I found a good ol' fashion paper notebook that I could throw into my gym bag did the trick. Later I would put it into a spreadsheet for graphs.

Fitnotes is great. Free but you can pay a one-time "supporter fee" to get slightly expanded functionality. Its on android, not sure about apple.

It ticks all your boxes, except open-source. But you can export all your data

So, there is a comment I made in a post about a year ago, I'm gonna repost it here too:

I have some (many) apps to share (I really like gathering my data, lol, and I try to do that with open source apps).

1)Fast and fitness (workout tracker)

I've been using Fast and Fitness for about a year and I really like it. You set up your profile, you create the exercises and even create programs if you want (I have made a few). It can even register body metrics (weight, fat/muscle/water percentage, height etc.).

You can import and export various stuff seperately in csv which is really helpful (like history/exercises/programs etc.). Here I have exported my exercises, my programs and uploaded the exercise pictures I use so you can import them on your app (in case it fails you could tweak the files on PC to make it work, but I just tested it on a fresh install of the app and it worked).

To do so, just open the app, create your local profile, export the records of your profile so that it creates the fastnfitness folder on your downloads folder, throw the the files I shared with you inside the export foldee and then import them with this order(!):

• exportExercises.csv

• exportPrograms.csv

• exportProgramTemplates.csv

• manually assign each photo to each exercise (a bit tedious and optional)

2)Fito track (running/cardio workout tracker)

I'm using Fito Track to track my running workouts (route on map, distance, time, speed, elevation etc.), but I think it can be used for any cardio kind of exercise (like swimming). It too can export/import many things and can be used with smartwatches.

3)openScale (body metrics tracker)

I use openScale for about 1.5years to mainly to track my weight, fat/water/muscle percentage, the measurements of my fat calipers etc.

4)Gadgetbridge (smartwatch connector to phone)

If you want an open source way to connect to your phone any smartwatch/fitness tracker watch you have, Gadgetbridge seems to be doing the job (I did it once to use a watch with FitoTrack)

5)MotionMate (step counter)

Just a simple and reliable step counter I'm using. It's the only one so far that seems to register almost all the steps (apart from my xiaomi device's built-in step tracker). It has no export/import function, but I have root access, so I can import/export its databases and successfully export it on my pc (or import it back to my phone) and edit it with a db browser and a sheey editor.

6)Energize (food intake and and body metrics tracker)

I've used Energize a few times to check how much I'm getting of each nutrient. It makes it easier as many items are in a database and you just scan it (even works for many Greek products, since I'm Greek).

7)Pain diary (Well, a pain tracker)

I've used Pain Diary a few times to register the pain I felt on my body after some workouts.

Link to comment (it's in the fitness community of lemmy.world): https://mander.xyz/comment/1704758

Hevy is really good but it's a small fee

Jeffit is the one I like most. Not open source.

I've tried a few open source. Liked massive the most, but none I love. Wger and gymroutines the other two that are fine.

I like jeffit charts too.

None of these recommend when to start adding weights tho, or atleast not to my knowledge.

either hevy or trainheroic