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The Journals of Gerontology Series A: Biological Sciences and Medical Sciences 58:M740-M745 (2003)
© 2003 The Gerontological Society of America

Effects of Long-Term Resistive Training on Mobility and Strength in Older Adults With Diabetes

L. Jerome Brandon1,2,3, Debbi A. Gaasch1, Lisa W. Boyette1 and Adrienne M. Lloyd1

1 Rehabilitation Research and Development Center, Veteran Affairs Medical Center, Decatur, Georgia.
2 Department of Kinesiology and Health, Georgia State University, Atlanta.
3 Department of Rehabilitation Medicine, Emory University, Atlanta, Georgia.


   Abstract
Top
 Abstract
Methods
 Results
 Discussion
 References
 
Background. Strength training has been shown to be beneficial in older adults. However, very little data exist on the effects of strength training in older diabetics.

Methods. 31 community-dwelling older adults with diabetes (mean age = 66.1 years) were randomly assigned to either an exercise (EX) or control (CO) group. The EX group trained the plantar flexors, knee extensors, knee flexors, hip extensors, and hip flexors muscle groups at 50%, 60%, and 70% of 1-repetition maximum, 2.6 days a week, for 24 months. Mobility tests included the timed up and go, 50-foot walk, and walking up and down 8 stairs. Strength and mobility for both groups were evaluated at 6-month intervals.

Results. There was a group and time effect as the EX group increased 31.4% (p <.001) in strength for all muscle groups after the first 6 months of training, and the strength gains were retained for the duration of the training intervention. There was also a group and time effect for mobility as performance increased 8.6% and 9.8% (p =.032 and p = 0.031) for the first 6 and 12 months, respectively, but decreased to 4.6% above baseline at the end of the intervention. There were essentially no changes from baseline strength or mobility values for the CO group.

Conclusion. In conclusion, these data suggest that a moderate-intensity resistive-training program can improve mobility and strength for the duration of a 24-month intervention in older adults with diabetes, thus potentially reducing the rate of mobility loss during aging.

OLDER adults with diabetes (especially type 2) have greater body weight (subcutaneous fat deposits), reduced muscular insulin sensitivity, altered thermogenesis, and decreased peripheral neurological, muscular, and circulatory functions (1–4). Andersen and colleagues (5) concluded that diabetics experience up to 50% muscle weakness compared with nondiabetics in knee extension and plantar flexion strength due to diabetes-related neuropathy. These lower-extremity muscle groups are highly associated with mobility and have the added issue of age-related decreases in older adults with diabetes, which results in greater frailty and falls incidence (6–8). Since older diabetics have altered muscular function and excess fat weight that has to be supported and transported, they have a greater strength need than nondiabetic older adults (6,9–11).

Strength training has been reported as a safe and effective countermeasure to sarcopenia and age-related strength decrements in older adults (1,3,12). Most existing strength-training studies with older adults were designed to investigate the effects of short duration (12 months or less) training interventions and did not consider the effects of long-term strength training on mobility in older adults with diabetes (12–15). While some studies indicate that strength training can increase strength and mobility in older adults (16,17), the nature and duration of the training benefits need further clarification, and this is especially true for older adults with diabetes (14). This study was designed to determine the nature and duration of mobility and strength benefits associated with a 24-month strength-training intervention in older diabetics. The hypothesis evaluated was that mobility and strength of the exercise (EX) group would increase significantly when compared with a control (CO) group, and the increases would last for the duration of the training.


   METHODS
Top
 Abstract
 Methods
Results
 Discussion
 References
 
Research Design and Subjects
A randomized repeated-measures controlled trial with 2 groups (EX and CO) was used in this study. Subjects were recruited from a Veterans Affairs Diabetic Clinic, a computerized research center database, local diabetic clinics and senior centers, and by word of mouth, where participants told friends of the study. Between 15% and 28% of the subjects were recruited from each site. Fifty-two of 442 (11.8%) of the older community-dwelling adults with diabetes contacted to participate in this study volunteered as subjects; however, 16 EX and 15 CO (mean 66.1 years) completed all assessments and are included in the analyses (see Table 1). Many were involved in community activities such as various clubs, and walking, but were not actively involved in exercise programs. All of the volunteers were taking either oral hypoglycemic medication or insulin. Preexercise session blood glucose mean values ranged from 135 to 153 ml/dL and postexercise blood glucose means ranges from 85 to 95 ml/dL during the 24-month training intervention. Based on self-report, mild peripheral neuropathies were present in 12 of the EX group and 9 of the CO group. Institutional human subject approval was obtained for the study. All subjects signed informed consent forms, and obtained physician approval to participate in the study.


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  		Table 1. Subject Recruitment, Screening, and Dropouts.

