I am just starting HRV for the last 5 days. My scores are typically 54 - 58 which is very low by your chart. For most of the year, I was biking 3 days a week for 40 minutes at medium to high load (ave HR would be 150 - 165 during those rides). As of April, the rides increased to last for 1-2 hours still maintaining a high HR - preparing for a 100 mile ride in early June which I comfortably completed with no soreness after. Late June to early July, I switched to running at a comfortable pace for 3-5 miles multiple days a week (much lower intensity than the biking). Then I was diagnosed with Plantar Fasciitis. No more running.
I've always had very strong cardio. My biking partner jokes that I get stronger the farther we ride. I grew up a competitive swimmer. This background is what surprised me to see my HRV in the mid 50s.
For the past 3 weeks, I've done no endurance training - to provide a period of time to recover. I've been doing a warmup every day with stretching (total of 25 min). My new trainer (started 3 weeks ago) says I am lacking the proper sleep (I agree) with averaging 6 hours of sleep that is usually interrupted once or twice. I also travel A LOT - can be flying every day for 4 consecutive days.
I eat very healthy (only liquid I drink is water and lots of it). For the past 3 weeks, I've been all protein and veggies with a little fruit.
Can the sleep and travel alone be causing my low HRV? How long could it take for me to get my HRV into the 70s?