2 3 4 Relationship between perceived exertion and blood lactate 5 concentrations during incremental running 6 test in young females 7 8

40 41 Background: To investigate more practical handling of Borg’s ratings of perceived exertion 42 (RPE) and category-ratio scale of RPE (CR-10), we evaluated interrelationships between RPE, 43 CR-10, and blood lactate concentrations ((La)b) during incremental treadmill running tests for 44 young females with different aerobic fitness levels. 45 Methods: Oxygen consumption, heart rate, (La)b, RPE, and CR-10 were measured from 46 distance runners (DR; n = 15), race walkers (RW; n = 6), and untrained females (UT; n = 11). 47 These variables corresponding to the lactate threshold (LT) and onset of blood lactate 48 accumulation (OBLA) were compared among these groups. 49 Results: The UT had significantly lower RPE at LT than DR and RW, although the CR-10 at 50 LT was not significantly different among these groups. The CR-10 at OBLA was significantly 51 lower for the UT than DR. The relationship between (La)b and CR-10 was approximated well 52 by two linear regression lines, meaning that an intersection was observed between (La)b and 53 CR-10. The CR-10 at the intersections ranged from 3.1 to 3.2 without any significant group 54 differences, and those scores were not significantly different from those obtained at the 55 intersections. 56 Conclusion: These data proposed that “CR-10 ≈ 3” would be a non-invasive criterion for 57 evaluating exercise intensity corresponding to the LT for young females regardless of their 58 aerobic fitness levels. 59 60