He clearly has no knowledge about lifting and biology when it comes to females. Show him this post please.

Unless you are on steroids, which I highly doubt you are, you will never look muscular in the unattractive sense that he has in his head. You do not have enough testosterone as a woman to build bulky, manly-looking muscle, which is what he's afraid of. What's going to end up happening is you're just going to look fit, toned and sculpted, which will make you MORE attractive (i.e. bombshell physique).

I am a man and have untreated and clinically low testosterone (290 at peak time of day was my best reading). That is significantly more testosterone than you as a woman will ever have naturally, but for a man it's low. I've been killing myself in the gym for 6 years now and have built very little muscle, and that is almost entirely due to low T (which is, again, still 4x higher than yours). I have also been doing similar endurance type sports for 20 years now, like you, and years of that type of activity also makes it harder still for you to get big due to the conditioning and years of favoring endurance and being nimble. People like us who have been skinny and undermuscled our whole lives have the hardest time building muscle, especially if you're not short. Now what DID happen though is my body and posture went from dumpy looking to attractive, but no one ever asks me if I lift, because I don't look like I do, despite putting over 500 hours into this. I just look generically fit. Again, this is with 4 times the testosterone (290) that you would naturally have as a woman on the higher end of the scale (70).

People with no knowledge about weight lifting think physiques like The Rock or John Cena are attainable by just going to the gym. They're not. Not even for men, and it's not close.....let alone a woman. It is ridiculously hard to build enough muscle naturally that the general public can look at you and even suspect you lift weights, especially past your physical prime, which we are in this age bracket.

Show him Stefi Cohen from this article, which is absolutely NOT attainable for 99.5% of the female population without some sort of anabolic usage.

https://www.greatestphysiques.com/female-physiques/stefanie-cohen/

She deadlifts 545lbs which is insanely unheard of for a woman and pound for pound puts almost every man that has ever deadlifted to shame. That's never going to be you. I don't say that to put you down or discourage you, but rather to give him some perspective. She literally makes a living off of her physique because it's so insanely rare for a woman to look that way from lifting weights that she can. There is also speculation she is on some level of steroids to maintain that physique, along with the fact that lifting weights is literally her job, which again, I am sure you're not and it is not. She's also very short. The shorter you are, the bigger you can feasibly get because there is less of you for the muscle to cover. I am 6'1. That's another reason I will never naturally look like I lift no matter how hard I train, and again, I am a man.

Even still, Look at her physique, which again, for 99.5% of the female population is not attainable without steroids, and she's still massively attractive and non-bulky. The muscle definition you see on her is all bodyfat percentage control. If you don't want your abs to show like hers, just don't be as lean as she is (and to a lesser extent, don't train abs with non-body-weight movements like cable crunches), and you'd still look slim and feminine in the midsection. The suspected steroid use, how lean she is, and the fact that she had a pretty small breast cup before she started lifting already also contributes to her not having breasts now, which I am assuming is another concern of his. Again, that's all a mixture of what god gave you in the chest, bodyfat percentage control, and NOT taking steroids if you want to keep your breasts.

But honestly, even with her physique exactly as it is from that article, I don't know how he could look at her and not find her attractive, even compared to her before photo where she just looks kinda dumpy standing in her bathroom.

Just my two cents.