Practical Demonstrations of Ergonomic Principles


WOMAN: A series of short
video clips have been generated that are supplemental
to the written document entitled “Practical Demonstrations
for Ergonomics Principles.” This written document discusses
several ergonomics principles, including neutral versus
non-neutral postures, power versus pinch grips, fatigue failure and back pain, moment arms and lifting, and hand tool selection
and use. These supplemental video clips
introduce you, the trainer, to unique demonstration devices used throughout
the written document. This is a moment arm simulator. Essentially, it’s a balance
with a scale attached to one end and a counterweight
attached to the other end to account for the weight
of the scale. Here we have the fulcrum. If I take a five-pound weight and place it directly
at the fulcrum, you can see that no force
registers in the spring scale. If I now take the same weight and move it a certain distance
away from the fulcrum, as such, I’ve increased the moment arm and you can see a force
registers in the spring scale. If I increase the distance
of that moment arm again… …I now see that the force
in the spring scale increases. So, even though the weight
of the object remained consistent throughout, simply by increasing
the moment arm, I increased the force registered
by the spring scale. The concept of moment arms
can also be applied to the body. If we look at
the low back muscles, we can consider them
to be our spring scale and the pelvis
to be the fulcrum. As I move the weight further
from the pelvis, I’ve increased the moment arm and increased the force
in the low back muscles. If I move the weight
closer to the pelvis, I’ve decreased my moment arm and then decreased the forces
in the low back muscles. In this document,
we discuss two types of grips — a power grip, where you curl
your fingers towards your palm, and a pinch grip,
where you take your thumb and press latterly
against your fingers. The forces generated
by these two types of grips can be measured
with hand dynamometers. For the power grip, you can use a hand dynamometer
such as this one. Here you can adjust
the grip width and you can also view the force
that’s generated by the grip. If I press
with my maximum effort, you can see the force I’m able
to register here on the dial. I can then zero that force… and ask another person to again
exert their maximum effort and compare my force exerted
to theirs. Similarly we have a hand
dynamometer for the pinch grip. Again, I exert my maximum effort and can view the force generated
by looking at the dial. This dial can also be zeroed so that another subject could
also exert their maximum force. This is the portable EMG device. It emits an audible sound
as muscle activity increases. It consists of two switches. The top switch
is an on/off volume switch, and the bottom switch
is an intensity switch. This switch
will have to be adjusted based on the muscle group
you’re using to account
for the audible signal. It also comes
with three electrode leads — two red and one black. These electrode leads
are attached to electrodes which can be bought in packs that look roughly like this. In this document,
we use the portable EMG device to look at four areas
of the body — the forearm, the biceps,
the shoulder… and the low back. Take note that for each area of
the body we place the electrodes approximately one inch apart
from one another. Now I’m gonna use
the forearm as an example for how to hook up
the portable EMG device. Take your black electrode lead and attach it
to the center electrode, then take your two remaining
red leads and attach them
to either electrode. If I turn on the device, I hear no audible signal while
he’s in this neutral posture. However, if I now ask him to contract
his forearm muscles… [ Beeping increases ] …you can hear the intensity
of the device increases greatly. If I ask him to relax… [ Beeping decreases ] …again, we see
that the intensity decreases. [ Beeping increases ] [ Beeping decreases ]

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