Exercise as it relates to Disease/Importance of physical activity and skeletal muscle fat infiltration in older adults

This article is an orginial critical analysis of; Effects of physical activity on strength and skeletal muscle fat infiltration in older adults:a randomized control trial by Bret Goodbaster et al. - Applied physiology - Americal physiological society 2008

What is the background of the research?
The loss of muscle and increase in skeletal muscle fat is highly associated with ageing, and how closely fat interacts with muscle both metabolically and chemically. It's been established in the literature that fat can infiltrate into muscle as we age. Relationships have been reported between accumulation of fat in muscle and the decline of muscle cells. Intermuscular adipose tissue (IMAT) is the term to describe this fatty infiltration in the muscle, referring to where the lipids (fats) are stored in adipocytes located underneath the deep fascia of muscle fibres (also termed as intramuscular fat). This refers to between the muscle fibres (intra) and also between the muscle groups (inter where there is visible storage of lips in the adipocytes). This reduction in muscle mass in the ageing population is a result of the greater fat infiltration into the muscle which is associated with functional decline and increased risk of mobility loss in older men and women. The association between low muscle mass and functional decline seems to be a function of underlying muscle strength. Of course, traditional techniques of doing so involve improving exercise and diet, but the effectiveness on whether physical activity can influence this decline on muscle cells and it's muscle fat infiltration is understudeied method gaining ground with distince advatiages fo declining this aging skeletat muscle fat infiltration.

Where is this research from?
This study was supported by a Cooperative Agreement with the National Institute on Aging (UO1-AG-022376).

This study can be found on Pub med: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2584841/

The author: Bret Goodpaster

Bret Goodpaster is part of the Department of Medicine, University of Pittsburgh, Pittsburgh, Pennsylvania and has been publishing 231 articles on health disease and physiology since 1993 and actively involved in the research and publication on health and physical activity.

What kid of research was this?
This study was a ranomized control trial which looked at the effectiveness of physical activity on strength and skeletal muscle fat infiltration in older adults. The research involved 52 subjects who were measure for baseline strength and CT scanning and were randomized into either a physical activity (PA) or successful aging health educational control (SA) group.

What did reasearch involve?
The intervention took its effect through different phases: adoption (weeks 1-8) ;transition (weeks 9-24) and maintenance (weeks 25 to end of intervention). The initial intervention in the early stage of phase 1 was primarily centre-based with a shift to home-based activity in the transitiion and mainentance phase. In the adoption phase, participants were given three 40 to 60 min supervise physical activtiy sessions per week which were conducted in the centre. Progressing along to the transition phase of the intervention there was more emphasis on home-based exercise and centre0based exercise was reduced to 2 time per week. The home-based exercises included training of the endurance/strengthening/flexibility. In the maintenance phase participants were encouraged to peform home-based physical activity a minimum 5 days per week. This was all in comparison to the control group ho participated in attention and health education. Participants were slinto into small groups weekly for the first 26 weeks and then monthly on health topics relavent to older adults and physical activity. Physical activity and peformance over the duration of this intervention in both groups were measured via extensor strength, body weight adn axial CT-derived images of midthigh skeletal muscle (CSA) and adipose tissue at base line and 12 months. With the knee extensor strength determined at 60°/s with a Kin-Com dynamometer.

Results
Specific torque was reduced in the control group. This effect was not observed in the physical activity activity group, with a between-group difference in the change in specific torque (Figure 1).

Both groups lost muscle strength as well as a reduction in the CSA although this was not statistically different between the 2 groups (Figure 2 and 3).

IMAT increased in the control group but not in the physical activity. There was an 18% increase of IMAT in the SA controls in this 1 year trial. This gain was nearly completely preventred by physical activity. This gain of fat, however was clearly depot specific; the subcutaneous thigh adipose tissue did not significantly change in either group (Figure 4).

Interpretation and Critical analysis
On of the key findings of the study was that the physical activity group prevented further loss of muscle strength in the older adults who in comparison with the control were on the steep slop of functional decline. The degree of strength loss being ~22% during the 1 year trial in the control group. Another novel finding was the reduced knee extensor strength in both the PA and control groups. Although these results were statistical different these results indicate that even with physical activity program there still a reduction of the maintenance of the muscle strength in the PA group which has to be further looked into. This is a possible direct caveat of the methodology, as the participants were given three 40 to 60 min physical activity supervised and unsupervised sessions focussing on endurance /strengthening/flexibility but the intensity at which the exercises was conducted was not outlined and consistent throughout the 1 year trial. The intensity is very important in physical activity to stress the body in a strenuous amount. In the Australian physical activity guidelines clearly state "all healthy adults aged 18-65 years should participate in moderate intensity aerobic physical activity for a minimum of 30 minutes on 5 days per week or vigorous intensity aerobic activity for a minimum of 20 minutes on three days per week. Another key finding was that the physical activity group at the end of the trial in comparison to the SA group prevented the increase in IMAT associated with ageing. This ~18% increase in IMAT in control group show that these effects on physical activity can be a strategy to compute the age associated decline in muscle mass and strength. This key finding true effect on the population or the clinical significance is possible to be another caveat to the methodology. There was limited information on any pre-existing conditions of these adults. Ageing also comes with a vast number of complications and degenerating changes that may influence to carry out these interventions to it's full potential. For example, patients with multiple conditions including neurocognitive and cardiac disorders would find these as barriers to performing the recommended amounts of exercise. All of which can impact their ability for adequate mobility and participation in the intervention.

Conclusion
Effects of physical activity can be a strategy to combat the age associated increase in muscle fat infiltration and prevent the functional decline associated with it.

Adequate physical activity can have changes in muscle fat infiltration, maintain strength and torque at muscle and prevent loss of muscle mass.

Practical advice
An adequate dose of physical activity intervention including intensity and time has to be given to see clinically significant changes.

Underlying pathologies of the older populations have to be considered of ageing populations and their compliance over the course of the intervention.

Further information/resources

Muscle mass, muscle strength, and muscle fat infiltration as predictors of incident mobility limitations in well-functioning older persons - https://pubmed.ncbi.nlm.nih.gov/15860469/

Sarcopenia: characteristics, mechanisms and functional significance’ - 

‘Protein-containing nutrient supplementation following strength training enhances the effect on muscle mass, strength, and bone formation in postmenopausal women’ - https://dx.doi.org/10.1152/japplphysiol.00935.2007