ergonomic handles for cookware

Foreword

Ergonomics has delivered many improvements to the size, texture and shape of handles in recent years. However improvements in hand, wrist and arm posture have remained elusive due to the difficulty in changing handle alignment without introducing a different set of problems when the utensil is used in a different way. In addition, past attempts at altering handle alignment have required the production of left and right handed versions of the product.

My solution to this problem is simple and fun to use. A handle is designed in such a way that the head of an object can be moved effectively by means of "playful" movements of the fingertips on the handle instead of the usual "hammer" or "pen" type grips. The user immediately begins to notice greater feel and control of the head.

A saucepan may be held and used in many different ways, each of which has a profound effect on wrist and arm posture which determines ultimately the level of user comfort.

Wrist posture and the neutral wrist

It is well understood that the neutral wrist position is the most desirable posture to achieve and maintain for all activities where hand, wrist and arm actions are involved. The neutral wrist position may be defined as the alignment of the hand to the forearm where there is neither pronation/supination, flexion/extension nor ulnar/radial deviation.

In studying how any tool or utensil is used it is obvious that it would be impossible to gain a neutral wrist position at all times. However this does not distract researchers from one of the main postural aims of ergonomic tool design, namely:

The provision of tools and implements which develop and maintain the neutral wrist position throughout a wide variety of tasks while offering the user a choice of gripping positions.

When attempting to improve an existing design it is necessary to examine five fundamental postural issues concerning even the best examples of existing tools and to determine their effect on the neutral wrist.

1. What wrist actions are required to hold an implement at a given work surface?
2. What wrist actions are required to use an implement?
3. What wrist actions could be substituted for finger and palm actions?
4. What planes of the body do the head of an implement align with most frequently?
5. Is the widely accepted head / handle alignment for an implement under review the most appropriate?

What wrist actions are required to hold an implement at a given work surface?

For any implement, the primary holding wrist movements may be listed.

(Further studies would indicate secondary and tertiary wrist movements involved for holding implements. Indeed it is also worthwhile considering upper arm movements, compensations in stance and awkward hand to eye co-ordination)

Wrist actions for holding implements (Table 1.)

NB Ulnar and radial deviations or flexions and extensions pass through neutral position at optimal height for any particular head/ handle alignment.

Holding any of the above implements at the required position will give an insight into the wrist movements involved, particularly if the implement is held for any length of time.

It soon becomes apparent that an improvement in wrist posture will be achieved if the magnitude of any of the above wrist movements can be reduced or eliminated. In addition each wrist movement is without its reciprocating partner and therefore more likely to cause discomfort as the strain is constant with no resting phase.

Studies on posture indicate that the greater the amplitude of a posture, the less it is tolerated for a prolonged time. (Bhatanger et al, 1985; Boussena et al, 1982)

Studies by Mital et al (1985) on maximum volitional torque exertion (pronation/ supination) for screwdrivers and Yuh-Chuan Shih and Mao-Jiun J. Wang(1997) on maximum volitional torque exertion (ulnar/radial deviation) for handwheels, demonstate that operating heights influence the amount of exertion that can be applied to a tool. It is no surprise that the operating height which allows the maximum torque to be exerted is that where the "holding" wrist movement is neutral in terms of flexion and extension for the wrench and neutral in terms of ulnar and radial deviation for the screwdriver.

Applying this principle in the area of wrist posture suggests that the non-neutral movements in Table 1. are of great significance when changing the design of tool. Successfully reducing the amplitude of wrist posture will inevitably lead to greater comfort for the user.

What wrist actions are required to use an implement at a given work surface?

In the same way that the movements for holding were listed, it is worthwhile to list the primary wrist movements used in using an implement in order to complete the picture.

Wrist actions for using implements (Table 2.)

It is of considerable interest that in studying the movements to use an implement, in contrast to the movements for holding an implement, the wrist movements involved consist of matching pairs of complementary actions. (with the exception of the saw, chisel and certain spanner/wrench movements which are operated by means of upper arm action – Table2.)

There are two options for reducing wrist movements involved in using an implement.

In the case of implements making substantial demands for "using" wrist movements, serious thought should be given to a motorised version.

Alternatively, it may be possible to substitute some wrist movements with an improved version of finger and thumb controlled manipulation already used by people with above average manual dexterity, particularly if the forces required to operate the implement are light to moderate. It would be reasonable to consider the toothbrush, knife and saucepan in the list in Table 2. as possible candidates.

What wrist actions could be substituted for finger and palm actions?

The big disadvantage of finger and thumb control is that it is only available to users of above average dexterity.

The sides of the handle, even on a rounded oval cross section handle, tend to dig into the user’s hand and cause pressure points. In addition the fingers have to carry out a balancing act on part of the handle which does not feel as if it has been designed for a gripping and manipulating function nor is it a simple task to apply pressure evenly throughout a rotation.

The turning moment (Rotation Control) initiated by finger or thumb control in a conventional handle is limited by the small degree of divergence between the long axis of the handle and the rotation control axis formed by drawing a line through the Rotation Controls.

Enhanced Rotation Control

There is an opportunity to improve the scope of finger, thumb and palm actions by the following innovation which is the first aspect of Enhanced Rotation and Tilt. (Rotilt)

The section of the handle where the thumb and or first digit contacts is increased in width to provide enhanced rotation of the implement.

