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 .
Weight Training Improves Walking Endurance in Healthy Elderly Persons
Physical disability is common among older persons living within the community . The Framingham Disability Study [ 1 , 2 ] reported that , among community-dwelling persons older than 70 years of age , 49 % of women and 27 % of men have substantial mobility or work limitations . More recently , a 4-year prospect i ve trial of healthy elderly persons with no disability at baseline showed that lower-extremity physical performance at baseline was highly predictive for the subsequent development of disability [ 3 ] . Muscle mass , strength , and endurance decrease with age , and a close correlation between short-course walking speed and the size and strength of leg muscles has been shown in institutionalized nonagenarians [ 4 ] . Furthermore , resistance training in this population has been shown to result in increased measures of physical performance and corresponding increases in muscle strength , size , and short-course walking speed [ 4 , 5 ] . Our goal was to determine whether resistance training would improve walking endurance and lower-limb strength in nondisabled , community-dwelling elderly persons . Methods Twenty-four sedentary , healthy persons ( 11 men and 13 women ) were r and omly assigned within sex groups either to a 12-week resistance-training program or to sedentary control status .  The mean age of the participants was 70.4 4 years ( range , 65 to 79 years ) , and no differences in mean age were seen between groups ( 69.9 4 years in the resistance-training group ; 70.7 5 years in the control group [ P > 0.2 ] ) . The  resistance-training group was composed of 6 men and 6 women ; the control group consisted of 5 men and 7 women . Participants did symptom-limited treadmill stress tests at baseline , and we collected expired gas to determine peak aerobic capacity . We used a Horizon Metabolic Measurement Cart ( Sensormedics , Yorba Linda , California ) to analyze expired air .  Participants were excluded if they had angina or electrocardiographic ischemia ( defined as ST-segment depression more than 1 mm ) during the exercise test ( n = 2 ) , if their resting blood pressure was higher than 160/90 mm Hg ( n = 4 ) , or if they had a noncardiopulmonary limitation of exercise capacity , such as claudication , arthritis , or cerebrovascular disease ( n = 1 ) . We tested 29 participants to arrive at the final study sample of 24 persons . No participants were receiving calcium- or -blocking medications or estrogen-replacement therapy , and none had diabetes . We determined body composition by using underwater weighing and correcting for residual volume [ 6 ] . Leg-muscle mass was determined by dual-energy x-ray absorptiometry [ 7 ] . Strength was evaluated on a Universal Gym apparatus ( Universal , Cedar Rapids , Iowa ) by measuring the single repetition maximal lift for leg extension , leg flexion , and bench press . We measured submaximal endurance capacity on the treadmill by first having participants walk for 5 minutes at an intensity of 50 % of their previously determined peak aerobic capacity . Participants then gradually increased their walking intensity to 80 % of peak aerobic capacity by 10 minutes of the continuous protocol and proceeded until exhaustion ( n = 24 ) or 45 minutes , at which time the test was terminated . Because none of the participants had angina , claudication , or exercise-limiting arthritis , exhaustion was defined as a combination of leg fatigue , dyspnea , and overall body fatigue . During endurance testing , heart rate , blood pressure , oxygen uptake , and perceived exertion [ 8 ] were measured at 5-minute intervals until exhaustion . After 12 weeks , variables were measured again , and walking endurance was measured at the same absolute workload as before conditioning . The weight-training regimen consisted of three sets of eight repetitions of seven exercises done using a Universal Gym apparatus 3 days per week . The exercises ( and primary muscles exercised ) were leg extension ( quadriceps ) , leg curl ( hamstrings ) , arm extension ( triceps ) , arm curl ( biceps ) , lateral pull-down ( latissimus dorsi and biceps ) , bench press ( pectoralis major and triceps ) , and squat ( gluteals and quadriceps ) . A rest period of 1 to 2 minutes was taken between sets . The participants began at a resistance of 50 % of their single repetition maximum . The resistance was then increased progressively until participants were exercising at 80 % of their single repetition maximum by week 9 . Strength was retested intermittently , and the training loads were adjusted as required . The participants did not train aerobically . Controls were instructed not to alter their home activity habits . A two-factor analysis of variance was done on baseline measures , with sex and training groups as the factors [ 9 ] . Women differed from men in baseline measures of fitness , strength , and body composition , but no sex-group interactions were seen . Pre- to postconditioning measures were analyzed using repeated-measure analysis of variance with results separated by sex . Data collected during the submaximal