Human factors and ergonomics / 1.3 /
Physiological Factors

When people use a product they can put strain and stress on their body. Sitting for long periods of time, or being required to turn a handle put stress on the body. Designers need to collect data to inform their design decisions. 

Comfort (in the context of this subtopic) is being free of physical pain. Comfort is an important consideration for designers simply because it influences the way users interact with products. Perceptions of comfort vary from person to person. A good example of this is the difference in preferences for sleeping mattresses. Some people will prefer a very firm or hard mattress, while others a soft and cushiony one. 

Considerations for designers

• Adjustability: For designers, being aware of these different preferences could influence how they incorporate adjustability into their designs. Users could choose to adjust the product (i.e. the softness of the chair) or select options that address their preferences (i.e. choosing a firm over a soft mattress).

• Pleasure: Comfortable products are pleasurable to use. Focusing on the comfort will increase user acceptance of a product. If something is not comfortable to touch, users will not want to interact with it. 

Fatigue is a feeling of tiredness or weakness happening over time. Because fatigue happens over time, it is important for designers to consider the impact of prolonged use of their designs on the human body. Fatigue can also lead to Musculoskeletal disorders (MSDs) in the muscles, nerves, blood vessels, ligaments and tendons. Risk factors can include: 

• lifting heavy items

• bending

• reaching overhead

• pushing and pulling heavy loads

• working in awkward body postures

• performing the same or similar tasks repetitively

Fatigue can also affect decision-making and performance. In short, you are simply too tired to perform at your best. Considerations for designers:

• Performance:  Designs should reduce fatigue as much as possible, and enable the user to perform at an expected level for as long as possible. 

• Health and Safety: Fatigued users are more likely to injure themselves or other. In addition, injuries can be permanent, or cause chronic (consistent) pain. 

A poorly designed tool handle may encourage the user to hold it or use it in a manner that is unsafe or harmful.

Biomechanics relates to the mechanism of living things (how they move). Biomechanics includes research into the operation of muscles, joints and tendons, force, repetition, duration and posture. 

Understanding how humans move and interact with products in different situations has always been an important part of the design process. With the advent of modern technology and especially with the advancements in motion capture technology, how designers and design teams can access and analyse this data has dramatically improved. 

Biomechanics is the study of the mechanical movements of our body. It focuses on how our body moves and how it is affected by different forces. 

For designers, understanding the range and ability of the human body can help us design products that can comfortably, safely, and efficiently meet the needs of users. Designers should consider biomechanics for two reasons:

• Develop an inclusive design that takes into the physical abilities, strength, and movement of the user; and,

• Avoid harming the user by increasing the risk of musculoskeletal disorders (MSD)

To achieve this, designers should consider these four factors below:

• Force - The amount of compression, pushing, twisting, pulling, etc., that a person can exert. It is directly related to muscle strength. Designers should consider the amount of force required to do an action (turn a knob, tighten a lid, pull a zipper, squeeze a handle, etc.). It is also important to consider the user group and how much force the typical user is able to exert: Young children and the elderly have lower muscle strength than some in their 20s, for example

• Repetition - How frequently a task is repeated. Tasks that are repeated at a high frequency can impact the body in a negative way. Designers should consider how frequently a task needs to be done, and in most cases, reduce the frequency and intensity of the task as much as possible. For example, workers at a workstation may develop musculoskeletal disorders if they are required to repeat a task over and over again. The ergonomics of workstations should reduce this risk as much as possible. 

• Posture - The position the body is in, whether standing, sitting, or lying down. Designers should consider the posture the user takes when performing the task. It is important to minimize physical stress on the body, while also allowing the body to be supported appropriately. when designing a computer workstation chair, the designer would need to consider the seated posture of the user which also allows them to type comfortably.

• Duration - How long the task is performed or repeated. Designers should consider duration along with frequency.  Even small durations, repeated many times, can damage human tissue.