I started Keto 3 weeks ago and have noticed a big drop in my athletic ability. I am a very active person, I have competed in long distance kayak/canoe paddling for many years and regularly run, lift weights and do other cross training.
I am on paddling off season now, but I run with a Polar HR watch and it gives me a “Running Index” after each session, which is basically a HR v Speed algorithm to measure fitness. For the past year this has been hovering between 55 and 57, but has now plummeted to 49 to 51 on most runs since starting Keto and I generally feel little energy or power in my legs when doing aerobic or anaerobic exercise. (Or from a 2850 to a 2500 Cooper test if this is a more familiar measure). (https://support.polar.com/en/support/tips/Running_Index_feature)
My weightlifting is unaffected though and I can pretty much lift what I could before.
My resting heart rate is much higher now too, it is usually in the mid 50s, but is now mid 60s. Also, when running to get my heart rate to 90% plus I would normally need to focus and push myself very hard (or a big hill!), but now it just creeps up there without me realizing it or feeling like I am working hard.
I started Keto as despite my high levels of activity and conventionally healthy eating I had been putting on a couple of kilos a year since turning 40. In this respect the diet has been successful as I have dropped 4kgs and don’t feel hungry or otherwise deprived.,
Thanks for any advice you can give.