Reducing Basals, exercise and drops in BGS when on a bike or rowing, Need advice

Good morning,

T1 here for 42 years. I row on a rowing machine or I ride a bicycle as primary forms of exercise and do so for 40mins to an hour. If I don’t put my basal rate at ZERO during, or even half an hour prior, I end up low during exercise typically 50-60 BGS. Then approximately 1 hour later, after exercise is over, I put my basal rate back to normal and usually I end up 140-160 about an hour after. What is everyone else doing in this situation? Are you doing a temporary higher basal to deal? Are you taking a smaller correction amount to now knock down the higher BG. Yesterday was on the bike for an hour. Set temp basal at 0% for 1/2 hour prior and during ride. Still was at 50 BG with 15 minutes left so took 12 Grams of carb and continued on. Finished ride around 80 BGS and then the rise happened. Corrected at 165 BGS with half the normal correction amount, still end up bottoming out 4-5 hours later.

Can anyone who has been at it longer than me give me their routine that works? I just keep going low and dealing with it but I know there has to be a better way. Thanks for any insight.

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I think you’re having problems with exercise control mostly due to timing your temp basals. Try experimenting with setting your temp basal rate for two hours before you start the exercise. I suggest you set the duration of the temp basal for the expected duration of your exercise.

Make notes and record your results. It’ll help to zone in on what works best for you.

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Would love to help with my routine for the same situation but so far I haven’t figured it out myself. I do find that those post-exercise lows are deceptive. At least in my case I experience a pretty significant bounce-back within 30-40 min. after getting back from my bike ride, so I try not to over-treat those lows, though when you get down to 50 or below that’s easier said than done.

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I’ve been having much the same problem as @David_Eddy and I’ve been wondering if it’s because there’s a time lag involved in when the basal insulin is actually taking its effect, which means you really need to dial it in at some point ahead of the exercise. But it’s hard to know how to figure that. Is it really two hours? I.e., if I’m planning a 45-minute ride at 5pm, I should actually run the temp basal starting at 3pm and ending at 3:45 p.m.?

When I drastically reduced basals for a couple hours for a bike ride, I invariably got quite high within 30 minutes of ending the ride, even if during the ride, my bg’s were decent. I think part of that issue is that because I didn’t perfect the insulin levels, I would end up having to eat something during the rides, which while keeping me safe during the ride (and not too high, either), once the ride is over, bg’s continue to climb to levels out of my preferred zone. Now that I’ve switched from biking (too dangerous around here) to long walks, I’m better able to manage my bg’s and I should give some credit to the CGM which on some days is quite accurate–accurate enough to alert me to an impending low or high condition in time to prevent overtreatment in either direction.

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The two-hour lead time for a temp basal change works for me. The best solution, however, is for you to do the experiment, document it, and adjust as necessary. The two-hour recommendation came from Gary Scheiner, I believe. I think the peak for rapid acting analog insulin is published at 90 minutes. Since this is a change to a basal deivery, I believe leading by 120 minutes accounts for the time this small change starts to register in your blood glucose.

And yes, I set the temp basal duration for the expected duration of the exercise. Again, personal experimentation will give you the best info. Write stuff down; that always helps me.

So, for a forty-five minute 5 pm ride, I would change the basal starting at 3 pm. The caveat I offer is that I know that life has a way of interrupting even the best laid plans. A delayed exercise start will require other counteractions.

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Pehaps you should experiment with “less drastic” temp basal reductions. I’ve found a marked difference between a 100% reduction (basal off) and a 90% reduction. Some basal insulin is much different than no basal insulin in my body.

Do the experiment. Write it down. Adjust and redo as needed.

Yeah, that’s the absolute hardest problem with this whole disease. Not to mention my BG seems to react entirely differently to the same exercise at different times of day. Fortunately the times are pretty predictable when I’m using the bike for my commute. Of course then there’s the problem in the middle of a busy work day of remembering to set this. But that’s what all those different little electronic reminders are for.

Terry4, Thanks. Great advice and I will heed it. I just finished reading Sugar Surfing and clearly the mantra from that it is record, redo, record. I have been trying stuff ad hoc but not recording. I like the recommendation of not going to 100% but something less than that, and further ahead and seeing what happens. I ride late (I have a great bike light) so I am usually not hitting the road until 815pm and getting back around 930pm. Will let you know how I make out over the next couple. I am rowing today but have the same experience there so will give some of those recommendations a shot! Thanks all.

