Effect of tongue exercise on protrusive force and muscle fiber area in aging rats

Abstract

Purpose: Age-related changes in tongue function may contribute to dysphagia in elderly people. The authors' purpose was to investigate whether aged rats that have undergone tongue exercise would manifest increased protrusive tongue forces and increased genioglossus (GG) muscle fiber cross-sectional areas.

Method: Forty-eight young adult, middle-aged, and old Fischer 344/Brown Norway rats received 8 weeks of tongue exercise. Protrusive tongue forces were measured before and after exercise. GG muscle fiber cross-sectional area was measured in exercised rats and was compared with cross-sectional areas in a no-exercise control group.

Results: A significant increase in maximum tongue force was found following exercise in all age groups. In addition, a trend for increased GG muscle fiber cross-sectional area and a significant increase in variability of GG muscle fiber cross-sectional area was identified postexercise.

Conclusion: The findings of this study have implications for treatment of elderly persons with dysphagia using tongue exercise programs. Specifically, increases in tongue force that occur following 8 weeks of progressive resistance tongue exercise may be accompanied by alterations in tongue muscle fiber morphology. These changes may provide greater strength and endurance for goal-oriented actions associated with the oropharyngeal swallow and should be investigated in future research.

Figures

Figure 1

Schematic of the tongue force operandum.

Figure 2

Representative cross sections of the genioglossus (GG) muscle in young adult, middle-aged and old rats in the control (no-exercise) and exercise groups.

Figure 3

The number of tongue presses at or above a preset threshold level in one representative rat per age group across the 8 weeks of tongue exercise training.

Figure 4

Maximum tongue force averages (i.e. average of the top 10 forces produced in one session per week) in one representative rat per age group across the 8 weeks of tongue exercise training.

Figure 5

Maximum voluntary tongue force (MVTF; g) was significantly greater following 8 weeks of tongue exercise (post-training) versus baseline measures within the exercise group. (t=11.44; p<.0001>

Figure 6

Number of tongue presses per two minutes significantly increased following 8 weeks of tongue exercise across all age groups (t=4.13; p=.0004).

Figure 7

Muscle fiber cross sectional area (μm2) was not significantly different as a function of age (F=.95,p=.39), but there was a trend toward larger cross sectional area following the 8-week exercise period in comparison with control animals (F=3.17, p=.08)

Figure 8

Variation (in mean standard deviation [SD]; μm2) was significantly larger in the exercise group in comparison with control animals.