Biomedical Engineering Reference
In-Depth Information
motion under restriction of constant angular velocity controlled by an isokinetic
training machine.
In the isokinetic contraction, the constant velocity is not the velocity of the
linear muscle contraction but joint angular velocity. This causes by the reason
that the joint angular movements are affected of the length of the lever arm of
the muscle origin and insertion. Little attention has been paid to these differences.
These days, isokinetic machines, for example, Cybex (Bohannon, 1991), Biodex
(Kelli, 1996), are widely used in the rehabilitation medicine and sports medicine.
Those machines are used in many researches for the relationship between the
muscle strength and the contraction velocity. This contraction is based on the
researches of Hill (Hill, 1938). However, those machines cost expensive depending
on its actuation device (actuator is usually servomotor with high torque).
In order to develop an isokinetic exercise machine with low-cost, high safety
and high performance, we have developed isokinetic and iso-contraction exercise
machine by using a magnetorheological (MR) fluid brake. The primary purpose
of this study is to make the mechanical model of the human joint movement on
the consideration of the length of the lever arm effect. The secondary purpose is
to develop the isokinetic machine to enable to evaluate the muscle strength in the
constant linear velocity of the muscle contraction.
In this report, we describe development of the isokinetic and iso-contraction
exercise machine. We use MR fluid as a working material of the brake. Because
of the rapid response of the MR fluid, this brake performs superior response
compared with conventional brakes. In other words, a simple and safe training
machine with accurate velocity control can be realizedwith this brake. High-speed
control (up to 900 [deg/s] at elbow joints) could be performed with this machine.
Additionally, we suggest an iso-contraction exercise by using this machine and
discuss experimental results.
11.2 CONVENTIONAL ISOKINETIC EXERCISE & PROPOSED
ISO-CONTRACTION EXERCISE
11.2.1 Conventional Isokinetic Exercise
Muscle strengthening exercises are used for such purposes as medical rehabilita-
tion, improving physical strength and athletic performance. A widely practiced
exercise is isometric, in which persons with arthritis, for example, contract their
muscles without joint movement while pushing an immovable wall. Recent
emphasis is being placed, however, on isokinetic exercise rotating the joints at
a certain speed with special training equipments to produce uniform movement
applying appropriate reaction against autonomous movements by trainees. Isoki-
netic exercise has both advantages and disadvantages (Miura, 1992).
Advantages include:
(A) Sufficient muscle strengthening throughout the whole range of motion.
(B) Load is automatically set as needed for each angular velocity.
