Muscle physiology review complete with studies on how training impacts the muscles.

2. Muscle/Neural Physiology
Overview
 Gross Structure of
the Muscles
 Micro Structure of
the Muscles
 Muscle
Contractions
 Factors Which
Effect Force
Production

4. Gross Structure of the
Muscles
 Muscle
 Myotendinous
Junction
 Tendon
 Periosteum
 Bone
From Brooks, Fahey, and White.
(1996).

5. Gross Structure of the
Muscles
 Epimysium: Covers
the muscle
 Fasiculi: Bundles of
muscle fibers
 Perimysium: Covers
bundles of muscle
fibers
 Endomysium: Covers
muscle fibers

6. Gross Structure of the Muscle
From McArdle, Katch, and Katch.

7. Endomysium
 Surrounds each
muscle fiber
 Basement membrane:
glycoproteins and
collagen, freely
permeable
 Satellite cells
From Brooks, Fahey, and White. (1996).

8. Endomysium, Cont.
 Plasma membrane/
sarcolemma:
transport, action
potential, acid-base
balance
 Contains small
indentations, called
caveolae.
 Provide additional
lengthening during
fiber stretching (10-
15%)

10. Microstructure
 Skeletal muscle is:
 75% water
 5% inorganic salts
 20% proteins
○ 12% myofibrillar proteins
○ 8% enzymes, membrane proteins, transport
channels, etc.

11. Microstructure, cont.
 Sarcomere: Contractile unit of the muscle
 Myofibrils: Protein filaments in the muscle fiber
 Mitochondria
 Sarcoplasmic Reticulum: Interconnecting tubular
channels
 Terminal Cisternae: Lateral end of SR, stores
calcium
 T Tubules: Transports action potential into
myofibrils

12. Microstructure
From McArdle, Katch, and Katch.

13. Sarcomere
 Actin
 Myosin
 H zone: center, no
overlap
 M line: bisects H
zone
 A band: dark,
overlap
 I band: light, actin-
only
 Z line: borders
From Brooks, Fahey, and White.
(1996).

14. Sarcomere
From McArdle, Katch, and Katch.

15. Sarcomere
 -Actinin: hold actin in place at Z disc
 C protein: holds myosin tails in correct
alignment
 M proteins: hold actin and myosin in
correct alignment
 Titin: connects myosin to Z disc

16. Arrangement of Actin and
Myosin
From McArdle, Katch, and Katch.

17. Arrangement of Actin and
Myosin, cont.
From McArdle, Katch, and Katch.

18. Actin
 Globular Actin
 Filament Actin
 Tropomyosin:
blocks binding
sites on actin,
calcium must shift
 Troponin: where
calcium binds,
shifts tropomyosin
From Brooks, Fahey, and White.
(1996).

19. Myosin
 Light meromyosin
 Heavy meromyosin
 Subfragment-1
(head)
 Subfragment-2
(hinge)
From Brooks, Fahey, and White. (1996).

20. Sarcoplasmic Reticulum
(SR)
 Interconnecting
tubular channels
 Lateral end
terminates in a
vesicle that stores
calcium
 Surrounds A-band
and the I-band
From Brooks, Fahey, and White.
(1996).

21. T-Tubules
 Run into the fibers
 Transmit the action
potential deep
within the muscle
fiber
 Triad
From Wilmore & Costill. (1994).

23. Muscle Contraction

24. Sliding Filament Theory
 Sequence of
Events:
 Acetylcholine
released
 Action potential
depolarizes the T-
tubule
 Calcium binds to
troponin-
tropomyosin
From Brooks, Fahey, and White
(1996).

25. Contraction Cycle

26. Sliding Filament Theory
 Actin combines with
myosin-ATP
 Crossbridge
activation continues
in the presence of
calcium
 Calcium
concentration
decreases as
stimulation ceases

27. Cross Bridges
From McArdle, Katch, and Katch.

28. Cross Bridges, etc.
 Calcium binds with
troponin, shifts
tropomyson.
 Crossbridge
attaches to actin
and flexes,
shortening
sarcomere.
 More cross bridges
= more force!
From McArdle, Katch, and
Katch.

