Running - will it lower my biking fitness?


I have been running for almost a month now. I do two 1 hour runs(~10km - mileage) per week and I run to maintain my bone density instead of going to the gym which is shut as of now. I really feel much better off the bike after I started running.

My FTP is 302W which puts me at 4.1w/kg. I have completed sweetspot base low volume 1, sweetspot base low volume two and I am currently in the 6th week of short power build low volume. Before I started running, I used to do endurance rides on those days which I currently run. Those endurance rides would be 1 hours and 30 minutes to 2 hours in length. My heart rate while running at an endurance pace is more than 150bpm which is 10bpm higher than my heart rate at my power zone 2. The question is, will I loose my biking fitness if I continue the runs. I plan to do a 2h30m to 3 hour endurance ride every week. I also have no issues completing the planned workouts. They are getting tougher as I am nearing the end of my short power build as each workout is taking a lot out of me. I have never done any anaerobic capacity training before so that is why I am probably saying this lol

Quite the contrary for me personally. I did 18 TR workouts between Jan 1 and April 1 while training for a marathon. My bike workouts were specifically threshold progressions so that I’m sure had an impact. Never did more than 2 T workouts a week. If I managed a 3rd one, it was pettit or mount field. Hell sometimes I did 1 T workout a week.

My FTP went from 290 to 311(4.5w/kg)

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Running itself isn’t going to lower your biking fitness. But if you’re replacing bike workouts with run workouts so that your bike volume is now lower, then yes you will probably lose some bike fitness. And if the running starts to interfere with your recovery and mean that you aren’t as fresh for key bike workouts then that will also lower your bike fitness, or at least hamper you from making the gains that you would have done otherwise.

If it’s a bit of extra running on top of the biking you were previously doing, and it’s not interfering with the quality of your bike workouts, then it won’t cost you fitness and might gain you a little bit of fitness (and maybe body composition improvements) simply through doing more aerobic exercise. But adding a bit of extra biking instead of extra running would get you even more bike fitness :wink:


Anecdotal, but I stopped running for the second half of my last build phase. Usually did a 5k once a week before that. Started getting sore knees, playing with bike fit (went back to what I had started at in the end as nothing helped), contemplating shorter cranks etc. Went for an easy 5k run day after ramp test and next workout bam no knee issues.

I’ve looked around and seen other anecdotes about it helping people. I think it strengthens some of the muscles which don’t see much activation during cycling but which assist with maintaining a fluid pedal stroke.

So I’d say, might it impact your “biking fitness”? Maybe. But like you noted it also helps with bone density, and for me at least it seems to help with injury prevention on the bike, so even if it slows my progress a tiny bit versus doing more endurance rides with that time, I think it’s worth it in the long run.

I used to run decent marathons (2:47) - and now time trial - I found that long distance running helps your endurance in winter but did nothing for your FTP - probably because as mentioned you have to lower the volume cycling and can’t do as many threshold/vo2 bike sessions. I then stopped running and my TR FTP is now 300W @ 60.5 kg - as I am still a small runner. I am 51 and as mentioned would like to maintain bone density - went to the gym but they are currently closed so I have started running again for this and for some lockdown variety. I am going to cap it at 30-40mins though. No more 23 mile long runs on a Sunday morning. I think this is a good compromise for maintaining bone density and variety but not compromising my main sport - that said it comes back pretty quickly and I am already back running 4+ miles in 30 mins so it doesn’t take much of my time due to my running background.

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Interesting… I don’t have any issues slowing my progression as this is my first season of structured training. I am just 19 and I have plenty of years to make those gains I believe. As of now, running is not impacting my trainerroad workouts and I don’t reduce the workout intensity. Two 1 hour runs per week is keeping me motivated as of now. Overall, I just feel much better off the bike when I run.


