Participants

10 males and 10 females were, in several steps, selected from a greater sample of active commuters. The first step in this process was requesting participants via advertisements in two main Stockholm morning newspapers in May and June 2004. The inclusion criteria required being a minimum of 20 years old, living in the County of Stockholm, (except for in the Municipality of Norrtälje), at least once a year walking or cycling the whole way, and of any distance to one's work or place of study. This first step of recruitment resulted in 2148 volunteers.

A paper questionnaire (The Physically Active Commuting in Greater Stockholm Questionnaire 1; PACS Q1) was sent home to the volunteers. Only the questions relevant for selecting our participants were used. This included gender, age, how physically strenuous their professional jobs were, as well as commuting frequencies per week for each month of the year and commuting time. The commuting distance based on routes drawn in maps by each respondent was also used (15). For details on the recruitment process as well as the questionnaire used, see Stigell and Schantz (12), Stigell [(20), p. 67] and the supplementary material in Schantz et al. (21).

Our sample was selected from the single mode pedestrian category (n = 277), i.e., those subjects who only walked, and never cycled, to work. Other criteria were that they had ages and route distances close to the median values of the male and female pedestrians, respectively (12). They also rated their daily professional jobs as light or very light physically. Letters describing the physiological studies, the test procedures, and a health declaration [for details, see (19)] were sent to the pedestrians who fulfilled the criteria. The right to terminate the tests at any time, and without having to stipulate a reason, was emphasized in the letter. A signed informed consent of participation and the health declaration was returned.

Based on this information, individuals with invalid route distances as well as with high blood pressure, or on medication that could affect normal HR were excluded. The remaining individuals were contacted by telephone to answer any potential questions, and to book test times. Telephone contacts continued until we had 10 females and 10 males who fulfilled the criteria and were willing to participate (Table 1).

Characteristics of the walking commuters (mean and standard deviation, SD).