Why did I just bonk on a 7 k run?

I was out on my regular lunchtime run today, regular distance (7k) regular pace (5 min/km +/- 15 secs or so), and about 20 minutes in I felt as though I bonked, my legs felt like jelly and it felt like I had no fuel. All I wanted was a pint of orange juice (with the pulp). I’m trying to figure out where I went wrong with my nutrition and fuelling.

Yesterday at 4 pm I did a 2-hour trainer ride, with several VO2 max efforts. I fuelled the workout with Gatorade (2 bottles) and Biosteel (1 bottle). Felt great, hit all my target numbers. Got off the bike and had a PBJ sandwich. Went home and had dinner probably an hour and a half after getting off the bike. At 8 pm, I had a bowl of porridge. Went to bed as normal, slept as normal.

This morning, I had three slices of toast with PB and honey at 7 am, then a bowl of 3 Shredded Wheat with milk at 9.30 am. Went out running at 11.30 am and had some sort of blood sugar crash.

Why would this happen? I’m in good shape right now and feel like I should have had a “full fuel tank”.

How did you sleep last night?

How did you sleep last night?

I slept the same as usual. I have lots of kids, so it was interrupted, but that is always the case. I haven’t slept straight through the night in about 20 years.

This happens to me about 2-3 times per year. It feels awful, but if you slow down the feeling will pass after 15-20 minutes or so. There are some threads floating around on here about similar experiences. Some sort of reactive hypoglycemia If I recall correctly. DrAlexHarrison can likely provide more input.

This happens to me about 2-3 times per year. It feels awful, but if you slow down the feeling will pass after 15-20 minutes or so. There are some threads floating around on here about similar experiences. Some sort of reactive hypoglycemia If I recall correctly. DrAlexHarrison can likely provide more input.

Yeah, I remember reading about reactive hypoglycemia, but I thought that happened when you eat within say an hour of going out running. I hadn’t eaten for two hours. The thing that is weird is that I followed my regular patterns (in terms of timing my food intake and also in terms of what I ate) but got a bizarrely anomalous response from my body.

Why would this happen? I’m in good shape right now and feel like I should have had a “full fuel tank”.
Yep, you had reactive hypoglycemia. Blood sugar crash.

Your fuel tanks were full. Full fuel tanks don’t prevent reactive hypoglycemia at all.

Fuel tanks take time to get up and running. If your muscles are all of a sudden calling for blood glucose, (as they do when you start running), it takes a moment for your liver to catch the message and start pumping it out. If your stomach was finished titrating all your shredded wheat into your bloodstream, then there was bound to be a drop in blood sugar as your muscles vacuumed up what little was immediately available.

The better shape you’re in, the more likely you are to be insulin sensitive. That 9:30am meal of shredded wheat and milk was likely in and out of your blood stream by the time you took your first step. Sometimes when you’re fit and insulin sensitive it’s wise to sip a bit of carbs right as you go out the door. Even for a simple short run. The app I just posted about has this feature built in. It’s a checkbox for “fasting before training.” It causes the app to recommend “hypoglycemia prevention mode” basically. Now, you weren’t fasted of course. But sometimes when I’m not 100% sure that I’m still finishing digestion of my most recent carb intake, I still hit the checkbox because I tend to be VERY prone to hypoglycemia symptoms at the onset of training.

Thanks for the explanation, a small cup of Gatorade just before heading out running will be my plan in future. I’m curious though - how come this is the first time I’ve had this sort of crash on a lunchtime run while using the same fuelling schedule? I know I always fuel at the same times because I am an elementary school teacher and we have recesses at the exact same time every day - I always eat a snack at 9.30 and then run at exactly 11:23!

Can be pace-dependent. If feeling good, folks sometimes push pace earlier than normal and cause this.

a small cup of Gatorade just before heading out running will be my plan in future.

Be careful. This could actually make the problem worse.

Have Gatorade with you, but a higher blood sugar level pre-run could make the problem worst.

I experience this too and never understood what it was so thank you for this concise explanation! Would a sufficiently low intensity warm-up provide time to “tap into” your glycogen stores so this doesn’t happen?

a small cup of Gatorade just before heading out running will be my plan in future.

Be careful. This could actually make the problem worse.

Have Gatorade with you, but a higher blood sugar level pre-run could make the problem worst.
If consumed in the 15 minutes prior to exercise it act much more like intra-workout fuel, and is a better preventative than taking it when you ‘need’ it after you feel blood sugar tanking. By that time, it’s too late.

