Variable Resistance – Implication for Variable Resistance – Implication for Swimming TrainingSwimming Training

Type of Muscle ContractionType of Muscle Contraction

StaticStatic

DynamicDynamic

Angle of Pull – Invention of Isokinetic Angle of Pull – Invention of Isokinetic machinemachine

Swimming – Training for optimum muscle Swimming – Training for optimum muscle power and strength improvementpower and strength improvement

By Jackson Pui Man Wai, Ph.D.By Jackson Pui Man Wai, Ph.D.

First-Class leverFirst-Class lever 第一型槓桿第一型槓桿

Second-Class leverSecond-Class lever 第二型槓桿第二型槓桿

Third-Class leverThird-Class lever 第三型槓桿第三型槓桿

40 kg x 1 m = 40 kgm40 kg x 1 m = 40 kgm 20 kg x 2 m = 40 kgm20 kg x 2 m = 40 kgm

(20+5) kg x 1.6 m = 40 kg(20+5) kg x 1.6 m = 40 kgmm

Muscle Angle of Pull - Tension Relationship

Source: Fox, Bower, and Foss. The Physiological Basis of Physical Education and Athletics.

Muscle Angle of Pull - Tension Relationship

Source: Fox, Bower, and Foss. The Physiological Basis of Physical Education and Athletics.

LF

LW

LW

LF

L W

LF

Effect of Angle of Pull on Muscle tensionExperimental setting

LF

LW

LW

LF

LW

LF

Effect of Angle of Pull on Muscle tensionRealistic setting

Open SystemEnergy of muscle force converts to energy of acceleration

F = ma

a = F/m

a F,

Thus F a

Closed system

Energy cannot be dissipated by acceleration, energy of acceleration is absorbed as energy of resistance.

F = ma = mR (constant V)

R Fthus F R

Isokinetic Knee Extension and Flexion

Torque curves of quadriceps and hamstring muscle groups of normal subjects performed at 22.5°·s-1

~147~147°°

~117~117°°

CYBEX II Isokinetic DeviceShoulder Adduction and

Abduction

THE ENDTHE END