Lifelong athlete. 37yr old male. College baseball player. Have been lifting weights for 15 years. Very consistent with my diet, in fact I have my diet dialed in and track calories eat nothing but whole foods.

I've been running for over a year, off and on due to calf and achilles injuries but mostly on. I am on week 10 of a 20-week half marathon plan.

If you look at me, I look very fit. People assume I am very fit because I have decent muscle mass and I'm pretty lean (around 10-11%bf right now). But I really struggle running. I just ran a 7-miler for my long run and it killed me. A freaking 12:53 pace, started at 5am and finished around 6:30am. I am deliberately running in zone 2 to build my endurance base using my Garmin watch and chest strap. I couldn't have run any faster if I wanted to. Running so slow but my average heart rate was 149bpm. All of my other health factors are very good. 48bpm resting heart rate. 7-8 hours of sleep a night. Weight lifting 3 days a week. Running 3 days a week. All blood work in January was great.

Before I focused on my endurance I got my mile time down to 7:33 at around 80-90% effort. I just feel like I should have a better base by now and even though building the mileage takes time I feel like I'm way too slow for how long I've been running.

Am I doing something wrong? Any advice or feedback for me?