Duration: 1.5 hours (approximately)
The efficiency by which athletes transfer raw metabolic power to mechanical power (velocity) is known as 'exercise economy'. In a group of otherwise similar athletes, economy makes the difference between a top, bad or indifferent athlete.
For example: the more efficient you are, the more power/velocity you can generate for the same oxygen (O2) cost. So, the less oxygen it requires to achieve the power output, the better.
Does not require any equipment other than expired air.