Study design. Gray rectangles indicate a high-intensity interval exercise (HIIE) session; gray triangles within high-volume, high-intensity interval training (HVT) indicate a 10-km cycling time trial; each rectangle and/or vertical pair of rectangles and/or vertical pair of rectangles and triangles, represents a training day; arrows indicate a skeletal muscle biopsy. Each test in both the pre- and post-HVT phase was separated by 48–72 h. 20k-TT, 20-km cycling time trial; GXT, graded exercise test; rest, skeletal muscle biopsy at rest; +0 h, skeletal muscle biopsy taken at the end of the HIIE session; +3 h, skeletal muscle biopsy taken 3 h after the completion of the HIIE session.