In brief:We studied the physiological effects of a four-month, 6,400-km run on a well-trained 60-year-old man from Quebec. The subject was tested three days before starting the run and on the third day after finishing it. Percent body fat, Vo2max, anaerobic threshold, hemoglobin, hematocrit, and blood glucose were measured. We found no changes in hemoglobin, Hct, glucose, or Vo2max after the run but observed a weight loss of 5.4 kg. Anaerobic threshold increased 10.2% and 13.9%, expressed in percent of Vo2max and ml*middot;kg−1min−1, respectively. We concluded that the run had no negative effect on the physical fitness and health of the subject according to the physiological variables we measured.