Read the passage below carefully, and then choose the best answer:
Frozen Fitness
A man stands over a bathtub that is filled with ice. Although it is the middle of winter, he slowly slides into the tub and submerges his body underneath the water. Within seconds, he begins to shiver, but after a few minutes he is able to settle down. Despite the temperature, he will remain in the tub for the next 30 minutes. He is taking advantage of cold thermogenesis, a growing trend that could improve people’s health. Thermogenesis is an internal process that mammals undergo to generate heat when they are subjected to cold temperatures. In modern society, humans rarely requires this ability because we have heated homes and offices during the winter season. Recent studies, however, indicate that by doing so we could be missing out on some wonderful health benefits. Being subjected to cold temperatures regularly has been shown to boost men’s testosterone levels. It also boosts metabolism, which allows people to burn fat more efficiently. Some people have reported that cold thermogenesis also provides a mental lift once you have overcome the initial shock of the cold water. The positive effects of thermogenesis were known before, but it only started to become popular after the 2008 Olympics. One man who helped spark this craze was Ray Cronise, a NASA scientist and entrepreneur. He was reading an article that reported Michael Phelps ate 12,000 calories per day while training. The calories were so high that led him to believe that something else besides exercise was helping Phelps to stay thin and muscular: the icy water in the swimming pool. So he conducted his own experiment by drinking several glasses of ice water and exposing himself to cold water. After six weeks of this regiment, he had lost 30 pounds. There are several routines that a person can adopt if they are interested in starting their own thermogenesis routine. One method is ice baths. This method may be a bit too drastic for average people though. Instead, people may want to begin by dunking their face in cold water for a few seconds, and then gradually increase the time. Next, they can progress to cold showers and baths before moving on ice baths. An even more convenient way is to place an ice packet on the back of your neck for 15 to 20 minutes every evening. Although these methods may be extreme, many are willing to give them a go to improve their health
6. What does the phrase “by doing so” in paragraph 2 refer to?
