Effect of swallowing related fatigue on eating and drinking behaviors across the age spectrum

Study design

The current study utilized a cross-sectional design with a non-randomized purposive sampling procedure. The study was conducted between June 2024 and January 2025. The study received approval from institutional ethics committee of Kasturba Medical College Mangalore (IECKMCMLR-11/2022/452).

Participants

A total of 400 participants were included, and categorized into three groups: 127 healthy young adults ranging from 18–40 years (Group A), 124 healthy middle-aged adults, ranging from 41–59 years (Group B) and 149 healthy older adults 60 years and above (Group C). Participants were recruited as healthy volunteers from the community. Specifically, older adults were approached from local old age homes and yoga centers, while the young and middle-aged adults were recruited from general community. Written informed consent was obtained from the participants prior to collecting relevant data. Participants with any speech, language swallowing or cognitive deficits as well as those who avoid hard food textures and have gluten intolerance were excluded from the study. All participants underwent neurological screening that included detailed case history and structured cranial nerve examination (cranial nerve functions, motor and sensory status) performed by the principial investigator (a Speech-Language Pathologist). This process ensured the exclusion of individuals with neurological conditions. Participants who are on non-oral modes of feeding, or have any surgery to the oral structures involved in swallowing were excluded from the study as well.

Materials

The TWST utilized 150 ml of room temperature bottled mineral water which was provided in a plastic cup. For the TOMASS test, a Parle Monaco cracker, measuring 4.4 cm in diameter and weighing 6.67 g was used. Parle Monaco TM is a commercially available cracker commonly used in India for the reliable assessment of mastication and swallowing in adults. The timing was recorded using a stopwatch.

Procedure

The participants were provided the SERF scale to evaluate the severity of swallowing related fatigue. After filling the form, the study cohort was then subjected to the following quantitative tests, i.e., TWST & TOMASS.

• Participants were seated comfortably during the assessments. For assessing the liquid consistency, the participants were provided with 150 ml of water in a paper cup with the instruction to drink “as quickly and comfortably as possible”. Temporal measures were recorded from the moment the cup touched the patient lips till the last laryngeal elevation post swallow. Number of swallows were documented by visual observation of thyroid cartilage displacement.

• To assess the masticatory efficiency for solids, we provided the participants with one cracker with the instruction, ‘consume this cracker as quickly and comfortably and when you are done with swallowing the cracker, say out your name loud and clear’. From this test we measured the number of bites, number of masticatory cycles taken for that cracker, number of swallows and most importantly the amount of time taken to consume the cracker.

Both the procedures were video recorded for analysis purposes. A digital camera (AUSHA^® 5K sport action camera) was mounted on a tripod (Digitek DTR 520BH) to capture four quadrants involving the head and neck. The researcher adjusted the frame of capture until the following landmarks were present in the frame, the head superiorly, clavicle inferiorly, nose anteriorly, and ear posteriorly.

• Lastly to assess the swallowing safety and efficacy of swallowing, the mealtime assessment scale (MAS) was administered by the researcher. Here, the participants were asked to complete a normal meal, whereas the researcher observed the behaviors and the patterns of eating and completing a meal by the participant. The meal comprised of a typical staple diet covering rice or medium sized chapati, lentils, and vegetables ranging up to (∼120 calories per food item).

For interrater reliability, 20% (n = 78) of the samples were chosen randomly, and analyzed by a second rater who was a post graduate student blinded to the analysis conducted by the first rater. The measures that were included for the reliability studies (interrater reliability and test–retest reliability were the parameters of TWST and TOMASS.

SERF has been formulated to evaluate swallowing related fatigue wherein the first six questions target the localized fatigue in swallowing musculature and last six questions target the general fatigue in terms of mealtime and behavior (Brates, Harel & Molfenter, 2022). The list of questions of SERF has been listed out in Table 1. Hence, we decided to analyze the objective tests by correlating it specifically with localized fatigue as well as fatigue related to mealtime behaviors. Spearman Correlation was carried out to assess the degree and strength of correlation between the quantitative tests and severity of swallowing related fatigue.

