Muscular Strength

Force-Length Relationship

&

Force-Velocity Relationship

How Could You Increase Force?

↑ # of Cross-Bridge (i.e. Actin-Myosin)

↑ Force Production

Force-Length Relationship

0

20

40

60

80

100

Sarcomere Length (joint angle)

% M

ax

imu

m T

en

sio

n

Too Short ! Too Long !

How do we measure Muscular Force?

Isolated Muscle*Linear Force (in N or lbs)

Human Body*Angular Force

(Torque; N*m or ft*lbs)

Terminologies

• Isometric Contraction“same length”

• Isotonic Contraction“same tension”

• Isokinetic Contraction“same speed”

Force-Velocity Relationship

-1 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 1

Eccentric ConcentricContraction Velocity (m/s)

Mus

cle

Ten

sion

Fatigue and Fiber Type

• As a muscle contracts maximally many times the ability to generate force will decrease

• The degree to which force decreases can be measured by percent torque decline or fatigue index

• A rough estimation of fiber type can be made based on the decline in force production

Lab Procedure

• Torque vs Angle (3 subjects)Isometric Contraction@ 90˚ , 130 ˚, 170 ˚

• Torque vs Velocity (3 subjects)Isokinetic Contraction @ 60 ˚/sec, 180 ˚/sec, & 300 ˚/sec

• 50 Repetition Fatigue (1 subject)50 reps isokinetic contractions (180˚/sec)