Heart rate inflection point estimates the anaerobic threshold in overweight and obese young adults

Anaerobic threshold (AT) can be determined by heart rate variability (HRVT) and by heart rate inflection point (HRIP), which is associated with lactate and ventilatory thresholds. Thus, this study aimed to compare the HRVT and HRIP in normal weight (NW: 22.18 ± 1.90 kg m⁻²), overweight (Ov: 27.12 ± 1.39), and obese (O: 32.85 ± 2.40) young people (21.62 ± 2.09 years old; n: 61). AT was determined by: (1) HRVT using two criteria: HRVT₁: first workload with SD1 index <3 ms; HRVT₂: first workload with a difference <1 ms in the SD1 index between two consecutive stages; and (2) HRIP: identified on the maximum distance between a polynomial adjustment and the linear values of HR. The HRIP was identified at similar workloads (NW: 89.35 ± 32.45; Ov: 83.57 ± 24.45; O: 105.71 ± 29.80 W) and heart rate (NW: 130.78 ± 15.32; Ov: 126.29 ± 11.71; 136.24 ± 13.43 bpm). No significant differences (p > 0.05) between criteria, methods or groups, and a significant (p < 0.05) correlation (r 0.28–0.63) were observed for all variables between HRVT₁ and HVRT₂; for workload between HRVT₁ with HRIP (r 0.28); and to rate perceived exertion between HRVT₁ (r 0.28) and HVRT₂ (r 0.48) with HRIP, with a good agreement for HR between all the methods used for AT identification. In summary, obesity does not seem to interfere on the identification of AT, and HRIP can be used as a reliable method for untrained young people with a wide BMI range.