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Force, Exertion and Repetition


Force, simply 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.

Although 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.

  • The 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 muscular fatigue.

  • Avoid 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.
    Corrective 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 elevated position.


Pipette Forces – Facts and Fiction

There’s 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.


Tip Acquisition

The actual forces required to acquire a tip can vary greatly due to a variety of factors, including tip quality, fit dimensions and user technique.

Over the 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.

During tip 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.

When selecting 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 the tip.


Aspirating and Dispensing

Pipette manufacturers 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 levels.

Ergonomic 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.

     


Tip Removal

Many pipette 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.

Ergonomic 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.

The Ovation Solution

The Ovation BioNatural Pipette was specifically designed to address each of the force-related concerns.

  • 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.

  • Ovation 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.