All of your runs should start with a warmup and end with a cool-down. These two bookends to your run will help you prepare for your best effort and recover at the end of your workout.
A good warmup dilates your blood vessels, ensuring that your muscles are well supplied with oxygen before you give them a vigorous workout. It also raises the temperature of your muscles for optimal flexibility and efficiency.
By slowly raising your heart rate, the warmup also helps minimize stress on your heart when you start your run.
The cool-down keeps the blood flowing throughout the body. Stopping suddenly can cause light-headedness because your heart rate and blood pressure might drop rapidly. Winding down slowly allows them to fall gradually.
While you will often hear that the cool-down helps you work the lactic acid out of your muscles and prevent delayed onset muscle soreness the next day, research has not found this to be the case.
The cool-down is a good mental transition between a hard effort and the end of your workout.
Stretching used to be part of every warmup and cool-down, but the evidence doesn't find that it has the benefits it was thought to bring. Static stretching before, during, or immediately after exercise hasn't been proven to prevent injury or delayed onset muscle soreness.
Dynamic stretching after a warmup has some evidence it might be beneficial for performance. This form of stretching is done with exercises that take your muscles through their full range of motion. Dynamic stretching exercises also mimic the actions you'll be taking in your workout.
Stretching cold muscles is never a good idea, so if you decide to include stretching, do it after you have warmed up or as part of your cool-down.
Take these steps for your warmup:
At the end of your run, take these steps:
If you think you benefit from stretches, you can do them after your run or as a separate activity. Typical post-run stretches include the hamstring stretch, quad stretch, calf stretch, low lunge stretch, IT band stretch, butterfly stretch, hip and backstretch, arms and abs stretch, and triceps stretch. Use these tips for proper stretching:
Research is just catching up with what runners have been doing for decades (and their coaches have been teaching). Warming up is beneficial, but you can probably skip the stretching if you don't find it works for you. Enjoy your run.