29. Contraction and the Sarcomere
From McArdle, Katch, and
Katch.

30. Types of Contraction
 Isometric: external force = force
developed
 Concentric: external force less than
force developed
 Eccentric: external force greater than
force developed

31. Experimental Terms
 In Vitro: muscle is excised and studied
in solution
 In Situ: muscle is surgically exposed in
the anesthetized animal, stimulated
electronically
 In Vivo: muscle is studied during normal
physical activity

33. Factors Affecting Force
Production
 Cross Sectional Area
 Velocity of Shortening
 Angle of Pennation
 Sarcomere and Muscle Length
 Muscle Fiber Type

34. Cross Sectional Area
 Muscles with a
larger CSA have the
capacity to produce
more force than
muscles with a
smaller CSA
 This is due to more
sarcomeres in
parallel (thus more
cross bridges
possible)
 Komi, P.V., 1979

35. Velocity of Shortening
 Force production is
inversely related to
velocity of
shortening (no time
for many cross
bridges to form)
From Brooks, Fahey, and White (1996).

36. Angle of Pennation
 Muscles with
greater pennation
have more
sarcomeres
running parallel
 Muscles with less
pennation have
more sarcomeres
in series
From Brooks, Fahey, and White (1996).

37. Sarcomere and Muscle
Length
 Length-tension
relationship
 Resting length
 What this means in
terms of flexibility
training
 Komi, P.V., 1979

38. From Frog Semitendinosus
Fibers
Effects of Sarcomere Length on
Force
0
20
40
60
80
100
120
0 1 2 3 4
Sarcomere Length
%ofMaximumTension
Adapted from Edman, K.A.P. (1966).

39. Muscle Fiber Types
 Methods of classifying muscle fiber
types (Staron, 1997):
 Contraction speed (fast or slow)
 Color - myoglobin and capillary content (red
or white)
 Enzymatic properties and speed of
contraction (slow oxidative, fast oxidative
glycolytic, fast glycolytic)
 pH sensitivity of myofibrillar ATPase

40. Myofibrillar ATPase
sensitivity
 Differences in pH sensitivity are
correlated with myosin heavy chain
content and therefore contractile
properties.
 mATPase-based fiber types:
 I, Ic, IIc, IIac, IIa, IIab, IIb

41. Muscle fibers under the
microscope
 3: Type I
 5 (white): Type IIb
 1, 2, 4, 7 , 8: Type
IIab
From Staron, R.S. (1997).

42. Muscle Fiber Type
Characteristics
Fast twitch, high force,
fast fatigue (type IIb)
Fast twitch, moderate
force, fatigue
resistance (type IIa)
Slow twitch, low
tension, fatigue
resistant (type I)
Trainable or inherited?
From Brooks, Fahey, and White (1996).

43. Colliander, et al. (1988).
 27 male subjects
 Subjects performed 3x30 maximal
unilateral knee extensions using
isokinetic equipment, 1 minute recovery
between bouts
 Measuring how peak torque decreased
between the first and third bout

44. Colliander, et al. (1988).
 Found that peak torque decreased an
average of 20% from the first bout to the
third.
 Those individuals with a greater
percentage of fast twitch fibers had the
greatest peak torque but also the
greatest decline in peak torque.

45. Colliander, et al. (1988).
Peak Torque,
bout I
Peak Torque,
bout III
% Decline
FT Group (~71%
area)
192 139 28%
ST Group (~57%
area)
144 129 10%
Fast twitch or slow twitch fiber area as a percentage of muscle cross
sectional area

46. Ounjian, M., et al. (1991).
 Excised motor units from the tibialis
anteriors of 7 cats.
1 2 3 4 5 6 7
Type FF FF FF FF FR S S
Contracti
on Time
23.
2
17.
6
26.
9
24.
5
24.
4
45 55.
8
Tension 21.
4
15.
9
15.
4
41.
8
10.
4
15.
4
3
Fatigue
Index
.01 .01 .1 .06 1.0
2
1 1
Fatigue index: ratio of tension after 2 minutes of stimulation to the
maximum tension elicited during the test

47. Bottinelli, R., et al., 1999
 Force-velocity
curves for fiber
types

48. Bottinelli, R., cont.
 Power-velocity
curves for fiber
types

49. Bottinelli, R., cont.
 Calcium sensitivity
for fiber types

50. Karlsson, J., et al., 1978
 % Slow twitch
fibers and maximal
oxygen uptake
From Karlsson, et al. (1978).

51. Karlsson, J., cont.
 % Fast twitch
fibers and maximal
isometric strength
From Karlsson, et al. (1978).

53. What the texts say about
hypertrophy
 Essentials (2000), pg. 65:
 “The process of hypertrophy involves both
an increase in the synthesis of the
contractile proteins actin and myosin …
within the myofibril and an increase in the
number of myofibrils within a muscle fiber.”

