As work structures have changed, so have the forms of stress that occur at work. Nowadays, the main form is often mental stress, for example, time pressure or over-demanding tasks, rather than heavy physical work or other types of physical stress. In the field of ergonomics, unlike in colloquial speech, the term "stress" is considered to refer to the whole package of influences on workers at work, whereas "strain" is defined as the impact of the stress on a particular individual. Thus, strain is a human's reaction to stress. That also means that the same type of stress can result in different forms of strain in different people.
In order to ensure the safety, health and well-being of workers at the workplace, the work, work systems, products and environments should correspond to human beings' physical and mental abilities. Standards concerning mental stress can help to achieve this – as can ergonomics standards in general – if they are consulted by other standards makers, designers, manufacturers and work designers during the actual development phase so that safety is "designed into the product" right from the outset as stipulated by, for example, the Machinery Directive.