I’ve just started running, I do a mile on monday (rest day) and this seems to lesten the shock to the system of my second run which I do in the morning of my easy day (wedneday) doing the easy tr session in the evening , I then do my hard session on the evening of the thursday, does seem that any ache from the running doesn’t stop the threshold workout that I usually do on a thursday

I think the heavier you are, the more detrimental running can be on your cycling fitness. This is because running beats down heavier riders more than lighter riders. I enjoy running but at age 52, 166 pounds, and 5’10", I keep my runs short and easy if I have a hard cycling workout the next day. If I do a hard run my cycling legs are always heavy the next day.

Here’s a mostly useless anecdote to muddy the waters a bit. I was an avid runner for several years, putting in about 40 miles a week and racing several times a year. Repeated running injuries pushed me give up running and start cycling, and I rode almost exclusively outdoors for ~5 years while doing my best to maintain some structure. When I was in good cycling shape, my FTP was in the 240-250 range.

Before starting TR in late 2019, I started running again (two 40-minute runs a week) and added some strength training (two 20-minute sessions a week). My first TR ramp test put me at 205 watts :sob:, and it took several weeks before I saw any increases. After 6 months of pretty faithful TR workouts, my last two ramp tests put me at 225 and 220 watts.

It’s hard to draw firm conclusions about the effect that running has had on my cycling fitness since I have changed several things in the past year. My FTP is lower, so at least by that measure I am a less fit cyclist. But I love the more balanced fitness I get from having running and strength training in the mix. And with the analytics from tools like TR and, it’s clear that my current cycling training is much better targeted to the goals of each workout than what I did in the past (i.e. I think I had some holes in my fitness that I am slowly filling in). So I expect to continue to improve and eventually meet or exceed any previous measures of cycling fitness, while continuing my running and strength training.

I’m almost 52, so past my physical peak but not willing to concede anything to age just yet. I’m taking to heart what Joe Friel writes in “Fast After 50” :slight_smile:

If I were going to run again I’d probably do MAF style, low intensity, low heart rate running so that injury didn’t pop up.

I had some mild knee pain as mentioned above. Some general circuit/weight training fixed all that.

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I find the run beneficial overall, great for shifting weight and good for aerobic fitness. Needs to be handled right though.

I’m a bigger guy as well, so the pounding does affect the bike the next day. I stick to grass and follow the Long Distance Tri plan without the swims - so mostly base running. I found that SSB and Build was too much with the runs.

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Its all a compromise.

if you are not interested in getting faster on the run, then easy running on your rest days or doing an easy short bike ride followed by an easy run will not break you and will definitely not make you slower.

If your goal is to be a faster runner that might be a different story. It will be very hard (although not impossible) to add hard running wo and also do hard bike rides on back to back days.

Dont worry too much. Running and cycling mix very well…like rum and coke.

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I like what Chad says about Strength Training (which applies to this to)
Do you want to be the best cyclist you can be, or do you want to be the best human you can be who cycles.

Running might affect your cycling fitness, but in the grand scheme of things does it matter? Is it making you a better/fitter/more resilient person? If it is then I’d say go for it, even it means you can’t bike as hard/fast/for as long


Used to be a pretty serious triathlete and back then I felt the two complemented each other really well as I was very conditioned to perform well in both sports. Now after a several year break from running I find when I do try and mix in some running it really compromises my ability to execute on my TR plan. I’m so deconditioned from running that even a 15-30 min run impairs my ability to complete my bike workout the next day.

I did that for about 4 weeks and I was able to maintain by FTB, but I certainly stopped gaining over that period.

My “endurance” pace is around 6:50/km and I try my best to not go hard on my runs except while going uphill where I need to increase my cadence and so does my heart rate increase. I am planning to add in another short run after a weekend endurance ride. I did run two days in a row and my back and shoulders are a bit sore(probably my body isn’t used to running) so I need to be careful on increasing my running mileage.

You could consider a more “little and often” structure to your running if that fits into your routine. Those 1 hour runs will leave a few aches and increase RPE on your next bike workout. Something like 4 X 30min sessions per week? You could do some of your runs after your easier bike workouts too.


