Neuromuscular Control of CT and LCA Muscles in Human Vocal Pitch and Register Regulation: Insights from sEMG Analysis

Precise regulation of vocal pitch and register relies on the activity of intrinsic laryngeal muscles. This study aims to elucidate the neuromuscular mechanisms of the cricothyroid (CT) and lateral cricoarytenoid (LCA) muscles during pitch modulation and register transitions, and to further investigate their associations with voice quality.

Sixteen healthy participants were recruited to produce five sustained vowels while performing pitch glides spanning the Chest and Falsetto registers. Surface electromyography (sEMG) signals of the CT and LCA muscles were measured using a validated approach, along with synchronized speech signals. Subsequently, sEMG features were extracted and analyzed for correlations with pitch and voice quality metrics.

During pitch regulation, the CT and LCA muscles exhibited directionally symmetric activation patterns ("rise-fall-rise" during pitch ascent and "fall rise-fall" during pitch descent) regardless of vowel type. Their control over pitch was stable in the Chest/Falsetto register but less stable in the Transition region. Additionally, muscle activation improved voice quality in the Chest register, yet had constrained effects in the Transition region and Falsetto register.

The CT and LCA muscles show activation patterns of different intensities, which contribute to precise pitch control and register transitions. The core function of these two muscles lies in pitch regulation, while voice quality modulation is not solely determined by them.

This study provides non-invasive empirical evidence revealing muscular control strategies in human phonation, thereby advancing the understanding of the physiological mechanisms underlying voice production and offering implications for vocal training and clinical assessment.