An exercise physiologist is investigating the efficacy of active recovery versus passive rest on post-exercise blood lactate clearance. They select a sample of 24 endurance athletes and randomly assign them to one of two recovery protocols after completing a standard high-intensity treadmill run:

• Condition X (Active Recovery): The athlete walks on a treadmill at a speed of 4.5 km/h at a 0% incline for 10 minutes.
• Condition Y (Passive Rest): The athlete sits completely still in a chair for 10 minutes.

At the end of the 10-minute period, the physiologist measures each athlete's blood lactate concentration in millimoles per litre (mmol/L) via a finger-prick blood sample.