Light headed during anaerobic workouts?

I attempted San Joaquin +3 yesterday, and had to stop about 30 minutes into the effort because of extreme light-headedness. The ride started off okay, with the workout feeling as tough as any other TR workout. But as it went on, I was feeling worse and worse and could feel my heart hammering away. I persisted through this - after all, TR isn’t supposed to be easy :rofl:

When the valley @ 32 mins finally came, I thought it’d be enough time for my heart to calm down. Suddenly, a wave of light-headedness hit me and I could feel my heart pounding, despite being it being around 150 bpm. I had to pop off the bike and lie down on the couch for a little while.

Has anyone else had a similar experience with the anaerobic efforts? Should I mention this to my doctor?

I’m more of a steady state rider, and am new to these anaerobic/VO2 max efforts apart from those in the TR plans. A few other facts:

  • I did Ansel Adams -2 last week, and excelled at it (bumping up the intensity up each set, with the final one at 143%)
  • I’ve failed a few of the general build workouts before, due to muscle fatigue rather than feeling light headed
  • I ate my brekkie roughly 45 minutes before my ride, and had some ride snacks between my efforts

I wonder if the light-headedness has happened because I’m not used to these type of efforts, and would love to hear your thoughts.

Possibly dehydrated? That’s about what I feel like when I get home from a ride 3 or 4lbs down in water.


I have felt that too.
Staying on top of nutrition with a steady flow of carbs during the session really helped me.
I my case, I think light-headedness might be caused by low blood sugars/hypoglycemia.


I get it sometimes when I come off high power too quick. I’m also prone to light headedness if I stand up too quickly after lying down for a while. Forget what it is called but my blood pressure regulation works with a bit of a delay. My solution on the bike is to keep my head low when I’m cutting back on power quickly.


It sounds like it was probably dehydration. I do my rides early in the morning and don’t drink much water before them.

Thanks for your replies!

I have had this feeling like once or twice while running. And its usually close to the absolute max HR ( ~202bpm). On a bike…could be that OR nutrition.

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It’s a relief to know it’s been infrequent for you. I’ll ask my doctor anyway - just in case :slight_smile:

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When in doubt, ask a doctor. Thats always the right answer!

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Who needs doctors when you can just ask random internet people :slight_smile:


:point_up: This.

It may also be worth having your breakfast earlier as 45 minutes is rather short to digest before a workout. I’ve heard the TR team talk about eating 2/3 hours before workouts for maximum benefit, with a banana or similar 15/20 mins before the workout too.

It’s worth playing with timings - I personally find 2 hours to be spot on for a typical 1-2 hour workout.

Good luck!


do you have a big fan going and cool temps in the room? also important along with the hydration aspects mentioned

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The thing you’re referring to is orthostatic hypotension

Bingo! This place is better than google :grinning:


I agree with this. But sadly not everyone has time for something like this.
I wake up at 5ish to wo. I cant wait 2 hours to do a 90 min ride and a 50 min run.
Last week i had the opportunity to actually wait to do my ride (about 2hrs after breakfast) and was one of the easier rides ive ever done. Yes it was pettite, but it was stupidly easy. I was doing almost 100 rpms no problem. I even though about ramping the power a bit.

I also think that 45 minutes may not be enough but that is dependant more upon what you eat for breakfast. If you are having a fair amount of protein than this will slow digestion and could have an impact on your ride. If you are eating close to your workouts than I would choose foods with less protein and more carbohydrate and get your protein after the ride.

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Ready Brek or similar quick oats are great for this :+1:

I get the same issue when I am dehydrated. An hour before your workout top up on hydration. During the workout make sure you are keeping hydrated. Use hydration fuel as well.

Someone recently put it to me, hydration is like the conveyor belt in your body conveying all the nutrients and your fuel. If your even slightly down on hydration then that fuel is slower to get to your muscles and system so it slows you down.

Also seek advice from a professional, ask about hydration strategies. Maybe get a sweat test done.

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@brendanhousler Thankfully it’s winter here, and I’ve also got a fan going. I’ll definitely keep cooling in mind as it gets really really hot here in the summer!

Thanks for all of your replies everyone! Would recommend Dr TrainerRoad Forum to all my cyclist mates :rofl:.

I’m thinking more and more that it’s to do with dehydration. I’ve stubbornly refused to use electrolyte tablets in indoor workouts (somehow I feel like it’s a ‘waste’ if I’m not riding outside). Might try to change that up in today’s workout and see how I go.

I’m mostly concerned about it being something to do with my heart. That being said, I’m in my mid 20s and think this is unlikely. And, judging from your replies it seems like this may be a nutrition thing. I’ve booked in an appointment with my doctor just in case.

Feeling happy that I’ve bonked indoors rather than in the middle of a 30 minute climb :smile:

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You can just slam a 1/2tsp of salt and chase it with some water. No need for products.

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I’ve had this happen to me in the past, for various reasons: 1) bonking (= not enough glycogen); 2) overtraining (usually accompanied by higher than normal HR at a given level of power output); 3) getting sick; 4) being hungover (= dehydration); 5) hyponatremia (= too much water); 6) hypoglycemia (= not enough blood sugar, could be a medical problem); 7) subconsciously holding my breath (or not breathing deeply enough / hyperventilating); 8) overheating (you’d notice a higher than normal HR, ~+10 bpm).

Yes, I’ve made pretty much ALL the mistakes at one point or another.

I think we can rule out bonking (workout is too short). You can probably eliminate most or all of the other possibilities based on your situation.