the number of studies targeting physical activity ( pa ) behavior in older adults has increased markedly over the past decade . such studies have largely been effective at increasing pa among older adult participants , and have demonstrated comparable results across home - based and center - based formats [ 1 , 2 ] . relatively little is known about the extent to which intervention effects are maintained over the long term , although results from previous research suggest that recidivism upon cessation of intervention is a reality across a variety of populations and behaviors [ 1 , 38 ] . while studies examining adherence at shorter time points ( e.g. , 6 months ) are more common , long - term followups in older adults remain sparse . as a result , strategies to foster pa adherence over the long term in an aging population remain to be identified . to date , much of the research surrounding pa has focused on identifying strategies to increase adoption . while the evidence supporting the beneficial effects of a physically active lifestyle on chronic disease management is vast , similar to pharmacologic therapies , the benefits of pa are directly proportional to adherence rates . thus , behavioral researchers and public health officials must now also consider the challenge of developing effective strategies to facilitate pa maintenance . in addition to post - intervention trends , studies on the individual characteristics that determine long - term patterns of adherence are needed . previous research suggests that psychosocial factors and previous pa behavior are significantly associated with higher pa levels in older adults [ 6 , 7 , 11 , 12 ] however , the role of factors such as comorbidity , physical function , and physical performance in determining long - term pa maintenance or decline in older adults remains unclear . thus , it is unclear whether there may be subgroups of individuals who respond differentially to the cessation of a behavioral intervention . examining how pa levels change following an intervention and identifying the characteristics of those who benefit the most and least is a necessary and important precursor to developing targeted evidence - based programs that promote long - term activity adherence in older adults . the veterans life study [ 13 , 14 ] is a 12-month randomized controlled trial of pa telephone counseling ( pac ) to increase pa in older veterans . one year after finishing the study , attempts were made to contact all participants to participate in followup data collection . the first aim of the study was to examine pa levels during a 12-month nonintervention period and determine the effect of participation in the intervention on post - intervention changes . the second aim was to examine behavioral and psychosocial predictors of pa during the post - intervention period . the third aim was to identify three classes of post - intervention pa trajectories : maintenance , gains , and losses and explore the behavioral , functional and psychosocial characteristics of these three groups . a complete description of the veterans life study has been reported elsewhere . in brief , this study was a randomized controlled trial comparing a 1-year multicomponent physical activity counseling ( pac ) program with usual care ( uc ) . the durham veterans affairs institutional review board reviewed and approved the research protocol , and written consent was obtained from all participants . participants in this study were older male patients followed at the durham veterans affairs medical center ( vamc ) primary care clinics . to participate , patients had to be 70 years of age or greater , able to walk a short distance without human assistance , not regularly participate in pa , not suffer from dementia or severe hearing / vision loss , and be free of serious or terminal medical conditions that would preclude safe engagement in pa . participants were randomized to one of two groups at baseline : pac ( n = 199 ) or uc ( n = 199 ) . the pa objectives for the pac group were to walk or perform lower extremity physical activity for 30 minutes or more on 5 or more days of the week and to perform 15 minutes of lower extremity strength training on 3 days each week . uc consisted of usual care received within the context of visits to primary care providers within the same time frame . guided by social cognitive theory   and the transtheoretical model of behavior change , the pac consisted of baseline physical activity counseling , telephone counseling , endorsement of the study by the patient 's primary care provider , automated telephone messaging from the primary care provider , and individualized progress reports . the pac intervention components and consort diagram illustrating participant flow across the 1-year life of the study have been discussed in detail elsewhere . this study resulted in significant improvements in functional performance and pa in the pac group but not the uc group .   to determine whether participation in the veterans life study resulted in sustained behavior change 12 months after intervention and identify factors that predict behavior change , attempts were made to recontact all participants one year after finishing the program to ask them to complete measures on - site at the durham vamc . of the 199 men randomized to pac , 177 completed the study and 123 gave consent for the followup assessment ; resulting in a 70% followup response rate . of the 199 men randomized to uc , 176 completed the study and 115 gave consent for the followup assessment ; resulting in a 65% followup response rate . we measured minutes of moderate - intensity endurance pa and minutes of moderate - intensity strength pa using the community healthy activities model program for seniors ( champs ) [ 17 , 18 ] . the champs questionnaire assesses the duration of a range of physical activities from which moderate activities can be separated . minutes of endurance pa were calculated as the sum of brisk walking , running / jogging , cycling / stationary cycle , and aerobic machine items from the champs . minutes of strength pa were calculated as the sum of moderate / heavy weight lifting , light strength training , and general conditioning items from the champs . rapid gait speed ( meters / second ) was assessed over two trials of an 8-foot walk test . two items were used to assess self - efficacy separately for walking / endurance activities and strength training activities ; the content of these items was created to be consistent with the veterans life study counseling . the first question asked participants ,  how sure are you that you could walk or do another type of endurance exercise for 30 minutes or more on five or more days of the week ? the 30 minutes do not have to be all at the same time .  