I look forward to reading Sugar Surfing when it comes out in the e-book edition. I read the free chapter 5 online and like it. I think I’ve been using some of the same techniques for a while and it’ll be interesting to see them from a slightly different perspective and context.

I do quite a bit of bike riding (actually a recumbent trike) and typically cover around 50 miles on each ride. While I don’t have it down perfectly, here is my general routine:

  1. Basal @ 50% 1-2 hours before the ride.
  2. Eat and bolus @ 50% 1-2 hours before the ride.
  3. Try not to panic when my BG is north of 200mg/dl immediately BEFORE the ride.
  4. Basal @ 0% until 0.5-1 hour before the end of the ride, then 100% (aka normal).
  5. Monitor BG using CGM during the ride, use fingerstick tests when
    stopping for a break.
  6. Consume glucose tabs and/or a protein bar for trending below
    75mg/dl, or as appropriate.
  7. Try not to panic when my BG drifts below 60mg/dl (refer to step 5).
  8. Drink copious amounts of water before during and after.
  9. After eating and before bed, set TBR to somewhere between 70-90%
  10. Pay close attention to CGM trending, adjust as appropriate.

Lately, I have been considering adding some protein to my before riding meal, maybe peanut butter or eggs. This is mainly because, I still go low during most rides and I can keep pedaling for quite some time @ 50mg/dl as long as I have taken some aggressive treatment to bring my BG up.

(Edited to fix numbering)

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I’ve been riding a bit longer lately, gearing up (and down…) for the Tour de Cure in Chicago this weekend, 60 miles in 3 1/2 hours or so was the last longish training ride. I’ve also been riding my bike to work when I can fit it in and the weather cooperates.

I like to try to eat early. If my CGM is cooperating, I’ll bolus while in bed when my alarm goes off at 4:00 AM, or maybe a half bolus to get a head start on DP and breakfast. Sort of play it by ear, putz around and then head downstairs to get breakfast going and confirm where my BG is, maybe calibrate if things are in order. Usually after 1/2 hour, the correction will be pounding and DP down and I can get away with cereal. Then I get the other things together and leave by 6:30 or so. I will fuel the ride to work 12 miles but there are quite a few hills for IL on the way, as there’s two branches of a river to be crossed so it’s not totally fast and I ride my hesher/ commuter bike rather than my faster road bike. If my BG needs a boost, I’ll try a yogurt as that works fast but really keep an eye on IOB so that it’s gone or mostly gone but also watching out for cereally spikes. I have a CGM so I have more keeping an eye on it on the way and just kind of go with the flow. I have a messenger bag with my lunch, meter, etc. and have Smartie/ Jelly Bean mix stuff I use for lows if I need a boost. It’s pretty cardio but there can be annoying commuter adrenaline encounters, occasionally needing to have my middle finger administered for the accelerate past and then turn right without a turn signal sort of maneuvers but mostly it’s pretty much fun.

On the three hour rides, I also have been pregaming with a yogurt, will ride 20-30 miles and then have 1/2 sandwich, about 20G of carbs and have the other half another 15-20 miles later, no bolus and that worked pretty well. On the Tour de Cure last year, I ate sandwiches at most of the stops. I don’t recall the exact pattern but I’ll see if I can have a better record of it this year. For scientific purposes. I’m seeing Dr. Ponder’s Chicago presentation the day before.

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YogaO, acidrock23:

Thanks to you both.

So last night I rowed rather than cycled. I end up dropping basal 90% for 1.5 hours prior and then kept it dropped at 90% for the 40 minutes of rowing. The CGM started going nuts with 15mins left saying I was 55 which I wasn’t buying so I rowed on. Got off and tested and I was 80! Awesome, very happy. Stopped the temp basal and then when back to 100%. Then things went crappy. At 12am, BG was 156 which I corrected. I was worried about lag effect of the exercise so the pump suggested .85 but I only took .50, which was probably a mistake. Was 139 at 3:50a and took another correction, pump suggested .65 and I took .50. All was good in the am. Gentlemen, if nothing else, I feel like I am close. I think I need to attempt upon finishing putting a temp basal that is somewhere in the neighborhood of 110-120% of the usual. Seems that for me that temp basal of 90% less than the usual for the extended period pre exercise and then during is just too little insulin for later, regardless of any lag effect. My sensor this go round has been off by 30 or so which has been particularly annoying.

