Muscular strength
The greatest amount of force that muscles can produce in a single maximal effort. (Kg)
Power
Work per unit time
force x velocity
Muscular endurance
ability of a muscle group to perform repeated contractions against a light load for an extended period of time
Muscular power
the ability to exert a maximal force in as short a time as possible
Benefits of strength training
Slow down the muscle loss that accompanies aging process
increase functional mobility
Increase the size and strength of muscle fiber
Increased tendon, ligament and bone tensile strength
Stronger muscles better protect the joint that they cross
improve physical appearance
Better strength in muscles of the trunk = prevent common postural problem
Stronger muscle = less likely to be injured
Improvement in self concept and self esteem
3 types of Muscular contractions
- Dynamic (isotonic ) contractions
- Isometric contraction
- Isokinetic contraction
Dynamic (isotonic) contraction
Dynamic
Range of motion when muscle perform work
Concentric contraction - muscle shortens
Eccentric contraction - Muscle lengthens ( used in resisting gravity )
Isometric contraction
Static contraction . No change in angle of the joint or the length of the muscle. eg. Jackson upright row test
Isokinetic Contraction
Muscle is shortened at constant velocity
Exert maximal force throughout the full range of motion
Usually need electronic equipment
Purpose 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 Rep Maximum
Maximum amount of weight lifted once
Estimated One rep maximum = (weight lifted )/ [1.0278 - (n x 0.0278)]
Dynanometer techniques
Usually consist of a spring of some type
deform when a certain amount of force is applied to it
eg. Hand grip dynamometer
Measures isometric strength
Computer assisted, isokinetic methods
Using isokinetic machine, but many of these machines can also test strength in isometric, concentric, and eccentric modes.
Strength assessment considerations
- Standardized instructions should be given
- Warm up should be uniform duration and intensity
- Ensure that the angle of measurement is consistent
- Consider individual differences in body size and proportions
- Test and training mode specificity are important
- Safety
- Test admin must know what they are doing
Effect of various factors on Strength
- Muscle cross sectional Area
- Body size,
- Muscle fiber composition
- Mechanical factors
- Sex and Age
- Muscle cross sectional Area
- Muscle Cross Sectional Area - there is a strong positive relationship between muscle
CSA and strength.
Muscles increase in strength by increasing their size and by enhancing the recruitment and firing rates of their motor units.
Hypertrophy accounts for most increase in muscle
Hypertrophy
Increase in size of cell
Hyperplasia
Increase in number
Myonuclear addition
Myofibrillar proteins increase
Myofiber CSA increase
Body size
Body Size - there is a positive correlation between body size or mass and absolute strength.
There is a negative correlation between body mass and the strength/mass ratio. The strength to mass ratio directly reflects an athlete’s ability to accelerate his or her body.
Muscle fiber conposition
For a given size of muscle, positive correlation between % of fast twitch fiber and strength
Mechanical factors
Force exerted by a muscle is affected by:
- Initial length of the muscle fiber
- The angle of the pull
- The speed of shortening
Sex
Average male is physically larger than average female
Difference in body composition = average male has more muscle and less fat due to testosterone
Larger muscles are stronger muscles
Body proportion differences
Cultural factors - less emphasis on strength activities for females
