilitates contraction.
May produce more forceful contraction.
Improves rate of force development.
– Improves capability to exert steady forces.
Resistance training synchronous recruitment
(continued)
Mechanisms of Muscle Strength Gain: Motor Unit Recruitment (continued)
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 a combination of improved motor unit synchronization and motor unit recruitment leads to strength gains.
Mechanisms of Muscle Strength Gain: Motor Unit Rate Coding
Limited evidence suggests that rate coding increases with resistance training, especially rapid-movement, ballistic-type training.
Mechanisms of Muscle Strength Gain: Autogenic Inhibition
Normal intrinsic inhibitory mechanisms
Example: Golgi tendon organs
Inhibit muscle contraction if tendon tension too high.
Prevent damage to bones and tendons.
Inhibitory impulses by training
Muscle can generate more force.
May also explain superhuman feats of strength.
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
Mechanisms of Muscle Strength Gain: Muscle Hypertrophy
Hypertrophy: increase in muscle size
Transient hypertrophy (after exercise bout)
Due to edema formation from plasma fluid
Gone within hours
Chronic hypertrophy (long term)
Structural change in muscle
Fiber hypertrophy, fiber hyperplasia, or both
Figure 10.2a
Photos courtesy of Dr. Michael Deschene’s laboratory.
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Figure 10.2b
Photos courtesy of Dr. Michael Deschene’s laboratory.
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Mechanisms of Muscle Strength Gain: Chronic Muscle Hypertrophy
Maximized by high-velocity eccentric training, which disrupts sarcomere Z-lines (protein remodeling).
Concentric training may limit muscle hypertrophy, strength gains.
Stimulated by intensities as low as 30% 1RM and as high as 90%.
Caused by both high-rep (low-load) and low-rep (high-load) training.
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Mechanisms of Muscle Strength Gain: Fiber Hypertrophy
More myofibrils
More actin, myosin filaments
More sarcoplasm
More connective tissue
Resistance training protein synthesis
Muscle protein content always changing
During exercise: synthesis , degradation
After exercise: synthesis , degradation
Mechanisms of Muscle Strength Gain: Hormones and Hypertrophy
Fiber hypertrophy facilitated by testosterone
Natural anabolic steroid hormone
Synthetic anabolic steroids large increases in muscle mass
Growth hormone (GH)
Insulin-like growth factor 1 (IGF-1)
Elevated post exercise levels not required for anabolism and strength
Mechanisms of Muscle Strength Gain: Fiber Hyperplasia
Cats
Intense strength training produces fiber splitting.
Each half grows to size of parent fiber.
Chickens, mice, rats
Intense strength training produces only fiber hypertrophy.
But difference may be due to training regimen.
(continued)
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Figure 10.3
Mechanisms of Muscle Strength Gain: Fiber Hyperplasia (continued)
Humans
Most hypertrophy is due to fiber hypertrophy.
Fiber hyperplasia also contributes.
Fiber hypertrophy versus fiber hyperplasia may depend on resistance training intensity or load.
Higher intensity causes (type II) fiber hypertrophy.
Fiber hyperplasia may occur only in certain individuals under certain conditions.
(continued)
Mechanisms of Muscle Strength Gain: Fiber Hyperplasia (continued)
Can occur through fiber splitting.
Also occurs through satellite cells.
Myogenic stem cells involved in skeletal muscle regeneration
Activated by stretch, injury
After activation: proliferate, migrate, fuse
Figure 10.4
Adapted by permission from T.J. Hawke and D.J. Garry, “Myogenic Satellite Cells: Physiology to Molecular Biology,” Journal of Applied Physiology 91 (2001): 534-551.
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Animation 10.4
When you are in the normal view of the PowerPoint slides, you should right-click on the image and then choose “Open hyperlink” to play the video. In the slide show view, you will simply click on the image to play the video. You must have an Internet connection in order to link to the streaming video.
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Mechanisms of Muscle Strength Gain: Neural Activation and 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 requiring time to occur
Hypertrophy major factor after first 10 weeks
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
Mechanisms of Muscle Strength Gain: Immobilization
Major changes after 6 h
Lack of muscle use reduced protein synthesis.
Initiates process of muscle atrophy.
First week: strength loss of 3%-4% per day
– size (atrophy)
– neuromuscular activity
(Reversible) effects on type I and II fibers
Cross-sectional area , cell contents degenerate.
Type I is affected more than type II.
Mechanisms of Muscle Strength Gain: Detraining
Leads to in 1RM.
Lost strength 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 10.5
Adapted by permission from R.S. Staron et al., “Strength and Skeletal Muscle Adaptations in Heavy-Resistance-Trained Women After Detraining and Retraining,” Journal of Applied Physiology 70 (1991): 631-640.
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Figure 10.6
Mechanisms of Muscle Strength Gain: Fiber Type Alterations
Training regimen may not outright change fiber type, but . . .
Type II fibers more oxidative with aerobic training
Type I fibers more anaerobic with anaerobic training
Fiber type conversion is possible under certain conditions.
Cross-innervation
Chronic low-frequency stimulation
High-intensity treadmill or resistance training
(continued)
Mechanisms of Muscle Strength Gain: Fiber Type Alterations (continued)
Type IIx type IIa transition common
20-week heavy resistance training program:
Static strength, cross-sectional area
Percent type IIx , percent type IIa
Other studies: type I type IIa with high-intensity resistance work + short-interval speed work
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Interaction Between Resistance Training and Diet
Resistance training increases protein synthesis.
Consume 20 to 25 g protein after resistance exercise for muscle growth.
Consume 1.6 to 1.7 g protein per kg body weight per day to increase muscle mass.
Small doses (20 g) every 2 to 3 hours are recommended for protein synthesis.
Larger doses (20-25 g) recommended immediately after resistance training.
Mechanism of Protein Synthesis with Resistance Training and Protein Intake
Controlled by mTOR (mechanistic target of rapamycin)
Integrates input from insulin, growth factors, amino acids.
Dictates transcription of mRNA.
Synthesizes ribosomes.
Stimulated by insulin
Translation
Amino acids converted into protein via mRNA
Figure 10.7
Dickinson, J.M., Volpi, E., & Rasmussen, B.B. (2013). Exercise and nutrition to target protein synthesis impairments in aging skeletal muscle. Exercise and Sports Sciences Reviews, 41, 216-223.
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Animation 10.7
Video 10.1
When you are in the normal view of the PowerPoint slides, you should right-click on the image and then choose “Open hyperlink” to play the video. In the slide show view, you will simply click on the image to play the video. You must have an Internet connection in order to link to the streaming video.
In this video, Luc von Loon on the role of protein in adaptations to resistance training.
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Resistance Training for Special Populations: Age
Children and adolescents
Myth: Resistance training is unsafe due to growth plate, hormonal changes.
Truth: It is safe with proper safeguards.
Children can gain both strength and muscle mass.
Elderly persons
Helps restore age-related loss of muscle mass.
Improves quality of life and health.
Helps prevent falls.
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Strength Training in Older Adults
Increases in strength dependent primarily on neural adaptations
No difference across sex or race
Same response as in younger but blunted
Decreased mTOR signaling response
Smaller increases in myofibrillar protein and muscle size
25-50 g protein necessary to stimulate muscle protein synthesis
Resistance Training for Sport
Training is not worth it beyond the basic strength, power, and endurance needs of the chosen sport.
Training costs valuable time.
Training results should be tested with sport-specific performance metrics.
