Just a brief side comment here -- I started with a fitbit
IMHO fitness trackers are OK and certainly walking more is going to get you more fit but structured exercise is what really takes you to the next level and for that Garmin devices are the dominant tools because they have a lot of capabilities for structured exercise routines esp endurance sports.
And I would be very remiss if I failed to mentioned DC Rainmaker's Blog / Review site which is pretty much the gold standard for what I can tell for reviews of fitness oriented measurement devices -- everything from the Apple Watch to the Fitbits to the Garmins, Polars and Suunto
Now as an enthusiast cyclist I measure the following items to track fitness (and yes my friends think I am an obsessive nutcase but I find it fascinating and very empowering). And it takes a lot more than one sensor to do this.
- Heart Rate
- Watts Generated at the pedals
- Cadence of bike pedals
- Speed of bike
- Duration of the exercise
- Blood Oxygen Saturation (not happy with that device)
- Heart Rate Variability
- Sleep length and Quality
- Muscle quality and body fat
I've worked my way through fitbit - polar watches and sensors-- wahoo iphone stuff -- and now mostly garmin stuff. My bike has 6 sensors on it now (if I counted correctly).
Much of this is feed into a mathematical model of exercise stress and fitness
Using an Open Source tool
And an automated AI coaching program
Which dynamically plans my workouts and estimates my fitness level, recovery state, etc. and works pretty darn well I think
And no way am I way clever enough to figure all this out -- its basically a shadow copy of how the professional cyclists train and so this technology has trickled down to the likes of me.
But there is a sort of breakpoint between a Fitbit Blaze which my wife has and is only so-so for exercise IMHO vs the dedicated fitness devices e.g. Garmin Forerunner, Garmin Edge, Suunto Ambit etc. and the like ... so if you see a gym or running or cycling or rowing or strength training in your future please take a look at DC Rainmaker's website.