It is difficult for me to say when it is easier to exercise: in winter or in summer. In summer, it is easier just to go out and spend time outdoors. It might not be always as easy during winter months. During winter, the only solution might be going to the gym. When the weather outside is bad, it might not be usually possible to exercise outdoors. Gym is the only solution in such cases. I know people who like to exercise in summer but never exercise in winter when it is too cold to spend time outdoors. They believe that going to the gym is not as effective as spending time exercising outdoors.