Note: sorry about the dis-synchronization earlier. I appologize for such confusion.
A lot of students feel that their left hand fingers are much less dexterous than the right ones, that they have much less control over their left hands/left side of the body for some reason. It is simply not true.
It is all about the CONTROL and SPACE.
First of all, relax the left side of your body, especially the left shoulder and left upper arm. I do find a lot of my students have this problem of tensing the left side of their bodies a lot. With constant tension without any relaxation- as for the forearm, hand and fingers as well, the movement- for body to move along the keyboard and the fingers across the keyboard- is without no doubt slowed down and not as smooth, under control and at ease as we would like it to be.
Remember, your upper body- and even your lower body – is movable when you sit at the piano, and of course when you are playing. Sit tall, and move your upper body from side to side following the musical phrases. Do not fold your waist to the sides; simply SHIFT sideways. You can of course fold to the front sometimes when necessary, when you are reaching for the extreme low or high register.
[qt:http://teresawong.dyndns.org:9001/video/rach.m4v 640 360]
Again, create SPACE to the left side of the body. Relax the shoulder and upper arm. FEEL it and you will understand what I am talking about. If not, try deliberately tense up your left shoulder and upper arm. Then completely relax them. Then, try playing something on the keyboard and feel the sensation of EASE(with CONTROL), SMOOTHNESS and FREEDOM across the keys.
P.S. The piece demonstrated in the video should be Rachmaninoff’s Op. 23 No.5, not Op.32.