Why increasing your aerobic power makes you less efficient

Using computer simulations of the skeletal muscle metabolism, Swedish researchers including Svexa’s CSO Filip Larsen have found that increasing your aerobic power output (VO2max) comes with a mandatory trade-off; loss of efficiency.

-“It is a little bit like shifting to a lower gear when driving a car; your engine will require more fuel but you can power up steeper hills faster.”

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The reason stems from a metabolic bottleneck in the mitochondria, often called the powerhouse of the muscle. The bottleneck is a protein complex deep inside the mitochondria termed “complex I”. At lower power outputs such as during long endurance rides on your bicycle, the muscles energy stores are burned efficiently using complex I to full extent. When power output is increased complex I reaches it full capacity, so to be able to match the energy requirements mitochondria start to bypass complex I choosing a metabolic strategy with a higher capacity but a lower efficiency. This allows the muscles to produce more power, but also more heat. Going into power mode thereby means that your energy stores are zapped faster and the athlete risks hitting the wall before reaching the finish line.

“We validated the computer model using metabolic measures in cyclists. We were surprised by how accurately our model could predict both the metabolic response to exercise as well as world-record running speeds”

Competitive athletes usually perform physiological testing to assess their aerobic threshold, functional threshold power (FTP) and VO2max to optimize their training. The authors now propose a new physiological breaking point where metabolism switches between efficiency mode to power mode, that they term “complex I max” (CImax). In the trained cyclists in this study this occurred around 55-65 % of maximal heart rate. Knowing, and increasing, this breaking point will give athletes and coaches an advantage when designing training protocols and will be valuable from a strategic perspective when racing long endurance events.

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