PRT had a large positive effect on strength ( 41 trials , 1955 participants ) , but there was statistical heterogeneity that was not explained by differences in study quality , participant characteristics or the exercise program .
REVIEW ER 'S CONCLUSIONS PRT appears to be an effective intervention to increase strength in older people and has a positive effect on some functional limitations .
However , the effect of this intervention on more substantive outcomes such as measures of disability or HRQOL remains unclear .
BACKGROUND Muscle weakness in old age , is associated with physical disability and an increased risk of falls .
Progressive resistance strength ( PRT ) training exercises ( i.e. movements performed against a specific external force that is regularly increased during training ) are design ed to increase strength in older people .
OBJECTIVES To assess the effect of PRT on measures of physical disability , functional limitation and impairment in older people  , and identify adverse events .
Resistance Training To Counteract the Catabolism of a Low-Protein Diet in Patients with Chronic Renal Insufficiency
Chronic renal insufficiency , regardless of cause , generally progresses to end-stage renal disease ( 1 ) . Malnutrition and muscle wasting in chronic uremia often parallel the progression of renal failure ( 2 ) . They also contribute to excess morbidity and mortality in patients with renal disease ( 3 ) . Protein-restricted diets delay the progression of renal disease ( 4 , 5 ) and alleviate uremic symptoms ( 6 ) . Although nutritional status , as assessed by biochemical and anthropometric indicators , may be maintained during protein restriction ( 6 , 7 ) , studies have shown that deterioration of nutritional status is associated with low energy and protein intake in patients with chronic renal insufficiency ( 8) . Resistance training increases nitrogen retention ( 9 ) , protein synthesis ( 10 ) , and expression of insulin-like growth factor I in skeletal muscle ( 11 ) ; ameliorates losses of muscle mass and function ; and enhances quality of life ( 12 ) in both healthy and unwell persons . The anabolic potential of resistance training counteracts the catabolism of HIV infection ( 13 ) and myopathy secondary to corticosteroid use in cardiac transplantation ( 14 ) , the loss of lean tissue during energy restriction for obesity ( 15 ) , and the interleukin-mediated myopathy of chronic heart failure ( 16 ) . However , its utility as an adjunctive treatment off setting the catabolism of a low-protein diet in uremic patients is not known ( 17 ) . We conducted a r and omized , controlled trial to determine whether resistance training would preserve lean body mass , nutritional status , and muscle function through alterations in protein turnover ( synthesis and oxidation ) in patients with moderate chronic renal insufficiency who were consuming a low-protein diet to slow the progression of renal failure . Methods Study Design Patients older than 50 years of age with chronic renal insufficiency were r and omly assigned to a low-protein diet plus resistance training or a low-protein diet plus sham exercises ( referred to as low-protein diet alone ) . Patients were asked to follow a low-protein diet ( 0.6 g/kg of body weight per day ) for 2 to 8 weeks ( run-in period ) before r and omization . They continued the low-protein diet for an additional 12 weeks after r and omization ( intervention period ) ( Figure 1 ) . The Human Investigation Review Committee at Tufts University , Boston , Massachusetts , and collaborating hospitals approved the study , and written informed consent was obtained from all patients . Figure 1 . Flow of patients through the study . * The post office returned letters because addresses were incorrect or persons had relocated . No patients withdrew , experienced ineffective interventions , or were lost to follow-up . One patient in each group had incomplete postintervention measures because of health-related reasons . HNRCA = Jean Mayer U.S. Department of Agriculture Human Nutrition Research Center on Aging . Study Sample Patients were recruited from the nephrology clinic at New Engl and Medical Center , Saint Elizabeth 's and Newton Wellesley Hospitals , and the Lahey Hitchcock Clinic , all in Boston , Massachusetts .  Screening procedures took place at the Jean Mayer U.S. Department of Agriculture Human Nutrition Research Center on Aging ( HNRCA ) at Tufts University . These procedures included sociodemographic and health history question naires ; physical examination ; electrocardiography ; blood hematology , chemistry , and urine analyses ; and a treadmill stress test .  Eligibility criteria included serum creatinine concentrations between 133 and 442 mol/L ( 1.5 and 5.0 mg/dL ) and physician approval to follow a low-protein diet .  A nephrologist confirmed renal diagnosis by review ing renal biochemistry results and clinical records . Exclusion criteria were myocardial infa rct ion ( within the past 6 months ) , any unstable chronic condition , dementia , alcoholism , dialysis or previous renal transplantation , current resistance training , recent involuntary weight change ( 2 kg ) , albumin level less than 30 g/L , proteinuria greater than 10 g/d , or abnormal stress test results at screening ( 18 ) . Reasons for early withdrawal from the study included loss of more than 25 % of initial body weight ; need for dialysis or transplantation ; development of any serious condition requiring hospitalization or precluding exercise ; and signs of malnutrition , such as a decrease in serum transferrin levels to less than 1.5 g/L or a 15 % decrease in hemoglobin or leukocyte count to below baseline levels . Diet Dietary intake of macronutrients and micronutrients and adherence to the low-protein diet were monitored twice per week during the run-in period and weekly during the intervention period by 3-day assisted dietary records ( including week and weekend days ) and regular meetings with the study dietitian , who was not blinded to group assignment . Dietary data were coded and analyzed by using Nutritionist-IV software ( N-Squared Computing , San Bruno , California ) . Patients collected