The Influence of Age, Eating a Meal, and Systematic Fatigue on Swallowing and Mealtime Parameters.

Fatigue is widely accepted as a clinically relevant factor in the diagnosis, treatment, and management of dysphagia. Despite the relative importance that is placed on swallowing-related fatigue, the occurrence and effects of fatigue during swallowing is unclear. The goal of this study was to explore effects of eating a meal on measures of tongue strength, endurance, and other parameters of swallowing function under normal conditions compared to when the tongue is intentionally fatigued. Thirty healthy females, 15 "Young" (18-35 years old), and 15 "Old" (70 + years old) were seen for two data collection sessions one week apart. On both days, pre-meal measures were collected, then participants consumed a standardized meal based on a previously published protocol (half a bagel with peanut butter and 8 baby carrots) followed by post-meal measures. An additional pre-meal fatigue task was included on one of the test days (counterbalanced), involving maximal tongue presses until participants could not achieve 40% of baseline maximum pressure. Pre- and post-meal measures included anterior and posterior maximum tongue pressures, saliva swallow pressure, tongue endurance, surface electromyography (sEMG), the modified Borg scale, and the Test of Mastication and Swallowing of Solids (TOMASS). Linear mixed effects regressions compared pre- and post-meal outcome measures (1) on the non-fatigue day and (2) between fatigue and non-fatigue days while controlling for participant and age. The fatigue task caused significant reductions in maximum anterior and posterior tongue pressure. After a normal meal (i.e., without fatigue), we found decreased anterior pressures in the older group only. Older participants also had decreased saliva swallow pressures after the meal compared to pre-meal, while this measure increased post-mean in the young participants. When compared to the non-fatigue meal, eating a meal after tongue fatigue resulted in significantly lower post-meal posterior pressures, regardless of age group. The same pattern was observed with posterior functional reserve. Our results demonstrate that a systematic, participant-specific tongue fatigue task induced measurable changes in maximum tongue pressure. A meal by itself was observed to reduce anterior tongue strength and saliva swallow pressures only in older participants. Overall, it appears that older adults may be more vulnerable to fatigue-induced changes in tongue strength, though the relationship between these measures and changes to functional swallowing remains unknown.