Biomedical Engineering Reference
In-Depth Information
(C) Less potential for muscle damage.
(D) Muscle strength and torque of joints are easily determined
Disadvantages include:
(E) Expensive equipment.
(F) Acceleration properties of the system and artifacts during deceleration
decrease reliability in muscle strength measurements, in terms of uniform speed
and measurement results, when the reference speed for the exercise are set at 200
deg/s or more.
(G) Equipment must be prepared for individual muscle groups.
We can find from the above that isokinetic exercise is more effective than
isotonic exercise and is superior in evaluating exercise results. Muscle contraction
modes ensure replicable evaluation by maintaining constant muscle length in
isometric contraction and load in isotonic contraction.
In isokinetic contraction based on A.V. Hill's theory (Hill, 1938) on the rela-
tionship between contractile speed of muscle and its tension, muscle contraction
speed is not consistently controlled in practice because speed decreases at the start
and finish of movement and increases in the middle, rather than because of kinetic
joint structure.
11.2.2 Hill's equation
A.V. Hill formulated the relationship between force of muscle and its contraction
speed as follows: (Hill, 1938.)
b
(
P
0
−
P
)
V
=
(11.1)
+
P
a
where
P
denotes force,
V
contraction speed, and
P
0
maximum force at a speed
of zero.
a
and
b
are experimental constants and determined in order that the
experimental data fits to the formula (11.1). As shown in
Fig. 11.1
, the P-curve
shows that the force decreases with increasing speed (Winter, 1990).
+
0
Lengthen
Shorten
Velocity
Figure 11.1
Hill's curve.