I’d really recommend a big swig of it as you step out the door. In this ~60-min run scenario, it’ll keep blood sugar elevated for the duration of the run, most likely.

It’s consuming in the 25-75 or 30-90 minute window pre-workout (depending on what you’re reading) that really exposes you to massive rebound hypoglycemia. Consumption 30-60 minutes pre-workout basically means you hit your peak blood sugar as you’re starting a workout. Peak blood sugar means it was turning around and coming down whether you increase activity level or not. Pair that with the rapid pull of glucose into newly working muscle cells and you have yourself a rough first 15-30 minutes of a training session.

I experience this too and never understood what it was so thank you for this concise explanation! Would a sufficiently low intensity warm-up provide time to “tap into” your glycogen stores so this doesn’t happen?
Yes, starting lower-intensity and working into it is a good way to stave off any impending hypoglycemia. It allows your liver to keep up with the muscular pull of glucose from the bloodstream. And it allows your gut to help keep up too, if you’re ingesting carbs from the first pedal stroke / foot strike.

a small cup of Gatorade just before heading out running will be my plan in future.

Be careful. This could actually make the problem worse.

Have Gatorade with you, but a higher blood sugar level pre-run could make the problem worst.
If consumed in the 15 minutes prior to exercise it act much more like intra-workout fuel, and is a better preventative than taking it when you ‘need’ it after you feel blood sugar tanking. By that time, it’s too late.

I’d really recommend a big swig of it as you step out the door. In this ~60-min run scenario, it’ll keep blood sugar elevated for the duration of the run, most likely.

It’s consuming in the 25-75 or 30-90 minute window pre-workout (depending on what you’re reading) that really exposes you to massive rebound hypoglycemia. Consumption 30-60 minutes pre-workout basically means you hit your peak blood sugar as you’re starting a workout. Peak blood sugar means it was turning around and coming down whether you increase activity level or not. Pair that with the rapid pull of glucose into newly working muscle cells and you have yourself a rough first 15-30 minutes of a training session.

Be careful. Some cases of reactive hypoglycemia are caused by high levels of insulin in the system combined with an event that triggers insulin sensitivity (like low intensity excercise). Taking a shot of gatorade can just make things worst.

I experience this probably about once a month. However, it seems to come on more often during easy runs- I’ve never had it happen during a workout. It seems like it happens more often when I am out of routine.

Are there any health risks associated with running through this? When it happens I have found that, while it’s not a good feeling, I can run through it. Is there anything that people who experience this should be concerned about? Thanks.

Does heat make it worse?

For pretext, my typical workout starts around 3 to 3:30 pm and I have had little to nothing for nutrition in five or more hours.

A couple of days ago I had a race pace workout (9’ @ rp, 3’ rest X 4). Normally (even in the summer) this isn’t an impossible workout. Two days ago I “bonked” (or something) about 7’ into the second interval. I mean I felt like I couldn’t move and it came on out of nowhere. In minute 5 I’m feeling fine and right on rp. In minute 6 I start thinking “What am I feeling?” In min 7 I’m done, done. I have to change my route home to the shortest route and can barely jog through it.

I notched it up to it being +80f when we haven’t seen those temps in a while and I’m not heat acclimated any more.

Is this hypoglycemia or something else?

a small cup of Gatorade just before heading out running will be my plan in future.

Be careful. This could actually make the problem worse.

Have Gatorade with you, but a higher blood sugar level pre-run could make the problem worst.
If consumed in the 15 minutes prior to exercise it act much more like intra-workout fuel, and is a better preventative than taking it when you ‘need’ it after you feel blood sugar tanking. By that time, it’s too late.

I’d really recommend a big swig of it as you step out the door. In this ~60-min run scenario, it’ll keep blood sugar elevated for the duration of the run, most likely.

It’s consuming in the 25-75 or 30-90 minute window pre-workout (depending on what you’re reading) that really exposes you to massive rebound hypoglycemia. Consumption 30-60 minutes pre-workout basically means you hit your peak blood sugar as you’re starting a workout. Peak blood sugar means it was turning around and coming down whether you increase activity level or not. Pair that with the rapid pull of glucose into newly working muscle cells and you have yourself a rough first 15-30 minutes of a training session.

Be careful. Some cases of reactive hypoglycemia are caused by high levels of insulin in the system combined with an event that triggers insulin sensitivity (like low intensity excercise). Taking a shot of gatorade can just make things worst.
I think we agree here and are just in disagreement about the time course of consumption of sugar, and the resultant insulin secretion and it’s effects on blood sugar levels.

