Most People Should use a Footrest . . .

Ergonomics has always placed great emphasis on the physical sizing of the workplace whether it be the measurements of tool handles, machines, chairs, or anything else that is contacted by people.

Anthropometric data is applied in two ways:  

1. to fix the static measurements of workplaces, 

2. to determine the amount of space people occupy when they are performing work tasks.  

Most workstation design is based around a simple fit of the person to the furniture, but there are a lot of conflicting issues that can rarely be adequately resolved even when an adjustable chair is provided.  

Consider the problem

In the design of seated workstations - desks, benches, machines [including cars], there are two critical relationships that must always be addressed:

1. The height of the seat relative to the height of the worktop,

2. The height of the seat relative to the surface on which the feet rest. [see illustration at

   right]

With modern adjustable chairs it is easy to obtain a comfortable arrangement between the seat and the worktop. This height can vary with the nature of the task you are performing. If you are using a keyboard, you need to set your seat height so that your elbow is approximately level with the desktop. If you are reading or writing, you often want to set the seat a little lower so that height 1 is slightly higher than it is for keyboard work. 

Height 2 is usually what is left after you have set height 1. This can present problems if the desk or bench is too high. 

When the worktop is too high, there can be a problem with obtaining proper support for the feet for people whose feet do not easily reach the floor. Any serious mismatch is a problem and more than simply a matter of comfort or discomfort. 

Compression of the thighs caused by the seat being too high must be avoided at all times. If the lower legs are partly or wholly suspended from the seat and the person’s thighs are pressed into the seat cushion, there may be reduced blood flow, and particularly if the pressure is prolonged and substantial. Pressure behind the popliteal crease will also cause this problem. 

While the sustained compression of soft tissues in the legs would be expected to be uncomfortable, various studies have concluded that many people will quite happily sit higher than their [shod] popliteal height, and often without complaint. One explanation for this might be that people prefer to sit at a height that allows free movement of their arms over the work surface. In order to achieve this they appear to be willing to forego leg comfort, although they may not become aware of the discomfort until the work activity is well under way. It is worth noting here that the concept of comfort has been defined as the absence of discomfort. In other words, we do not necessarily register comfort, we register discomfort. Practicing Ergonomists observe this phenomenon on a daily basis. Many people demonstrate an ability to work in quite adverse postures without complaint – possibly because they are so focused on the work that they sublimate other physical sensations such as moderate discomfort in one or more body regions. This is not however an acceptable state of affairs! 

When the problem is one of the seat being too high, the usual and obvious solution is a form of foot support that can either be integral with the workstation [a footboard, foot rail, etc] or a separate, loose footrest. Any of these options, properly selected and designed can make up for any dimensional mismatch. People will often demonstrate a desire for leg support. Some of this behaviour may in fact be intuitive and is expressed by putting the feet on the base of the chair, on a rubbish bin or other box that may be under the desk, or by engaging in a greater amount of fidgeting!  Many Ergonomists have observed this when assessing typical screen-based and other seated workstations. 

Good foot support is a critical factor in the design of seated workstations, and not only for those people who may be a bit short in the leg.  

A footrest is a great benefit for many people but sometimes just a footrest is not enough, because the other critical factor is that of inactivity in the legs.

Inactivity in Seated Work

A common problem with screen-based work is that people sit in fixed postures for long periods with little or no exercise. With the improvements in chair design in the past 20 years, a well-designed, adjustable ergonomic chair can provide correct body support and seated comfort for all sizes and shapes of people. But with the sensation of seated comfort comes the perception that this seated position can be maintained for extended periods – a perception that is held by employer and employee alike. Contemporary work involving sophisticated information technology typically encourages this seated passivity. Some work even demands it, typically call centre work, data processing, secretarial, computer systems administration, and many others. There is a commonly held belief that if the furniture is ‘ergonomic’ then the person can be expected to remain at the task for as long as the day allows. But, as the ergonomics literature informs us, this is an illusion. It is well documented that maintaining fixed postures even using the best design of chair, will induce localized muscle fatigue around the neck, shoulders, arms, low back, etc. Other, less obvious problems are to do with poor blood circulation, compression of the gut, restricted breathing, and a general absence of physical effort that in time is almost certain to lead to reduced muscle tone and loss of muscle strength. 

