Title: The Scientific Principles of Strength Training
1The Scientific Principles of Strength Training
- Muscular Strength The amount of force a muscle
can produce with a single maximal effort - Mechanical Strength the maximum torque that can
be generated about a joint
2Torque about the elbow joint
- Strength determined by
- Absolute force developed by muscle
- Distance from joint center to tendon insertion
- Angle of tendon insertion
3Shoulder joint torque as a function of arm
position
4(No Transcript)
5Structural organization of skeletal muscle
From Principles of Human Anatomy (7th edition),
1995 by Gerard J. Tortora, Fig 9.5, p 213
6From Basic Biomechanics by Susan Hall (3rd
edition), Fig 6.6, page 153
6-6
7From Skeletal Muscle Form and Function (2nd ed)
by MacIntosh, Gardiner, and McComas. Fig 1.4, p.
8.
8From Basic Biomechanics by Susan Hall (3rd
edition), Fig 6.5, page 152
6-5
9From Basic Biomechanics by Susan Hall (3rd
edition), Fig 6.3, page 150
6-3
10From Exercise Physiology Theory and Application
to Fitness and Performance (6th Edition) by Scott
K. Powers and Edward T. Howley. Fig 8.6 P. 147
11A motor unit single motor neuron and all the
muscle fibers it innervates
From Basic Biomechanics Instructors manual by
Susan Hall (2nd edition, 1995), Fig TM 31
12From Basic Biomechanics by Susan Hall (3rd
edition), Fig 6.7, page 154
6-7
13From Basic Biomechanics by Susan Hall (3rd
edition), Fig 6.8, page 154
6-8
14- Types of muscle fiber Fast twitch vs Slow Twitch
- Type I Type IIa Type IIb
- ST Oxidative FT Oxidative - FT
Glycolytic - (S0) Glycolytic (FOG)
(FG) - Contraction speed slow fast (2xI)
fast (4xI) - Time to peak force slow fast
fast - Fatigue rate slow inter.
fast - Fiber diam. small inter.
large - Aerobic capacity high inter.
low - Mitochondrial conc. high inter.
low - Anaerobic capacity low inter.
High - Sedentary people 50 slow/50 fast, whereas
elite athletes may differ - e.g., cross country skiers 75 slow 25 fast
- sprinters - 40 slow
60 fast
15Factors affecting force Production
- Hypertrophy increase in the of myofibrils and
myofilaments - Hyperplasia increase in the number of fibers???
162. Rate Coding frequency of stimulation
From Basic Biomechanics by Susan Hall (3rd
edition), Fig 6.9, page 155
17- 3. Spatial recruitment
- Increase of active motor units (MUs)
- Order of recruitment
- I ---gt IIa -----gt IIb
- Henneman's size principle MUs are recruited in
order of their size, from small to large - Relative contributions of rate coding and spatial
recruitment. - Small muscles - all MUs recruited at
approximately 50 max. force thereafter, rate
coding is responsible for force increase up to
max -
- Large muscles - all MUs recruited at
approximately 80 max. force.
184. Velocity of shortening Force inversely
related to shortening velocity
The force-velocity relationship for muscle
tissue When resistance (force) is negligible,
muscle contracts with maximal velocity.
19The force-velocity relationship for muscle
tissue As the load increases, concentric
contraction velocity slows to zero at isometric
maximum.
20Force-Velocity Relationship in different muscle
fiber types
Type II fiber
Type I fiber
21Effect of Temperature on Force-Velocity
relationship (22oC, 25oC, 31Co, and 37oC)
22Force -Velocity Relationship (Effect of
strength-Training)
23Force-velocity Relationship During Eccentric
Muscular Contractions
24Force/Velocity/Power Relationship
Force/velocity curve
Power/velocity curve
Force
Power
30
From Basic Biomechanics by Susan Hall (3rd
edition), Fig 6.25, page 175
30
Velocity
25Effect of Muscle Fiber Types on Power-Velocity
Relationship
26Consequences of the force-velocity relationship
for sports practice
- When training for sports that require power,
train with the appropriate of 1 RM that will
elicit the most power. - 24 weeks of
- a). heavy weight-training b. Explosive
strength training
From Science and Practice of Strength Training
(2nd edition) V.M. Zatsiorsky and W.J. Kraemer
(2006) Fig 2.19 P. 39)
27- Why do elite weight lifters start a barbell
lift from the floor slowly? -
- They try to accelerate maximally when the bar is
at knee height. Two reasons - 1. At this position, the highest forces can be
generated as a result of body posture
28- 2. Because force decreases when velocity
increases, barbell must approach the most favored
position at a relatively low velocity to impart
maximal force to the bar.
