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Different impact of cycling and running on body composition during weight loss

What did I do?

After a few years that were quite impactful on a personal level, I bought a race bike last January and started cycling last year. As a side effect of resuming regular exercise, I gradually started paying more attention to other lifestyle factors. Over the course of last year, I lost some weight and improved my sleep, but both stagnated a bit after I lost track of my exercise routine a bit during last winter. Since the late 2019, I upped my game a bit and made some additional dietary changes (e.g., quitting coffee and alcohol, using MyFitnessPal to track my eating habits and no longer eating any snacks after supper) while I picked up cycling again. The Covid-19 outbreak gave me extra motivation to improve my health (just in case) and optimally use the ‘smart lockdown’ conditions to create some strong health routines and habits.

Throughout 2020, my stamina and overall health improved quite a bit, but I also lost a fair bit of weight on a nice and gradual pace. After getting back from our holiday in the Ardennes on August 1st, my cycling routines were forced to go on-halt for a while, as my race bike had multiple mechanical problems. Due to Covid-19, the global supply chains were drastically disrupted, so I had to wait until early October before I could get my needed parts.

As soon as I found out that it could take a while before I would be able to resume cycling, I picked up running as an alternative. I used to run a lot in the past (e.g., half marathons) but hadn’t consistently done so for years, so my body needed a little bit of time to get used to the impact of running. After a few very short runs with a very long recovery period, I bought some new shoes, which really improved my performance and recovery time.

During that period, I noticed that my weight loss curve was flattening a bit, despite the fact that my caloric deficits (the difference between calories burned and calories eaten) were similar to the period before. I initially thought that it was probably a sign that my metabolism might be changing a bit after a period of structural weight loss. More recently, I started wondering if the running routine could perhaps have a different impact on my body composition than my cycling routine did.

How did I do it?

Since I step on my Withings Body Cardio every morning after getting out of bed, I have quite a bit of data on my body weight and composition. In 2020 I only miss a bit of data in July due to our holiday. To improve the comparability of my weight, fatmass, muscle mass and bone mass data, I standardized all values. This means that I subtract my mean from each value, and then divide it by my standard deviation. As a result, all values are on the same scale and represent relative changes in comparison to my own average values. The plot below (click on it to enlarge if it is blurry in your browser) visualizes these relative changes in my body weight, fatmass, muscle mass and bone mass over 2020. The vertical line is the start of August, when we got back from our holiday and I switched from cycling to running that month.

What did I learn?

The chart above shows that despite the switch from cycling to running, my fatmass (yellow-ish line) actually kept decreasing at a similar pace as the period before. Apparently it wasn’t my metabolism that changed and my caloric deficits were having a similar effect on my fatmass loss, but my overall weight loss (purple line) stagnated a bit due to another reason. The chart clearly shows that before the vertical line I was losing muscle mass (blue line) and bone mass (red line) during my overall weight loss. However, after making the switch from cycling to running, my muscle mass and bone mass actually started to trend up, causing my overall weight loss to stagnate.

While I find it very intuitive that running has a very different impact on my body’s muscles and bones than cycling, I found this visualization quite an eye-opener. It made me feel a little bit better about my current weight loss process, but also increased my appreciation of running. I absolutely love cycling and will continue to do so, but over the past few months, I have decided to keep running as well. Sticking to my running routine gives me an alternative to cycling if I am to run into mechanical problems again in the future, but apparently also has a different impact on my body composition. To me, running is the most pure form of exercise that you can think of from an evolutionary perspective, so it might be healthy to have a body that can deal with the impact of running if needed.

PS: If you want to recreate the above plot with your own Withings data using RStudio, you can download my code in this notebook.

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