Dynapenia Loss of Muscle Mass and Muscle Strength in Older Adults

Question: Discuss about theDynapenia Loss of Muscle Mass and Muscle Strength in Obese and Nonobese Older Adult. Answer: Many major changes occur during ageing that have a negative effect on the functional status of the older adults. These include the progressive decrease in the strength, mass and quality of the muscle that affects the locomotion and muscle strength. One of these conditions is the dynapenia that focuses on the muscle size being the primary risk for this condition. It is age-related and predisposes the older people to functional mobility and limitations. However, the force-generating skeletal muscle properties are the potential antecedents for this condition. There is low muscle mass and function that is associated with dynapenic condition. The maximal voluntary strength greatly declines with the ageing process and contribute to the mortality and physical dependence. Dynapenia is also coined as sarcopenia where the direct muscle mass reduction is associated with strength loss and age-related reduction of mobility (Manini and Clark 2016). The following argumentative essay deals with the question that intramuscular fat accumulation as the cause of dynapenia and related mechanisms and risk factors associated with the dynapenic condition. Dynapenia is an age-related muscle strength loss that is not caused by muscular or neurologic diseases. This condition predisposes the older people towards an increased risk for the mortality and functional limitations in the older people. Loss of muscle power and strength is called the dynapenic condition. Muscle force production is greatly controlled by the skeletal muscle factors and neurologic properties (Cuthbertson et al. 2015). The ability of the nervous system to activate the voluntarily skeletal muscle is impaired and voluntary deficit like decrease on excitatory drive and motor-neuron excitability that results in suboptimal discharge rate of the motor unit. This limiting capacity of the motor units results in the reduction of muscle strength. There is also incomplete or non-occurrence of collateral reinnervation that affects the muscle strength. Dynapenia is the intramuscular mass reduction rather than mass accumulation that results in muscle strength loss. There are potential muscular mechanisms that cause the dynapenic condition in older adults. Recent studies have shown that older people loses 1% of the thigh muscle each year and shows variations in the atrophy degree among the older people (Kalyani, Corriere and Ferrucci 2014). Muscle wasting in the older people occurs due to the metabolism of muscle protein as the balance between the degradation of protein synthesis is the major responsible factor that maintains the lean mass. Arguably, according to a recent finding, the protein synthesis of the basal muscle does not change in the young band older people and it is not generally altered in the older adults in terms of synthesis or breakdown of the protein synthesis. According to Mitchell et al. (2016) it is indicated that there is an exhibition of decreased accretion of the muscle proteins after the consumption of small amounts of the essential amino acids in their diet. The changes in the metabolism of the muscle protein are also the contributors to muscle size loss and muscle weakness with the dynapenic condition being the cause for dynapenia. Along with the anatomic structure and muscle size, the muscle of the aged people differs in the composition that also determines the dynapenic condition. There are several studies where it has been shown that the ageing factor increases the intramuscular adipose tissue that is between the muscle fascicles and intermuscular adipose tissue that is between the muscle groups. Recent studies have shown that the adipose tissue cytokine production is directly linked with the decrease production of muscle force. This provides the theoretical basis for the intramuscular fat reduction with dynapenia and loss of muscle strength. Arguably, a recent study has shown that the direct relation between the strength loss and increase accumulation of the intermuscular adipose tissue. Sarcopenia is the condition that is associated with the muscle mass loss and dynapenia is the loss of mass strength or force due to age-related muscle power and strength loss. According to Normandin et al. (2015) the conceptual; model for the dynapenic condition is related to the skeletal muscle force production that give rise to the dynapenic condition limiting the functionality and mobility. The lean muscular mass contributes to the 50% of the total body weight in the young people and it greatly declines with the advancement of age of 75-80 years reducing to 25% of the total body weight (Bouchard and Janssen 2015). This decline in the muscle mass is greatly related to the mobility status in the older adults with the decrease in the strength of the muscles with mass during ageing. In a study conducted by Moretti et al. (2015) showed that the quadriceps muscle called the vastus lateralis decreases by 40% during 20 to 80 years. This progressive imbalance and mismatch between the muscle strength and mass during the ageing have deterioration on the muscle quality. Physical inactivity is probably another cause that contributes to the muscle strength and mass in the older adults. The skeletal muscle loss results in the decrease in the basal metabolic rate by about 30% during the 20 to 70 years of age. The decrease in the duration and intensity of the physical activity is associated with the low energy expenditure and ageing process. Moreover, there is also decrease in the postprandial expenditure of energy as a result of decrease in fat oxidation. This shows that inadequate protein intake by the older adults can result in muscle mass loss and strength in the older adults. Inactivity during ageing is the strong factor that results in decline of muscle structure, mass and strength defining the sarcopenia and dynapenic condition (Murton et al. 2015). Sedentary lifestyle, hind limb suspension, spaceflight, bed rest leads to the microcirculatory skeletal muscle disturbances, protein loss, fiber-type switching, atrophy and contractile property changes . Oxidative stress is a factor that mediates muscular atrophy in response to the unloading process. Unloading is a process in which there is decrease in the number of myonuclei and increase in the apoptosis of the myonuclei in the skeletal muscles. Age-related dynapenic condition at the tissue and cell level is characterized by the expanded motor units, fiber necrosis, type II myofiber atrophy and type grouping, inacresed collagen, intramyocellular lipids and other conditions. Fat infiltration is another reason that characterizes the ageing muscle that occurs between the muscle groups at the macroscopic