***TASK*** the task is to summarize an input biomedical literature in six sentences 
    ***INPUT*** the input is a biomedical literature 
    ***OUTPUT*** the output is the summary of an input biomedical literature in six sentences 
    ***DOCUMENTATION*** 
    ***EXAMPLES*** 
    Input: Background Measuring the strength of individual foot muscles is very challenging ; however , measuring muscle morphology has been shown to be associated with strength . A reliable method of assessing foot muscle atrophy and hypertrophy would therefore be beneficial to research ers and clinicians . Thus , the aim of this study was to evaluate the test-retest intra-observer reliability of ultrasound to measure the morphology of the primary toe flexor muscles . Method The abductor hallucis , flexor hallucis brevis , flexor digitorum brevis , quadratus plantae and abductor digiti minimi muscles in the foot , and the flexor digitorum longus and flexor hallucis longus muscles in the shank were assessed in five males and five females ( mean age = 32.1 ± 10.1 years ) . Muscles were imaged using a GE Venue 40 ultrasound ( 6 - 9 or 7.6 - 10.7 MHz transducer ) in a r and om order , and on two occasions 1 - 6 days apart . Muscle thickness and cross-sectional area were measured using Image J software with the assessor blinded to muscle and day of scan . Intraclass correlation coefficients ( ICC ) and limits of agreement were calculated to assess day-to-day repeatability of the measurements . Results The method was found to have good reliability ( ICC = 0.89 - 0.99 ) with limits of agreement between 8 - 28 % of the relative muscle size . Conclusion The protocol described in this paper showed that ultrasound is a reliable method to measure morphology of the toe flexor muscles . The portability and advantages of ultrasound make it a useful tool for clinical and research setting Abstract Reliability refers to the reproducibility of values of a test , assay or other measurement in repeated trials on the same individuals . Better reliability implies better precision of single measurements and better tracking of changes in measurements in research or practical setting s. The main measures of reliability are within-subject r and om variation , systematic change in the mean , and retest correlation . A simple , adaptable form of within-subject variation is the typical ( st and ard ) error of measurement : the st and ard deviation of an individual ’s repeated measurements . For many measurements in sports medicine and science , the typical error is best expressed as a coefficient of variation ( percentage of the mean ) . A biased , more limited form of within-subject variation is the limits of agreement : the 95 % likely range of change of an individual ’s measurements between 2 trials . Systematic changes in the mean of a measure between consecutive trials represent such effects as learning , motivation or fatigue ; these changes need to be eliminated from estimates of within-subject variation . Retest correlation is difficult to interpret , mainly because its value is sensitive to the heterogeneity of the sample of participants . Uses of reliability include decision-making when monitoring individuals , comparison of tests or equipment , estimation of sample size in experiments and estimation of the magnitude of individual differences in the response to a treatment . Reasonable precision for estimates of reliability requires approximately 50 study participants and at least 3 trials . Studies aim ed at assessing variation in reliability between tests or equipment require complex design s and analyses that research ers seldom perform correctly . A wider underst and ing of reliability and adoption of the typical error as the st and ard measure of reliability would improve the assessment of tests and equipment in our disciplines This prospect i ve , blinded study investigates the test retest reliability of measures of muscle thickness made by one sonographer across two cohort groups ( n = 29 ) of people hospitalised with acute stroke . Reliability was assessed in cohort one ( n = 14 ) for measurements made bilaterally at the anterior and posterior upper arms , the anterior and posterior thighs ( total of eight measurements ) and in cohort two ( n = 15 ) , for measurements made bilaterally at the lateral forearms , the anterior abdominal wall and the anterior and lower legs ( total of eight measurements ) . Reliability estimates varied between measurement sites ; intraclass correlation coefficients ( ICCs ) ranged from -0.26 ( lateral forearm , paretic side ) to 0.95 ( anterior thigh , nonparetic side ) , percent mean differences ranged from 0.42 % ( posterior upper arm , nonparetic side ) to 14.68 % ( anterior lower limb , nonparetic side ) and method error ranged from 1.08 ( abdomen , nonparetic side ) to 9.69 mm ( posterior lower limb , nonparetic side ) . Only four measurement sites ( anterior upper arm , posterior upper arm , abdomen and anterior thigh ) were within the acceptable ranges ( ICC 0.60 to 1.00 , mean percent difference range 0%-5 % and method error range 0 - 5 mm ) and considered reliable to use for measures of muscle thickness in people hospitalised with acute stroke The present study was performed to develop regression-based prediction equations for skeletal muscle ( SM ) mass by ultrasound and to investigate the validity of these equations in Japanese adults . Seventy-two Japanese men ( n=38 ) and women ( n=34 ) aged 18–61 years participated in this study and were r and omly separated into two groups : the model development group ( n=48 ) and the validation group ( n=24 ) . The total and regional SM mass were measured using magnetic resonance imaging ( MRI ) 1.5 T-scanners with spin-echo sequence . Contiguous transverse images ( about 150 slices ) with a slice thickness of 1 cm were obtained from the first cervical vertebra to the ankle joints . The volume of SM was calculated from the summation of digitized cross-sectional area . The SM volume was converted into mass units ( kg ) by an assumed SM density of 1.04 kg l−1 . The muscle thickness ( MTH ) was measured by