The effectiveness of a treadmill versus a StairMaster for cardio largely depends on individual goals and preferences. According to the Mind Pump hosts, here are some key points to consider:

1. Versatility:

   • The treadmill is deemed the most versatile cardio machine. It allows various forms of movement such as walking, running, and interval training (HIIT), and can be adjusted for different inclines. This makes it suitable for both low and high-intensity workouts 1.

2. Functional Training:

   • Walking or running on a treadmill is more functional since it mimics natural movements. Sal Di Stefano notes that it’s useful for practicing technique and form, making it beneficial for general cardiovascular health 1.

3. Full-Body Engagement:

   • Justin Andrews mentions choosing equipment like the assault bike or rower for full-body engagement. While not directly compared to the StairMaster, this point underscores the value of engaging both the upper and lower body, which the StairMaster can also achieve to an extent with proper posture and use 1.

4. Joint Impact:

   • The elliptical and bike are noted for being low-impact alternatives which might be beneficial for people with joint issues. Although not specifically compared, the StairMaster could offer an intermediate impact level compared to the treadmill and these low-impact options 1.

5. Muscle Engagement and Efficiency:

   • Adam Schafer highlights that repetitive and high amounts of cardio, like running extensively on a treadmill or hitting the StairMaster hard every day, can hinder muscle growth. This can be specifically counterproductive if one is trying to build muscle, particularly in areas like the glutes 2.

In conclusion, if versatility and functionality are key considerations, the treadmill might be more effective. However, if aiming to engage the lower body intensely with potentially less impact on joints compared to running, the StairMaster could be a better fit. The most effective form will ultimately depend on individual goals, preferences, and physical considerations.