Limits on a runner’s pace

In the picture

1. 1A mask over nose and mouth: exhaled air is sampled for oxygen and carbon dioxide.
2. 2A chest strap around the ribcage: heart rate is recorded while the runner moves.
3. 3A screen on the cart: a rising line levels off as oxygen use reaches its ceiling.
4. 4Red blood cells inside a thigh vessel: oxygen-carrying blood moves toward working leg muscle.

Examples

• A runner can hold a conversational pace for a long time but must slow down after a few minutes at sprinting pace.
• Climbing several flights of stairs quickly leaves you out of breath; your legs burn and you slow down.

Quiz: Limits on a runner’s pace (Age 17)

1. 1

   What does VO2 max represent?

   • The fastest pace a runner can sustain before lactate starts to build up
   • The heart rate recorded while a runner moves
   • The highest rate at which the body can use oxygen during hard exercise
2. 2

   What does the lactate threshold mark?

   • The fastest pace a runner can sustain before fatigue rises sharply
   • The maximum amount of oxygen the lungs can hold
   • The point where oxygen use first begins to rise during exercise
3. 3

   Why does fatigue come quickly when a runner goes above the lactate threshold?

   • Red blood cells stop carrying oxygen to the legs
   • Lactate builds up faster than it can be cleared
   • Oxygen use reaches its absolute ceiling

The answers, each with its explanation, are in the app. This lesson has left the free week, so its quiz is part of the subscription.