A number sequence of a different kind

Question

My brother and I spent some time hanging out this weekend and he taught me a specific sequence of numbers during a particular activity.

58, 567, 57, 578, 58, 58

What does it represent and what were we doing?

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Some more sequences:

357, 356, 357, 45, 346, 357
135, 245, 235, 24, 235, 135
357, 467, 457, 46, 457, 357
81012, 81011, 81012, 910, 8911, 81012
6810, 7910, 7810, 79, 7810, 6810
81012, 91112, 91012, 911, 91012, 81012
91012, 91113, 91112, 911, 91112, 91012

Hints:

- Our activity didn't require electricity
- Taught is a key word. These sequences are memorised for a specific purpose.
- The sequence lengths are important. To elaborate upon this, the fact that there are the same number of groups per sequence is very useful information.
- My brother knows these sequences very well because he uses them for a living.

Answer 1

It looks like fingering instructions for some strange scales on a guitar. That would explain why

1. there's always six of the numbers,
2. they can always be split into concatenated strictly rising finite sequences of small integers with small differences (like 91112 -> 9 11 12),
3. the individual entries do not exceed 12 by much,
4. the fourth sequence is one element shorter.

It's also compatible with the provided hints. The only problem is that I tried playing them and they don't sound like anything usual. But that could simply be a nonconventional style or not the default tuning, perhaps even a different but related instrument.

Update: You were playing guitar and practising the following scales (only first octave listed, then it repeats as high as fingers reach without leaving position):

• 5 8 5 6 7 5 7: A C D E♭ E G A: hexatonic blues scale from A [1]
• Lines 1 and 4 in "Some more sequences" (differing only by a constant shift of 5 positions, i.e., G->C): G A B C D E♭ F G: "major minor" scale as described in [2]
• Lines 2, 3, 5, and 6 (ditto, from F, G, B♭, C, respectively): F G A B C♯ D E F: "Lydian raised 5th" [2]
• Last line: C♯ D E F♯ G♯ A♯ B C♯: "Phrygian raised 6th" [2]

Alternatively, all the heptatonic scales could just be of one type (e.g., all major minor), just not starting from the base tone. The most likely explanation, subjectively speaking, is that they are "melodic ascending minor" scales [2] from C, D, E, F, G, A, B, C (this would be the full C-major scale in order). But the above is a more precise formulation for as a matter or principle you wouldn't start a scale on something that is not its first tone.

Answer 2

Is this some kind of dance with six steps which can be performed doing serveral of those 6 step sequences? I noticed that the last number is the same as the first number in each sequence.

The numbers might indicate positions on a floor which you have to touch with your arms and legs.