From Lungs to Muscles
If getting more oxygen into your lungs doesn't limit your ability to run faster, what does? Getting more oxygen to your muscles. And you do that by increasing the performance of your cardiovascular and metabolic systems, not by taking deeper breaths. You can improve your cardiovascular and metabolic performance by running intervals, running longer, and running more miles.
To get the most cardiovascular benefit from your interval training, run at 3K (2-mile) pace or slightly faster, which corresponds to your maximal rate of oxygen consumption (VO2max). Maintain this pace for 3 to 4 minutes and jog 2 to 3 minutes to recover between reps.
More: 3 Workouts to Increase VO2Max
Longer runs and a higher weekly mileage enhance your blood vessels' oxygen-carrying capability by increasing blood hemoglobin concentration. They also create a larger capillary network surrounding your muscle fibers and increase muscles' density of mitochondria, which enhances the delivery and use of oxygen, respectively.
Training your cardiovascular and metabolic characteristics improves your ability to transport and use oxygen, which delays the accumulation of carbon dioxide, making you feel less out of breath. So next time you're running up a hill and think, "I can't catch my breath," don't blame your lungs.
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