Obviously people do not sit perfectly still all the time they are sitting working. We know from the work of Branton and others that people fidget when they sit. They do not maintain the exact same posture all the time. As Branton noted from his research into sitting, fidgeting is part of sitting behaviour. It is largely autonomic in nature and is clearly to do with the body seeking relief from sustained muscle contractions and localized pressure on soft tissues in the legs and thighs in particular. But the overall effect of continuous sitting, even if the person fidgets, is that there is relatively little significant muscle activity of a kind that will usefully contribute to healthy blood circulation through the body. The preferred solution is to design work so that it is sufficiently varied in its nature and activities. People should be able to frequently change their posture, engage in some simple activity using the larger muscle groups, and not be constrained in the same posture for long periods or for recurring episodes. This preferred condition however is often difficult to achieve in organizations where productivity and technology drive the design of work and the use of the human resource. If the attitudes to work design are difficult to change, then other approaches must be sought. 

Inactivity has Implications for Health

While sitting too high is significant in itself, another issue is that of the onset of oedema caused by sitting for long periods without relief. Pottier, Dubreuil and Monod [1969] studied the effects on people sitting on exaggeratedly high seats and concluded that only 25% of lower leg oedema was attributable to thigh compression [the other 75% being attributable to inactivity].

Kroemer and Grandjean [1997] noted that static muscle activity, including sitting for long periods may deny the muscles an adequate flow of blood through a lack of contractile activity. The consequences may vary from discomfort to more damaging effects over time. Stranden [2000] observes that it is well known that prolonged sitting may lead to swelling of the lower leg, increased blood pressure and a reduction in leg temperature.  Winkel [1986] observed that blood flow could be adequately maintained if people took frequent short breaks from sitting and moved around for a few minutes.  This is still  a desirable work practice, but we know from experience that it is very difficult for people to remember to take breaks, particularly when they are performing mentally demanding work.  One effective alternative would be to provide a means of exercising the legs while the person is sitting, and if this could be combined with a foot support, two important ergonomic objectives could be met simultaneously.

It is worth noting that inactivity in the legs has been identified as a principle cause of deep vein thrombosis [DVT] that has afflicted numerous airline passengers in recent years.  This is such a serious issue that airline passengers are advised by airlines to exercise their lower leg muscles in order to reduce the risk of DVT.   Prolonged sitting [4 hours or more] is considered to be a causative or aggravating factor for people who are susceptible [through other factors]. Whilst sitting at work is not the same as sitting in an aeroplane where there is often less opportunity or incentive to leave the seat for rest breaks, the same underlying problems apply to office work, even if probably at a lesser degree of acuity.

Approaches to the Prevention of Oedema [Edema] in Seated Work

Preventive measures for leg oedema include pulsating seat cushions, compression stockings, and exercising the leg muscles while sitting. Winkel [1981, and other studies] found that frequent but intermittent exercise was sufficient to reduce or eliminate all of the swelling of legs that could be associated with prolonged sitting. Hence the reasoning behind the development of Flexx. 

There are numerous products on the market that have foot massage as the underlying functional principle, and others that are even called ‘dynamic’ footrests. There are various concepts behind these and footrests that incorporate a treadle action is used on several of these. Most of these footrest designs have a single footplate, which means that both feet move at the same time and in the same direction. 

About Flexx™

The designers of Flexx came to the project after years of having observed all of the problems of people sitting to work. It was clear that most conventional footrests were not easy to use or they only fitted a limited number of people adequately. Many people reject footrests as they consider them to be awkward to use and obstructive in the leg space under the desk. It is quite common to find the footrest in the rear of the leg space, unloved, abandoned and forgotten. And the rigid footrest, which is at its best when it is adjustable for height, still fails to provide the other equally important function – exercising of the leg muscles to promote healthy blood flow and encourage good muscle tone. 

The designers of Flexx realized that a different principle was required. In essence, the footrest had to be more than a rest – it had to be an exerciser of the legs while also giving support. 

The Flexx Foot and Leg Perch has as its underlying principle the concept of an unstable platform. The idea behind this is that the reactive, springy support invokes a natural response in the user to engage in exercising their leg muscles. Thus the concept of Flexxercises™ which activates not only the lower leg muscles but also the thigh muscles and other muscles around the lower pelvic area. While the user can perfectly readily rest their feet on Flexx statically, the unstable platform tends to encourage movement. And having the footplate split into left and right panels means that the legs can be exercised independently of each other. 

