Classical piano pieces by such composers as Beethoven, Mozart and Chopin likely sounded much different when the masters first performed those works than they do today. Pianos themselves have changed considerably — but so, too, has technique.

Over the past decade, a growing number of musicologists have begun to take a closer look at how technique shapes not just the sound of music, but also the audience’s emotional response to it.

“Music has one foot in physics and one foot in aesthetics,” said Rolf Inge Godoy, a professor of musicology at the University of Oslo. “Body motion is essential for shaping the outcome of the sound, both in terms of what you actually hear and in terms of the visual impact on an audience.”

Dr. Godoy uses optical motion capture — also employed by the animation industry — to study the physics of musical movement. Infrared cameras capture light from reflective markers placed on a cellist’s hands or a percussionist’s body, recording the performer’s motion at up to 500 frames per second and at an accuracy to one-third of a millimeter.

Computer algorithms then make associations between the motion data, what is heard and what listeners say they felt.

Recently Dr. Godoy turned the technology on a fascinating question: How were such classical pieces as Mozart’s Variation K. 500 and Hummel’s Etudes, Opus 125, originally played, and how might that have made a difference in sound and in audience reaction?

To find out, Dr. Godoy struck up a collaboration with Christina Kobb, a doctoral candidate at the Norwegian Academy of Music and head of theory at Barratt Due Institute of Music in Oslo. Ms. Kobb has developed an unusual expertise: She has learned how to play the piano according to techniques described nearly 200 years ago.

As a visiting student at Cornell University in 2010, she researched 19th-century pedagogical piano treatises — essentially, instruction manuals for piano playing. The techniques that they described, she realized, differed drastically from those she had been taught.

“I was not following even the most basic instructions given to beginners at the time,” Ms. Kobb said. “I wondered, ‘Would this make a difference in my playing?’ ”

For the next three years, she gradually replaced her modern way of playing with 19th-century technique, gleaned from around 20 treatises. Most were written in Vienna in the 1820s, while a few were published in France and England. Her primary source, however, was “A Complete Theoretical and Practical Course of Instructions on the Art of Playing the Piano Forte,” the seminal 465-page treatise published in 1827 by Johann Nepomuk Hummel, one of Mozart’s students.

“It’s hard enough learning how to play once,” she said. “I had to become conscious of every motion in my hands and fingers, things that normally I would do automatically, by habit.”

While modern players tend to hunch over the keys and hold their forearms nearly perpendicular to the keyboard, 19th-century style dictated that pianists sit bolt upright. The posture prevented players from bringing their weight to bear on the keyboard, instead forcing them to rely on smaller finger movements. The elbows were held firmly against the body, with forearms sloping down and hands askew.

As Ms. Kobb became more fluent in this approach, she found that certain movements — jumping quickly between disparate chords, for example — became swifter and more fluid. “The elbow against your body serves as a sort of GPS, so you always know where you are,” she said.

Chords and scales sound smoother and can be played faster, Ms. Kobb also found, and dramatic pauses between notes — often a matter of physical necessity rather than of style — are lessened. The old style also allows the performer to be more discriminatory and subtle in choosing which notes to stress, Ms. Kobb learned, producing a performance that is subdued by today’s standards.

“There’s a different physical feeling to playing, as well as a different outcome,” she said.

To identify the sources of those differences, Dr. Godoy and his colleagues recently attached 46 pieces of reflective material to Ms. Kobb’s fingers and arms, and then filmed her playing on an electric piano. After analyzing her movements, the researchers will be able to tell precisely which differences in technique account for each variation in the music as it is played in the old and modern styles.

“The correlation between bodily effort and sound output is really what we’re aiming to find out, but in order to do that we need to perform extensive statistical analysis, which is tremendously time-consuming,” Dr. Godoy said. He expects the results of the data analysis in three to four months.

“We are exploring those connections to get a better understanding of what music is,” Dr. Godoy added. “What is its power, and why do people respond so strongly to it?”

For her part, Ms. Kobb now plans to delve deeper into the repertoire of Romantic composers. “It’s time to restore the early techniques to try to bring us even closer to the way music sounded at the time of Beethoven,” she said.