Although its very individual to predict exactly how you would respond to adding a second activity, we reviewed the science behind running AND cycling here:


@yajvans A few things from experience as an ex-triathlete who now mainly time trials and has followed TR for a year or two.
Disclosure: I probably did over 50 Tri races including 2 ironman (and ITU Age gp world champs) when between 40 and 45. I am now 61. Started serious TT 2 years ago. Have done over 70 TTs in the past two years, and last year was racing from 10s to 50, 100miles and a 12hr TT (236m). My FTP peaked around 245 last year.

Some thoughts, prompted by your question:

  1. Heart rate. It is normal that HR zones for cycling are around 10bpm lower than running as cycling is not weight bearing. (Swimming HR zones are lower again).
  2. When I did Triathlon, I suspected there was a secret that no-one shared - that spreading the load across muscle gropups made it wasier as you get older. Swimming helped recovery in other disciplines
  3. I am much much quicker on time trials now, that when I did triathlons. However I think this is partly down to kit, wheels, aerodynamics etc. (112miles ironmann leg 6hrs. 75miles average 20mph at ITU world champs. Now 4:22 for a 100m TT and nearly averaged 20mph for the 12hr. and regularly averaging 20mph in long training rides.) Then Scott Waimea aluminium 650c wheel. Now Carbon TT bike with disc rear etc, pointy helmet, skin suit etc, (Of course for triathlon, you have to leave something in the tank from the bike to the run, whereas in a TT I am definitely emptying the tank by the end and could not possibly run - I can hardly even speak sometimes).
  4. When doing ironman training, the pattern is often, build a winter with long slow bikes, but get that marathon in early (April), then settle back on the running, improve bike and maintain run, through the summer. Then introduce longer brick sessions. In other words it is demanding to try and maintain both disciplines so long season periodisation, across disciplines, is important. (I my experience anyway).
  5. Overall, I found that cycling improved by running endurance, (as I used it during marathon training) as it was non-load bearing. So I could do a 3 hr ride and that was nowhere near as tiring (or hard on the muscles) as a 3 hr run.
  6. However, I am less sure it works the other way. I have seen some really good runners struggle with cycling, as the muscle groups are different. (not all obviously). However, I am less convinced that running helps cycling so directly (more impact, shorter duration, different muscle groups etc.).
  7. During Covid/lockdown I have been unable to cycle (prostrate problems) so returned to running and quite enjoyed it, once I built up a bit of condition (4-6 miles and up to an hour). Had op now, so plan return to cycling and training for 2021 from July (I hope). I do plan to keep running occasionally, just to get back into it. I quite enjoy it. However, I imagine, come the serious TT racing season, that will stop.

So, in summary.

  1. If you enjoy running, do it as well.
  2. Millions of triathletes mix and match. Real talents can excel at both. (The longest distance in that 12hr TT was set by a triathlete - but that is quite another story) . (But I am not planning a return to ironman - just in case my wife is listening!)
  3. My experience is that there is a compromise. Cycling Race Season planning might dictate the mix.
  4. Ultimately, as others have said… Do what you enjoy. There is always Duathlon :slight_smile:

I hope this experience helps… Will you loose cycling fitness? Only trying it will tell…

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My anecdotal evidence suggests it won’t. Actually quite the contrary. I get the impression that it helps to improve my work capacity.

For context sake, my watts per kg are slightly higher than yours. I operate on the mid and high volume sweetspot base and sustained power build plans. Running currently averages 3 runs and 1.5 hours per week. Will likely grow that to 4 runs and 4 hours over the next few months.

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Thanks for the information! Prostate issues do sound serious and I hope you got it checked out @PhilSJones!

I used to run before I started biking but I wasn’t serious about it. I never had a running watch and was solely running based on RPE. Now I have a running watch and I make sure to stick to a pace which I can sustain for a while which is around 6:40/km to 7:40/km so I don’t really thrash myself on the runs. I just did Matthes +1 which is a VO2 max workout and I was able to complete it without lowering the intensity.

@dmalc I am actually finding it to be the opposite! In today’s VO2 max workout I noticed that my RPE was lower even at 180+ bpm. I was able to hit my targets as mentioned above. Doing an easy run after a workout also seems like a good idea!

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