Flexx addresses the need to provide raised support under the feet. The minimum height with Flexx fully compressed is approximately 60 mm [to the top of the bend at the front] although the resting height will vary with the weight of each person’s legs.  The resting height also varies with the relative distance of Flexx from the chair – the closer to the chair, the more the effect of the weight of the legs; the further from the chair the less the compression on Flexx due to leg weight.  

Flexx has the advantage of being far more varied in the way it can be used both for leg support and for leg exercise. It provides exercise in differing ways according to where it is placed on the floor. When it is close to the chair, the user’s lower legs are more vertical and the action tends mostly to be in the thighs. When Flexx is pushed further away from the chair, the action is more in the calf muscles. 

It is easy to move Flexx around by putting one foot into the space below the footplates and lifting slightly. Flexx weighs only 1.75 kg so there should be little or no risk associated with this one-legged lifting action. Once in place, Flexx resists moving by virtue of the grippy material underneath. 

It has been observed in trials with Flexx that people tend to sit back into their chair backrest more than if they are using a static footrest or no footrest as all. Ergonomists know that there is a tendency for many people to sit away from the chair backrest. Unsupported sitting is common amongst computer users but sitting this way denies the user the benefit of the backrest in providing support for the lumbar spine. Numerous studies have highlighted the increased muscle activity in people sitting unsupported. But the dynamic nature of Flexx means that people intuitively brace their trunk against the chair backrest in order to free their legs to ‘operate’ the unstable platform of Flexx. But the unstable platform can provide steady, stable support when the user wants. The person does not have to be Flexxercising™ all the time as the suggestion of ‘instability’ might suggest, even though the soft, springy nature of Flexx tends to become somewhat addictive [dare one say].  

So Flexx can contribute to an improvement of the overall sitting posture by encouraging better use of the chair backrest. However, there is an important consequence of this particular attribute that must be noted here. One of the principal reasons for people not sitting into the backrest is that they have their monitor screens set back too far onto the desktop. There seems to be an unspoken convention that the screen should be positioned towards the rear of the desktop – this may be an unwitting mistake by the IT people who think they are doing us a favour by maximizing the clear desk space at the front. But if the monitor is beyond the nature focal length of the eyes, people will tend to sit forward to bring it into easy and clear focus, and thus they move away from the backrest of the chair. This is an important subtlety that will be noted in the instructions for the use of Flexx. Users will be advised to check this condition and if necessary move their screen closer to account for the likely change in their sitting posture

Flexx has its own aesthetic derived from the spring design. It presents as a piece of sculpture rather than as just another piece of forgettable office equipment. Whereas most footrests are dark in colour, Flexx is intentionally made to be visible under the desk so that it cannot be forgotten or overlooked.

The type of reference data commonly used by Ergonomists and Designers when designing workstations is an important resource, but it does not capture the dynamic nature of the human body at work. Workstation design rarely provides an active workplace. Flexx was designed to overcome this omission.

The two critical height relationships in the design of seated workstations must match the physical dimensions of all of the people who will use the workstation. Even getting these right is not enough in itself. The person sits in a largely static posture while they work. 

A chair that is too high can cause pressure to the back of the knee.  It reduces the flow of blood to a leg that may already be deficient in blood flow because of inactivity.

An ad hoc footrest where none is provided in the workstation. It is common to see people using boxes for foot support when they sit at desks.

Sitting can be painful! These are the body sites where people often experience discomfort due to spending most of their day in a chair. The problem is often one of poor posture, which can be exacerbated by inactivity. The body hates to be kept still. Exercising is needed.

A major benefit of Flexx is that it pushes your back into the chair backrest. A lot of people sit forward, away from the backrest and are therefore unsupported. This increases fatigue and causes slumping, further compressing the gut and restricting healthy breathing. 

The contraction and relaxation of muscles acts as a pump to make blood flow through the body.  Without frequent muscle activity, this flow WILL be reduced.  When sitting, reduced blood flow most affects the legs.

Sustained [static] contraction of muscles causes blood flow to be restricted.  This occurs when the muscles are used continuously, such as when having to hold ourselves upright without a good backrest on the chair.

Lack of exercise still allows the blood to circulate, but the reduced rate of flow can be insufficient to prevent blood pooling in the feet.

Blood will pool in the feet of people who sit still for long periods – such as when at work. Blood circulation can only be restored by exercising the muscles.

You may have to bring the monitor closer when you use Flexx as you will be sitting further back in the chair. This is a good thing – your overall posture will have improved.