We put on our headphones every day, but who considers what allows singers to reach the high notes? Swiss researchers, that’s who.

“Although young professional singers can easily sing at very high pitches, older singers often complain about having to exert substantially more laryngopharyngeal force to reach high vocal pitches compared with their younger days,” wrote Claudio Storck with the University Hospital at the University of Basel in Switzerland.

In the study published online Jan. 8 in the Journal of Voice, high-resolution CT scans were performed on 44 female professional singers at the “fundamental mean speaking frequency” and the first and second octaves above it, Storck et al. wrote.

The team from Basel, Switzerland fed those scans into a software that could visualize various parts of the throat and create 3D models of the throat. They found younger singers able to hit higher notes due to the increased flexibility in the larynx cartilage, while older singers tend to have firmer, inflexible cartilage and must exert more effort to reach higher pitches.

“A flexible larynx is beneficial for a well-functioning singing voice. Or, in other words, a stiff thyroid cartilage can hinder the fine-coordination of the vocal tract in controlling the singing voice,” Storck et al. wrote. “The singer therefore has to compensate by using other muscular techniques when singing at high pitches, which can lead to uncomfortable sensations in the throat.”

The study authors noted that this study was done within the framework of a larger project, and therefore examined female singers only. Further research would be necessary to determine if these findings are applicable to male singers.