To "cross-train" in fitness routines means to engage in multiple types of exercises. This approach helps enhance overall physical performance and reduces the risk of injury by balancing muscle strength, improving flexibility, and preventing overuse of specific muscles. For example, a runner may incorporate swimming or cycling to build cardiovascular endurance while minimizing stress on their joints. Cross-training can also help maintain motivation and prevent workout boredom, as individuals explore various modalities that contribute to their overall fitness.