Use of heart rate cutpoints to assess physical activity intensity in sixth-grade girls

We calculated individual heart rate-oxygen consumption (BR-(V)over dot O-2) regression lines for 49 sixth-grade girls based on a treadmill test. From these data, we determined (V)over dot O-2 at HRs of 140 and 160 b . min(-1) and 50%, 60%, and 75% of maximal heart rate reserve (MHRR), and the relationship between (V)over dot O-2 and %fat at given heart rates. Results indicated traditional 140 and 160 b . min(-1) HR cutpoints were at the low end of exercise intensity (46 and 63% (V)over dot O-2max) and were negatively correlated with %fat. Heart rates at 50%, 60%, and 75% MHRR corresponded to 52%, 62%, and 76% of (V)over dot O-2max. Although the best method for analyzing HR data to describe physical activity intensity is unknown, use of 140 and 160 cutpoints may not describe vigorous or very hard exercise in adolescent girls as well as 75% MHRR. Researchers should also consider the effects of adiposity when using specific heart rate cutpoints.