Examine changes in demographics of participants and performance trends at the Western States 100-Mile Endurance Run (WSER) since its inception in 1974. Name, age, sex, and finish information was obtained on runners in the WSER from 1974 to 2007. Linear regression analyses, ANOVA, and t-tests were used to examine participation and performance trends. The mean age of participants increased (P < 0.001) to around 45 yr, with men being an average of 3 yr older (P < 0.001) than women. The increase in average age of starters was accounted for by the growth in participation among women >or=40 yr and men >or=50 yr, and by the decreasing participation among men <50 yr. Between 1986 and 2007, there was an increasing participation among women to around 20% of all starters. With this came improved (P < 0.01) finish times for the top 5 overall women and the top 5 women in the 30-39 and 40-49 yr age groups, whereas performances among the men did not improve over this time span. Average ages of the top performers increased (P