level and in between the myocytes at the microscopic level. A study conducted by Buch et al. (2016) shows that deposition of lipid in the intramyocellular is correlated with the fat mass percentage that is the measure of adipose deposition. There is a de-novo hypothesis given by Cuthbertson et al. (2015) showed that chronic diseases increases with age prevalence that contribute to the dynapenic condition of decrease in skeletal muscle strength and mass. In addition, the presence of specific disease or age is also linked with the oxidative stress, pro-inflammatory cytokines, denervation, amino acid bioavailability and decrease in vascular perfusion, anabolic and catabolic hormones. These mechanisms greatly affect the characteristics of skeletal muscle associated with dynapenia, sarcopenia, increase protein degradation, motor neuron function and decrease protein synthesis and intramyocellular lipids. There is loss of intramuscular strength and mass that results in conditions for sarcopenia and dynapenia. Heat-shock protein 70 is the inhibitor of caspase independent and dependent apoptotic pathways and regulates the muscle size through apoptosis and inhibition of the necrotic muscle fiber distribution. Muscular atrophy of the type II fibers and loss of muscle fiber results in decline of muscle mass in older people. Loss of muscle size due to reduction of myofibrillar proteins and fiber number reduction results in muscle weakness in the older adults. The structural and functional decline of the neuromuscular system is witnessed as a cause that has a detrimental effect on the activities of daily life and dependence in the older adults. Muscle weakness is related to the neural activities impairment and skeletal muscle intrinsic force generation capacity reduction (Lee et al. 2016). Recent study has shown that the magnitude and number of the associations for inability or low physical performance is more related to the decrease in muscle strength rather than muscle mass (Yang et al. 2014). Muscle size decline is not only the sole contributor of the physical inability in older people but, also decline in the muscle strength that is the main cause for dynapenia. This loss of muscle strength is the main factor for the muscle weakness resulting in dynapenic condition. There are many factors that contribute to the dynapenic condition that is muscle weakness or loss of power like the muscle fiber transformation, changes made in the contractile proteins, adipocyte infiltration into muscle fibers and deterioration of capillary blood supply, muscle contractile reduction and neural activation impairment. There are other factors that also contribute to the dynapenic condition like excitation-contraction coupling, reduction of the functional reserves and vital capacity reduction. It is actually an age-related condition that is associated with conditions of reduced muscle strength (Aubertin-Leheudre et al. 2016). Decrease in the strength of the skeletal muscle and contractile protein synthesis with increased protein degradation rate of the muscles shows the functional and structural damage in the older adults. It has been studied in both rodents and humans that the mitochondrial skeletal muscle dysfunction is associated with advancing age. The reason for this is the mitochondrial DNA copy number decrease, mRNAgenes that encode mitochondrial muscle proteins and mitochondria protein synthesis rate (Correa-de-Araujo and Hadley 2014). Chemical or neuronal mediators also play an important role in the signaling of the hypothalamus from the periphery that stimulates the sympathetic nerve center signaling and paraventricular nucleus in the hypothalamic center. In humans, the protein synthesis in the skeletal muscle decreases with advancing age. Some studies showed that the MyHC synthesis rate and decrease in mitochondrial proteins, whereas, there is a high rate of sarcoplasmic protein synthesis in th e older people (Miljkovic et al. 2015). Despite of the small amount of the proteins, it has a faster turnover rate that contributes to the synthesis of the skeletal muscles. Those proteins that have a slow turnover rate play a major role in the skeletal muscle protein synthesis. There are various low and high risk factors that contribute to the dynapenic condition in the older adults above the age of 60 years. The low risk factors are measured for the grip strength and the knee extensor strength. In addition, there are neural factors that determine the etiology of dynapenia. Nerve conduction, excitatory potential, motor unit estimations and reflex excitability estimates are the ones that have an effect on the dynapenic condition. There are also muscular factors that causes the dynapenic condition like sarcopenia, decrease in muscle mass, hormonal imbalances and chronic diseases like myopathies are the contributors of dynapenia condition. These are the factors that contribute to the dynapenic condition involving the neuronal and muscular factors (da Silva Alexandre et al. 2014). Contrary to the above discussion, intramuscular fat accumulation is the condition when there are intramuscular triglycerides or triacylglycerol or intramyocellular triacylglcerol (IMTG) inside the fibers of the skeletal muscles. This is stored in the lipid droplets in close proximity to the skeletal muscle mitochondria that acts as an energy reserve at the time of exercise. The condition of this excess fat accumulation is associated with conditions like type2 diabetes and insulin resistance. There are also viral infection like lipodystrophy or human immunodeficiency virus (HIV) are also associated with the intramuscular fat over-accumulation that contributes to the condition of AIDS wasting syndrome. Skeletal intramuscular loss is the reason for the dynapenic condition that gradually results in the loss of muscle power or strength in the older people (Kim and Choi 2013). Aging and loss of muscle strength is related to the inability to perform daily activities and reduces the mobility and dependency. All these factors and conditions show that the intramuscular fat accumulation is not the cause for the dynapenic condition. Dynapenia is an age-related muscle strength loss that is not caused by muscular or neurologic diseases. The lean muscular mass contributes to the 50% of the total body weight in the young people and it greatly declines with the advancement of age of 75-80 years reducing to 25% of the total body weight. This condition predisposes the older people towards an increased risk for the mortality and functional limitations in the older people. It is the intramuscular mass reduction rather than mass accumulation that results in muscle strength loss. Therefore, the above argument illustrates that intramuscular fat accumulation is not a cause for dynapenia. 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