1. Principles of Skeletal Muscle Adaptation
Brooks ch 19 p
Outline
Myoplasticity
Protein turnover
Fiber Type
Training adaptations
Adaptations with inactivity, injury
Age associated changes

2. Myoplasticity
Altered gene expression - resulting in an increase or decrease in amount of specific protein
tremendous potential to alter expression in sk ms
molecular basis for adaptations that occur due to exercise tx in sk ms proteins
20%of sk ms is protein, balance is water, ions...
All types of protein can be regulated by altering gene expression
Fig 19-1 cascade of regulatory events - impacting gene expression

3. Myoplasticity cont.
myoplasticity - change either quantity (amount) or quality (type) of protein expressed
Eg. Responses to training
type IIb - hypertrophy (enlargement) - inc amount of protein in fiber
larger fast II b fiber
Another fiber - hypertrophy
also repress gene for fast II b myosin HC, turn on fast Iiz myosin HC
not only enlarged, but change in contractile phenotype
larger, slower contracting fiber.

4. Protein turnover
Protein Turnover reflects 1/2 life of protein - time frame for existence
protein transcribed (DNA-mRNA)
translated then degraded
level of protein in cell governed by
synthesis / degeneration ratio
precise regulation of content through control of transcription rate
and/or degradation rate
capacity to regulate structural and functional properties of the ms
applies to both structural and contractile proteins and regulatory proteins
as well as enzymes involved in metabolism

5. Adaptation Sk ms adaptation characterized by
morphological
biochemical
molecular
variables that alter the functional attributes of fibers in specific motor units
adaptations readily reversible when stimulus is diminished or removed
Fig 19-2 intracellular and extracellular influences - reg gene pool expression
stimuli of sufficient amount for sufficient time- overload
lead to changes in expression of specific proteins - specificity

6. Signals for Adaptation
Insufficient energy balance
nutrition can also influence endocrine system - insulin
endocrine system independent influence
thyroid hormone
IGF-1 - insulin like growth factor 1
power developed by motor unit
load against which fibers contract
specific responses to demands
each result in acute changes in cellular environment
changes can lead to altered rates of protein synthesis and degradation
changes [ ] or activity of proteins

7. Phenotype
When protein structure of muscle is altered - phenotype change
outwardly observable characteristics of muscle
reflects underlying genes (genotype) and their regulation by several factors (exercise)
altered phenotypes - affect cellular environment as well
eg. Receptors, integrating centers, signal translocation factors and effectors - mechanisms not fully understood.

8. Muscle Fiber Types Elite athletes - specialized fiber typing
sprinter II b, endurance I
Fig elite - ends of spectrum
genetics - strong influence on fiber type disposition
Training studies - alter biochemical and histological properties - not fiber type distinction - (myosin isoform)
evidence, however, that intermediate transitions can occur in MHC expression - not detected with conventional techniques

9. Endurance Adaptations
Occurs with large increase in recruitment frequency and modest inc in load
minimal impact on X-sec area
significant adaptations to metabolic
Inc mitochondrial proteins
HK inc, LDH dec(cytosol), inc mito
2 fold inc in ox metabolism
degree of adaptation depends on pre training status, intensity and duration
Table 19-1 Succinate DH (Krebs)
response varies with fiber type - involvement in training
inc max blood flow, capillary density, and potential for O2 extraction

10. Adaptations to Resistance Training
Increased recruitment frequency and load
Hypertrophy - inc X-sec area
Hyperplasia - inc cell number
major adaptation is with hypertropyhy - inc max force generating capacity
Fig 17-28b - Force velocity after tx
move sub max load at higher velocity of shortening
enhanced power capacity
Fiber type specific adaptation
inc X-sec area of both type I and II
Fig month longitudinal study
II - 33% , I - 27% increase

11. Resistance Training
Fastest MHC’s repressed , inc in expression of intermediate MHC isoforms II x - II a
mito volume and cap density reduced with resistance tx
Fig % dec in mito protein
Fig cap density dec 13%
Adaptation with decreased activity
large reduction in recruitment frequency and /or load
reduction in ms and ms fiber X-sec area - dec in metabolic proteins
Fig 19-8

12. Injury and Regeneration
Induced by a variety of insults
trauma, ischemia, excessive stretch
eccentric exercise, dennervation
active lifestyle - continuous population of regenerating fibers
two phases
immediate - mechanical
secondary - biochemical - several days
Gender differences
Table size and strength
Table strength vs. X-sec area

13. Age Changes in Muscle
Reduction with age in ability to produce and sustain ms power
physical inactivity may contribute to this decline, but not predominant explanation
65 yrs muscle mass dec by %
peak at yrs
possible explanations
Fiber diameter
diameter quite consistent until 70
Fiber number
varied results - X-sec designed studies (measure subjects from different age groups)

14. Age changes Motor Unit remodeling
with age - alteration in normal turnover of synaptic junction
old - aggregation of type I
Fig Motor units and age
47 % dec in both genders
Muscle Function
strength - dec 8% per decade after 30
atrophy (refer back to fig 19-3)
power and endurance
30 % less in old - atrophy and other factors Fig 19-10,11

15. Response to Training
Muscle and fiber hypertrophy and performance improvements can occur together with resistance training in aged
Fig 19-12,13,14
following 12 weeks
110% increase in force (1 rep max)
9% inc in quadriceps area
34% inc X-xec area type I
28% inc X-sec area type II