You might not have heard of Dr. Iñigo San Millán, but he’s behind interesting research that sheds light on the metabolic effects of aero position and the balance between the two that’s used at the highest level of the sport to maximize time trialling performance.


Dr. San Millán says he put the final touches on his aerodynamic versus metabolic ratio research while working with Garmin-Transitions during the 2010 season, but he no longer works with them due to other obligations.

The mainstay of Dr. San Millán’s research, and what he described to BikeRadar as most important to both professional level time trialists and the weekend enthusiast, is to know that aerodynamic position is only part of a time trialist’s performance equation. All too often, he says, riders will spend thousands of dollars in the wind tunnel only to come out with a ‘technically’ faster position, which then slows down their actual performance in competition.

“We knew we needed to integrate the aerodynamic and metabolic testing in the wind tunnel,” said San Millán. “I’ve been lucky to work with four wind tunnels world wide [San Diego (US), A2 in North Carolina (US), Silverstone (UK), Epsilon (Spain)]. In 2006 I started to do some metabolic testing in San Diego and I was really shocked to observe that there are many aerodynamic positions that are very taxing, metabolically speaking.

Dr. San Millán calls it the ‘wind tunnel trap,’ which is a danger to any cyclist who bases their time trial position on aerodynamic data.

“Normally when a cyclist goes to the wind tunnel the aerodynamicist or engineer there gives them the fastest position — the famous CdA [coefficient of drag multiplied by frontal area], right, the magic number; the fastest position, but I started looking at the cardiovascular responses and especially the metabolic responses to those given positions and I was fully impressed,” said San Millán. “Many times the fastest position would not be really fast out there. They [the aerodynamicist] will tell you this position is going to give you three seconds per kilometer or 25 watts more power, but according to my data the position could imply a 30- or 35-watts lower output, so the net benefit could be a decrease by about 10 watts. That was the irony; they would pay US$3,000 an hour or maybe $15,000 for the entire day just to make that rider slower.”

During his time with Garmin, Dr. San Millán actually took to testing the metabolic output of riders while in the wind tunnel. His protocol called for the rider to ride at a higher wattage than normally prescribed by the wind tunnel engineers, the exact wattage varies per rider and is based on Dr. San Millán’s physiological testing of the rider.

Using that wattage, Dr. San Millán monitors the rider’s blood lactate levels and heart rate in the wind tunnel as the aerodynamicist tests and modifies their aerodynamic position, the key is to find the position that is aerodynamically fast, yet easiest on the rider’s metabolic systems.

Monitoring Rory Sutherland in the A2 wind tunnel

Dr. San Millán says that the second, third or sometimes even the fourth fastest aerodynamic position ends up – functionally – being the fastest position for the rider. He also says that longer the event, the more the metabolic effect should be factored. “For a prologue we don’t worry so much about having a costly metabolic position because it’s a very short effort so we can have a very aggressive position,” he said, “but for a 50km TT at the Tour de France, or the team time trial or for a triathlon, we really don’t want to use that position.”

Through his research and work with professional cycling teams Dr. San Millán has come up with a protocol that’s very relevant to any time trial enthusiast, whether they have access to a wind tunnel for not, we’ll call it the ABC protocol and guides a rider to the most important aero and metabolic position indicators.

The protocol helps a rider optimize their position for both aero and metabolic performance and limit the time spent finding it in the wind tunnel, should they have access.

“In the wind tunnel they do many, many, many positions and that means minutes, right, or hours and that means money,” said San Millán. “What we learned from going to the wind tunnel is that it’s more like an ABC. There are three or four major rules of aerodynamics so you start there and optimize the [aero] performance. We learned also from the metabolic testing there are also three or four rules when it comes to the metabolic affect so for the same time they usually spend at the wind tunnel, we can optimize everything, both aerodynamic and metabolic.”

Dr. San Millán’s aerodynamic protocol ABCs (and D)

A) Frontal area is the most important aspect of position, according to San Millán. A rider should try to minimize their chest’s bagginess. Keep your arms and shoulders as closed as possible.

B) Your aero extensions should be as long as the rules allow and he recommends the ‘ski’ style bend. Height of the handlebars isn’t as important as the reach, Dr. San Millán says go longer before lower with aero bar’s extension position, and don’t waste time in the wind tunnel raising and lowering your base handlebar.

C) Extension angle is crucial to both aero and metabolic performance. Dr. San Millán says there is a reason the UCI made the Praying Mantis position illegal — it’s very fast. For those racing non-UCI regulated time trials or triathlons, it’s the only position to use. To achieve this position angle the extensions so that your forearms sit at 45- to 50-degrees to the base bar. For those racing under rules you’ll need to go shallower, but he still says to aim for a 30- to 35-degree forearm angle.

D) While not necessarily a position change, Dr. San Millán says make sure not to forget about an aero helmet, as it will trump every other possible position change, save for what we’ve already mentioned.

Dr. San Millán’s metabolic protocol ABCs

A) First and foremost a high performance position must offer a relaxed upper body, especially through your arms. “Your arms are a great lactic acid clearing system,” he said. “However in order to clear lactic acid they must be relaxed.” If your arms are tense, they actually create more lactic acid instead of helping clear it, and allowing your body to use your arms to clear it has another benefit: the muscles break lactic acid down to glucose, which can then be used by the muscle groups that are working.

B) Core stability is important in two respects: first Dr. San Millán says that the position must allow the rider to engage his core, which is an attribute that must be balanced with the longer reach that benefits the aero position. Additionally, Dr. San Millán says that a rider should train both their core (off the bike) and on their time trial bikes. He recommends a minimum of two or three time trial training days per month, year round.

C) Explore and train your respiratory muscles. This means your aero position needs to allow for deep breathing. Dr. San Millán also recommends training your respiratory muscles in the off-season off the bike through the use of a respiratory exercise device, while not wanting to offer endorsement, he mentioned the SpiroTiger as a device he’s used with good results. He says athletes can decrease oxygen consumption by 5-percent or more through respiratory training.

Before Garmin, Dr. San Millán worked and consulted for a half dozen of the biggest teams in the sport, including ONCE, Saunier Duval and Astana over the last 15 years. Now, however, Dr. San Millán is directing a pilot performance lab set up by the University of Colorado’s School of Medicine, which is subsequently how he became a part of Garmin’s program (and the reason for leaving this past year). “Last year I created, to my knowledge, the first human performance program on a professional cycling team,” said Dr. San Millán. “It was something that I had been pursuing for many years, but unfortunately I just had too much work with the school of medicine the hospital and I had to quit Garmin this year because I couldn’t keep up with all the requirements.”


Dr. San Millán now consults for the United Healthcare team here in the US, since the domestic outfit requires less of a commitment, but allows him to stay connected to professional athletes and further test theories for his metabolic protocol.