After restarting a running regimen after a long winter of sipping hot chocolate around a fire, you might find that you become winded much faster than you were at the end of the previous summer. Think of your Vo2 max as a rubber band. Each time you get out there and go for a run, you are slowing stretching your band each day. The more that you stretch your band, the easier it is to take a deep breath, which sends more oxygen to your muscles. When you take time off for the winter, your rubber band, unfortunately, reverts back to normal. Supplements that contain ingredients that aid in sending oxygen to muscles, such as cordyceps and inosine, will help you expedite improving your Vo2 max. At the end of the day, it really depends on you and your dedication to get out there every day, but supplements can offer a little bit of assistance.