The XIX Summer Olympic Games were held in Mexico City, October 12-17, 1968. The altitude affected different events in different ways. Here is a table of the winning times or lengths in some of the track & field competitions in the Summer Games from 1960 through 1980.
MEN 1960 1964 1968 1972 1976 1980 100m 10.2 10.0 9.95 10.14 10.06 10.25 200m 20.5 20.3 19.83 20.0 20.23 20.19 400m 44.9 45.1 43.86 44.66 44.26 44.60 800m 1:46.3 1:45.1 1:44.3 1:45.9 1:43.5 1:45.4 1500m 3:35.6 3:38.1 3:34.9 3:36.3 3:39.17 3:38.4 5000m 13:43.4 13:48.8 14:05.0 13:26.4 13:24.76 13:21.0 10000m 28:32.2 28:24.4 29:27.4 27:38.4 27:40.38 27:42.7 Marathon 2:15:16.2 2:12:11.2 2:20:26.4 2:12:19.8 2:09:55.0 2:11:03.0 High Jump 7-1 7-1 3/4 7-4 1/4 7-3 3/4 7-4 3/4 7-8 3/4 Long Jump 26-7 3/4 26-5 3/4 29-2 1/2 27-0 1/2 27-4 3/4 28-0 1/4 WOMEN 1960 1964 1968 1972 1976 1980 100m 11.0 11.4 11.0 11.07 11.08 11.06 200m 24.0 23.0 22.5 22.40 22.37 22.03 400m 52.0 52.0 51.08 49.29 48.88 800m 2:04.3 2:01.1 2:00.9 1:58.55 1:54.94 1:53.42 Long Jump 20-10 3/4 22-2 1/4 22-4 1/4 22-3 22-0 3/4 23-2
Source: The 1991 Information Please Sports Almanac.