The exponential increase of scientific publications in the mitochondrial field shows the growing interest in mitochondria. However, the lack of methodological consistency in many published projects on mitochondrial respiratory function complicates a quantitative inter/intra-laboratory comparison of datasets. This deficiency manifests the need to improve the quality in science[1]. In this context, the MitoEAGLE COST Action is a powerful framework committed to evaluate and enhance the reproducibility in mitochondrial physiology as a basis to establish a novel mitochondrial database related to Evolution, Age, Gender, Lifestyle and Environment. Permeabilized muscle fibers are widely used to evaluate mitochondrial function in health and disease[2]. Therefore, our main goals are to: 1) compare protocols used in different research laboratories, 2) analyze factors which contribute to experimental variability, 3) define optimal experimental conditions in muscle studies, 4) elaborate guidelines for evaluating mitochondrial function in muscle tissue, 5) establish reference values on mitochondrial respiration, particularly as a test of the skills in preparing high-quality permeabilized muscle fibers, and 6) generate a database. To achieve our aims, two unique studies are currently in progress: 1) 17 international research groups performing independently experiments on respiration in permeabilized fibers of mouse soleus muscle, following the same experimental procedure[3]; 2) a blinded international study measuring simultaneously in the same laboratory respiration of permeabilized human skeletal fibers by high-resolution respirometry and assessing the effect of different experimental conditions[4]. Our results contribute to face the reproducibility crisis and provide the basis for establishing the first database on mitochondrial respiratory parameters in muscle tissues.