B-mode ultrasound ( 5 MHz scanning head ) at nine sites on the anatomical SM belly . Strong correlations were observed between the site-matched SM mass ( total , arm , trunk body , thigh , and lower leg ) by MRI measurement and the MTH × height ( in m ) in the model development group ( r=0.83–0.96 in men , r=0.53–0.91 in women , P<0.05 ) . When the SM mass prediction equations were applied to the validation group , significant correlations were also observed between the MRI-measured and predicted SM mass ( P<0.05 ) . The predicted total SM mass for the validation group was 19.6 ( 6.5 ) kg and was not significantly different from the MRI-measured SM mass of 20.2 ( 6.5 ) kg . Bl and –Altman analysis did not indicate a bias in prediction of the total SM mass for the validation group ( r=0.00 , NS ) . These results suggested that ultrasound-derived prediction equations are a valid method to predict SM mass and an alternative to MRI measurement in healthy Japanese adults Abstract . This study aim ed to investigate the suitability of using ultrasonograph muscle thickness ( MT ) measurements to estimate the muscle volume ( MV ) of the quadriceps femoris as an alternative approach to magnetic resonance imaging ( MRI ) . The subjects were 46 men aged from 20 to 70 years who were r and omly allocated to either a validation or a cross-validation group . In the validation group , multiple and simple regression equations , which used a set of MT values determined at mid-thigh and thigh length ( l ) and the product of π , (MT/2)2 , and l [ π·(MT/2)2·l ] , respectively , as independent variables , were derived to estimate the MV measured by MRI . Because the two equations were cross-vali date d , the data from the two groups were pooled to generate the final prediction equations : MV (cm3)=(MT × 311.732)+(l × 53.346 ) –2058.529 as the multiple regression equation and MV (cm3)=[π·(MT/2)2·l] × 1.1176 + 663.040 as the simple regression equation . In the multiple regression equation , MT explained 75 % of the variation in the MV measured by MRI .  The r2 and the st and ard error of the estimate ( SEE ) of the equations were 0.824 and 175.6 cm3 ( 10.6 % ) , respectively , for the multiple regression equation and 0.829 and 173.7 cm3 ( 10.5 % ) , respectively , for the simple regression equation . Thus , the present results indicate that ultrasonograph MT measurements at mid-thigh are useful for estimating the MV of knee extensors . However , the observed SEE values suggest that the prediction equation obtained in this study may be limited to population studies rather than individual assessment s in longitudinal studies BACKGROUND AND AIMS sarcopenia has been indicated as a reliable marker of frailty and poor prognosis among the oldest individuals . We evaluated the impact of sarcopenia on the risk of all-cause death in a population of frail older persons living in community . METHODS we analysed data from the Aging and Longevity Study , a prospect i ve cohort study that collected data on all subjects aged 80 years and older residing in the Sirente geographic area ( n = 364 ) . The present analysis was conducted among those subjects who were between 80 and 85 years of age at the time of the baseline assessment ( n = 197 ) . The main outcome measure was all-cause mortality over 7-year follow-up . According to the European Working Group on Sarcopenia in Older People ( EWGSOP ) criteria , the diagnosis of sarcopenia required the documentation of low muscle mass and the documentation of either low muscle strength or low physical performance . Cox proportional regression models were used to estimate crude and adjusted hazard ratios and 95 % confidence intervals of death by the presence of sarcopenia . RESULTS using the EWGSOP-suggested criteria , 43 subjects with sarcopenia ( 21.8 % ) were identified . During the 7-year follow-up , 29 ( 67.4 % ) participants died among subjects with sarcopenia compared with 63 subjects ( 41.2 % ) without sarcopenia ( P < 0.001 ) . After adjusting for potential confounders including age , gender , education , activities of daily living ( ADL ) impairment , body mass index , hypertension , congestive heart failure , chronic obstructive pulmonary disease , number of diseases , TNF-α , participants with sarcopenia had a higher risk of death for all causes compared with non-sarcopenic subjects ( HR : 2.32 , 95 % CI : 1.01 - 5.43 ) . CONCLUSIONS our results obtained from a representative sample of very old and frail subjects show that sarcopenia is associated with mortality , independently of age and other clinical and functional variables The increase of elderly in our society requires simple tools for quantification of sarcopenia in inpatient and outpatient setting s. The aim of this study was to compare parameters determined with musculoskeletal ultrasound ( M-US ) with muscle strength in young and elderly patients . In this prospect i ve , r and omised and observer blind study , 26 young ( 24.2 ± 3.7 years ) and 26 old ( age 67.8 ± 4.8 years ) patients were included . Muscle thickness , pennation angle and echogenicity of all muscles of musculus quadriceps were measured by M-US and correlated with isometric maximum voluntary contraction force ( MVC ) of musculus quadriceps . Reproducibility of M-US measurements as well as simple and multiple regression models were calculated . Of all measured M-US variables the highest reproducibility was found for measurements of thickness ( intraclass correlation coefficients , 85–97 % ) . Simple regression analysis showed a highly significant correlation of thickness measurements of all muscles of musculus quadriceps with MVC in the elderly and in the young . Multiple regression analysis revealed that thickness of musculus vastus medialis had the best correlation with MVC in the elderly . This study showed that measurement of muscle thickness , especially of musculus vastus medialis , by M-US is a reliable , bedside method for monitoring the extent of sarcopenia 
    Output:
    
This systematic review shows that ultrasound  is a reliable and valid tool for the assessment of muscle size in older adults .