Force, Exertion and Repetition
defined, is the energy required to accomplish a task. Exertion, on the
other hand, is the effort the individual needs to expend to accomplish
the task. Although the force needed for a task may remain constant, exertion
can vary based upon several factors such as posture (positioning of the
body while performing a task), repetition (the number of sequential times
the task needs to be performed) , and the environment in which a task
is performed (such as in a hood or other protected area). For example,
the amount of force or energy needed to move a five pound object a distance
of one foot is well defined. Now consider moving that same five pound
weight the same distance repetitively 50 times. The amount of exertion
or effort needed to complete the task on the 50th time will be far greater
than the effort needed to complete the task the first time.
there may be little that can be done to reduce the repetitive nature of
pipetting, there are several things that can be done to reduce the exertion
or effort required to complete the task, as well as minimize the negative
effects of over exertion.
first and most important step is to maintain proper posture while pipetting
(see section on Posture). This will help to
maximize your available strength, reduce tension and stress and limit
awkward static positions. Static work produces fatigue quickly. Blood
brings oxygen to the muscle groups to allow them to function properly.
During periods of rest, the demand for oxygen is low. In dynamic work,
such as exercising, the demand for oxygen increases. Through an increased
heart rate, blood flow is increased and therefore the supply of oxygen.
However, in static work such as holding the arm in an elevated position
while pipetting, oxygen demand is increased due to the static load placed
on the shoulder muscles but blood flow is not increased and there my
be constriction of vessels at pressure points. Such static work produces
fatigue quickly, causing tension, soreness and pain.
- Avoid arm, wrist and hand positions that can reduce strength. Correct posture allows the muscle groups to function freely without
restriction (neutral positions). Deviation from these neutral positions
places stress on the muscle groups, reducing available strength. This
means more exertion will be required to complete the same task than
if the arm, wrist and hand were in a more correct posture. Although
it may be impossible to avoid certain arm, wrist and hand movements
due to the nature of the work, using a pipette that minimizes rotation
and deviation and thereby reduces stress on the muscle group is recommended.
- Take mini breaks. Various
US governmental agencies have recommended that continuous pipetting
be avoided. To avoid muscle fatigue, pipetting should be limited to
20 minutes or less. By taking a short break, the muscle groups rest
and recover. During peak periods of pipetting it has also been recommended
that the workload be distributed to several people and/or additional
staff be brought in to assist with the task, and that tasks be rotated
among several individuals
- Avoid elevated arm positions. Keep work items within easy reach to limit extension and elevation of
arm. Arm/hand elevation should also not exceed 12” from the worksurface.
- Keep elbow
posture near a 90° position.
action: Available strength diminishes when the elbow is raised or lowered.
Keep work items within easy reach and limit work where arms are in an
Forces – Facts and Fiction
a lot more to pipette forces than meets the eye (or in reality, the thumb).
In fact, aspirating and dispensing is only one function of pipetting that
requires the use of the thumb muscles. Tip acquisition and ejection usually
requires excessive forces that contribute significantly to muscle fatigue.
A strong interrelationship also exists between posture and force –
the need for additional exertion increases as posture deviates from neutral
positions. Therefore, when considering forces while choosing a pipette,
one should focus on the actual exertion that may be required and not only
force measurement data.
forces required to acquire a tip can vary greatly due to a variety of
factors, including tip quality, fit dimensions and user technique.
past several years several tip manufacturers have offered “universal”
tips designed to fit a variety of pipette brands. This multi-fit capability
is usually accomplished through the use of a conical-shaped seal area.
The pipette is forced into the tip until a seal is formed. In many cases,
users are observed “tapping” the pipette into the tip several
more times to ensure a proper seal.
From an ergonomic
perspective, when jamming a pipette into a tip, the user typically exerts
a level of force that is well beyond the pipette’s intended design.
While this excess force is considered by some as preferable to a tip falling
off during use, the ergonomic effects cannot be overlooked.
acquisition (jamming on the tip) the user often tightly grips the pipette
to prevent the pipette from slipping through the hand. This “clenched
fist” grip causes unnecessary tension in the forearm and hand muscles,
and contact stress in the palm of the hand. The forces necessary to remove
the tip may also be increased. Because the tip is forced onto the pipette,
the user needs to apply additional force to the tip ejector mechanism,
further exacerbating contact stress on the thumb and increasing exertion
by the thumb muscles.
pipette tips, a comparison of the manufacturer’s recommended tip
dimensions and the dimensions of alternate tips should be considered.
The selected tip should fit snuggly onto the pipette, ensuring proper
sealing with minimal force and without the need to tap the pipette into
Aspirating and Dispensing
have attempted to reduce plunger spring forces with magnetics or electronic
enhancements. Measuring the amount of force required to actuate a pipette’s
plunger is rather straightforward, and often published by manufacturers.
Data on required thumb forces should be considered in conjunction with
other ergonomic factors when evaluating overall pipetting stress and force
Technologies Corporation, an independent consulting firm specializing
in workplace ergonomics, conducted a series of tests using traditional
axial-designed pipettes and VistaLab Technologies’ new Ovation BioNatural
Pipette. The testing revealed that the Ovation pipette showed a significant
reduction in the amount of force required by the thumb throughout a full
cycle of pipetting.
manufacturers have provided mechanisms to assist in detipping. However,
as mentioned in the Tip Acquisition discussion above, if a tip is applied
with more force than the pipette’s intended design, the detipping
mechanism may require additional force or not work at all. Data on required
tip removal forces should be considered in conjunction with other ergonomic
factors when evaluating overall pipetting stress and force levels.
Technologies Corporation, a consulting firm specializing in workplace
ergonomics, conducted a series of tests using traditional axial-designed
pipettes and VistaLab Technologies’ new Ovation BioNatural Pipette.
The testing revealed that the Ovation pipette showed a significant reduction
in the amount of force required to eject a tip.
BioNatural Pipette was specifically designed to address each of the force-related
- A loose,
relaxed grip is used in all pipetting operations, including tip acquisition.
- A gentle
push of the pipette’s nozzle into a tip is all that’s needed
to acquire a tip.
- An audible
“click” provides feedback to confirm that the tip is seated
properly and additional effort is not needed .
- Easy on
– easy off. Ovation’s proprietary “energy release”
button ejects tips with a gentle push.
requires less force throughout all pipetting tasks. A summary of the
various force comparisons discussed above shows a significant reduction
in the overall amount of force required when pipetting.