Over break, I signed up for a spin class, which I do frequently at home. This Sunday I registered for a 9:30 AM class. I was pretty tired, so I snoozed my alarm and ended up running late with no time to eat beforehand. The class started out well and was fun but difficult, and about 20 minutes in I suddenly started to feel faint and my vision went a little hazy. I eased up and had some water, and I started thinking about why I felt that way.
Since I hadn’t eaten anything since dinner the night before, I realized my blood glucose levels were probably low. During intense exercise, my muscles were using glucose rapidly and breaking down their glycogen stores. Because I was fasting overnight, my liver glycogen was likely already somewhat depleted, so maintaining normal blood glucose was harder. My liver would have had to rely more heavily on gluconeogenesis, which is an energy-expensive process, to keep my blood glucose up. As the demand for glucose increased during the workout, it became harder for my body to match that demand, which could explain why I felt faint, lightheaded, and low-energy.
I also thought about the pasta and eggplant parmesan I’d eaten the night before. While a high-carbohydrate meal helps replenish glycogen, an overnight fast can still significantly reduce liver glycogen levels, especially before morning exercise. So even though I had eaten carbs the night before, it makes sense that I could still experience symptoms of hypoglycemia during intense activity. I took it easy for the rest of the class and recovered, but I found it fascinating to understand a biochemical explanation for what might’ve happened and why eating before a morning workout is so important.
This was a thoughtful and insightful post on how biochemistry relates to our everyday life. Your explanation of what happened in your spin class fits well with the biochem concepts we have been covering. I appreciated how you connected the symptoms you were experiencing (haziness, feeling faint, etc) to the mechanisms of glucose regulation during exercise. It is interesting that fasting overnight reduces liver glycogen stores, and because the liver is responsible for maintaining blood glucose levels, that depletion can make hypoglycemia more likely in the morning. Even though your muscles also store glycogen from the pasta the night before, they cannot release that glucose into the bloodstream. Thus, your body was relying on gluconeogenesis to keep up with the demand in maintaining stable blood glucose levels. I though you did a great job in analyzing your spin class experience through a biochemical lens and showing us the importance of getting some pre-exercise carbohydrates to maintain blood glucose during morning workouts.