Can Exercise Make You Sick?

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After Saturday’s triathlon, I was riding high.  I was SO ridiculously proud of myself and felt on top of the world.  My plan was to come home, eat a hearty lunch, and take a long nap.  Unfortunately, sleep never really happened.  The Husband needed to run some errands, and Henry wanted to play.  I didn’t get to ‘recover’ the way that I wanted to, and 12 hours later, I started to feel sick.  Body aches, a runny nose – the symptoms eased up Sunday morning, but after a busy day, the illness came back full force.


Exercise is, of course, good for you in a number of ways.  One benefit of exercise is that boosts your immune system and helps prevent illness.  In fact, exercise actually increases the production of immunoglobulins (antibodies that attack illness on a cellular level).  Exercise also boosts the production of natural killer cells, which fight cancer.  (Source)

The key, however, appears to be exercising in moderation.  Moderate exercise is usually define as 30 – 60 minutes of, well, moderate effort five days a week.  Intense exercise is more than an hour of exercise at near maximum effort.  Interestingly enough, intense exercise actually suppresses the immune system.  The suppression can last anywhere from a few hours to several days; the length of the suppression seems to be directly related to how hard and how long you engage in exercise.  That’s why many people catch colds following a marathon and – I’d wager – why I’m feeling so sick after Saturday’s triathlon.


Here’s a summary of a rather interesting experiment that illustrates the point:


Scientists from the University of Illinois and other schools first infected laboratory mice with flu. One group then rested; a second group ran for a leisurely 20 or 30 minutes, an easy jog for a mouse; the third group ran for a taxing two and a half hours. Each group repeated this routine for three days, until they began to show flu symptoms. The flu bug used in this experiment is devastating to rodents, and more than half of the sedentary mice died. But only 12 percent of the gently jogging mice passed away. Meanwhile, an eye-popping 70 percent of the mice in the group that had run for hours died, and even those that survived were more debilitated and sick than the control group.  (Source)

Furthermore, one study found that the mortality ‘sweet spot’ for running is about 15 miles a week.  Researchers found that runners who completed 15 miles a week had the lowest all-cause mortality rate; runners who ran greater distances had a higher mortality rate (it’s worth noting all runners had a lower mortality rate than non-runners).  The research author said that:


Our paper on the potential dangers of excessive endurance exercise is meant to shed light on a largely underappreciated risk of extreme exercise such as marathons and ultra-marathons. Over years to decades this type of prolonged strenuous running can take a toll on cardiovascular health, in essence causing premature aging, scarring, stiffening, thickening of the heart and blood vessels.


Does this mean we should entirely avoid intense exercise?  Well, not exactly.  It does mean that if you’re just concerned about the health benefits of exercise, you can rest assured that there’s nothing ‘wrong’ with sticking to moderate exercise, both in terms of intensity and duration.  If you find intense events fun, that’s okay, too.  Just be wise about how frequently you do them and how you train when you’re already feeling under the weather.  Occasional intense exercise isn’t necessarily bad for you – you just need to be smart about it. 

The biggest takeaway?  Rest days are very important, for both muscle and for immune system recovery.  And after an intense event (like a marathon or triathlon), be extra careful about getting enough sleep, eating nutrient-rich foods, avoiding sick people, and washing your hands.  I don’t know about you, but I’m always looking for a good reason to nap, and now I have one!


Have you ever gotten sick immediately after a big race?



  • Beks August 27, 2012, 1:31 pm

    I’ve never run a race before, but last year, when my office started doing a Biggest Loser program, I was working out a lot that first week, but I got really sick really quickly (upper-respiratory), so I “took a break” (ie, didn’t work out again for a month), and blamed it on my sickness. I think it was just too much too fast, but now I’m taking it easy and working on getting better endurance.

  • Cait @ Cait Strides August 27, 2012, 1:33 pm

    Yes! After my last half-marathon (in which I PRed), I never got a chance to sit and rest before making a 4 hour drive home. I felt so sick by the time I got home that I actually threw up, which is something I never do! I felt “off” for the next 2 days.

