I'm 173 cm with about 45 kg weight (underweight). In the same ride of 30 km with short but steep uphill and downhill, if I drink coffee I tend to feel better when riding, but about two hours after the ride I would feel weak and shaking. Note that I drink about 150 ml moccachino. I don't feel like this if I don't drink coffee. Is there an explanation to this? Am I maybe intolerance of coffee? Maybe I don't eat enough? Personally I don't really enjoy the taste of anything other than moccachino.

  • As a health question this would be off topic, but as a performance question it wouldn't. Do you measure your times? Perhaps you go faster after coffee and tire yourself out, because you feel better. There's some research on caffeine and exercise tolerance, and some people tolerate exercise on an empty stomach better (sugar in your drink probably doesn't count). What do you eat before the ride? Does this differ depending on whether you have coffee?
    – Chris H
    Commented Jan 5, 2018 at 12:03
  • Could you expand on what your normal caffeine intake is, and what you normally eat during these rides?
    – JohnP
    Commented Jan 5, 2018 at 19:13
  • Caffeine used to be on the banned substances list. But that would need more than one espresso, rather some 20. Caffeine speeds up the the metabolism of sugar. That is why I think that you are more likely to suffer from hypoglycaemia (low blood sugar) after a long ride without food and considering your low weight. Have a check-up from an MD.
    – Carel
    Commented Jan 5, 2018 at 19:30
  • @Carel - IIRC, it was removed in 2004 or 2005.
    – JohnP
    Commented Jan 5, 2018 at 19:36
  • 1
    It might help to get your weight up, till you are 'just underweight' rather than 45kg at 173, that is in the anorexia part of seriously underweight. With a very low weight your body will react much more strongly on exercise and the reactions on caffeine as it has no reserves at all to cushion the effects. Seek medical help if you can not get your weight up alone, it is a common enough problem.
    – Willeke
    Commented Jan 6, 2018 at 15:40

3 Answers 3


A recent documentary on the BBC in UK covered some aspects of ingesting caffeine prior to exercise. A written summary is here:


Without reviewing the science in detail, it basically suggests that for endurance type activities, caffeine blocks receptors in the body, leading the brain to "perceive" less pain and fatigue, allowing someone to exercise longer. The article states an optimum amount of caffeine to be 3mg per kilo of bodyweight (somewhere between 1 and 2 large cups of filter coffee for average man / woman). To experience the benefit you should drink the coffee approximately one hour before starting the activity, and the effect will last for "a few hours". If you regularly drink a lot of coffee (or take other sources of caffeine), it is likely the impact will be reduced.

Your experience may just be the effect of the coffee / caffeine wearing off, plus any lessened impact due to the amount of caffeine you ingest on a daily basis.

Of course, other factors may be causing your fatigue, but your question specifically asked about effects of coffee / caffeine.

  • 1
    The article under reports the amount of caffeine necessary, and studies are a bit mixed on whether abstaining increases the effects.
    – JohnP
    Commented Jan 5, 2018 at 19:18

2 hours is about how long your body has glycogen stores for. So you're bonking because your body has used all the available glycogen.

The caffeine will be making fats easier to process instead of glycogen, theoretically leaving you with more "on-tap" at the end of your ride. But you are a scrawny wee twig and lacking in mass, so for you there is less fat available, and the bonk wall will be steep and and immediate, a figurative wall.

Your solution is to eat more while riding. Start with a gel every ~30 minutes and see how you feel at the 2 hour mark. Gels are basically easily-digested sugar slop with some flavour.

If you don't like gels, then try a square of chocolate. Break it up and freeze it overnight, and store it in a top tube bag or somewhere else not directly on your person. Chocolate is also a significant component of your drink, making it a good substitute that can go with you on the bike.

A moccachino is 2/3 cocoa and milk, with an espresso shot, topped with milk foam and dusted with powdered chocolate and optional chocolate syrup.

  • Gels can be expensive, so shop around. For brands, GU is great but spendy and has nice chocolate and espresso variants. SIS are fair priced but larger and I personally haven't found a flavour I like, and there are perfectly good cheap ones from High5/Wiggle.
    – Criggie
    Commented Jan 5, 2018 at 22:27
  • 1
    Other things to try (as some people really don't get on with gels and many others don't get on with only gels): energy drink powders; sweets (jelly babies are popular); bananas; dried fruit.
    – Chris H
    Commented Jan 5, 2018 at 22:52
  • 1
    I would have to find it again, but there was a study that suggested sucking on a sweet hard candy convinced the body it was getting more food, so it released more glycogen. I'll do some digging for that.
    – JohnP
    Commented Jan 6, 2018 at 0:56
  • 1
    I'm no fan of bananas either. It was all OK until I had to clean the remains of one off the inside of a pannier after lying the bike on it. But some people swear by them. My personal preference is a mix of gels, dried fruit/nuts and snack bars.
    – Chris H
    Commented Jan 6, 2018 at 9:09
  • 1
    You usually chose a greener banana for riding that you would chose for straight away eating, so that it doesn't go black and soft quickly. That's the trick. They are naturally wrapped, you can even eat half and keep the other half in your pocket without too much of a mess, and Id say they go easier on the stomach than man processed gels/bars, which can be bad for the belly in higher quantities
    – gaurwraith
    Commented Jan 6, 2018 at 22:38

I suggest taking a break from caffeine before riding for 2 weeks to reset the body and see how you cope with your normal mileage

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.