Learn And Master Holding Your Guitar
Classical position of holding an acoustic guitar
The standard method for holding a classical guitar is to sit down, place it across your left leg and, using a footstool, elevate your leg to a point where your guitar is at an approximately 30 degree angle to you.
It lets the guitar rest against your chest and legs, leaving both arms free to move without having to exert additional pressure and tension to hold it, and the guitar is placed in a position that will project the sound acoustically to the back of the room.
However, most guitarists who have learned to play without taking this position find this method very uncomfortable, and many experts in ergonomics say that this position places stress on your lower back.
The 90-Degree Method
In the 90-degree method, your feet should be flat on the floor, and your knees at an 90 degree angle to your feet. Your legs should be bent at a 90 degree angle to your knees, and your trunk should be at a 90 degree angle to your legs, bent at your hips. Your back should be straight, and your shoulders parallel to the ground.
Many people also find a guitar strap useful.
Try to keep your hand, wrist and forearm in a straight line. This correctly aligns the muscles and relaxes your hand position.
Make sure you can see the knuckles of both of your hands when you play. To do this you need to have a uniform curve in each ginger, and each hand needs to be in a midrange position. Bending the wrist on either hand tends to flex or extend the muscles, which will inhibit your playing technique.
Try to keep your left and moving parallel to the fingerboard, with your left-hand thumb on or near the center of the guitar neck in line between the index and middle finger.
Practice in front of a mirror during the first couple of times of playing the guitar so you can check your posture and hand positions until you feel comfortable.

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Learn & Master Guitar