If you step out your door and immediately start walking briskly or running, you may be putting yourself at risk of injury and cheating your workout. A warmup before either of these activities increases your core temperature so you burn calories more efficiently, enhances circulation to working muscles and improves your muscle elasticity. A warmup takes as little as five minutes, so you have no excuse to skip it.
Prior to the main portion of your workout, do five minutes of an easy cardio activity. You could walk up and down the stairs in your house, march in place or simply walk a block or two at an easy pace. Next, focus on warming up the muscles you'll use during your walk or run with dynamic stretches. Circle your ankles six to eight times in each direction. Swing each leg 15 times front to back from the hip joint and then move them in a figure-8 motion for 10 to 20 repetitions. Plant both feet firmly on the ground and circle your hips 10 times each direction. Circle your arms and shrug your shoulders several times to loosen up your upper body. Other warmup activities might include lunges, squats and high knee hugs.
You may be tempted to hold a hamstring or hip stretch for an extended time before your walk or run. Whether this is learned from high-school PE or an instinct, skip it. A meta-analysis published in a 2013 issue of the "Scandinavian Journal of Medicine and Sport" concluded that static stretching before exercise may compromise your performance and doesn't prevent injury.