The Hallmark of Aging


The Hallmark of Aging

Sarcopenia is the hallmark of aging responsible for significant muscle mass loss seen with advancing chronological age. It is associated with decreases in functional ability due to its impact on strength; most notable are losses in mobility and increases in fall risk. This loss of muscle can begin as early as the 3rd decade of life, and results in the loss of 5-10% of one’s vastus lateralis mass by the 5th decade.1 Upon reaching age 50, the sarcopenic rate accelerates causing the loss of as much as 30-40% of the vastus lateralis by age 80.1Collectively, these factors contribute to a decreased quality of life, frailty, and increased mortality. A recent meta-analysis of studies comprised of approximately 2 million men and women demonstrated that strength loss was a strong predictor of mortality across the life span, regardless of comorbidities.2 When broken down by body region, increased grip strength had a 31% reduction in all-cause mortality risk compared to those with decreased strength.2 In the lower extremity, increased knee extensor strength had a 14% reduction in all-cause mortality.2 In addition to the physical and medical burden imposed upon aged persons, the financial burden of sarcopenia in the United States is substantial as well. Annually, treatment of ailments associated with the condition amount to $40.4 billion.10 To combat sarcopenia, the American College of Sports Medicine recommends older adults perform a combination of resistance training at 70-80% 1RM at least two times per week, and participate in 150-300 minutes of moderate intensity aerobic training weekly.3 However, less than 10% of those >65 years old met both guidelines and only 14% met the resistance training guideline.4 More recently, resistance training has taken on an increasingly important target given its superior ability to impact physical functioning via strength translation.11

Why do we see sarcopenia

It’s not fully understood why older adults lose muscle mass simply due to increasing age. A MPS_old-1couple potential causes may provide reasons why BFR could provide a potential solution. It seems sarcopenia, though not as a rapid, may follow a similar mechanistic behavior to the disuse atrophy observed in a number of studies. Dubbed, anabolic resistance, these studies revealed protein ingestion that would typically impart an anabolic stimulus, no longer does so, regardless of age.5 To counter this, it seems young persons must prime the system via resistance exercise, while also getting a full complement of essential amino acids. This is tougher for the aged person, because there is a decreased anabolic response to a meal and a workout in the older adult compared to the younger adult. For example, young adults require approximately 20g of protein to fully activate muscle protein synthesis whereas the elderly require 40g to reach the same level of activation.14 Similar disparities are observed with resistance training. Muscle protein synthesis in young adults will continue to respond favorably as the individual approaches their 1RM. The elderly, however, have no increase in muscle protein synthesis beyond 60% of their 1RM (Fig. 1).15
FSR_oldA second potential cause, and thus a target for combatting sarcopenia with BFR could be the fact that older persons have a decrease in capillary density compared to their younger counterparts.16 The resultant change in perfusion limits the delivery of oxygen, nutrients, and growth factors, helping to explain the blunted anabolic response to a bolus of protein. BFR has been shown to elicit an angiogenic response via
the release of vascular endothelial growth factor that occurs following a bout of BFR exercise.17Additionally, a few other studies have demonstrated local vascular responses that may be desired in targeting this potential cause of sarcopenia.18,19
The light load nature of BFR exercise can be friendly to aged joints and soft-tissues, thus making it less threatening and potentially better tolerated than heavier loads. A few studies have demonstrated both the efficacy and effectiveness of this intervention in aged persons. In fact, a recent review paper by Centner that pulled from 11 studies and 238 participants, indicated that the addition of BFR to a resistance or aerobic exercise program was almost certain to elicit an MPS_RETanabolic response in the exercised muscle(s).12Exercise at low intensities performed with BFR has been shown to increase muscle protein synthesis (MPS) post exercise by over 55%; this is similar to that observed in young adults.20 Over a 12-week training program, older adults (>60 years old) who performed BFR resistance exercises combined with moderate-vigorous intensity walking demonstrated similar changes in muscle hypertrophy and strength compared to those who performed HIT resistance training (70-80% 1RM) and moderate-vigorous intensity walking; albeit with 37% less volume.6 The reduced volume, along with the light weight nature of the intervention translates to significantly less mechanical stress on arthritic or painful joints.the release of vascular endothelial growth factor that occurs following a bout of BFRexercise.17Additionally, a few other studies have demonstrated local vascular responses that may be desired in targeting this potential cause of sarcopenia.18,19
HIT_MPS
In addition to resistance training with low loads, BFR has the unique ability to increase muscle CSA and strength when coupled with low intensity, short duration aerobic activities. Following 6 weeks of low intensity treadmill training, Abe and colleagues observed 7 and 16% increases in knee extensor and flexor isokinetic strength respectively.8 This was followed by a similar study by Clarkson and colleagues who found a three-fold greater improvement in the 30 second sit-to-stand test, and a 2-fold improvement in the TUG compared to a work matched control.9 Findings from both studies confirm that BFR during low intensity aerobic activities is not only able to add muscle and strength, but these changes directly translate into functional activities.
“In summary, as the United States society ages and as the incidence of musculoskeletal procedures correspondingly increases, improved rehabilitative interventions focused on minimizing sarcopenia, dynapenia, improving mobility, and preventing falls is required. Initial BFR exercise studies in older adults show promise as a potential clinically relevant intervention. BFR exercise can be combined with walking, body weight exercise, elastic band resistance exercise, and traditional resistance exercise. Furthermore, as the clinical adoption of this intervention continues, additional objective measures of its utility, limitations, and contraindications will become more readily apparent for the patient.”13


References

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