This randomized, parallel, controlled study, will investigate the effect of regular exercise on GM composition, inflammatory status, and insulin sensitivity, in the progression from normal glucose tolerance (NGT), to prediabetes (pre-D), to type 2 diabetes (T2D). Following baseline assessment of glucose tolerance, the participants will be randomly assigned to either a 12-week, thrice-weekly exercise training program followed by 4 weeks of detraining, or will remain sedentary for the 16-week intervention. Thus, the six study groups will be: 1) NGT group (NGT), NGT individuals - no exercise, 2) NGT exercise group (NGT+Ex), NGT individuals that will participate in training and detraining, 3) pre-D group (pre-D), pre-D individuals - no exercise, 4) pre-D exercise group (Pre-D+Ex), pre-D individuals that will participate in training and detraining, 5) T2D group (T2D), T2D individuals - no exercise, and 6) T2D exercise group (T2D+Ex), T2D individuals that will participate in training and detraining. Assessment of physiological measures, anthropometric characteristics, body composition, glucose tolerance, insulin sensitivity, complete blood count, lipidemic profile, GM composition, inflammatory status, oxidative stress, and muscle performance, will be conducted before and following 12 weeks of the exercise training intervention and following 4 weeks of detraining for all participants.