Effects of the Head Lift and the Recline Exercises on the Neuromuscular Control of Swallowing: An Electromyography Study in Older Adults

Abstract

Rehabilitative exercises are commonly used to strengthen the submental muscles and improve swallowing function in older adults; however, the underlying neuromuscular mechanisms that lead to these improvements have not been delineated and could be important in determining what types of deficits or patients may benefit most from these exercise regimens. This project focused on two well-known head/neck exercises, the Head Lift Exercise (HLE) and the Recline Exercise (RE).A randomized clinical trial with 2 arms - a 6-week RE or HLE regimen - was conducted. Data were collected on 18 older adults (age range 60-82; RE n=9; HLE n=9) pre-treatment, post-treatment, and at 6-weeks follow-up, and included a VFSS and a surface electromyography (sEMG) study. Results of the VFSS showing hyolaryngeal excursion gains post both regimens have been published (Fujiki et al., 2019). This study focuses on the sEMG data. Surface EMG activity was collected from submental muscles during swallows of self-administered standardized volumes of liquids and solids. We evaluated neuromuscular control through the following outcome measures: normalized mean amplitude, burst duration, and time to peak amplitude.None of the outcome measures significantly changed across time for either exercise group. However, additional exploratory analysis examining the relationship between the percent change of all outcome measures from pre- to post-exercise revealed two interesting findings. A strong negative relationship was found between percent change of normalized amplitude and time to peak amplitude in thin liquids (r = -0.925, p = 0.0001) and pudding (r = -0.901, p = 0.0001). In this sample of participants, this work shows biomechanical swallowing gains post-exercise but no changes in neuromuscular effort and timing to achieve those gains. These paired results could suggest that these participants exhibited improved function of their swallowing mechanism without the need of the underlying musculature to produce significantly more effort. Interestingly, additional exploratory analysis further revealed a strong negative relationship between percent change in normalized amplitude and time to peak amplitude. This could indicate that two different mechanisms were used to achieve the documented biomechanical gains. That is, some participants may have required decreased effort during a functional swallow, while other participants may have achieved these gains with increased effort but decreased reaction time. To our knowledge this is the first study that offers insights on differential neuromuscular mechanisms that older adults use to achieve gains in swallowing with therapeutic exercise, and upon future validation could have important implications on how and when we prescribe these exercises in patients with swallowing disorders in clinical settings.