The more fit your heart is:
The resting heart rate decreases because the interior dimensions of the ventricles increase (they can hold more blood) thus increasing stroke volume at rest. Because a given intensity of activity requires a given amount of oxygen, the cardiac output at a given intensity is essentially the same whether one is trained or untrained. Since more blood is pumped with each contraction (with a trained heart), the heart beats fewer times per minute to achieve the necessary oxygen delivery. The benefit of a heart not needing to work as hard to deliver the same amount of blood is obvious.
- The stroke volume during exercise becomes greater therefore, maximal cardiac output is significantly greater following training because of the increase in stroke volume.
- Since a given intensity requires a given amount of oxygen, the heart rate at any given sub-maximal intensity will be lower.
- Example: An untrained person that runs a 10-minute mile pace measures his heart rate at 150 bpm. After a few months of proper aerobic training, that same person may only raise his heart rate to 125 bpm at the same 10-minute mile pace. Aerobic training produces new capillaries in active skeletal muscles, increasing the area for the exchange of oxygen.
- Aerobic training increases the mitochondria density (more of the muscle cell is occupied by mitochondria) which leads to a significant increase in the amount of aerobic enzyme activity in the cell.
The bottom line is that the treadmill/METs program is designed to increase in speed and incline as time progresses. It is not programmed to achieve a steady speed or reset to 0 grade. It will always get faster and more inclined.
Therefore the heart, as the test progresses, will always need to work harder to accommodate the increase in speed and incline. The test shows how hard the heart is working to try to accommodate this increase in speed and incline.
A more fit heart will, because of increased stroke volume and the increased ability to use oxygen due to increased aerobic enzyme capacity, perform the treadmill test more efficiently with a lower heart rate and a longer time to reach the sub-max rate which is based on the patient’s age.
Source: American Council on Exercise Personal Trainer Manual
Aerobic vs. Anaerobic Exercising
The test we do at the Health Center is a measure of your cardiac fitness based on the length of time it takes you to get to a calculated heart rate based on your age. The intensity and workload is the same for everyone that steps on the treadmill. The only thing that changes is the target heart rate that you are trying to get reach. The longer it takes you to get to that heart rate, the more fit your heart is.
The type of exercise you do dramatically affects the test results. If you do only anaerobic training (very high heart rate) you essentially are training your heart to respond to workloads and/or exercise with a high heart rate. So even when you are doing something that you perceive is not very hard (light jogging, fast walking, our treadmill test) your heart will responding the way it has been trained, with a high heart rate.
If you exercise to build an aerobic base (70%-80% of your maximum heart rate) you are training your heart to respond to workloads and/or exercise with a gradual heart rate increase, which is obviously healthier. When you do have to work hard like in a fire or during a rescue, your heart will still get anaerobic; just not as quickly and not as high a heart rate. Again, this is healthier.
On the flipside, anything less than 60 percent of the maximum heart rate usually benefits beginners and/or those recovering from an injury.
Lastly, there is a time and a place for anaerobic training. Doing the mountain, stadiums, skills course...are very good exercises to teach your heart to work in an anaerobic capacity. But you should first build an aerobic base, then work in the anaerobic. As the “Worlds Fittest Man” and six time Triathlete of the Year writes; “the improvement you can get in performance from developing your aerobic fat burning system is huge compared to the improvement in performance you can get from doing the high-end anaerobic carbohydrate burning workouts. And our bodies cannot develop both systems very well at the same time. Which means that to build a base properly, an athlete has to have the patience to work the aerobic system exclusively for a huge block of time.” This base building could be as short as a three-month period.
