Why Can’t the Hand Stay Stretched Through Fast Octaves?

In fast octaves, the thumb and fifth finger must of course preserve the octave span. A stable distance, however, does not require the palm to be forced open from beginning to end. When finger abduction, a fixed wrist and downward key pressure become one continuous effort, the forearm soon develops a familiar burning tightness. As tempo rises, it is easy to mistake that tension for control.

Research can identify where loading occurs, but it cannot prescribe one movement for every pianist. A surface-electromyography study of professional pianists found that octave tasks and ordinary repertoire excited different forearm regions, with a consistent area of high activity on the dorsal forearm during octaves. Another study comparing wrist positions found the lowest overall muscle activity with the wrist in a neutral position. These findings support a restrained conclusion: octaves are not merely a local action of two fingers, and a persistently bent or fixed wrist can leave unnecessary work in the forearm.

The useful distinction in practice is between forming the span for a moment and maintaining tension continuously. Play two octaves slowly. After each strike, allow the keyboard's reaction to return the hand slightly before preparing the next shared descent. If the palm still feels as though it is gripping a plank, the previous stroke has not finished. Speed comes from a cycle of striking, rebounding and travelling, not from compressing one effortful posture. Listen for a clear beginning to each octave without the dull tail created by pressing the arm into the keybed.

https://pmc.ncbi.nlm.nih.gov/articles/PMC8939780/

https://www.jstage.jst.go.jp/article/jsehs/64/4/64_293/_article/-char/en

If you would like to continue this kind of practice in an app, you can try Geoffrey Chen's piano learning and practice app, <a href="https://apps.apple.com/us/app/scoreflow/id6796205656">ScoreFlow</a&gt;. The essential test remains your own listening and physical sense of release after each keystroke.