In addition, a spiral shape is developed between the two rotation controls which has the effect of keeping maximum palm and palmer surface of the digits in contact with the handle irrespective of how the implement head is aligned.

As will be seen later, this enhanced rotation facility may be utilised on an implement with a tilted head to regain the conventional head/handle alignment.

What planes of the body do the head of an implement align with most frequently?

Whereas implements may be held in many different ways to best suit a particular purpose, activities involving hand held implements or tools require the user’s hand to align the tool and thus the handle to surfaces that are substantially parallel or perpendicular to one of the three planes of the body. (fig. 4.)

Yet, as has been shown in Table 1., working with a tool or implement on any particular side of one of these boxes is not as comfortable as it might be due to the wrist action associated with relating to a height or alignment even before any work is carried out by the implement. The extent of wrist extension, ulnar deviation etc. encountered when using a tool parallel or perpendicular to an anatomical plane may not be described by the user as uncomfortable but nevertheless more wasteful in terms of energy expenditure than maintaining a neutral position. In addition, the user’s scope for further increase in amplitude of posture without discomfort is reduced.

Is the widely accepted head/handle alignment for a particular implement the most appropriate?

Let us consider some empirical evidence which suggests that the conventional alignment of implements may not be the most appropriate.

In the hand saw, it can be observed that the user adopts an angled posture in order to eliminate flexion from the wrist. This has a cost in terms of poor lines of sight and increased whole body movement. (So much for the adage "Let the saw do the work")

In the hammer, again the user adopts an angled stance and in the process tilts the head thereby losing quality of binocular vision and worse, placing an eye in the path of likely shrapnel from the head of the nail.

In the saucepan, the user lifts the pan with the wrist almost in extreme pronation or supination.

In the knife, the wrist is often in ulnar deviation at worktop height.

In the above examples it appears that:

When relating to horizontal or vertical surfaces closely linked to the Planes of the Body, the work/tool interface is at an angle of 15 30 degrees. In order to eliminate unnecessary wrist strain a corresponding handle to head tilt (produced by rotating the handle about the head) of similar magnitude will provide an improved alignment.

If it is true that the work/head tool interface is 15 – 30 degrees when relating to work surfaces in the neutral wrist position and it can be shown that the "planes of the body" are the planes aligned to for the majority of tasks carried out with a particular implement, it follows that a handle designed to reduce the effect of the "tilted head" thereby producing the neutral wrist position in as many different planes as possible without making an object more difficult to hold or manipulate in other planes, will be able to define new levels of comfort in terms of better wrist, and arm posture.

This hypothesis forms the second aspect of the Rotilt innovation where the enhanced rotation controls (fig. 3.) are combined with the tilted head. (fig. 5.)

Designing an implement in such a way that the handle is rotated in relation to a face, blade or trim of the implement head until a neutral wrist position is gained (the head alignment being perpendicular or parallel to a given plane of the body as the handle is grasped in such a manner where the hand develops maximum contact with the handle, offers the user a comfortable head/handle alignment for most positions of use.

This tilted alignment is further enhanced, particularly throughout the planes which lie at some point between the planes of the body already mentioned, by the addition of an enhanced primary rotation control which reduces the tilt, thereby reproducing the more conventional head/handle alignment when required. Previous attempts to alter head/handle alignments such as described by Fell (1934) for toothbrushes, Tichauer (1976) for pliers and Emanuel, Mills and Bennett (1980) for hammers and other tools have failed to take into account the need to reproduce conventional head/handle alignment and intermediate positions between conventional and "altered" alignment.

The shape of this control is formed by altering the section of the handle in contact with the thumb or index finger. It is spirals from the body of the handle to a position where the end is coplanar to said face, blade or trim of the implement.

This control is operated in conjunction with the enhanced secondary rotation control which is derived from the existing shape of the handle which contacts the heel of the palm or the third joints of the third and fourth digits.

The role of each rotation control is of equal importance, finger or thumb pressure being applied to the extremity of either side of the control depending on the desired alignment of the implement head or whether the user is left or right handed.

Summary

The relevance of the findings discussed is shown in the following chart

In much of the task analysis carried out before designing an implement, holding and using wrist movements have been considered as being interchangeable. This almost certainly hinders understanding of handle function and has resulted in little assistance for over-stressed wrist joints.

Appendix 1.

Basic guidelines in the use and selection of any implement.

• The implement should function effectively. For example a saucepan handle assembly should make it easy to lift, carry and empty the pan.

• The handle should fit the operator. Not only should the handle fit the user’s hand properly, but it should also match the user’s capacity and skill.

• The handle should not produce fatigue.
• The handle should provide sensory feedback. The user should be able to sense pressure, impact, texture etc.
• Smooth cylinders are generally not the best shape for most implement handles.
• Form fitting handles (handles with ridges to fit the fingers) should be avoided.
• Handle materials should provide enough friction for an adequate grip.

Appendix 2.

Comparison of rotilt with other handle types.

Appendix 3.

The issue of handedness

The human hand has the flexibility in the palm adjacent to the third joints of the first to fourth digits to accommodate a flattened taper or flattened spiral where in the case of the right hand, most of the weight of the pan is borne by the palm and in the case of the left hand most of the weight is borne by the third joints of the second,third and fourth digits. This feature of human anatomy allows an asymmetrical tilted handle to align the pan to the horizontal plane irrespective of which hand is used.