Dynamic versus fixed pillow height systems and cervical muscle function: a randomized crossover trial

Abstract

BACKGROUND: Pillow height and mechanical support influence cervical alignment and neuromuscular load. However, the physiological effects of dynamically adjustable pillow systems remain poorly defined. AIM: To compare the effects of fixed and dynamically adjustable pillow height inserts on cervical muscle oxygenation, neuromuscular modulation, and comfort in healthy young adults. DESIGN: Randomized crossover trial. SETTING: Controlled laboratory setting simulating sleep-related postures. POPULATION: Thirty healthy adults (18-45 years) without cervical or musculoskeletal disorders. METHODS: Participants underwent six pillow conditions: no pillow (NP), non-adjustable polyester pillow (NA), three fixed inserts (memory foam [MF], latex [LT], polyester fiber [PE]), and a dynamically adjustable air-based (DA). Muscle oxygen saturation (SmO<inf>2</inf>) of the sternocleidomastoid (SCM) and upper trapezius (UT) was assessed using near-infrared spectroscopy. Surface electromyography (EMG) was analyzed via root mean square (RMS) and zero-crossing (ZC) slopes, representing adaptive motor unit recruitment and firing modulation. RESULTS: Repeated-measures ANOVA revealed a significant pillow effect for SmO<inf>2</inf> (SCM: η2P=0.24; UT: η2P=0.14, P<0.05). DA and PE inserts showed superior SmO<inf>2</inf> across phases, with DA yielding the highest levels and fastest reoxygenation. Both DA and PE conditions exhibited steeper RMS and more negative ZC slopes during activity, indicating more efficient neuromuscular adaptation. Comfort ratings were highest for DA (VAS 75.52±16.94 mm). CONCLUSIONS: DA pillows may enhance cervical oxygenation, adaptive neuromuscular control, and comfort compared with fixed-height systems. CLINICAL REHABILITATION IMPACT: DA pillows may provide individualized ergonomic support to improve cervical alignment and comfort.