Every year the same thing happens to nearly all of us. The weather starts changing, the holidays start approaching and the comforts of great food and warm beverages and sitting in front of the game all coalesce into winter weight and fatigue. What is interesting about this phenomenon is that is traces back to our ancestors...not the obsessive football watching on the big screen, but the hibernation-oriented winter seasons. The difference now is that life's stressors and requirements are much different now for us than they were for them then. 
For all intents and purposes our lives continue on in a very similar manner with responsibilities at work, at home and to others. We continue to have very similar, if not greater health stressors due to the cold and flu season, during this season of the year. However, this is when most of us neglect our fitness and our health. We generally tend to workout less or not at all, we increase our caloric intake dramatically and we become more sedentary.
