Of these, the one with the most room for improvement in experienced athletes is usually economy. Examples of areas where skills, and therefore economy, might be improved for cyclists are pedaling mechanics, cornering, and aerodynamic body position. Bike handling in a group is also a critical skill. If you ever feel nervous when riding shoulder to shoulder with others, you're wasting energy. Swimmers typically devote more time to economy than other endurance athletes as their sport is skill intensive.
Water is a very unforgiving medium in which to move.
Slightly misplaced body parts can create tremendous energy-robbing drag. A good time to work on skills is on easy training days. There may be three or four such sessions a week with each devoted to one or more skills in which you are weak. Try to achieve 30 to 32 right foot strikes for each 20-second repeat. Walk back to the start point to recover.