I’ve always enjoyed long walks. I’m pretty introverted, so spending two hours with an audiobook while strolling around the area is usually pretty enjoyable. As a kid, I did some hiking in the mountains of Colorado, and I enjoy the outdoors, so it doesn’t have to be walking on flat surfaces. Thus, I’ve been trying to do good walks when I can post-surgery; it’s what they suggest, after all!
The walking has been fine. I can pretty easily to 3 miles on city streets at this point, and I suspect I could do more. In the last week or so, though, I’ve kind of wanted to challenge mysel a bit more, so I’ve started to add hiking on local trails. I went out to Daley Ranch recently, and while there were a few parts which challenged me in my current state, it was fun. Yesterday, though, I decided to try Double Peak trail in San Marcos.
It’s rated as “moderate”, about 2.5 miles to the top of a local big hill/mountain, with an elevation gain of about 1000 feet. I knew that that would be an interesting challenge, but buoyed by my success at Daley Ranch, I thought I’d give it a try.
I almost immediately ran into a problem I had seen at Daley, but which I had never before encountered before the surgery. Flats were fine and enjoyable, even slight uphills…but as soon as I hit any real ascent, I got out of breath within about 20 feet. I’d start uphill feeling good, and then quickly find myself gasping with legs that felt exhausted. The funny thing was that 30-45 seconds of rest would fix it, I’d start up again, and have exactly the same experience. This was very different from before the surgery–I’d be able to keep chugging along, tired but determined, for much longer stretches.
In little bits like that, I made it about 2/3 of the way up. At that point, I was not just feeling tired, but also having distinct feelings that this might not be a good idea, that my body was starting to respond badly to this. I got to the sign that indicated one mile remaining, saw the upslopes to come, and decided not to try it.
I think I could have gotten to the top–but I think it might have caused me harm. As it was, I descended, and instead walked the 3/4-ish mile flat trail around a pretty little lake at the bottom.
I’m a physiology instructor, and I’ve taught labs on muscle fatigue. I know that fatigue is complicated, and that there are multiple mechanisms involved, and that we don’t understand all of them. And I have a guess about what might have been going on. My current food intake is very, very small, about 300 calories per day–and that usually has less than 15g of carbohydrates. That probably means two things: severe ketosis, and low glycogen storage in my liver and muscles. Given all of the hype about how great keto diets are for fitness, it’s hard to believe that the ketosis is responsible for the rapid fatigue under load.
However, the low glycogen might be. Muscles can use fatty acids for energy quite well, as long as the energy demands aren’t too extreme. If I understand it correctly, fatty acids are converted to ATP through beta-oxidation of the fatty acid and then Krebs cycle/oxidative phosphorylation of the products. This is a very efficient but slow process, which means that the fats can produce lots of ATP but not very quickly. For sustained moderate exercise (walking around a lakeside flat trail, for example), that’s fine. My body can provide fatty acids in abundance. However, trying to push a 260-pound body up a steepish incline means the leg muscles need a lot of ATP very quickly. Normally, that would be accomplished with glucose metabolism…but in this case, my muscles and liver don’t have very much glycogen (glucose storage), so the available glucose is low. Thus, when I try to switch over to burning glucose for more intensive work, the muscles sputter.
That’s my current hypothesis, anyway.