the second item asked , how sure are you that you could do exercises for 15 minutes , three days a week , to make your legs stronger ?  responses for these two items ranged from 1 ( not at all confident ) to 5 ( extremely confident ) . a scale score was created by taking the average of the responses on the two items . number of chronic conditions was assessed using the older americans resources and services survey ( oars ) , which surveys 35 medical conditions . self - rated physical function was assessed using the physical function subscale of the medical outcomes study 36-item short - form health survey ( sf-36 ) . to measure the effect of the pac intervention on activity levels one year after completion of the study , we compared the activity levels of those formerly in the pac and uc groups . differences in minutes of moderate - intensity endurance pa and minutes of moderate - intensity strength pa between the two groups were tested using ordinary least squares , adjusting for 012-month change , 12-month pa status , and age , race , education , and number of comorbidities all measured at baseline . the association of behavioral and psychosocial factors with post - intervention change in pa was assessed using multiple regression analysis . we identified behavioral and psychosocial factors that in the literature are associated with physical activity behavior change in older adults : pa ( endurance and strength pa at month 12 ) , exercise self - efficacy ( month 12 ) , self - reported physical function ( month 12 ) , and rapid gait speed ( month 12 ) . two a priori regression models containing all five predictor factors were run ; one with 1224 month change in endurance pa as the outcome variable , and one with 1224 month change in strength pa as the outcome variable . each model controlled for age , education level , and number of comorbidities . we classified individuals from the pac group as maintainers , improvers , or decliners based upon their changes in pa levels from 12 to 24 months . in creating these categories we were cognizant of two issues : improve  and  decline  categories to capture changes in pa behavior that were sizeable and reflected a purposeful increase or decrease in effort , and ( 2 ) we wanted the  maintenance  category to have a similar buffer to minimize the risk of categorizing individuals as improvers or maintainers who had not substantively changed their pa behavior after intervention . thus , group membership was based on the change in moderate - intensity endurance and strength pa from month 12 to month 24 using the 12-month median value for each variable as the criterion . thus , improvement in minutes of moderate - intensity endurance pa was defined as an increase greater than 45  minutes / week from 12 to 24 months , while decline was defined as any negative change greater than 45  minutes / week . individuals were classified as maintainers when the change in endurance pa minutes from 12 to 24 months was less than or equal to 45  minutes / week . thus , improvement in minutes of moderate - intensity strength pa was defined as an increase greater than 75  minutes / week from 12 to 24 months , while decline was defined as any negative change greater than 75  minutes / week . individuals were classified as maintainers when the change in strength pa minutes from 12 to 24 months was less than or equal to 75  minutes / week . we also examined whether those who maintained , improved , or declined pa from 12 to 24 months differed significantly on the same behavioral and psychosocial factors identified in section 4.2 . we used a series of pairwise comparisons to determine whether meaningful differences in these characteristics existed between the three classes . as is commonly the case with exploratory analyses , caution is warranted when interpreting the pairwise comparisons as they do not correct for type i error . we conducted all analyses using sas version 9.1 ( sas inc . , cary , nc ) . demographic characteristics have been reported previously . to summarize , study participants were older men ( m age = 77 years , range = 7092 years ) of mixed educational backgrounds , with 26% receiving a college degree and 45% reporting a high school graduate equivalency or less . study participants reported approximately five chronic conditions ( m  sd ; 5.15  2.44 ) .    