You are on the right track. Since BOTH of your feet are doing this and only during race, you can likely rule out any significant underlying pathology (i.e. Morton's neuroma or lumbar radiculopathy).

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Fatigue is biochemical, not biomechanical.
- Andrew Coggan, PhD

I get this with some shoes but have never been able completely get rid of it, tends to happen more in races. It is bearable for me but been looking for solution. As of now i have decided its a nerve thing for me and some shoes just tend to affect some nerve in my foot more then others. I can't were a hoka clifton at all but i can wear a hoka odyssey. I also get less issues when i don't bike before.
My suggestion to you would be try different bike shoes and run shoes out and see if you can find some that lesson or get ride of issue.

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2024: Bevoman, Galveston, Alcatraz, Marble Falls, Santa Cruz

I had a similar problem, my foot would go numb during races, but usually only one foot, and while not necessarily painful it was difficult to race on.
At the time I was newer to the sport (not saying that you are) and I was running in a pair of Asics that was popular with other triathlete friends. I went to a running store and found out that I was running in a stability shoe when all I needed was a simple neutral shoe. Switching shoe types fixed me right up. At the time I also found that my quick laces were too tight and restrictive, and loosening them brought some relief.

Had this exact issue, just like you describe the numbness.

Used to even happen to me in a 10km effort. I think that my solution was two-fold:

1.) started running on the road more in training (almost all now) whereas I used to do alot of treadmill work. In my mind my feet werent used to the hard asphalt surface as they had been on a treadmill the whole time. Is there science here? Not really but definitely seems to have made a difference to me.

2.) making sure my shoes weren't laced too tightly.

really I attribute most of it to number one. I think it was a combination of the running surface (more road running) and also probably increased milage.

Reading your post with great interest, as I have encountered two IM clients with symptoms similar to yours. So I would like to find an answer too. However, an 'answer' for one may not be the answer for another.

Both went thru my entire checklist of shoe/foot/pedal interface as well as changes to the bike (seat height, bar height, ec). Some things improved, but not 100% on the numbness. I referred both of them out to PT, with all the standard tests (Slump, Schober, Gaenslen, Mackenzie, plus MRI's).

There is not a lot of information on bilateral foot numbness as it pertains to triathletes; that is to say we are excepting a wide range of causes such as diabetes to medications. Age seems to be a factor for my and others bike fitters' experiences - over 35, and more female than male.

S1 nerve impingement can also be at play, esp as you describe the calf issue. Or it's all part of a cascading failure of the lumbar/pelvic structure.

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Anne Barnes
ABBikefit, Ltd
FIST/SICI/FIST DOWN DEEP
X/Y Coordinator
abbikefit@gmail.com

Thought I would provide an update for those with similar symptoms. After seeing quite a few PT's and docs with no luck, I finally saw a running gait specialist and an orthopedic specialist that was not a surgeon. Turns out I have a slightly odd case of exertional compartment syndrome. In addition to the race issues, I slowly began to experience a subtle loss of power while training.