What had changed was Radcliffe’s ability to sustain the speed she’d always had over longer distances. By 2003, she was running as much as 160 miles per week on an eight-day cycle that included fifteen runs, twelve of which (or 80 percent) were done at low intensity. Her VO2max was still unchanged, but in that year, she set a still-standing marathon world record of 2:15:25 and ran a half marathon at an average pace of 5:00 per mile, or 2 seconds per mile faster than the pace she had run for 3000 meters (less than two miles) when her VO2max was at its peak.