as mentioned previously , 30% of the pac group and 35% of the uc group did not complete the followup data collection . thus , to determine whether these response trends introduced any bias into our results , we first compared those who completed 24-month followup ( n = 238 ) and those who did not ( n = 115 ) on treatment arm , demographic characteristics ( i.e. , age , race , education level ) , number of comorbidities , minutes of endurance pa , minutes of strength pa , rapid gait speed , and physical function . the only significant differences ( p < .05 ) between those lost to followup and those retained were on race and rapid gait speed . those who completed data collection at month 24 were more likely to be white and have a faster rapid gait speed than those who did not complete data collection at 24 months . among those study participants who completed assessments at 24 months , participants in the pac group reported more minutes of moderate - intensity endurance pa and moderate - intensity strength pa per week at 12 months compared to the uc group ( table 1 ) . as expected , after finishing the intervention , minutes of moderate - intensity endurance pa and minutes of moderate - intensity strength pa declined for both groups . although the declines in endurance pa were greater among the pac group , they did not differ significantly from those observed in the uc group (  = 21.5 , p = .22 ) ; the decline in minutes of strength pa , however , was significantly greater in the pac group (  = 23.1 , p = .01 ) . despite these declines over the last 12 months , minutes of moderate - intensity endurance pa and minutes of moderate - intensity strength pa remained higher among those in the pac group compared to the uc group . results of the multiple regression analysis indicated that the predictor variables accounted for 51.6% of the variance in post - intervention change in endurance pa . minutes of endurance pa at month 12 (  = 0.87 ) , minutes of strength pa at month 12 (  = 0.26 ) , self - efficacy (  = 20.62 ) , physical function (  = 0.96 ) , and rapid gait speed (  = 47.82 ) were all significant predictors of post - intervention change in endurance pa . collinearity diagnostics indicated high levels of collinearity between 12-month endurance pa and 1224-month endurance pa change . a subsequent regression model in which 12-month endurance pa was excluded as a predictor variable resulted in a much better fitting model . however , this model indicated no significant effects for any of the other factors and accounted for only 3.0% of the variance in post - intervention change in endurance pa ; demonstrating that previous endurance pa is the most important determinant of post - intervention changes in endurance pa . relative to post - intervention change in strength pa , results of the multiple regression analysis indicated that the predictor variables accounted for 33.2% of the variation . minutes of strength pa at month 12 (  = 0.59 ) , minutes of endurance pa at month 12 (  = 0.14 ) , and self - efficacy (  = 11.81 ) were all significant predictors of post - intervention change in endurance pa . collinearity diagnostics indicated low levels of collinearity between 12-month strength pa and 1224-month strength pa change . although collinearity among model variables was low , we determined a priori to run parallel models for endurance and strength ; testing a second regression model in which 12-month strength pa was excluded as a predictor variable . although this model provided a much better fit , no significant effects for any of the other factors were observed and this model accounted for only 7.6% of the variance in post - intervention change in strength pa . these results demonstrate that previous strength pa is the most important determinant of post - intervention changes in strength pa . figure 1(a ) shows the three classes for post - intervention changes in minutes of moderate - intensity endurance pa for the pac group . individuals who improved their minutes of endurance pa from 12 to 24 months ( n = 22 ) had moderate rates of endurance pa at month 12 ( m = 47.3 , sd = 62.8  minutes / week ) . individuals who declined in minutes of endurance pa from 12 to 24 months ( n = 39 ) had higher rates of endurance pa at month 12 ( m = 178.4 , sd = 155.0  minutes / week ) . individuals who maintained their minutes of endurance pa from 12 to 24 months ( n = 62 ) had the lowest rates of endurance pa at month 12 compared to the other categories ( m = 22.8 , sd = 67.9  minutes / week ) . figure 1(b ) shows the three pa trajectories for post - intervention changes in minutes of moderate - intensity strength pa for the pac group . individuals who improved their minutes of strength pa from 12 to 24 months ( n = 16 ) had moderate rates of strength pa at month 12 ( m = 54.7 , sd = 59.4 ) . individuals who declined in minutes of strength pa from 12 to 24 months ( n = 38 ) had higher rates of strength pa at month 12 ( m = 101.8 , sd = 59.1 ) . individuals who maintained their minutes of strength pa from 12 to 24 months ( n = 69 ) had the lowest rates of strength pa at month 12 compared to the other categories ( m = 30.3 , sd = 33.9 ) . characteristics of long - term maintenance , improvement or decline of minutes of moderate - intensity endurance pa are shown in table 2 . as expected , minutes of endurance pa at month 12 was the most consistent discriminant of post - intervention changes in endurance pa . specifically , the pairwise comparison analyses demonstrated that individuals who declined from 12 to 24 months had significantly ( p < .05 ) greater levels of endurance pa to start with ( at month 12 ) compared to those in the improve and maintenance groups . in addition to 12-month endurance pa , minutes of strength pa , number of comorbidities , self - efficacy , and rapid gait speed at 12 months were also significantly different across the three groups ( ps < .05 ) . however , these variables only significantly discriminated those in the maintenance group from the other two groups . specifically , individuals who maintained their minutes of endurance pa over the 12-month post - intervention period had the lowest rate of activity at 12 months , had more comorbidities , were less efficacious for physical activity , reported worse physical function , and had significantly slower gait speed compared to those in the improve or decline groups ( p < .05 ) . characteristics of long - term maintenance , improvement or decline of minutes of strength pa are shown in table 3 . as expected , minutes of strength pa at month 12 was the most consistent discriminant of post - intervention changes in strength pa . specifically , the pairwise comparison analyses demonstrate that individuals who declined from 12 to 24 months had significantly ( p < .05 ) greater levels of strength pa to start with ( at month 12 ) compared to those in the improve or maintenance groups . in addition to 12-month strength pa , only self - efficacy at 12 months significantly differed across the three groups ; with individuals who maintained their minutes of strength pa over the 12-month after intervention period being significantly less efficacious for physical activity compared to those in the improve or decline groups ( p < .05 ) . the literature is replete with research describing interventions aimed at improving pa ; with many of these interventions using behavioral theory - based approaches to modify pa [ 2125 ] . although declines in pa can be expected following cessation of intervention , there is hope that some behavioral benefit from pa interventions can be sustained beyond the intervention period . in this study we sought to determine if there was any maintenance of pa following a year of no contact with former study participants . as expected , given the cessation of all study - related contact and resources , minutes of moderate - intensity endurance and strength pa among pac participants decreased following the cessation of the home - based pa counseling program . however , despite these post - intervention declines in the pac group , minutes of endurance pa and minutes of strength pa at month 24 remained higher than baseline pa levels ( data not shown ) . moreover , pa rates in the pac group remained higher than those in the uc group at 24 months , suggesting some long - term benefit of pa counseling on pa behavior compared to usual care . consistent with our expectations and previous reports in the literature , pa at 12 months was the single most important predictor of post - intervention change in activity levels . however , higher levels of pa at month 12 were significantly associated with decreases in pa over the post - intervention period . these results suggest that altering behavior in the short term is not sufficient , in and of itself , to promote behavior maintenance . indeed , upon cessation of the intervention and the resources and support associated with it , older adults who were successful in changing their behavior during the intervention were the most vulnerable to post - intervention declines . these results underscore the importance of on - going support following a behavioral intervention to improve maintenance and reduce the likelihood of regressing back to a sedentary lifestyle . strategies to promote maintenance should be a systematic component of any behavioral intervention and warrant future study . self - efficacy , physical function , and gait speed also demonstrated significant effects on post - intervention changes in pa . however , pa at month 12 accounted for a major portion of the variance in post - intervention change in pa , such that in the absence of the 12-month measure of pa , no significant effects were observed for any of these other candidate predictors . these results , coupled with the nonsignificant bivariate associations ( data not shown ) observed between post - intervention change in pa and any of the predictor variables ( with the exception of pa at 12 months ) , suggest that these associations are not independent of pa at 12 months . that these pathways may be indirect is consistent with a social cognitive perspective in which behavior influences , and is influenced by , individual cognitions and abilities   and has been demonstrated in previous research with older adults [ 6 , 7 ] .   in an effort to better understand the individual variability following post - intervention behavior and develop tailored clinical interventions to promote physical activity , we conducted extensive exploratory analyses . based upon their post - intervention changes in pa , individuals were categorized according to three trajectory classes : improvers , maintainers , or decliners . we chose these three groups a priori , knowing that recipients of the intervention increased pa during the intervention period   and expecting that recipients would fall into three categories during the nonintervention period : improvers , maintainers , or decliners . however , upon examination of the changes in pa during the intervention across the three groups ( data not shown ) we discovered that these group descriptors did not accurately reflect the trends in our data . those who increased their minutes of pa post - intervention demonstrated small improvements during the intervention . in contrast , those who substantially decreased their minutes of pa post - intervention were those who had made the most gains during the intervention . to our surprise , those who maintained their minutes of pa post - intervention appear to not have taken to the intervention at all . thus , it appears that in this study the individuals most likely to maintain their activity levels post - intervention were those who abstained from making any changes to their behavior at all over the course of an intervention and would be more accurately described as nonresponders . despite this group comprising nearly 50% of the pac arm , previous analyses report significant improvements in pa during the intervention ; underscoring the need for individual - level analyses to detect and characterize these underlying patterns of behavior . in addition to characterizing the post - intervention change patterns in pa , we had hoped to identify characteristics that would differentiate those who improve , nonrespond / maintain , or decline in post - intervention pa ; selecting factors that could be used in clinical care to identify individuals who may need additional support or booster shots ( e.g. , self - efficacy , physical function , and physical performance ) . in this sample of older adults , the nonresponders / maintainers had more comorbidities , lower self - efficacy to continue exercising , lower physical function , and slower gait speed than either the improvers or decliners . this pattern