  • Anne August 27, 2012, 1:37 pm

    Very interesting, thank you !

  • Lauren August 27, 2012, 1:40 pm

    I did a ridiculous 25k trail race on Saturday. I took Sunday off but thought I’d feel ok riding today. After 15 minutes I got a flat tire and was forced to stop. I think the universe was telling me to take another rest day and let my body heal 🙂

  • Katie @ Talk Less, Say More August 27, 2012, 1:42 pm

    I hope you feel better soon!!

  • Jennie August 27, 2012, 1:42 pm

    Poor mice 🙁 What an awful experiment.

  • James August 27, 2012, 1:43 pm

    Recovery after such intense exercise as a triathalon negatively impacts your immune system, temporarily. You’ve worked your system hard, and now it’s busy repairing the damage and not fighting off invaders. It’s pretty common to come down with a cold or such after a marathon or other high intense or endurance events. You’re very right about rest days. They are just as important as training days.

  • Jenny August 27, 2012, 1:44 pm

    Very important post! While exercise is of course healthy, pushing yourself too hard is definitely unhealthy.

    I was on the verge of having a bad cold in June and decided to ignore it and run a 5-miler in the summer heat in NYC. I felt OK during the race, but 24 hours later I had a high fever. I ended up being sick for about 4 weeks with a sinus infection. Would it have happened anyway if I hadn’t run the race? Who knows, but I don’t think my body was happy with me that day. It’s hard for me to let go of the commitment aspect of it though, like, “I signed up for this race, I committed to it, I have to go” etc. etc. Work in progress.

  • Becca August 27, 2012, 1:47 pm

    Interesting and under-discussed topic in HLB world, I think.

    Recently, I was diagnosed with endometriosis, which is a huge mystery disease, in that doctors don’t know what causes it or how to fix it. There is a lot of trial and error in dealing with it. What I’ve found is that when I’m doing fairly intense exercise on a daily basis, my symptoms are actually worse. Unfortunately, it’s hard for me to get out of the “work more/work harder” mindset. I think it’s definitely true that intense exercise actually ISN’T always the best thing for our bodies. It can put your body into stress mode, even if you do rest properly. Now I just need to work on practicing what I preach…

  • Annette@FitnessPerks August 27, 2012, 1:49 pm

    This is SO true! Too much of a good thing actually can end up being a bad thing 😉 I also think there are ways to help the immune system out though–like resting right after the intense activity, lots of massage, sleep, good meals, and more sleep 🙂

    After my Half IronMan on Saturday, I had a mini massage, I slept for 12 hours that night, and drank a ton of water & tried to refuel well. I feel pretty awesome, and am so glad I didn’t get sick!

  • Rachel August 27, 2012, 1:50 pm

    Interesting post! I will definitely say that this has applied to me. When I was working really hard on losing weight over the course of a year and exercising extremely hard most days of the week, I was sick constantly. I got more illnesses that year than I ever did in my entire life. And they were all different kinds too: strep throat/other respiratory illnesses, I lost a toenail, I had a bunch of bladder infections, etc. My immune system was definitely suppressed during this time. After I finished all of my weight loss and scaled back on the frequency of intense workouts, I stopped getting sick all the time.

  • Laura @ Backstage Balance August 27, 2012, 1:51 pm

    I like running races and have definitely noticed the illness issue pop up post-race or post-long run. Most recently, I got sick while on vacation, interestingly enough the day after we hiked 10+ miles each the previous two days. I’ve learned to train intuitively, taking rest days more liberally if I’m feeling “off.” Eating clean + lots of veggies + vitamins are good, too.

  • Carina August 27, 2012, 1:53 pm

    Reading this post, as well-written as it is, unfortunately the only thing that sticks with me is how horrible and cruel it seems to have done that to those rats. I hate animal testing. It makes me sad.

    • Whitney August 27, 2012, 2:45 pm

      I thought the same thing! 🙁

  • Sam @ Better With Sprinkles August 27, 2012, 1:56 pm

    That’s an interesting thought – I’m sure a lot of people think the more exercise = the healthier you are.

