Which pairing correctly matches the training type with its primary muscular adaptation?

• A. High-intensity interval training — promotes mitochondrial biogenesis; Sprint training — increases activities of key glycolytic enzymes.
• B. High-intensity interval training — increases glycolytic enzymes; Sprint training — promotes mitochondrial biogenesis.
• C. High-intensity interval training — hypertrophy of slow fibers; Sprint training — reduces glycolytic enzymes.
• D. High-intensity interval training — decreases mitochondrial content; Sprint training — increases capillary density.

Answer: (A)

High-intensity interval training mainly pushes the muscle to boost its oxidative capacity. The intense bouts create a strong demand for aerobic energy during repeated work periods, which triggers cellular signaling that increases mitochondrial biogenesis and boosts oxidative enzymes. That means more mitochondria and greater capacity to produce energy through aerobic pathways, even though the work is performed in short, intense bursts.

Sprint-type training, on the other hand, relies on rapid ATP generation through glycolysis during very short, maximal efforts. The muscle adapts by increasing the activities of glycolytic enzymes, enhancing the glycolytic flux to power those short sprints and better handle the associated lactate production.

So the pairing—HIIT with mitochondrial biogenesis and sprint training with increased glycolytic enzyme activity—best matches the primary muscular adaptations expected from these training types.