If I’m understanding you correctly, you’re saying: be wary of pre-workout sugar consumption because it can spike insulin, and having high insulin at the onset of exercises is a recipe for worsened hypoglycemia. Right? If yes, I think we agree there.

What I’m saying is, if the sugar is consumed within the 15 minute window prior to starting exercise, it’s unlikely to raise insulin appreciably before exercise starts. It takes time for the sugar to make its way from the gut to the blood, and then for the pancreas to really start kicking out the insulin sufficiently to raise blood insulin levels. As soon as exercise starts, secretion of insulin goes down quickly, and circulating insulin concentrations quickly follow (downward).

I think the timing is the key point here. And I think we’re warning against the same thing, but maybe have different ideas about how the timing of sugar consumption affects the likelihood of hypoglycemia at the onset of exercise. Right?

Just trying to find where specifically you think I ought to be more careful in my recommendation. :slight_smile:

There absolutely is an early and rapid rise in pancreatic insulin secretion in response to consumption of sugar, which is why I recommended the following:

I’d really recommend a big swig of it as you step out the door.

Doing it that way ensures that the exercise will have blunted the insulinemic response by the time the sugar makes it to the blood stream in any meaningful quantity. Exercise is a powerful antagonist to insulin production in the pancreas, and promotor of glucagon production, among other things. For a phenomenal review, read this. Perhaps you are already expert on all this, but I just never know who I’m talking with on ST.

I’m proposing consumption just as one heads out the door to solve this particular users issue because I think waiting longer might be too late to provide the needed lift to blood sugar. If one waits until 15 minutes into exercise to consume, that does carry the benefit of guaranteeing not to worsen any rebound hypoglycemia, but it may sacrifice the benefit of rescuing one from the rebound hypoglycemia symptoms they’re about to experience. It’s “too little too late” in simple terms.

Let me know what you think!

I experience this probably about once a month. However, it seems to come on more often during easy runs- I’ve never had it happen during a workout. It seems like it happens more often when I am out of routine.

Are there any health risks associated with running through this? When it happens I have found that, while it’s not a good feeling, I can run through it. Is there anything that people who experience this should be concerned about? Thanks.
Nope. No health risks as long as you’re not hitting the deck. According to both the literature and my personal experience, it feels much worse than it is. Performance is minimally affected if it’s not a terrible bout of symptoms and you stay head-strong through it. But man it feels awful and it feels so much better to just back off and let your liver & gut play catch-up for a few minutes. :slight_smile:

Does heat make it worse?

For pretext, my typical workout starts around 3 to 3:30 pm and I have had little to nothing for nutrition in five or more hours.

A couple of days ago I had a race pace workout (9’ @ rp, 3’ rest X 4). Normally (even in the summer) this isn’t an impossible workout. Two days ago I “bonked” (or something) about 7’ into the second interval. I mean I felt like I couldn’t move and it came on out of nowhere. In minute 5 I’m feeling fine and right on rp. In minute 6 I start thinking “What am I feeling?” In min 7 I’m done, done. I have to change my route home to the shortest route and can barely jog through it.

I notched it up to it being +80f when we haven’t seen those temps in a while and I’m not heat acclimated any more.

Is this hypoglycemia or something else?
Heat typically doesn’t make hypoglycemia worse. But if you’ve lost your typical heat acclimation and you happened to get hypoglycemic on top of just feeling miserable / hot / dehydrated from the heat, it can be a double whammy. Nothing like hypotension + hypoglycemia to make you feel utterly terrible. Hypotension-like symptoms sometimes occur during first exposures to heat after spending most of ones training time in cooler temps. Those symptoms are often made worse by the person reducing the intensity of exercise, but still remaining hot. (Higher intensity of exercise typically overcomes hypotension unless you’re wildly dehydrated).

So, yes, you can get hypoglycemic, also feel a bit hypotensive, then slow your pace and make the hypotension feeling worse if you’re still in the heat. This happens to a great many folks in the early spring, or whenever their weather starts to rapidly warm up. Heat acclimation has vanished over the winter, and all of a sudden it feels like they’re out of shape.

Thanks for the insight. As a non-educated person in your field of work it’s difficult to judge, but your answers seem very helpful to me.

Appreciate it.

A gel approx 10 minutes before the start of the swim is my go to

Works good for me

Thanks
.