    Just proves that rest days are so, so important.

  • Angela @ Eat Spin Run Repeat August 27, 2012, 2:06 pm

    Firstly, I know this is late but CONGRATULATIONS on the race!! Sorry to hear you quicky fell under the weather though. I think moderation indeed is key, and although I’ve never been sick immediately after a race, I have been dealing with 2 injuries (one is now gone, thank goodness!) for the past 4 months. I’ve currently got a sprained SI joint which I did mid-half marathon, and the recovery is pretty slow. However, I’m thankful that I can do pretty much any other form of cardio except running, so while learning the lesson that moderation is key, this situation is also forcing me to get creative with my workouts.

  • Ali August 27, 2012, 2:17 pm

    I switched from walking 30+ miles a week (sometimes 13 miles a day on the weekends) to running 15-20 miles a week + weight lifting 3-4 times a week earlier this summer and I was ALWAYS sick. Always. You name it – heartburn, aches, fevers, stomach issues, sinuses, puffy/achy joints, fibromyalgia flare-ups, headaches, etc. About three weeks ago, I switched back to walking (my body just couldn’t take the stress anymore) and I have been feeling a lot better. The majority of those symptoms went away. It’s interesting that I can walk that much and feel great but run much less and feel awful – guess my body cannot handle the intensity! Oh well….

  • Julie (A Case of the Runs) August 27, 2012, 2:19 pm

    Just did… ran a half last week, rushed to the airport for a business trip, went from 90’s weather to 50’s and windy without adequate sweaters, ate suboptimally, and bam. Hah.

    I rarely get sick (it’s been close to 2 years since the last time), so I am pretty sure this was the cause.

  • Brigid August 27, 2012, 2:40 pm

    I’ve never done a race bigger than a 5K (or a swim meet where I did no more than 750 meters), so I can definitely say that no, I haven’t gotten sick after one. I do, however, make sure to take a day or two off from working out if my immune system is feeling compromised.

    I also wanted to let you know that I was trained to be a GOTR coach on Saturday. Your posts about the program totally inspired me, and I can’t wait for the season to start in two weeks!

  • Elizabeth M. August 27, 2012, 2:55 pm

    This used to happen to me ALL THE TIME. I would be super stoked for starting a new lifestyle, go into it 100% and then get sick. It was very frustrating. I was just doing too much too soon! After my first spin class I was sick for a few weeks.

    BUT, once you stick with it and do include that moderat intensity workouts, it makes a huge difference. I’ve been doing really wll not getting sick for close to 5 motnhs now 🙂

    Hope you feel better soooooon!

  • Stephanie August 27, 2012, 3:04 pm

    Come to think of it, I did have a problem breathing and developed a bad cough after my
    First half. I think it was definitely affected by my breathing during the race. Bummer!

  • Michelle@Peachy Palate August 27, 2012, 3:07 pm

    Interesting stuff! I guess in some ways it might be related to the adrenalin and build up to the race. The same happens to people with other events and occasions… you’re not sleeping properly and you don’t even realise it sometimes! Great post!

  • Kelli August 27, 2012, 3:15 pm

    I’ve been sick for a couple of days after both half marathons I ran. Even on my longer training runs, it is pretty normal for me to feel slightly sick to my stomach for the rest of the day. One of my goals in life was to run a half though, & now that I did 2 I don’t know that I’ll ever try another one. I enjoy shorter more intense cardio workouts & weight lifting much more, & don’t get sick from those things. Win win!
    Hope you feel better soon.

  • Katie (Goober Nut's Life) August 27, 2012, 3:18 pm

    Such a good post! Kind of needed to read that, I think, because I’m almost always trying to do intense exercises, thinking that it’s good for me, but reading this really opened up my eyes! Thanks for that! 🙂

    Hope you feel better soon!

