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Levers & Exercise Level 2 Fitness Instructor
Transcript of Levers & Exercise Level 2 Fitness Instructor
Levers and Exercise
Describe the effect of
levers, gravity and
resistance on exercise
There are different types of levers dependent upon the position of fulcrum, effort and resistive force.
Mechanical advantage gained by the lever.
Where the muscle is attached on a bone will have a major effect on the force or strength the muscle can apply.
First and second class levers enable us to lift heavy weights with a relatively small amount of effort. Third class levers however, do not give this a mechanical advantage. As most levers in the body are third class levers we can see the body is not designed to make lifting easy. With many of the attachments close to joints and the bones themselves quite long, the force needed to lift even light objects is quite large. For example, to abduct your arm with a 5 kg weight in your hand, the deltoid muscle would have to use a force equivalent to 150 kg to lift it to shoulder height. If the deltoid muscle was connected 2 cm further down the humerus, and our arm was 5 cm shorter, the force required would be greatly reduced.
Due to the structure of third class levers they do not offer the body advantages in strength. When considering range of movement and speed however, we find a much better system with these types of levers. If the deltoid was to contract and shorten in length slightly, we would still see a great distance moved by the hand. This allows us to produce great throwing and striking forces. This is especially when the length of the lever is increased by holding an object like a tennis racquet or golf club. The speed at which the hand would move is also much greater than the speed at which the humerus would move. Once again, holding a tennis racquet would greatly increase the speed of the most distal point in the lever. This is why tennis players can serve balls up to 200 kilometres an hour or more.
Other factors which can affect muscle performance include the arrangement of muscle fibres, the number and size of muscle fibres and the neurological training and recruitment i.e. how effectively the brain tells the muscles what to do. All of these things can be greatly improved with the correct training.
Components use in a lever
- nearly always the bone
Fulcrum - pivot point of the lever, which is usually the joint
- force that draws the opposite ends of the muscles together
- force generated by a factor external to the body (e.g. gravity, friction etc.) that acts against muscle force
- the degree to which a force tends to rotate an object about a specified fulcrum
Introduction to the Mechanics of Joint Action
The main framework of the body is covered by muscle, whose function is to permit movement. We know that to move or lift a load against another force, it is easier to use levers, and it is this principle which the musculoskeletal system adopts as well.
FIRST CLASS LEVER
fulcrum between force
SECOND CLASS LEVER
fulcrum one end the force at the other end, resistance between.
THIRD CLASS LEVER
fulcrum and resistance at opposite ends
while the effort is applied between the two
MOST COMMON in the human body
'Lever' refers to the arms and the legs. It is possible to perform base moves with either short levers (bent arms or legs) or long levers (straight arms or legs). By changing the length of the lever, either arm or leg, the instructor can generate numerous different variations from the one base move.
Not only do changes in lever length alter the way a base move can look, it also changes the intensity of the move. For example; jogging on the spot in the normal manner, bending the non-weight bearing leg behind you as you jog, is easier to do than jogging while keeping both legs straight throughout the entire movement pattern. By increasing the lever length or keeping the legs straight, the intensity of the exercise is increased. If the lever length is shortened, bending the arms or legs, the intensity of the exercise is decreased. Changes in lever length also change the range of motion of an exercise. Another example would be when performing an abdominal curl. If the arms are by the temples the exercise intensity is less than if the arms are extended above the head. Therefore the intensity of the exercises can be increased by placing the hands above head. The greater the range of motion, the greater the intensity of an exercise