Hi, Nate,
After 30 years of playing classical guitar with a traditional footstool, I developed back problems about two months ago that were seriously affecting my playing and comfort level. I switched to a Dynarette cushion* and the pain went away. However, it takes a real adjustment to play with two feet firmly on the ground after all those years using a footstool which results in a slightly higher posture for the guitar. However, the higher position has been a real benefit resulting in greater apparent finger strength and a cleaner more perpendicular approach to the fingerboard/strings for chord voicings and working in the upper register.
Viajero
Dynarette Guitar Support Cushion, XL 5 inches
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