  • Kathleen Ojo @ Onward; Inward August 27, 2012, 3:32 pm

    Very interesting study! I knew this already from experience – every time I start exercising after a break, I get sick. It never fails. Before I got pregnant I had been working out intensely for over a year and never once got sick, and was extremely healthy while pregnant too (I kept working out, just not as intense, and no running). I just started my exercise routine back up again now that I’ve had the baby, but I feel really sick after every intense session! The first time I ran, I woke up the next morning congested with a swollen throat and headache. At least I know that I just have to work through it, and once my body gets used to the intensity my immune system will rebound. I hope you’re feeling better!

  • Jess August 27, 2012, 4:15 pm

    I’m marathon training right now. I understand the bummer that is no naps after the long run or in your case the tri. (congrats by the way) I ran 19 miles yesterday and not a nap to be found. Welcome to the new life of being a mom/being in training, etc.

    The only time I’ve gotten sick while training was when I was overdoing it. When I try to do too much too fast. Maybe your body is telling you that it isn’t ready to races just yet. That’s totally ok. No one is going to judge you for stepping back. You have zero to prove to anyone other than yourself.

  • nutkin August 27, 2012, 4:28 pm

    another interesting tidbit on the subject . . . very intense, prolonged exercise cause your body to produce proteins called cytokines in order to fight inflammation. cytokines are also fever inducers, which explains why some people come down with flu-like symptoms after a hard, long race. i know i’ve had that happen a few times! it’s usually in the evening of race day and i start getting a fever and chills, which disappear by the following morning. kind of scary, but it’s just your body’s way of repairing itself.

  • Kylie @ immaeatthat August 27, 2012, 4:33 pm

    I’ve only run ONE marathon for that exact reason! After the marathon, I had body aches, congestion and terrible GI issues for about a week. My body just didn’t handle it well. I don’t think I’ll ever run one again. But then again I have this tiny itsy bitsy voice in the back of my head that wants to qualify and run the Boston Marathon. I’d think I’d endure a couple colds and awful GI issues for the chance to check that off the bucket list.

    And I’d never heard about that “mortality sweet spot” before. Very interesting:) I really enjoyed this post! I don’t know how you find time in the day to bring us all this wonderful information. You’re an inspiration!

  • Kristina August 27, 2012, 4:47 pm

    I finished my first half-IM at the beginning of August and then took an exhausting trip right afterwards. I fully expected to get sick right after the tri, but instead got sick at the end of the trip. It seems crazy but I think my body somehow KNEW that I (it) was going to be able to deal with being sick for a few days at the end of the trip and held out until that point.

  • Silvia @skinny jeans food August 27, 2012, 5:18 pm

    Dear Caitlin, honestly, on the weekend I thought you were a tiny bit..well, crazy… having just had a baby, moderate to not too much training, but doing a (small) triathlon. Triathlon??! — I think we all have our ‘energy’ that can be spent on ‘life’ — physically, intellectually, emotionally, and if something major happens this event consumes our supply. If we are not gentle enough with ourselves to keep this ‘supply’ above a certain (feel good) threshold, but wear ourselves out, the immune system get affected… and we get sick. We can get very sick. This can be too much stress, a death in the family, it can be marriage but also a divorce, a new baby, any major change in life circumstance, … we needs this energy to cope and to adjust. This is not the time to pack in too much it or prove anything. Gentle, gentle, gently — you deserve it (just like Henry).

    Otherwise, we end up like the poor rats.

  • Melissa August 27, 2012, 6:06 pm

    I am usually very healthy and rarely get sick but last year after my marathon I was completely down for the count just 1 day later. It was AWFUL and I stayed sick for several days (though no fever, so I didn’t miss work). I have vowed not to get sick after my marathon in October. I don’t know if I can totally prevent that but I will certainly try. Though now that I think about it, the aid stations are probably pretty “germy” places and I can’t exactly avoid that, so we’ll see!

  • Lauren @ The Homeostatic Mindset August 27, 2012, 6:40 pm

    So sorry to hear you’re not well- that is NO fun with a baby! 🙁

  • Katie @ Peace Love & Oats August 27, 2012, 6:41 pm

    Oh dear, I hope my parents do not get wind of this! Haha they already think that me training for a marathon is a bad idea!