Gender wise distribution and prevalence of swallowing related fatigue

Group A included 127 healthy young adults (62 males, 65 females). Group B had 124 healthy middle-aged adults (49 males, 75 females) and Group C was comprised of 149 healthy older adults (68 males, 81 females).

Based on the findings from the SERF scores, we observed the following prevalence rates across the three groups with healthy young adults reporting a prevalence rate of 15.74%. Middle-aged adults and older adults were found to have prevalence rates of 24.1% and 40.26%, respectively.

Descriptive statistics

Descriptive statistics for all the variables from the quantitative tests have been summarized in Table 2.

From Table 2 we can summarize the older adults had significantly poorer values in terms of swallow safety, efficacy and mealtime duration.

Inter rater and test-retest reliability

Table 3 depicts a summary of ICC values for all the parameters on TWST and TOMASS. As shown, the ICC values ranged from 0.71–0.98 across various parameters hereby indicating a moderate to high level of correlation for analysis amongst the two reviewers.

Table 3 shows very good to excellent test-retest reliability across both the quantitative tests. However, in terms of inter-rater reliability a wide variation was seen ranging from good to excellent inter-rater reliability.

Correlation analysis between swallowing related fatigue on drinking, eating and mealtime

Correlation between severity of swallowing related fatigue and its effect on drinking has been summarized in Fig. 1.

Figure 1 depicts very weak to weak correlation for TWST parameters against localized and general swallowing fatigue.

The effect of swallowing related fatigue on eating pattern across all parameters of TOMASS have been depicted in Fig. 2.

Figure 2 demonstrates weak to moderate correlation between TOMASS parameters against swallowing fatigue.

Impact of swallowing related fatigue across mealtime has been illustrated in Fig. 3.

From Fig. 3 we can determine that moderate to strong positive correlation exists between the domains in MAS against swallowing related fatigue.

Effect of age, gender and swallowing fatigue on drinking, eating and mealtime

A linear regression analysis was conducted to examine the effect of gender, age, and swallowing fatigue on drinking-related swallowing parameters: volume per swallow, time per swallow, and swallow capacity. The results have been summarized in Table 4.

From Table 4, the overall model revealed that gender significantly influenced both volume per swallow and swallow capacity, with males performing better in these domains. Age was significantly associated with increased time per swallow and decreased swallow capacity. In contrast, swallowing fatigue did not show a statistically significant effect on any of the drinking-related swallowing measures.

Similarly, a linear regression analysis was conducted to examine the influence of gender, age, and swallowing fatigue on various eating task parameters, including discrete bites, masticatory cycles, swallows per cracker, and total time which have been listed out in Table 5.

Gender, age, and swallowing fatigue significantly impacted multiple components of the eating task. Males demonstrated greater oral efficiency, with fewer bites, chewing cycles, swallows, and shorter total eating time. Age was associated with increased oral effort and duration. Notably, swallowing fatigue showed significant effects on masticatory effort, number of swallows, and eating duration, indicating that perceived fatigue can influence real-time eating behaviors.

Finally, linear regression analysis was performed to evaluate the influence of gender, age, and swallowing fatigue on mealtime outcomes namely swallowing safety, swallowing efficacy, and total mealtime duration, which has been illustrated in Table 6.

From Table 6 it was seen that in contrast to the drinking and eating tasks, gender did not significantly influence any of the mealtime outcomes. Swallowing fatigue and increasing age emerged as consistent and significant predictors of compromised mealtime performance, manifesting as reduced safety and efficacy as well as prolonged meal duration.

Comparative analysis of drinking, eating, and mealtime performance across age groups

Kruskal Wallis test was carried out to check for inter group differences on the quantitative tests across the age groups. The results have been summarized along with post hoc results in the Tables 7 and 8.

