BACKGROUND: High-intensity interval training (HIIT) has been shown to improve cardiorespiratory fitness (V˙O(2) max) but may ameliorate insulin sensitivity only in insulin-resistant humans. It is yet unclear whether these benefits persist after detraining and to which extent duration and effectiveness of metabolic improvements differ between individuals without and with prediabetes or type 2 diabetes (T2D). Understanding these differences is relevant for developing targeted exercise …