Unlike stubborn belly fat that never seems to go away, it is commonly thought that with muscle mass, if you don’t use it, you lose it. While this is partly true, it’s a little more complicated than that. Whether you’re coming off an injury or a long break from the gym, you’re probably wondering how much damage your rest period has done to your gains. Or maybe you’re actually looking to slim down your muscle mass…..Continue reading….
Source: TrifectaNutrition
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Critics:
The hallmark sign of muscle atrophy is loss of lean muscle mass. This change may be difficult to detect due to obesity, changes in fat mass or edema. Changes in weight, limb or waist circumference are not reliable indicators of muscle mass changes. The predominant symptom is increased weakness which may result in difficulty or inability in performing physical tasks depending on what muscles are affected.
Atrophy of the core or leg muscles may cause difficulty standing from a seated position, walking or climbing stairs and can cause increased falls. Atrophy of the throat muscles may cause difficulty swallowing and diaphragm atrophy can cause difficulty breathing. Muscle atrophy can be asymptomatic and may go undetected until a significant amount of muscle is lost.
Skeletal muscle serves as a storage site for amino acids, creatine, myoglobin, and adenosine triphosphate, which can be used for energy production when demands are high or supplies are low. If metabolic demands remain greater than protein synthesis, muscle mass is lost. Many diseases and conditions can lead to this imbalance, either through the disease itself or disease associated appetite-changes, such as loss of taste due to Covid-19.
Causes of muscle atrophy, include immobility, aging, malnutrition, certain systemic diseases (cancer, congestive heart failure; chronic obstructive pulmonary disease; AIDS, liver disease, etc.), deinnervation, intrinsic muscle disease or medications (such as glucocorticoids). Disuse is a common cause of muscle atrophy and can be local (due to injury or casting) or general (bed-rest).
The rate of muscle atrophy from disuse (10–42 days) is approximately 0.5–0.6% of total muscle mass per day although there is considerable variation between people.[5] The elderly are the most vulnerable to dramatic muscle loss with immobility. Much of the established research has investigated prolonged disuse (>10 days), in which the muscle is compromised primarily by declines in muscle protein synthesis rates rather than changes in muscle protein breakdown.
There is evidence to suggest that there may be more active protein breakdown during short term immobility (<10 days). Certain diseases can cause a complex muscle wasting syndrome known as cachexia. It is commonly seen in cancer, congestive heart failure, chronic obstructive pulmonary disease, chronic kidney disease and AIDS although it is associated with many disease processes, usually with a significant inflammatory component.
Cachexia causes ongoing muscle loss that is not entirely reversed with nutritional therapy.The pathophysiology is incompletely understood but inflammatory cytokines are considered to play a central role. In contrast to weight loss from inadequate caloric intake, cachexia causes predominantly muscle loss instead of fat loss and it is not as responsive to nutritional intervention. Cachexia can significantly compromise quality of life and functional status and is associated with poor outcomes.
Sarcopenia is the degenerative loss of skeletal muscle mass, quality, and strength associated with aging. This involves muscle atrophy, reduction in number of muscle fibers and a shift towards “slow twitch” or type I skeletal muscle fibers over “fast twitch” or type II fibers. The rate of muscle loss is dependent on exercise level, co-morbidities, nutrition and other factors.
There are many proposed mechanisms of sarcopenia, such as a decreased capacity for oxidative phosphorylation, cellular senescence or an altered signaling of pathways regulating protein synthesis, and is considered to be the result of changes in muscle synthesis signalling pathways and gradual failure in the satellite cells which help to regenerate skeletal muscle fibers, specifically in “fast twitch” myofibers.
Sarcopenia can lead to reduction in functional status and cause significant disability but is a distinct condition from cachexia although they may co-exist. In 2016 an ICD code for sarcopenia was released, contributing to its acceptance as a disease entity.Muscle diseases, such as muscular dystrophy, amyotrophic lateral sclerosis (ALS), or myositis such as inclusion body myositis can cause muscle atrophy.
Damage to neurons in the brain or spinal cord can cause prominent muscle atrophy. This can be localized muscle atrophy and weakness or paralysis such as in stroke or spinal cord injury.More widespread damage such as in traumatic brain injury or cerebral palsy can cause generalized muscle atrophy. Injuries or diseases of peripheral nerves supplying specific muscles can also cause muscle atrophy. This is seen in nerve injury due to trauma or surgical complication, nerve entrapment, or inherited diseases such as Charcot-Marie-Tooth disease.
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