The Kruskal-Wallis test revealed significant group differences in several parameters related to swallowing, eating, and mealtime performance. Within the Timed Water Swallow Test, there were statistically significant differences between groups for time per swallow (χ² = 42.54, p < 0.001) and swallow capacity (χ² = 45.42, p < 0.001), while volume per swallow did not differ significantly (χ² = 4.73, p = 0.094). Post-hoc pairwise comparisons using the Dwass-Steel-Critchlow-Flinger test showed that time per swallow progressively increased across all three groups: Group A vs B (p = 0.009), A vs C (p < 0.001), and B vs C (p = 0.001), suggesting a gradual decline in speed of swallowing with group progression, likely due to age. Similarly, swallow capacity was significantly reduced in Group C when compared with Group A (p < 0.001) and Group B (p < 0.001), indicating impaired efficiency in older adults.

In the TOMASS, group differences were evident across all the parameters. However, post-hoc analysis revealed that Group C required significantly more bites than Group A (p < 0.001). Masticatory cycles increased significantly between all pairs (A vs B, A vs C, B vs C; all p < 0.001), suggesting that chewing effort increases progressively across groups. Swallows per cracker were significantly higher in Group C compared to Group A (p = 0.025), and total time to complete a cracker was significantly longer for each group comparison: A vs B (p = 0.021), A vs C (p < 0.001), and B vs C (p < 0.001).

The MAS also revealed significant group differences in swallowing safety (χ² = 89.73, p < 0.001), efficacy (χ² = 101.14, p < 0.001), and mealtime duration (χ² = 73.30, p < 0.001). All three parameters showed significant pairwise differences across all group comparisons. For safety scores, Group B had higher scores than Group A (p = 0.039), Group C had significantly higher scores than both A (p < 0.001) and B (p < 0.001), indicating progressive decline in swallowing safety. Efficacy scores were also significantly worse in Group B compared to Group A (p = 0.005), and further worsened in Group C compared to both A and B (p < 0.001). Likewise, mealtime duration increased significantly between all groups, with Group C taking the longest time to complete meals (A vs B, A vs C, B vs C; all p < 0.001).

In summary, the results demonstrate that swallowing, chewing, and mealtime performance significantly decline across groups, with Group C (older adults) showing the most marked impairments. These include slower and less efficient water swallowing, increased oral effort during solid bolus management, greater swallowing safety and efficacy concerns, and prolonged mealtime durations. Group B (middle-aged adults) often exhibited intermediate performance between the younger and older groups, reflecting a possible transition in functional swallowing capacity with aging.

Limitations and future directions

This study has certain limitations that should be acknowledged. First, instrumental assessments of the pharyngeal phase, such as VFSS or FEES, were not used, which limits insight into deeper swallowing dynamics. Second, BMI was not collected, which could have provided further understanding of fatigue contributors. Additionally, denture status was not documented, despite its relevance to mastication efficiency in older adults. Future studies should aim to include these variables to enhance clinical interpretation and applicability.

The task-specific nature of the Timed Water Swallow Test and the Test of Mastication and Swallowing of Solids may have restricted the ability to fully capture the cumulative and complex effects of swallowing fatigue experienced during prolonged or varied mealtime tasks. Additionally, both tests primarily assess oral and preparatory phases of swallowing, potentially overlooking deficits in the pharyngeal and esophageal phases where fatigue might be more pronounced. The inclusion of a heterogeneous population comprising healthy young, middle-aged, and older adults may have diluted the observed correlations due to age-related differences in muscle strength, endurance, and baseline fatigue levels. Psychological factors such as motivation, mood, and stress, as well as environmental influences like the mealtime setting, were not controlled for, which could have impacted perceived fatigue and swallowing performance. Future research should explore longitudinal effects of fatigue management interventions on SERF and MAS scores and investigate their predictive value in clinical populations.