The triathlon discipline with the lowest barrier to participation, running only really needs a pair of running shoes. You can pretty much wear anything (as a whole host of costumed runners at any major marathon can tell you), but the single biggest investment you might need to make in running is with good running shoes.
Running shoes are where your feet meet the road. While different body types and running mechanics mean no one shoe can fit all, the most important part of running shoe selection is the right fit. A properly-fitting running shoe will feel secure on your foot and won’t move around as you go through your running stride. The heel cup should remain molded to your heel, the laces should keep your foot locked down without overly squeezing the top of your foot, and the toebox should give your toes enough room to move and expand.
How much cushioning and support you need depends on how you use the shoes and your personal preference. Some people use the same shoes to train and race in, while others prefer to use different shoes for speed, training, and racing. Some want to feel the road more, some want to feel like they’re running on clouds, some want the shoe to provide springiness for more speed.
The best way to determine what’s right for you as you start out in the sport is to try different kinds of shoes. Some of the world’s major running shoe brands as well as multi-brand running stores allow easy returns and exchanges within 30 days.
If you’re only just starting to run, your body needs to get used to the strain and impact of the motion. Your knees and hips bear forces equivalent two to three times your body weight with every step when running. Most beginners will benefit from a shoe that offers cushioning as well as support.
As you become fitter and your running motion becomes more efficient, you’ll likely start looking at going faster, or training at different paces. While you can keep the cushioned shoes for long runs, a lighter shoe with more ground feel and responsiveness will help you make the most out of speed and tempo sessions when you want to pick the pace up.
More advanced athletes prefer to keep a separate pair of shoes for racing. These are usually lighter with just enough cushioning to get you from start to finish, and usually requires a very efficient running style because it has less structure and support.
Rotating between pairs of shoes depending on what you use them for will help you get the most out of your training sessions because you can train at more specific paces and efforts. Shoe rotation also reduces running-related injury risk.
So to start with, find a good pair of cushioned everyday trainers. As you begin to run more often, you can pick up another of the same pair or find a lighter pair for faster running to start creating your shoe rotation.