Intensity and volume are continuously intertwined in training programs. The former refers to how hard you can push yourself while training, while the latter refers to how many sets, reps, and time you spend training. Are they equally important, or should one be prioritized over the other for cardiovascular performance?
Dr. Gommaar D’Hulst, a senior scientist at ETH Zurich, Switzerland, deciphered this question on Oct. 22, 2024, via a 2024 study in Sports Medicine encompassing 50 years of data and 6,000 participants. It turns out that high-intensity interval training is better than slow-state steady cardio or sprints for improving cardiovascular capacity. (1)
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What the Fick?
To understand training intensity, one must understand VO2 max, which is the maximum amount of oxygen a person can use during intense exercise. This is important because of the Fick equation, which determines oxygen intake versus intensity (i.e., how much oxygen the heart can deliver to the muscles via red blood cells).
As training intensity increases, VO2 max needs to be higher because that intense training demands more oxygen. Your training intensity will decrease if your VO2 max is not strong enough to utilize the oxygen being delivered.
Mitochondria
If you recall high school biology class, you might remember hearing about the “powerhouse of the cell” mitochondria. Mitochondria are the parts of a cell that produce energy. To keep it simple, you can produce more energy with increased mitochondria.
Capillaries
That begs the question: Which training modality is optimal for improving VO2 max? You already learned that high-intensity interval training (HIIT) is the answer, but why? The answer is capillaries — the smallest blood vessels of the vascular system that transport nutrients and oxygen to the cells.
Improving cardiovascular health via HIIT can produce more capillaries, which transport more oxygen to the cells, where mitochondria can use it to produce energy.
[Related: The Best Interval Training Workouts to Level Up Your Cardio]
Break It Down
To summarize, training with intensity is more beneficial than training for volume because the former is superior at improving VO2 max, producing more mitochondria in cells, and creating more capillaries to transport oxygen to the cells.
- More capillaries provide more oxygen to the cell.
- More mitochondria means more of that oxygen can be used for energy.
- Higher VO2 max means you can utilize that energy produced by the mitochondria.
So train with intensity because doing anything less is literally not maximizing your capacity.
Reference
- Mølmen, K. S., Almquist, N. W., & Skattebo, Ø. (2024). Effects of Exercise Training on Mitochondrial and Capillary Growth in Human Skeletal Muscle: A Systematic Review and Meta-Regression. Sports medicine (Auckland, N.Z.), 10.1007/s40279-024-02120-2. Advance online publication. https://doi.org/10.1007/s40279-024-02120-2
Featured image via Shutterstock/Maridav
