Training on low BF% (inc DEXA and Withings Scale results)


I took a DEXA this morning and it was surprising to see my body fat percentage of 7.2%. I was hoping to get some views on the implication of training and riding with low BF, and whether more BF would result in better power/weight ratio.

I have Mallorca 312 and HR Dolomites coming up, so of course fueling and body composition will be incredibly important.

Weight: 81.3kg
Heiight: 186.5cm
Age: 37
DEXA BF: 7.2%
Withings Scale (athlete mode): 5.1%
Bone Density z-score: 0.4 (this implies 0.4std above average for my age, which is good)
FTP: 356w

Thanks, i’m also between 4.5 and 5.5 on withings scale but never did DEXA.

Good test to take :+1:t3:

You must be really muscular, I’m same height and 76kg. Pretty lean but some muscles too. BF still way over 10%. Similar w/kg.

I did a deep dive on this a while back. People think that a Dexa scan is the gold standard for body fat but it’s not. Dexa is primarily a bone density scan test. They have some algorithms in the machine that will calculate body fat but there are tons of variables like which algorithm the operator chooses for the report, whether the person actually fits 100% on to the machine (big people usually do not). If you do the test on a different machine you’ll most likely get a different result. I’d just look at it as a ballpark estimate and not much more. I wouldn’t test regularly expecting enough precision to track one’s body fat percentage.

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I don’t know that more BF will result in a better power to weight, actually fairly certain it won’t. I’ve “dealt with this” same issue for 20 years - have not done dexa, but have done bod pod and hydrostatic multiple times participating in studies and regularly fall between 7-8%, and can compare to my garmin scale that says I’m 6%.

The only issue I’m aware of that I have in comparison to others who might be a few bf% higher is that I really have to be careful with the weather, especially on the bike. High 50s/low 60s and rain out on a bike ride and my day is wrecked fairly quickly if I haven’t brought the proper rain gear. Also, if it’s anywhere near 60 or below I absolutely have to bring a couple packs of “hot hands” with me just in case.

From a fueling standpoint, I’ve personally been able to experiment with anything and everything over the past 20 years from fasted 4 hour rides to 120g/hr and there wasn’t a difference I’m aware of due to having low BF - it’s still way more BF than you’ll ever use for fuel.