one 24-hour urine specimen for every 3-day dietary record . Protein intake was also estimated by urea nitrogen levels ( 19 ) calculated from urine collection s and was used to assess adherence , which was defined as intake within 15 % of the prescribed low-protein intake ( 0.6 g/kg per day ) . Patients were counseled to reduce their habitual protein intake by eating food sources with less protein or by reducing portion sizes of higher-protein foods . Behavior modification strategies , including tips , recipes , food models , and self-monitoring tools for protein counts , were provided . These strategies were adapted from the Modification of Diet in Renal Disease Study ( 20 ) . Exercise Muscle strength was determined twice before r and omization and once after 12 weeks by measuring one repetition maximum ( 1 RM ) ( 21 ) using Keiser resistance training equipment ( Keiser Sports Health Equipment , Inc. , Fresno , California ) . One repetition maximum is the heaviest load that can be lifted once in good form through the full range of motion . Five machines ( chest and leg press , latissimus pull-down , knee extension , and knee flexion ) were used to include functionally large muscle groups . The better of the two baseline measurements of 1 RM was used in analyses and to set initial training loads for patients r and omly assigned to resistance training . All exercise sessions were performed at the HNRCA three times per week under the supervision of an exercise physiologist . Vital signs and body weight were recorded before each session . Patients who performed  resistance training  had monthly 1 RM testing on each machine . Workload during training was adjusted to reflect 80 % of the most recent 1 RM . In addition , patients ' workloads were progressively increased as appropriate according to the trainer 's objective perception of patients ' difficulty with workloads at each session . Patients performed three sets of eight repetitions on each machine per session , which lasted about 45 minutes ( 21 ) . Patients assigned to the  low-protein diet alone performed five to eight sham exercises ( gentle movements while st and ing , sitting , and bending ) for the upper and lower body . These were design ed not to have a physiologic impact but to provide trainer contact time similar to that of the resistance training group . Study Measures All measures were taken before ( week 0 ) and 12 weeks after r and omization . Observers were blinded to study group assignment at all times , except during assessment s of postintervention muscle strength . Main Outcome Measures Total body potassium is the best single measure of body cell mass closely linked to functional status ( 22 ) , prognosis , and survival ( 23 ) . Body cell mass ( muscle and viscera ) comprises the metabolically active tissues where protein is targeted ( 24 ) . Potassium-40 represents approximately 0.0118 % of total body potassium . Loss of total body potassium occurs in patients following low-protein diets ( 25 ) and in patients with renal disease ( 26 ) , as well as in patients with many other wasting syndromes .  Total body potassium  was determined in the body composition laboratory at HNRCA , with a coefficient of variation of 5 % ( 24 ) . Regional body composition of the area involving the mid-thigh muscle was determined by computerized tomography of the nondominant thigh . A Siemens DR3 CT Scanner ( Somatom-Siemens , Erlangen , Germany ) was used to obtain an 8-mm scan at the midpoint between the inguinal crease and the proximal pole of the patella . Images were digitized and analyzed to the nearest 0.01 cm2 , as described elsewhere ( coefficient of variation , 0.5 % to 1.5 % ) ( 21 ) . Type I and type II muscle-fiber cross-sectional areas were determined from vastus lateralis muscle biopsies of the nondominant thigh , performed with a 5-mm Bergstrom needle ( 27 ) . Sections were stained with adenosine triphosphatase ( pH , 4.3 ) to visualize type I and type II fibers . A slide preparation was made for each biopsy specimen , and 50 to 150 fibers per patient were analyzed by light microscopy ( coefficient of variation , 3 % ) ( 11 , 27 ) . Anthropometry Body weights were measured to the nearest 0.1 kg on a Toledo Weight-Plate ( Bay State Scale & Systems , Inc. , Burlington , Massachusetts ) . Height was measured once to the nearest 0.25 cm , without shoes , by using a wall-mounted stadiometer . Body mass index was determined from body weight and height as kg/m2 . Biochemical Measures All measurements were collected in the fasting state in a blinded fashion at the nutrition evaluation laboratory at HNRCA ( coefficient of variation , 5 % to 10 % ) . Urea nitrogen and creatinine concentrations in serum and urine and levels of plasma insulin-like growth factor I were determined , as described elsewhere ( 25 , 27 ) . In addition , blood cell count ; hematocrit ; and levels of serum albumin , transferrin , and prealbumin were measured monthly to evaluate nutritional status . Glomerular Filtration Rate Glomerular filtration rate was measured as the renal clearance of 125I-iothalamate ( Glofil , Cypros Pharmaceutical Corp. , Carlsbad , California ) , with a coefficient of
PRT had a large positive effect on strength ( 41 trials , 1955 participants ) , but there was statistical heterogeneity that was not explained by differences in study quality , participant characteristics or the exercise program .
REVIEW ER 'S CONCLUSIONS PRT appears to be an effective intervention to increase strength in older people and has a positive effect on some functional limitations .
However , the effect of this intervention on more substantive outcomes such as measures of disability or HRQOL remains unclear .
BACKGROUND Muscle weakness in old age , is associated with physical disability and an increased risk of falls .
Progressive resistance strength ( PRT ) training exercises ( i.e. movements performed against a specific external force that is regularly increased during training ) are design ed to increase strength in older people .
OBJECTIVES To assess the effect of PRT on measures of physical disability , functional limitation and impairment in older people  , and identify adverse events .