Any podiatrist will emphasise the need to tailor your footwear depending on the activity you are doing. With the range of gym classes increasing all the time and due to advances in sports science and fitness trends, the need for a variety of different trainers has never been greater. Clearly you can always make do with a sturdy pair of running trainers; however, to ensure you can perform effectively, with better technique and form and with a reduced risk of injury, changing your footwear might not be such a bad idea.
It's always a good idea to know what type of gait you have and how your foot lands when you run or walk as this will determine the type of trainer you'll need to support the arch of your foot. Quite often good sports shops that specialise in footwear will be able to monitor you walking or running on a treadmill and advise accordingly, though seeing a podiatrist might also be necessary.
A suitable running trainer will help to cushion your body from the impact of running. They should fit comfortably, and like any shoe you should be able to move your toes around once they are on and not have them bunched up or hitting the end of the shoe when running. These trainers will be great for fitness classes that involve lots of running and are best suited for sports halls and outdoor bootcamp classes. They are perfectly suited for treadmills too, as well as indoor bikes, spinning, stair machines and rowers. However, they aren't good for weight training and exercises where stability is paramount due to heavy weight lifting and explosive movements.
Cross-training shoes are designed to accommodate a large range of different activities. They generally have less cushioning in the sole, which tends to be flatter and more solid, yet they can be used for short explosive sprints and cardiovascular activities. Some brands go further and provide different areas of grip to accommodate exercises such as rope climbs and suicide runs. Overall, this is probably the best value trainer you can buy because they work best for kettlebell training, indoor cardio, heavy weightlifting and circuit classes. However, they aren't quite as good for outdoor bootcamp classes. The reduced thickness of the sole reduces the chance of rolling your ankle and enables you to almost grip the floor with your feet. This is perfect when lifting heavy weights when your centre of balance may shift and require you to adjust your base to maintain good form.