Human: Which is more effective: a stationary bike or an elliptical trainer? Assistant: 
The answer to this question depends on your fitness goals and personal preferences. Both stationary bikes and elliptical trainers can be great options for improving cardiovascular endurance, but they each have their own strengths and weaknesses. For example, stationary bikes are better at increasing leg strength while elliptical trainers focus more on core muscles. Ultimately, the best way to decide which one is right for you is to try them both out and see which one works best for you.