It is good for you to look at your body conformations, and establish how dressing will affect you. You don’t want to wear shorts that are too tight that they affect the flow of blood in your body. If that is the case, you will not be able to hit your best time because your speed will reduce a bit. Also, if you are very thin, oversize running shorts will cause you a lot of problems. You have to choose running shorts which are flexible to allow easy body movements while keeping you comfortable as you run.
You need to also consider your style of running. If you are a marathon runner, you will need to wear shorts that are a bit light so that they don’t become a burden for you while running. For short distance runners, they can wear short and heavy running shorts, provided they are fitting them well and they are comfortable as well. If you are participating in running events that will require you to make jumps like steeplechase, you need to find running shorts that are short and not too tight. The shorts you will be wearing in such events will determine whether you will make the required jumps properly, or not.
Finally, you need to establish the purpose why you are running. If you are participating in a training session. If you want to train for a marathon race, you are allowed to used less time and heavy running shorts. If this is the case, you need to use more heavy and longer shorts to build your body physique and boost your running. On the other hand, if you are running a competitive race, then you need to find lighter and more comfortable shorts that can help you make movements effectively. If you are taking part in very strenuous activities while running, you should ensure that you get cotton shorts that can absorb some sweat, while leaving you comfortable.