Acidrock23 good look with the Tour de Cure. I keep meaning to do it and hopefully will do it next year.

I 100% think you will find a lot of it that you already do, minus the surf analogies. I think the 1 coolest take away I took from it was knowing what your insulin lag time is pre-meal and eating at the bend in the cgm data, ie when the insulin starts taking effect vs some pre-prescribed wait half an hour or something. My insulin at least in the am really doesn’t start kicking in for 45 minutes. I have just started to now bolus and wait for it and my post prandial rise is definitely less. I really liked his perspective that he gives. It is a pretty fun book to read.

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That’s a pretty good result overall that you can definitely tweak.

I find that one of my exercise classes that uses light weights, but lots of reps, requires me to lower my basal before and during the exercise and then increase to 130% for 2-3 hours afterwards. I would think that rowing could be similar.

Really useful to see how you and others are fine-tuning this stuff while I’m trying to do the same. This afternoon’s homeward bike ride is going to be my first try at doing the temp basal in advance. We’ll see how it goes. I’m needing to be cautious because these afternoon rides have a much more severe hypo effect than the a.m. ones, and also more severe than when I was riding for pure exercise a little later in the evening. I’ve also been having trouble controlling post-lunch peaks, so I’ve had correction boluses to deal with. For example last night my pump calculated I had like 0.85u IOB when I started out, so I ate about 20g carbs, and still ended up down around 60 at the end of the ride. When I just go for an exercise ride a little later in the evening, having driven to work, the lows haven’t been so problematic. It seems to work out best with BG around 130 at the start and after a 50-minute ride it usually ends up tolerably north of 70 at the end, just in time for dinner. That’s what I’m shooting for if I can just get it to work the same way an hour or so earlier!

On edit: I’m also trying the eat-after-the-bend technique today. I’ve been trying to push my boluses earlier but I haven’t actually waited to see the drop start in my CGM before. I’m aware of needing to be careful, but it makes sense to me. Humalog seems to take about 45 minutes to really get going for me, so I just bolused for my expected lunch carbs. We’ll see how that goes as well.

I think that depending on a number of factors, the primary of which is the GI of what you are eating, this could be a bit dangerous. My anecdotal experience to date is that eating at/after the bend is too late and I will have to chunk in some glucose tabs (or some additional fast-acting carb).

Edit: I am actually having this problem as I type this -argh!

Totally agree, and I’m doing it with an eye on my CGM today. Probably what I really need to do is always bring my own zero-carb lunch, but I’m a lazy s.o.b., and I like to allow myself some carb leeway when it comes to that meal, even if it’s just a couple of pieces of bread with a sandwich from one of the food trucks. Just about any prepared foods seem to end up having a lot more sugar and fat in 'em than you expect. So I’m hoping that if I give the bolus a little more of a head start that will level things out without having to do a correction or dual-wave bolus, so I end the day with my BG high enough for the bike ride with no IOB.

I mean, it’s either that or resorting to something radical, untested and probably dangerous to my emotional well being, like changing my lunch habits. It may come to that in the end, but baby steps, people, baby steps…

I find that my insulin resistance is highest in the morning. When my CGM starts to bend after my breakfast dose, it gently trends downward at a slow rate. It this slowly sinking action that allows me to eat breakfast 60-75 minutes after dosing without an immediate low post-meal. I find that I can eat dinner with as little as 15 minutes insulin lead time with good post-prandial CGM action.

We’re all aware that the CGM lags fingersticks. For me it lags 15-20 minutes. Perhaps it would be a good idea to do some experimental fingersticks when you think the bend is occurring and then time starting your meal based on that instead of waiting for the CGM down-trending bend. I know it kind of calls into question the usefulness of the CGM but once you do the fingersticks you can learn that your bend occurs x-minutes after dosing at this time of day. The CGM can then be used to confirm this tactic.

The pump’s IOB calculation is directly impacted by the duration of insulin action (DIA) selected at set-up. Over the years I have found that 3 hours is much too short for my personal DIA. There are tests for this but I’ve read the medical literature and now set my DIA at 5 hours. For me, this DIA then yields IOBs that work better to avoid unintended insulin stacking and a ticket on the gluco-coaster.

There was an extensive thread on duration of insulin action a while back. My memory is that most people are probably erring on setting this parameter too low. Then throwing in an aggressive exercise period into the mix amplifies that error.