Thanks for the vid.
[u]The shoulder ache.[/u] Watch the GT lesson vids on A. posture, instrument and arm placement, and most importantly, B. fretting hand mechanics and C. thumb placement. It's all covered in those initial lessons of Lisa's in GF1. If you have already watched them, then you should watch them again.
You could try using a strap too, but with an acoustic, IME it's not as critical as self-awareness of the above.
Secondly, from what can be seen and heard in the vid, it's difficult to relate it to what you describe you are attempting to do in previous posts. I couldn't see you demonstrating formed chords or fluid chord changes where muting of an adjacent string has pragmatic impact. The kind of slow, seemingly uncertain fumbling placement I saw is indicative of a need to build skills competency on each lesson's objectives step by step then putting them together as instructed in a further proceeding lessons until they make a meaningful whole which in turn will build into making music. Are you skipping lessons, or just expecting too much of youself in such a short time?
That said, I spotted a couple of things which could use attention and awareness, along with more info required tech query and possible need for some 'luthier love'.
[br]1. [u]Cut your fingernails on your fretting hand[/u]. This alone can interefere with getting clean notes on a fretted string as well as inducing inconsistent inaccurate placement. I noted the length of your fingernails on thumb and pinky (4th finger), reasonably supposing the fore, index and ring finger nails are a similar length and shape. Trim them [u]very[/u] [u]very[/u] short so they don't project beyond flesh and file them so they align with the gentle curvature of your fingertip or flatter and edges are blunt and smooth not sharp. You have fleshy fingers, so achieving an easy [u]lowest pressure contact by having fingers touching at as perpendicular an angle as possible for the chord to be formed is especially important if you want to avoid inadvertently muting adjacent strings[/u]. I'll take and post a pic of mine shortly. Edit: There you go. Image hotlinked.
[br]2. [u]You will find benefit in performing simple finger co-ordination and stretching exercises at least daily.[/u] GT has many. Start with and keep it easy and simple over four frets. Don't abandon it because its "hard" or "boring". Stick with them until they become doable, if not easy. And an analogy. IME playing guitar is a bit like playing tennis or squash racquets where one has to actively mentally urge the necessary parts of the body (legs) to immediately move it back to centre court [u]after[/u] running to every shot and striking the ball contradictory to the message the mind instinctively registers of 'job done'. It requires positive action maintaining mental and physical awareness preparing to accelerate and stretch again and again to the next anticipated fall of the ball [u]until the whole process becomes a coordinated instinctive whole and unaccustomed muscles are strengthened[/u].
[br]3. How old is your guitar? [u]Do you have any dented or damaged frets?[/u] Are they level? You can check with a steel straight edge rule. [u]Is the neck relief properly adjusted?[/u] It sounded to me that besides inadvertently muted strings, you also aren't getting clean fretted notes, but I couldn't discern from the vid if the cause was your finger misapplication to the string or buzz from irregular level frets. It might behove you to have your guitar checked by a luthier?
[br]Other than that. Follow the structured coursework on GT, and don't be in a rush to move ahead. Watching a lesson isn't the doing. The military use a proven KISS instructional formula which works on even the dumbest recruit capable of passing an entry IQ rest. It must if it worked on me! DIP. Demonstrate. Imitate. Practice. It works for guitar too. Broken down, its basically what GT do here in each lesson too.
