Effects of tongue position and lung volume on voluntary maximal tongue protrusion force in humans

• We analyze effects maximal voluntary tongue protrusion force as measured across a wide range of tongue positions.
• Maximal tongue force is reduced with protrusion beyond the incisors.
• Maximal tongue protrusion force occurs at 16 mm retraction with a ‘plateau region’ between 12 mm and 32 mm retraction.
• We also show increased protrusion force at total lung capacity and residual lung volume compared to FRC.

Maximal voluntary protrusion force of the human tongue has not been examined in positions beyond the incisors or at different lung volumes. Tongue force was recorded with the tongue tip at eight positions relative to the incisors (12 and 4 mm protrusion, neutral and 4, 12, 16, 24 and 32 mm retraction) at functional residual capacity (FRC), total lung capacity (TLC) and residual volume (RV) in 15 healthy subjects. Maximal force occurred between 12 mm and 32 mm retraction (median 16 mm). Maximum force at FRC was reproducible at the optimal tongue position across sessions (P = 0.68). Across all positions at FRC the average force was highest at 24 mm retraction (28.3 ± 5.3 N, mean ± 95% CI) and lowest at 12 mm protrusion (49.1 ± 4.6% maximum; P < 0.05). Across all tongue positions, maximal force was on average 9.3% lower at FRC than TLC and RV (range: 4.5–12.7% maximum, P < 0.05). Retracted positions produce higher-force protrusions with a small effect of lung volume.