How to Increase Your Aerobic Capacity When You’re Already Doing the Obvious Stuff

As part of my ongoing quest to qualify for the Ironman World Championship, I am working with a company called INSCYD (pronounced “inside”), creators of a physiological performance software tool that helps endurance athletes like me identify specific ways to improve their fitness.

A few weeks ago I performed a sequence of bike tests that are used to generate the data that the program uses to assess cycling fitness/performance. They were pretty tough, comprising a 20-minute time trial that I had to start with a 60- to 90-second all-out effort, a four-minute time trial starting the same way, and a handful of seated 15-second sprints in a high gear ratio. What’s special about INSCYD is that it uses performance data not only to measure performance variables such as anaerobic threshold power but also to estimate physiological variables such as VO2max with an impressive degree of accuracy.

My results seemed spot-on to me. According to INSCYD, my VO2max, or aerobic capacity, is 62 ml/min/kg (about average for an athlete of my performance level and age), my VLamax, or anaerobic capacity, is 0.23 mmol/l/s (extremely low, which is actually good for an athlete in Ironman training), and my weight-adjusted anaerobic threshold power is 4.5 watts/kg (extremely high). All of this was explained to me by INSCYD’s Greg Hillson when we went over the results over the phone. Greg further explained to me that, based on these results, my best opportunity to increase my cycling performance ahead of Ironman Santa Rosa is to increase my VO2max.

Sounds great in theory, but the best most effective ways to increase aerobic capacity are to train a lot and to perform brutally hard high-intensity interval workouts on a regular basis, both of which things I was already doing before I was tested. Referring to these methods as low-hanging fruit, Greg suggested I look to some next-level ways of boosting aerobic capacity a bit, including a particular carbohydrate-restricted workout protocol that was shown to increase cycling efficiency, cycling time to exhaustion at peak aerobic power, and 10K run performance among triathletes in a 2017 study.

I gave it—or a version of it—a try recently. Normally I start my afternoon workout between one and two o’clock, but on this occasion I waited until four o’clock to do an indoor cycling workout containing four, eight-minute efforts at threshold power and lasting 80 minutes in total. After showering and changing, I ate a low-carb dinner of salmon, eggs, and a green salad with oil-based dressing. This ensured that I went to bed with reduced glycogen stores and woke up the next morning even more depleted.

On any other day I would have made breakfast my first order of business, but in obedience to the protocol I instead hopped on the treadmill and ran for one hour at an easy pace. Done by 6:30 am, I then enjoyed a high-carb breakfast (whole-grain, low-sugar cereal with whole milk and fresh raspberries, orange juice, and black coffee).

I now have super powers. Just kidding. I won’t know what effect these sessions have had (and I plan to do one per week from here on) until I repeat the INSCYD tests between two and a half and three weeks before race day. But I trust the science and there’s really no risk. While you might expect a fasted morning workout to be rather miserable after a one-two punch of hard intervals and carbohydrate restriction the evening before, I felt completely normal.

Another next-level method of nudging aerobic capacity upward that Greg Hillson recommend I try is sauna training. And I’m totally game, but that’s a topic for another time. . .