Age-related changes in rat genioglossus, geniohyoid and masseter muscles

Aging-associated differences between perioral and trunk muscle characteristics

The physiological and functional changes from aging affect the systemic and swallowing muscles. While ultrasound is used to examine muscle characteristics, no previous studies have examined the relationship between age and perioral and trunk muscle characteristics, including stiffness. This study aimed to investigate the relationship between age and the characteristics of perioral and trunk muscles, including quality, quantity, and stiffness, using ultrasound. A total of 215 participants were recruited for this cross-sectional study: 98 younger adults (20-64 years) and 117 older adults (≥ 65 years). Muscle characteristics were assessed along with data on age, sex, body mass index, and number of teeth. The correlation between age and muscle characteristics was examined. Multiple linear regression was performed with muscle characteristics as dependent variables and age, body mass index, and number of teeth as explanatory variables. We found that only trunk muscle stiffness was associated with age, with a stronger correlation in quality and quantity than perioral muscles. Masseter muscle quality and quantity showed a higher correlation with age than those of the geniohyoid muscle. In conclusion, characteristics of the trunk and perioral muscles exhibit differences in age-related changes, highlighting the importance of maintaining both trunk and perioral muscle activity in older adults to prevent functional decline.

Myosin Heavy-Chain Messenger Ribonucleic Acid (mRNA) Expression and Fibre Cross-Sectional Area in Masseter, Digastric, Gastrocnemius and Soleus Muscles of Young and Adult Rats

Different demands on the muscles of mastication may influence their functional profile (size and distribution of muscle fibre types), which may change during growth and maturation, potentially influencing craniofacial growth. The aim of this study was to evaluate mRNA expression and cross-sectional area of masticatory muscle fibres compared with limb muscles in young and adult rats. Twenty-four rats were sacrificed at two different ages, namely 12 at 4 weeks (young) and 12 at 26 weeks (adult). The masseter, digastric, gastrocnemius and soleus muscles were dissected. Gene expression of myosin heavy-chain isoforms Myh7 (MyHC-I), Myh2 (MyHC-IIa), Myh4 (MyHC-IIb) and Myh1 (MyHC-IIx) in the muscles was measured using qRT-PCR RNA analysis, and immunofluorescence staining was performed to measure the cross-sectional area of different muscle fibre types. Different muscle types and ages were compared. Significant differences were found in the functional profile between masticatory and limb muscles. For the masticatory muscles, there was an increase in Myh4 expression with age, and this change was more intense for the masseter muscles, which also presented an increase in Myh1 expression, similarly to limb muscles. The fibre cross-sectional area of the masticatory muscles was generally smaller in young rats; however, this difference was less pronounced than in limb muscles.

Rehabilitation Nutrition for Iatrogenic Sarcopenia and Sarcopenic Dysphagia

Sarcopenia is a very important issue in rehabilitation medicine and nutritional care. The prevalence of sarcopenia in older people is approximately 50% in the rehabilitation setting, and also approximately 15% of inpatients without sarcopenia upon admission developed sarcopenia during hospitalization. There is a concern that secondary sarcopenia may occur iatrogenically during hospitalization. Iatrogenic sarcopenia is defined as sarcopenia caused by the activities of medical staff including doctors, nurses, or other health care professionals in healthcare facilities. Iatrogenic sarcopenia is categorized into activity-related, nutrition-related and disease-related-iatrogenic sarcopenia. Especially in acute phase hospitals, concentrating on the treatment of diseases with less attention to nutrition and activity is more likely to cause iatrogenic sarcopenia. Sarcopenic dysphagia is also an important aspect in rehabilitation medicine and nutritional care. Sarcopenic dysphagia is characterized by swallowing difficulty because of a loss of mass and function in whole-body skeletal and swallowing muscles. Sarcopenic dysphagia can be diagnosed using a 5-step algorithm for the condition. Iatrogenic sarcopenia and sarcopenic dysphagia are affected by nutrition, activity and diseases in a complex manner. Therefore, treatment of iatrogenic sarcopenia and sarcopenic dysphagia requires comprehensive interventions through nutrition management and rehabilitation. Rehabilitation nutrition is effective for preventing and treating iatrogenic sarcopenia and sarcopenic dysphagia. Rehabilitation nutrition can be practiced more effectively and comprehensively by using the rehabilitation nutrition care process, which is a systematic problem-solving method. Further research is required to verify the efficacy of rehabilitation nutrition for preventing or improving iatrogenic sarcopenia and/or sarcopenic dysphagia.