From Science and Practice of Strength Training
(2nd edition) V.M. Zatsiorsky and W.J. Kraemer
(2006) Fig 2.20 P. 40)
29Adaptations associated with strength training
- 1. Activates protein catabolism. This creates
conditions for enhanced synthesis of contractile
proteins during the rest period (break down,
build up theory)
From R.L. Leiber (1992). Skeletal Muscle
Structure and Function. Fig 6.1, p. 262.
30- 2. Neural adaptations occur to improve
intra-muscular and inter-muscular coordination. - Intra-muscular coordination affects the ability
to voluntarily activate individual fibers in a
specific muscle - Inter-muscular coordination affects the ability
to activate many different muscles at the
appropriate time
31- Intra-muscular coordination changes with
- training
- Untrained individuals find it difficult to
recruit all their fast-twitch MUs. With training,
an increase in MU activation occurs - Strength training also trains the MUs to fire at
the optimal firing rate to achieve tetany -
- MUs might also become activated more
synchronously during all out maximum effort
32- Consequently, maximal muscular force is achieved
when - 1. A maximal of both FT and ST motor units are
recruited - 2. Rate coding is optimal to produce a fused
state of tetany - 3. The MUs work synchronously over the short
period of maximal effort.
33- Psychological factors are also of importance
-
- CNS either increases the flow of excitatory
stimuli, decreases inhibitory stimuli, or both - Consequently, an expansion of the recruitable
motor neuron pool occurs and an increase in
strength results - Hidden strength potential of human muscle can
also be demonstrated by electrostimulation - Muscle strength deficit (MSD)
- (Force during electrostimulation-Maximal
voluntary force) x 100 - Maximal voluntary force
- Typically falls between 5-35
34- Electrostimulation
- Possibility exists to induce hypertrophy through
electrostimulation - However, does not train the nervous system to
recruit motor units - Bilateral Deficit
- During maximal contractions, the sum of forces
exerted by homonymous muscles unilaterally is
typically larger than the sum of forces exerted
by the same muscles bilaterally - Bilateral training can eliminate this deficit, or
even allow bilateral facilitation -
35Other benefits of strength training
- Increase in resting metabolic rate
- Each additional pound of muscle tissue increases
- resting metabolism by 30 to 50 calories per
day 10,950 to 18,250 calories a year 3-5 lb
of fat - Increase in bone mineral content and, therefore,
bone density - Increases the thickness and strength of the
connective tissue structures crossing joints such
as tendons and ligaments helps prevent injury - Increased stores of ATP, Creatine Phosphate (CP),
and glycogen - Aids rehabilitation from injury
- Aging gracefully! Less falls in latter years
- Looking better, feeling better. Greater
self-esteem
36Metabolic stress of resistance training
- Classed as only light to moderate in terms of
energy expenditure per workout -
- Standard weight-training does not improve
endurance or produce significant cardiovascular
benefits like aerobic type activity does - Circuit-training increases metabolic stress
37Delayed onset of muscle soreness (DOMS)
- The intensity and the novelty of a workout
influence how sore you become - Lactate does not cause muscle soreness due to
- 1. Lactate returns to baseline within an hour of
exercise - 2. After exercise, lactate is in equal amounts
within the muscle and the blood - 3. DOMS is specific, not generalized
- Muscle soreness is due to the physiological
response to muscle fiber and connective tissue
damage (microtears) - White blood cells enter the muscle tissue, clean
up the debris of broken proteins, and then
initiate the regeneration phase
38Muscle Soreness (continued)
- Edema (increase in fluid) to the area accompanies
the above response - The pressure from edema is thought to produce the
sensation of soreness -
- Also, metabolic by-products released from the
macrophages may sensitize pain receptors - Next stage is the proliferation of satellite
cells - help form new myofibrils - Eccentric contractions cause the greatest amount
of soreness