54. Hypertrophy vs. Hyperplasia
 Hyperplasia: increase in the number of
muscle fibers
 Has been seen in cats

55. McCall, et al. 1996
 Hypertrophy vs. hyperplasia study
 Studied 15 college-aged men
 12 week training study:
 8 exercises
 3x per week
 3x10-RM weights
 1 minute rest between sets

56. Results
 Preacher Curl 1-RM went from
approximately 36 kg to approximately 44
kg after 12 weeks
 Biceps brachii CSA increased by 12.6%
 Triceps brachii CSA increased by
25.1%

57. Fiber Types and
Hypertrophy
 Type II fibers
were consistently
larger than Type I
 Type II and Type I
increased area
after 12 weeks
 Type II increased
area more
(17.1% vs. 10%
increase)

58. More Results
 % of fiber types was unchanged after 12
weeks
 No change in estimated number of
muscle fibers after 12 weeks
 Increase in capillary density after 12
weeks, 12.7% in Type I and 22.6% in
Type II

59. Conclusions
 No hyperplasia evident. Could be study
wasn’t long enough or difficult enough,
however…
 No increase in number of Type II fibers
 Type I and II increased area, Type II
increased more
 Increase in capillary density
accompanied hypertrophy for both I and
II, type II more

60. Satellite Cells and Hypertrophy
 Studies of rats shows that knocking out
satellite cells impairs their ability to
undergo hypertrophy.
 People:
 Petrella et al (2008)
 16 weeks of strength training
 Divided their subjects into non-responders,
moderate responders, and extreme
responders.

61. Petrella et al (2008), cont.
Non
Responders
Moderate
Responders
Extreme
Responders
Satellite Cells 0% 50% 200%
Myonuclei per
fiber
0% 9% 26%
Fiber CSA 0% 20% 75%
Table shows percent change after 16 weeks of training.

62. Research and Hypertrophy
 DeFreitas et al (2011):
 25 untrained men, trained for eight weeks.
3x8-12 to failure on leg extension, leg press,
and bench press.
 Muscle CSA increased by 10%
 Strength increased by 24%

63. DeFreitas et al (2012)
 The timing of the gains is interesting:
 Muscle CSA made biggest increases at the
end of weeks 1, 3, 5, and 6. Leveled off at
weeks 7 and 8.
 Strength made biggest increases in weeks
3, 4, 7, and 8.
 Importance of variety for CSA?
 Importance of CSA for strength?

64. Matta et al (2011).
 40 subjects, 12 weeks of periodized
strength training, 3x/week (1 day light, 1
day medium, 1 day heavy).
 Bench press, pulldown, triceps
extension, biceps curl
 Study meant to look at how the biceps
and triceps react to training

65. Matta et al (2011)
Biceps Triceps
Proximal (near
shoulder) thickness
12% 2.2%
Mid thickness 7.5% 6.7%
Distal (near elbow)
thickness
5% 7.1%
Muscles don’t experience hypertrophy uniformly
Different muscles respond differently to training

67. Kawakami, et al. (1995).
 Studied 5 men
 Subjects performed triceps pushdowns
with the right arm, 3x/week, for 5x8x80%
 After sixteen weeks, triceps cross
sectional area increased by average of
33.3%
 Angle of pennation of triceps fibers
increased by average of 29.1 degrees

68. Kawakami, et al. (1995).
 Study suggests that changes in CSA as
a result of training is accompanied by an
increase in muscle fiber pennation
angles.
 Follow up studies by Kawakami, et al.
have confirmed that this occurs as a
result of training.

69. Kawakami, et al. (2000).
 Relationship
between muscle
size and
pennation angle,
comparing
untrained
subjects with
bodybuilders.

70. The Muscles are Very
Adaptable
 Nimphius et al
(2012).
 Looking at elite
softball players.
 Followed training for
20 weeks
Week Weights Other
1-3 General
Prep
General Prep
4-11 Strength Conditioning
11-18 Power Speed/Agility

71. Nimphius et al (2012)
 Results, end of study:
 1-RM increased by 10%
 Speed, agility, aerobic capacity
increased
 Vastus lateralis muscle thickness
increased 3.5%
 VL angle of pennation decreased by 4%
 VL fascicle length increased by 10%

72. Nimphius et al (2012)
 Results are deceptive:
 Muscle lost thickness over first seven
weeks, gained after that
 Angle of pennation increased during first
seven weeks, decreased over last seven
 Fascicle length shortened over first seven
weeks, increased over last seven

73. Nimphius et al (2012)
First 7 Weeks Last 7 Weeks
Weights Strength Focus Power Focus
Other Conditioning Focus Speed/Agility Focus
Muscle Thickness Decrease Increase
Angle of Pennation Increase Decrease
Fascicle Length Decrease Increase