of results , together with the significantly lower level of pa at 12 months seen in the nonresponders / maintainers , suggests that the nonresponders / maintainers have physical , functional , and psychosocial disadvantages that make them even less likely to respond to an intervention that is largely home based and unsupervised . in a previous pa clinical trial of individuals undergoing three months of supervised exercise followed by six months of home - based exercise , we observed significant improvements in fitness and physical function ; largely driven by changes occurring during the supervised period . subsequent analyses indicated that nonadherence to home - based pa could be traced back to low levels of pa during the supervised portion of the trial . physical function , physical performance , comorbidity , and symptoms were also related to nonadherence in the home setting . these studies , along with our results here , suggest that we can identify characteristics of individuals who may be poor candidates for home - based interventions and who require on - going support once an intervention has ended . we expected that factors such as self - efficacy , physical function , and physical performance might distinguish between the improvers and the decliners . however , none of the variables examined proved fruitful . instead , the differences between these two trajectories rest solely on initial ( month 12 ) pa levels . this may be due , in part , to the relatively small sample size in each group and concomitant lack of statistical power . these results have implications for future pa interventions , however , for they suggest that consistent with health promotion guidelines [ 3 , 28 ] , individuals who are active at high levels at the end of an intervention are in need of extended resources and support if these changes are to be sustained . our decision to classify participants as maintainers , decliners , or improvers in the manner that we did may be unique . unlike other studies that have assessed success or failure to long - term pa adherence relative to meeting activity guidelines [ 3 , 11 , 29 , 30 ] , here , success was defined relative to the individual ; thus taking into account individual limitations and barriers . although our pa counseling was directed towards meeting national goals of 150 minutes per week or more of pa , we recognized that this goal was not achievable for many of our participants and endorse the call for older adults with comorbidities to be as physically active as they are able . first , although every attempt was made to collect 24-month followup data from all of the study participants , and thus minimize drop - out bias , we were unable to do so . however , we did attempt to address this limitation by examining the differences between those who completed measures at 24 months and those who declined participation at 24 months . these analyses suggest that our sample may be biased toward the more physically active and better functioning . however , no significant between - group differences were reported by treatment arm or on other dimensions of health status or self - reported physical function . second , we recognize that one possible explanation for the pattern of pa change observed here may be attributed to regression to the mean . however , we believe that the significant effects of the intervention demonstrated previously in the pac group   indicate recidivism following the end of an intervention , likely due to the removal of intervention supports and expectations , and not due to some random effect as implied by regression to the mean . third , although we included variables that demonstrated significant associations with pa in previous studies [ 3 , 7 , 29 , 31 ] , we acknowledge that our models did not include other intrapersonal , interpersonal , or environmental factors which may influence behavior change . despite calls for more studies of long - term pa participation and maintenance [ 9 , 29 , 32 ] , we have much to learn , underscoring the difficulty in understanding ( and altering ) pa , a complex behavior . however , in this study we did identify a number of important factors which are related to changes in pa behavior over the long term . one of these factors , self - efficacy , is a modifiable construct and as such , is worthy of more investigation . future studies of long - term maintenance that consider other variables such as environmental supports and barriers are needed . importantly , our results also suggest that home - based pa may be of limited benefit to certain groups of lower functioning and highly sedentary older adults . thus , similar to strategies to increase adoption and maintenance of pa , tailored approaches that target at - risk populations and accommodate individual , functional , and behavioral barriers may also be needed for sustained behavior change .
this study assessed the sustained effect of a physical activity ( pa ) counseling intervention on pa one year after intervention , predictors of sustained pa participation , and three classes of post - intervention pa trajectories ( improvers , maintainers , and decliners ) in 238 older veterans . 
 declines in minutes of pa from 12 to 24 months were observed for both the treatment and control arms of the study . 
 pa at 12 months was the strongest predictor of post - intervention changes in pa . 
 to our surprise , those who took up the intervention and increased pa levels the most , had significant declines in post - intervention pa . 
 analysis of the three post - intervention pa trajectories demonstrated that the maintenance group actually reflected a group of nonresponders to the intervention who had more comorbidities , lower self - efficacy , and worse physical function than the improvers or decliners . 
 results suggest that behavioral counseling / support must be ongoing to promote maintenance . 
 strategies to promote pa appropriately to subgroups of individuals are needed .