  • Wendy August 27, 2012, 6:46 pm

    I have. A couple years ago I ran a half marathon at a very fast (for me) pace. I ended up passing out at the finished because I pushed myself so hard (uh, not smart). Then, the week after the race, I came down with a case of bronchitis. It was awful.

  • Samantha @ Mama Notes August 27, 2012, 7:08 pm

    I think it can! I did crossfit once and worked out so hard I could hardly drive home afterwards, I was just so out of it. It was my first crossfit workout and I just overdid it, but anyways, I got a really bad headache the day after that lasted for 3 days and I think it was from exercise.

    • Antoinette July 31, 2015, 10:22 am

      After being under extreme stress for several years health issues caregiving for a terminal mother I had finally got back to the gym… My trainer had me do a full 90 min hard workout and since then I’ve had headaches nausea muscle pain beyond pain… I think I ripped and tore all 830 muscles in my body! Several days later I’m. Still in crazy pain and toxins that made me sick! I don’t feel much like eating I just want to take it slow! Everything hurts so bad!!! I need to be able to work out and still do my job. And caregiver for my family! How long will this last and or will it pass??? It’s been 5 days now… Help!!!!!? Thx Antoinette

      • Caitlin July 31, 2015, 10:24 am

        You need a new trainer. That was incredibly dangerous of that trainer to do to you – he should’ve eased you back into it. Eat healthy foods and drink water and try to gently move your body by going on a walk or something. It will pass!

  • Amber K August 27, 2012, 7:42 pm

    I have gotten sick during exercise before, but I think I almost always was probably feeling a touch of it before I even started. Which is why I can’t ever say the phrase “I’ve never regretted a workout” because I soooo have.

  • Molly @ RDexposed August 27, 2012, 7:42 pm

    A rat running for 2.5 hours? I may volunteer for death in the situation.

  • Lindsay August 27, 2012, 7:59 pm

    So funny you posted this today – I did a 5k on Saturday that I didn’t train for in the slightest (not even one day… yikes), and then went to work as a bartender for 9 hours directly afterwards. I felt like I was dying on Sunday, and I still feel pretty awful today – fever, chills, headache, just “off.”
    So yeah… glad to know it’s not just me. 😉

  • Catherine August 27, 2012, 7:59 pm

    For a couple months of my life, I’m pretty sure that I was addicted to running. Maybe it was the endorphins or something, but I would run EVERY single day after work for 90+ minutes. I didn’t get sick or anything, but I became anxious and extremely moody… almost as though I was producing an excess of adrenaline all day long. I thought it was so odd because exercise is supposed do the exact opposite, right? When I finally settled down and started exercising more moderately and taking rest days, I started to feel the more positive mental effects associated with exercise. I really believe that even the healthiest habits can become very unhealthy if done to an extreme. I also think that “moderation” is relative to an individual person’s level of fitness. Right now I’m also getting back into exercise after having a baby so my idea of moderation is not the same as it was a year ago.

  • Katy August 27, 2012, 8:49 pm

    I ran my first half marathon two weeks ago. I felt good suring the race (besides going too fast in the beginning and needing to slow down. After the race I felt fine, drank water and Gatorade and ate some crackers. Once I got home and showered I went to make lunch and all of a sudden felt horrible. I didn’t want to eat or drink anything and I was nauseous. That afternoon my husband called a nurse line and they told him to take me to the ER. I reluctantly went and I was treated for dehydration….they didn’t know if it was from the race or if was sick but addrenaline delayed me feeling sick. I also had a high white blood count so I had to get a ct scan to make sure I didn’t have appendicitis (I didn’t). Then the next day I got a sinus infcction. Needless to say I am really scared to ever run a lond distance again. 5ks and maybe some yoga are in my future!

  • Alett August 27, 2012, 9:53 pm

    I had the opportunity through my running club to run the Boston marathon in 2010. My family came down from Canada to support me (not necessarily a good thing). Needless to say between the family drama and the marathon itself I came down with a wicked sinus infection just days after the marathon. My first ever. Plus! I managed to burn the roof of my mouth really badly with balsamic vinegar/olive oil mix. It was the appetizer at the restaurant we went to post race. I guess my mouth was really dry from all of my panting over the 26.2 distance; when I went to take my first bite of bread with the vinegar mix it burned the roof of my mouth – the doctor could believe how awful it looked when I went to see her about the sinus infection! LOL

  • Emily @ Perfection Isn't Happy August 27, 2012, 10:35 pm

    I wrote a post about this a few months ago! I do believe that exercising too much can make you sick! Hope you’re feeling better!

