VO2 max may be the most widely used term in exercise physiology. Every serious runner has heard of VO2 max, but many have only a vague notion of what it is and whether it is a significant factor in determining running performance. Let’s take a look at what VO2 max is, how important it is for distance runners, and how to train to improve it.
What is VO2 max?
VO2 max (or maximal aerobic capacity) is the maximal rate at which the body can transport oxygen to the muscles so that it can then be used to produce energy. This is one of several important factors in determining running performance, along with lactate threshold, running economy, and intricate aspects of the brain and muscle that allow one runner to withstand fatigue more readily than another.
The higher your VO2 max, the more energy you can produce aerobically relative to your bodyweight. Everything else being equal, if you can produce more energy aerobically, you can maintain a faster pace. Maximal aerobic capacity is arguably the
single most important physiological variable influencing performance in races from 1500m to 5,000m. A high VO2 max is significant for longer races too, but the longer the competition, the more important other factors—such as lactate threshold—become for performance.
What determines your VO2 max?
The range of your VO2 max is set genetically; meaning that some runners are naturally gifted with a relatively high maximal aerobic capacity and others are not so lucky. Where you fall within your range, however, depends on how much and how hard you train. VO2 max increases substantially with the correct types of training. With six months of training, many previously unfit folks can increase their maximal aerobic capacity by over 25 percent. If you have been running reasonably seriously for several years, however, you should expect less dramatic increases because the rate of improvement decreases as you approach your genetic potential.
The three major components of your body’s plumbing that determine your VO2 max—oxygen transport, oxygen delivery, and oxygen use—involve getting oxygen from your lungs into the mitochondria of your muscle cells. Let’s look at how each is affected by training:
1. Oxygen transport: Oxygen is transported through your blood vessels attached to hemoglobin in your red blood cells. An increase in your hemoglobin or red blood cell levels allows more oxygen to be transported to your muscles, which increases your VO2 max. That is why many world-class runners train at altitude. Running at sea level, however, does not cause a substantial increase in the number of red blood cells per unit of blood.
2. Oxygen delivery: The amount of oxygen-rich blood that can be transported from your lungs to your muscles is determined by the size and strength of the left ventricle of your heart and your maximal heart rate. Your maximal heart rate does not change with training, but your left ventricle (which pumps blood to the rest of your body) increases in both size and strength with training.
3. Oxygen use: Running leads to a variety of adaptations that allow your muscles to use more oxygen, such as an increase in the number of capillaries providing blood to your individual muscle cells and an increase in the amount of mitochondria in your muscle cells where aerobic energy production takes place.
How to improve your VO2 max?
Intensity: What is the optimal workout to make the largest gains in your VO2 max? There are two schools of thought. Some coaches believe that doing speedwork substantially faster than VO2 max pace jolts the body to increase maximal aerobic capacity. The other school of thought (to which I adhere) is that the greatest stimulus to improve your VO2 max is provided by running at an intensity that requires about 95 to 100 percent of your current VO2 max. For serious runners, the running speed at this intensity equates to about 3,000m to 5,000m race pace.
Duration of intervals: You will improve VO2 max most rapidly by running repetitions of two to six minutes in duration (typically about 600m to 1600m), which can be done on the track, roads, trails or uphill. Shorter intervals are not as effective in providing this stimulus because you do not maintain the optimal intensity range long enough. The total amount of time accumulated at very close to your current maximal aerobic capacity is the key.
Length of workout: Aim to do 4,000m to 8,000m of intervals per workout. If you run less than 4,000m of intervals, you will still provide a training stimulus, but your rate of improvement will be slower. If you try to run more than 8,000m of intervals at this intensity (good luck), you will likely be unable to maintain the appropriate pace for the entire workout and will require several days of recovery.
Two-time Olympian Pete Pfitzinger is an exercise physiologist.