A strict regime can become boring over time, and become less challenging for the body. Just exercising indoors keeps us away from enjoying the complete mental benefits of exercise.
Throwing in a different activity or sport can be just the shake up one needs to bring back some motivation. It also challenges the body to move in new and different ways, working on all muscle groups. Stepping outdoors for exercise is associated with increased energy levels and revitalization, as well as positive emotional states.
Changing walking/running routes, going for a trek, or a run in the park, and playing a new sport, all promote brain activity and revitalization. They also help with body coordination, balance, agility etc. Routine exercise can become monotonous. A change can be good!
Spend an hour or two during holidays playing a sport with the family, or go for a hike or a jog in the park.