Week 10 - Levers / Segmental sequencing Flashcards
Case Study that may be in exam
Scenario Trent is recovering from a groin strain he endured on his right side during football training. A previous assessment of his range of motion indicated that he had 10° of active hip abduction range.
Task Perform a goniometric assessment of Trents right ‘active’ hip abduction range of motion. Explain the result to your client using lay terminology.
Active hip abduction range is assessed while patient is lying on their side with legs extended.
In which of these positions would the diver be able to rotate faster? Why?
Left. Angular momentum is conserved once we are in the air. When we bring our body closer to the centre of mass, we decrease our moment of inertia and therefore increasing angular velocity.
Which way will the see saw rotate and with how much torque?
m1 = 20kg, m2 = 30kg, r1 = 1.2m, r2 = 1.2m
Boy
T = F*d
T = (20*9.81)*1.2
T = 235.44 Nm anti-clockwise
Girl
T = (30*9.81)*1.2
T = 353.16 Nm clockwise
353.16-235.44 = 117.72 Nm
The seesaw will turn clockwise with a torque of 117.72 Nm
How close to the axis would the girl have to move to balance the seesaw?
m1 = 20 kg, m2 = 30 kg, r1 = 1.2 m, r2 = ???
Balanced means ΣT = 0
Tboy = Tgirl
- 44 = F*d
- 44 = (30*9.81)*d
- 44 = 294.3*d
- 44/294.3 = d
d = 0.8m
r2 = 0.8m
Define a lever
Rigid structure hinged at one point, with forces applied at another two points
Basic purpose of a lever
Transmit energy from one place to another
A lever consists of: (5)
Fulcrum = axis of rotation
Applied force - causes the movement/motion
Force arm - moment arm of applied force
Resistance force - resists the movement/motion
Resistance arm - moment arm of resistive force
Examples of levers in the body
Many arrangements in the body serve as levers.
The rigid lever = bones
Fulcrum/axis = joints
Motive/applied force/torque = Muscles (concentric contractions)
Resistive force/torque = Weight of segment
Explain mechanical advantage
Mechanical advantage = force arm / resistance arm
When a MA = 1 you have no mechanical advantage
Applied Force Arm > Resistance Arm (MA > 1)
= Applied force has the advantage = strength advantage
Applied Force Arm < Resistance (MA < 1)
= Resistance Force has the advantage = speed and ROM advantage
Classes of levers and mnemonic to remember
What goes in the middle?
FRE 123
1st, Fulcrum in the middle (seesaw)
2nd, Resistance in the middle (strength)
3rd, Effort in the middle (speed)
What type of lever is this?
Force arm > Resistance arm
Second class lever (strength)
What happens to the change of lever classes when we go from a concentric bicep curl to a eccentric bicep curl?
Concentric is a 3rd class lever, and it will flip during eccentric to a 2nd class lever
Eccentric or concentric contraction and which lever class?
Red arrow is applied force arm
Blue arrow is resistance arm
Concentric phase and level 3 class for speed
Eccentric or concentric contraction and which lever class?
Blue arrow is applied force arm
Red arrow is resistance arm
Eccentric phase, 2nd class lever for strength
Applied force arm > Resistance arm
Where is the point of application of a muscle force?
Where the tendon attaches to the bone
What is the rotary component in a muscle force system?
A perpendicular force acting on the bone in movement
What is a stabilising and dislocating component of a muscle force system?
A dislocating component is a straight line from the rotary component away from the joint. And the Stabilising component is a straight line from the rotary component towards the joint.
Coaching implications for beginners in relation to segmental sequencing
Small no. of segments
Distal segments don’t lag back
“Stiff” movement of
Joints Lack of sequencing
Small range of motion
Coaching implications for skilled athletes in relation to segmental sequencing
Large no. of segments
Segments lag and whip
“Free” movement of joints
Proximal to distal sequencing
Large range of motion