  • Lea @ Greens and Coffee Beans August 27, 2012, 11:22 pm

    I always get sick after exercising in the cold. Maybe because of the suppressed immune system thing? I didn’t know that happens but it would definitely explain it. When I was younger my dance studio would participate in Christmas parades and I would always get a horrible cold after! It never failed.

  • Ashley August 28, 2012, 5:51 am

    I read this yesterday and woke up with a sore throat today! Ironic? Kind of.

    Guess those 50mi weeks are catching up with me…but taper starts next week. I’m so close!

  • Angie August 28, 2012, 7:26 am

    My parents trained to WALK a marathon a few years ago, and, as you can imagine, they spent many hours training. They would do a multi-hour training walk on a Saturday morning, go home and shower and then host a tailgate party for a college football game! During the training, my mother got every virus that went around and was frequently sick for longer than she should have been because she insisted on continuing to train through the illnesses. After the race she got a sinus infection and was sick for weeks.

  • Catherine August 28, 2012, 8:58 am

    Good gracious, I needed to hear that today! The last few weeks I feel like I’ve been running myself into the ground with exercise, and I just feel tired, and my muscles aren’t recovering well. Last night I decided I absolutely need to take a day off and let my body recover. I slept in late this morning (haha, is it sad when 8 a.m. becomes “late”?), but sitting here eating my breakfast I started thinking, “I could maybe just lift some weights then go for a short walk…” Then I read this post, and it was just the confirmation I needed to actually take the day off from working out 🙂 Thanks!!

  • Amanda K. August 28, 2012, 1:08 pm

    Wait. I have a question. Since you’re still nursing, how did you sleep 12 hours?
    Weren’t you incredibly engorged and too uncomfortable to sleep?

    • CaitlinHTP August 28, 2012, 1:09 pm

      I got up for pumping 🙂

      • Amanda K. August 28, 2012, 1:11 pm

        whew. ok. i was like, TELL ME YOUR SECRET!!!

  • Ellen @ Wannabe Health Nut August 28, 2012, 2:03 pm

    I rarely ever get sick and can’t remember the last time I had the full-on flu. (Knock on wood!) Perhaps my “everything in moderation” rule is helping me more than I thought. Sooo…does this mean I can go eat an ice cream cone now?! 😉

  • diva d January 27, 2013, 12:45 pm

    Thank you for posting this. I thought I was losing my mind and that I was the only one that got sick after they started exercising.

    I am 47 and 100 pounds overweight. I’ve worked out before and been fine. But I started with a new trainer, doing weights and cardio – a lot with my body weight as the weight – and have gotten sick EVERY time I’ve started to do the program. This has been going on for 2 months. I start to workout, get a sinus infection, am laid out for 2 weeks, and try to start again only to get sick again. I’ve been on 3 courses of antibiotics since December 10. I will start more slowly this time, I guess? I don’t want to give up – I HAVE to get healthy.

  • Dave February 24, 2014, 4:02 pm

    I’ve had this issue for at least 15 years. Every time that I stop exercising for a while and then restart, I get sick (minor cold). This of course makes it difficult to continue exercising, so it often ends there. But I’ve also pushed through it a number of times and eventually I’m fine. As for my most recent episode (beginning 6 days ago), that’s different. I had stopped working out for about 4 months and decided to really jump-start my exercise by getting personal training at a reputable fitness chain that does only personal training. That started 4 weeks ago. I pushed myself as hard as possible during every session (3 times a week). I have a high tolerance for pain, so I basically would do almost every set until exhaustion. 6 days ago I got shingles…and I’m only 43. The doctor is pretty convinced that I just lowered my immune system so much that the virus kicked in.

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