What is one adaptation that occurs from endurance training in tactical athletes?

Increased mitochondrial density is a significant adaptation that occurs from endurance training in tactical athletes. Mitochondria are often referred to as the "powerhouses" of the cell, as they play a crucial role in producing ATP, the energy currency of the body, particularly during prolonged, aerobic activities.

Endurance training stimulates the production of more mitochondria within muscle cells, enhancing the body's ability to utilize oxygen for energy production. This adaptation leads to improved endurance performance and increased efficiency in energy metabolism, which is essential for the prolonged physical demands faced by tactical athletes. With a higher mitochondrial density, athletes can sustain activities at higher intensities for longer periods without experiencing fatigue.

The other options represent different adaptations not primarily linked to endurance training. Increased muscle fiber size is more characteristic of resistance training. Decreased heart rate during rest can occur with training but isn’t solely an adaptation from endurance training—it can also be influenced by other factors such as overall fitness. Improved anaerobic capacity is usually facilitated through high-intensity interval training, rather than standard endurance training focused on aerobic capacity.