Let’s start with who should always perform a cooldown after a workout. If you have any type of cardiovascular health issue, that means you.
People With Cardiovascular Problems
For individuals with compromised cardiovascular health, the sudden discontinuance of exercise can prove harmful. As soon as they stop activity, their blood pressure drops even as their heart continues to beat at a faster pace. Their heart rate takes longer to come down to a normal level. The combination of an elevated heart rate and dropping blood pressure may result in an irregular cardiac response. So athletes who have any type of cardiovascular issue should make gradual cooldowns a priority in their workouts—and of course they should consult with a doctor before even undertaking a workout plan. (Ask the Experts: Do I Really Need to Cool Down After a Workout?)
Healthy Individuals and Athletes
Here, the research about the benefits of cooling down isn’t as clear. In fact, it’s downright confounding. A study conducted by a team of Australian researchers concluded that cooling down after a bout of eccentric exercise did not prevent or reduce soreness after a workout. Another study found that performing a cooldown in conjunction with a battery of stretches was not an effective way to reduce running injuries. The control group (runners who did nothing after a workout) fared better than those who performed a cooldown.
However, I am not saying that cooling down is totally without merit. Cooldowns can prevent venous pooling (i.e., the collection of excess blood in the lower body), which can happen when exercises such as running, cycling, or lower-body resistance training are stopped. It can lead to dizziness or fainting.
Healthy individuals may want to wrap up their workouts with a short walk, some self-myofascial release (see Advantages of Using a Foam Roller Before and After Working Out.), gentle breathing techniques or light static stretching. If blood pooling is a concern, alternate between upper-body and lower-body exercises instead of focusing solely on your lower body, and conclude by performing those exercises at gradually lower intensities.
Try These Cooldown Routines
 Law RY, Herbert RD. “Warm-up reduces delayed onset muscle soreness but
cool-down does not: a randomised
controlled trial.” Aust J Physiother
 van Mechelen W, Hlobil H, Kemper HC, et al. “Prevention of running injuries by warm-up, cool-down and stretching exercises.” Am J Sports Med