Week 5 - Muscular Strength

Muscular strength

• The greatest amount of force that muscles can produce in a single maximal effort

Power

• Work/force per unit time - force x velocity

• Involves strength and speed

Benefits of Strength Training

• Slow down the muscle loss that normally accompanies the aging process

• Increase functional mobility so that daily activities are made both possible and easier

• Increase the size and strength of muscle fibers resulting in a greater physical capacity to perform

• Increased tendon, ligament and bone tensile strength

• Stronger muscles better protect the joints that they cross

• Better strength in the muscles of the trunk, helps to prevent common postural problems

• Stronger muscles are less likely to be strained and injured

• Improvements in self-perception and self-esteem for both patient and athletic populations

Dynamic (isotonic) contraction

• The bony levers move through a range of motion when the appropriate muscles perform work

  • Machines or free weights

  • Iso (same) tonic (tone)

Isotonic Concentration

• Dynamic

• Nautilus Machines

  • Accommodating resistance devices

  • Leverage characteristics change as the joint goes through a range of motion

  • Muscle is stressed more at more optimally at all joint angles

Concentric contraction

• The muscle shortens with varying tension as it lifts a constant load

Eccentric contraction

• The muscle lengthens while developing force

Isometric contraction

• Static contraction. Tension is developed but there is no change in the angle of the joint or the length of the muscle

Isokinetic contraction

• The muscle is shortened at a constant velocity determined by instrumentation which allows a person to exert maximal force throughout the full range of motion

Purposes of Strength Assessment

• Assess muscular fitness

• Identify specific areas of weakness

• Monitor progress in a rehabilitation program

• Measure effectiveness of a resistance training program

• Motivation for training

Strength Assessment Techniques

• One repetition maximum

• Dynamometer techniques

• Computer-Assisted, Isokinetic Methods

One Repetition Maximum

• Maximum amount of weight lifted once

Estimated One Repetition Maximum (1 RM)

• Estimated from repetitions to failure on machines

• Variable-repetition maximum tests

  • 1 RM = (weight lifted) / [1.0278 × ( n x 0.0278 ) ]

    • n = repetitions to failure (not to exceed 10)

Dynamometer Techniques

• a strength testing dynamometer usually consists of a spring of some type which is deformed a certain amount when a specific force is applied to it

  • ex: hand grip dynamometer

    • measures isometric strength

Computer-Assisted, Isokinetic methods

• equipment such as Biodex, KIN/COM, etc

• Isokinetic machine, but many of these machines can also test strength in isometric, concentric and eccentric modes

Strength Assessment Considerations

1. Standardized instructions should be given prior to testing

2. If a warm-up is given, it should be of uniform duration and intensity

3. Ensure that the angle of measurement on the limb or test device is consistent among subjects

4. Consider individual differences in body size and proportion when evaluating strength scores between individuals and groups

5. Test and training mode specificity are important for optimal expression of true strength gains

6. Safety is an important consideration when performing strength evaluations

7. Test administrators should well trained and have a thorough understanding of all testing procedures and protocols

Effect of Various Factors on Strength

1. Muscle Cross Sectional Area

2. Body Size

3. Muscle Fiber Composition

4. Mechanical Factors

5. Sex and Age

Muscle Cross Sectional Area

• Strong positive relationship between muscle CSA and strength

• Muscles increase in strength by increasing their size, recruitment, and firing rates of their motor units

Hypertrophy

• An increase in size of a cell such as a muscle fiber

• Account for most, if not all, of the increase in muscle cross-sectional area due to an overload training program

Hyperplasia

• An increase in number of cells such as adipose cells

Body Size

• Positive correlation between body size or mass and absolute strength

• Negative correlation between body mass and the strength/mass ratio

  • Large athletes dominate sport events which require a high level of absolute strength while smaller athletes dominate sport events which require a high strength/body mass ratio

Muscle Fiber Composiiton

• For a given size of muscle, there is a positive correlation between percentage of fast twitch fibers and strength

• More strength = more fast twitch

Mechanical Factors

• The force exerted by a muscle is affected by:

  • The initial length of the muscle fibers

  • The angle of pull of the muscle on the bony skeleton

  • The speed of shortening

Sex

• After age 16, the average female is about 2/3 as strong as the average male in terms of force produced

  • Trained male 1 vs untrained male 2 → larger difference

  • Untrained male vs untrained female → smaller difference

Reasons why average males are stronger are as follows

1. Physically larger (height and weight) than the average female

2. Differences in body composition - more muscle, less fat due to testosterone

3. Broader shoulder relative to the hips

4. Broader shoulders of the adult male allow more muscle to be packed onto the skeletal frame and create a mechanical advantage for muscles acting on the shoulder

5. Cultural factors

Females and muscles

• Females are equally as strong as males when strength is expressed per unit cross sectional area of muscle

• No difference between male and female muscle

• Cannot distinguish male muscle from female muscle under a microscope

Muscle Strength in Children

• Consider chronological age versus biological age when designing individualized weight training programs for children

• During this time period surrounding peak height velocity (age 11.5 in girls and age 13.5. in boys), young athletes may be at increased risk for injury

Max Muscle Strength

• Maximum strength of men and women is generally achieved between the ages of 20 and 30 years

  • muscle cross sectional area is usually the greatest