# Optimizing Metabolic Assessment: Maximal Fat Metabolism, Lactate Dynamics, and Cardiorespiratory Determinants at Different Pedaling Frequencies

## TL;DR

This study shows that pedaling frequency during exercise testing affects metabolic measurements, suggesting better methods for assessing fat metabolism in health and disease.

## Contribution

The study reveals that pedaling frequency alters metabolic diagnostics, emphasizing the importance of absolute fat oxidation metrics over intensity-based ones.

## Key findings

- Higher oxygen and carbon dioxide levels and lower fat oxidation were observed at 100 RPM compared to 50 RPM.
- Maximal fat oxidation intensity was significantly lower at 100 RPM, but maximal fat oxidation itself showed nonsignificant differences.
- Blood lactate concentration at maximal fat oxidation was higher at 100 RPM, suggesting pedaling frequency impacts metabolic diagnostics.

## Abstract

Accurate metabolic exercise testing is essential for assessing cardiometabolic health in both athletes and clinical populations with prediabetes and diabetes. This study investigated whether and how fat, carbohydrates and lactate diagnostics are influenced by ergometry testing pedaling frequency.

This randomized cross‐over repeated‐measures trial, examined human participants for cardiorespiratory oxygen uptake (V.O2) and carbon dioxide production (V.CO2), and blood lactate concentration (BLC), using two separate incremental load ergometry exercise tests until exhaustion, at higher versus lower cycling pedaling frequencies of 100 and 50 revolution per minute (RPM). Metabolic diagnostics of fatty acid oxidation (FAO), carbohydrates oxidation (CHO), maximal FAO (MFO) and associated MFO intensity (Fatmax) were estimated by stoichiometric equations and compared at 100 versus 50 RPM.

Higher V.O2, VC.O2, BLC and CHO and lower FAO were found for all submaximal intensities at 100 RPM than at 50 RPM (all p < 0.01). Fatmax power output was significantly lower (83.7 ± 20.3 vs. 99.8 ± 25.8 W, p < 0.05, effect size d = 0.70) at 100 than at 50 RPM. However, pedaling frequency‐dependent effects reflected nonsignificant changes in MFO (0.58 ± 0.16 vs. 0.52 ± 0.15 g.min−1, p = 0.12, d = 0.39), and also in the corresponding BLC at MFO (1.70 ± 0.45 vs. 1.30 ± 0.39  mmol.L−1, p = 0.06, d = 0.9).

Metabolic assessments should prioritize absolute MFO and BLC dynamical changes over Fatmax intensities, when interpreting fat‐oxidation capacity, particularly under varying pedaling frequencies. By jointly characterizing blood‐based and respiratory‐based diagnostics under different exercise assessment conditions, this study helps improve the reliability of diagnosing the metabolic status in both healthy individuals and patients with metabolic disease.