Contextualizing the Norwegian standardized intensity zone framework in an international sample of endurance practitioners

This study investigated potential differences in the adoption and use of endurance intensity zone scales across geographic regions, sports disciplines, practitioner roles, and performance levels. A total of 778 endurance practitioners completed a survey, with 710 responses analyzed for the number of intensity zones used, and 298 responses analyzed for lower percentage of maximum heart rate (%HR_max) demarcations within a 5-zone scale. A 5-zone scale (47%) was most frequently used. Norwegian respondents were 2.7 times more likely to use a 5-zone scale than all other regions combined. The lower limits of Zones 2-3 differed across regions, and Zones 1-3 across sports, particularly between running and cycling. Norwegian respondents reported the highest mean %HR_max lower limits of Zones 2 and 3. Cyclists self-selected the lowest mean %HR_max lower limits of Zones 1, 2, and 3. No differences were observed in zone demarcations across roles or performance levels. The results suggest that the standardized intensity scale developed for Norwegian elite endurance athletes has been broadly adopted across sports and performance levels. The widespread use of a single intensity scale is speculated to improve communication across sports. Cyclists may self-select lower zone demarcations in the low-intensity domain by virtue of longer session durations and lower mechanical stress, contributing to the popularity of "Zone 2 training" in cycling.