Resting metabolic rate (RMR) of recreational female CrossFit® practitioners: Agreement between indirect calorimetry and predictive equations and correlation between RMR ratio and metabolic hormone levels

Abstract

Resting metabolic rate ratio (RMR_ratio) is calculated dividing the RMR from indirect calorimetry (RMR_IC) by the RMR estimate by equations (RMR_e). RMR_ratio is a tool for energy suppression assessment and it can be useful in situations of low energy availability. To date, predictive equations have not been evaluated regarding their agreement with RMR of female CrossFit® practitioners. As such, we aimed to verify the agreement between RMR_IC and RMR_e and its correlation with metabolic hormones. This was a cross-sectional study with nonprobability sampling. Participants (healthy women aged 18–39 years, with at least 1 year of regular CrossFit® training experience) visited the laboratory once for blood collection and nutritional, body composition, and RMR assessment. RMR_IC was estimated using K5; COSMED®. We evaluated its agreement with the RMR estimated by several equations. Then, for each predictive equation, the RMR_ratio was calculated. We assessed triiodothyronine (TT₃), leptin, and insulin-like growth factor (IGF-1) levels. The Bland–Altman method was used to identify the agreement between the RMR_IC and the RMR_e. Thirty female recreational CrossFit® practitioners (33.11 ± 5.23 y) were assessed. The Cunningham (1980) equation was the one that most agreed with the RMR_IC. Still, RMR_IC did not differ when compared to TT₃ (p = 0.470), leptin (p = 0.848), and IGF-1 (p = 0.634) levels. Likewise, we found no differences when RMR_ratio was compared by the median and tertiles of hormones. In summary, our findings revealed that the RMR_e showed low agreement with the RMR_IC. Besides, the RMR_ratio did not differ according to the hormones TT₃, leptin, and IGF-1 of female recreational CrossFit® practitioners.