endurance study were analyzed for perceived exertion , heart rate , and systolic blood pressure ( excluding rest and exhaustion values ) by repeated-measure analysis of variance . Relations between variables were studied by linear regression analysis . Data are presented as mean SD . Analyses were done using BMDP New System for Windows , Version 1.0 ( BMDP Statistical Software , Los Angeles , California ) . Results After the 12-week resistance-training program , strength increased substantially in the  resistance-training group . The single repetition maximums increased by 29 % 24 % for leg extension , 65 % 79 % for leg flexion , and 29 % 15 % for bench press . When results were analyzed separately by sex and compared with results in controls , single repetition maximums for leg extension increased significantly among women ( P < 0.01 ) but not among men ( P = 0.12 ) ( Table 1 ) . Similarly , single repetition maximums for bench press increased significantly among women ( P < 0.01 ) but not among men ( P = 0.12 ) . Both women and men had increased single repetition maximums for leg flexion compared with controls ( P < 0.01 for women and P < 0.05 for men ) . It should be noted that the study was not design ed to fully address sex-specific outcomes . The control group showed no change in strength measures over the 12-week period , and the strength changes for each of the exercises in the intervention group when sexes were combined were significantly greater than the measures in the controls ( P < 0.005 ) ( Table 1 ) . Table 1 . Resistance-Training and Control Groups at Baseline and 12 Weeks Women in our study had lower measures of peak aerobic capacity at baseline than men ( 21.5 1.1 mL/kg min1 compared with 28.8 1.5 mL/kg min1 ; P = 0.03 ) and lower measures of strength as measured by single repetition maximum for leg extension ( 23.5 1.0 kg compared with 42.8 4 kg ; P = 0.001 ) , leg curl ( 5.3 0.4 kg compared with 14.4 1.5 kg ; P = 0.003 ) , and bench press ( 20.9 1.1 kg compared with 31.3 2.2 kg ; P = 0.008 ) . Neither women nor men showed changes in peak aerobic capacity after resistance training . No participant had significant changes in body weight , percentage of body fat , fat mass , or fat-free mass as measured by underwater weighing ( Table 1 ) . Analysis of regional body composition measured by dual-energy x-ray absorptiometry scanning showed an increased lean mass of the leg with weight training when compared with controls ( P = 0.02 ) ( Table 1 ) . This was due to an increase among women ( P < 0.02 ) ; no increase was seen among men ( P > 0.2 ) . Peak aerobic capacity was unaltered in both groups , regardless of sex . The primary outcome variable of interest was walking endurance time . After the resistance-training program , mean walking time until exhaustion for the resistance-training group increased by 38 % , from 25 4 minutes to 34 9 minutes . In contrast , no change was seen in the control group ( 20 5 minutes to 19 10 minutes ; P = 0.005 for comparison between groups ) . The increase in endurance time was due primarily to increases seen among men ( P < 0.02 ) rather than among women ( P > 0.2 ) . Mean exercise intensity , measured at 10 minutes of the endurance protocol at baseline , was 82 % of peak aerobic capacity in both the training group and the control group ( P > 0.2 between groups ) . Before the study intervention , none of the 24 participants completed the full 45-minute endurance protocol . After conditioning , 3 of the 12 participants who received resistance training and 1 of 12 controls completed the entire protocol . After conditioning , mean scores for perceived exertion for all submaximal data points from 10 minutes until the end of the walking endurance protocol ( not including the exhaustion point ) were lower in the resistance-training group than in the control group ( P = 0.03 ) ( Figure 1 ) . Mean submaximal heart rate and systolic blood pressure measures were lower after conditioning ; however , when groups were compared by repeated-measure analysis of variance , differences between groups were not significant ( Figure 1 ) . Submaximal or peak exercise oxygen consumption did not change during the endurance testing . Figure 1 . Conditioning data in the resistance-training group . For all 24 participants , significant relations were seen between change in walking endurance and change in strength measures for leg extension ( r = 0.48 [ 95 % CI , 0.10 to 0.74 ] ; P = 0.02 ) and leg flexion ( r = 0.46 [ CI , 0.07 to 0.73 ] ; P = 0.03 ) . Baseline peak aerobic capacity ( r = 0.10 [ CI , 0.48 to 0.3 ] ; P > 0.2 ) and baseline endurance time ( r = 0.41 [ CI , 0.22 to 0.73 ] ; P = 0.13 ) were not significantly related to change in endurance capacity in the resistance-training group of 12 participants . Discussion We show that healthy , community-dwelling elders can improve walking endurance and leg strength by participating in a resistance-training program . This finding is relevant to persons at risk for disability because walking endurance and leg strength are important components of physical functioning [ 3 ] . Resistance training improves walking endurance in at
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 .