 
Exclusion criteria included elevated blood glucose (>300 mg/dL), depression (Beck's Depression scale score >17) (18), altered cognitive function (Mini-Mental State Examination score <24) (19), and cardiovascular diseases, symptoms, or risks, including myocardial infarctions, congestive heart failure, strokes, hypertension (SBP [systolic blood pressure] >=140 and DBP [diastolic blood pressure] >=90), and atherosclerosis (20) (see Table 1 for the number of exclusions).

Power calculations were based on mean strength and mobility values from a previously published study (12). A power greater than 0.80 was obtained in this study, as 15 subjects per cell provides a power of 0.81 with a sensitivity of 1 standard deviation at an alpha level of 0.05.

Strength and Mobility Testing
Strength was assessed by 1-repetition maximums (1RMs) on 5 Nautilus (Atlanta, GA) stations and reported as relative strength (1RM/BW = 1RM in kg divided by body weight in kg) (17). During the strength assessments, 1.1 and 2.3 kg add-on weights were used to increase the accuracy of the assessment. Strap-down belts were used to stabilize the hip area and enhance hip flexion and extension assessments. Strength and mobility of the EX group were evaluated every 6 months during the 24-month intervention. The 6-month assessments were used to update training prescriptions and for the analyses in this study. Plantar flexors, knee extensors, and flexors (lower extremity—legs measured simultaneously), and hip flexors and extensors (trunk) were the muscle groups trained and tested in this study. The CO group was evaluated for strength at baseline and at 6-month intervals during the intervention.

The mobility tests in this study were modified from validated procedures in the literature and include the timed up and go (TUG), 50-foot walk (walk), and walking up (upstairs), and down (downstairs) 8 stairs (12,21,22). The TUG required the subject to rise from a chair, walk around a cone 10 feet away, walk, back to the chair, and sit. The walk test required the subjects to walk quickly and comfortably 25 feet, turn, and walk back to the start. Upstairs required the subjects to walk up a flight of 8 stairs carrying a 2.3-kg weight, and downstairs required the subjects to walk down a flight of 8 stairs with a 2.3-kg weight. The subjects were requested to perform the tasks quickly, but safely, as scoring was based on the time required to perform the tasks.

Procedures recommended by Lohman and colleagues (23) were used to measure circumferences and skinfolds. Body composition was estimated from skinfolds, as Jackson and colleagues' (24,25) equations were used to estimate body fat. The relationship between thigh skinfolds and thigh circumferences was used to estimate changes in muscle mass during the 24-month training intervention.

Intervention
To minimize injury risks, constant supervision, emergency equipment, and personnel were available during the testing and training. The training sessions were held Monday, Wednesday, and Friday during the first 6 months. After the first 6 months, the subjects were required to attend twice a week, but were allowed to attend all 3 sessions. Each subject was required to attend a minimum of 70% of the training sessions (based on 3 days a week the first 6 months and 2 days a week after the first 6 months) to be included in the data analyses.

Strength training was completed on an 11-station Nautilus machine. The subjects completed 3 sets of 8–12 repetitions per exercise. The intensity was 50%, 60%, and 70% for sets 1, 2, and 3, respectively. Each 1-hour session consisted of 50 minutes of strength-training exercises and 10 minutes of warm-up, flexibility, and cool-down exercises. Pre- and postexercise blood glucose levels were measured to ensure appropriate response before and after exercise sessions. Resting and recovery heart rates and blood pressures were measured each session to ensure appropriate physiological responses to exercise. For safety reasons, if a participant's blood pressure was above either 200 mmHg systolic or 100 mmHg diastolic (20), the individual was not allowed to exercise that session unless the pressure dropped below these values after a 30-minute rest. This occurred in 8 EX subjects during the 24-month training intervention.

Analyses
Means and standard deviations were calculated on all of the data. To evaluate overall lower body strength and mobility, composite strength and mobility (means of the individual strength and mobility variables, respectively) were calculated. Percent change was computed from the means. Mobility and strength responses were evaluated for differences between the EX and CO groups over time using repeated measures analysis of variance (ANOVA) and Scheffé post hoc tests. Subjects with complete data sets for a test period were included in data analyses. Variables with missing values were omitted from analyses.


   RESULTS
Top
 Abstract
 Methods
 Results
Discussion
 References
 
There was over an 85% training and retesting adherence rate for the EX subjects and a similar retesting rate for the CO subjects included in the data analyses. There was a cumulative 45% and 35% dropout rate among the EX and CO subjects, respectively, over the 24-month study (Table 1), but baseline individual and composite strength and mobility were not different between the completers and dropouts. These were relatively high dropout rates, but appeared to reflect the difficulty of getting diabetics committed to long-term exercise programs. Reasons for dropping out of the study: the study required too much time; their disease got worse or they experienced some other illness; their spouse became ill and they had to care for them; or they relocated to another city.

There were no differences in baseline physical characteristics between the EX and CO groups (Table 2). The thigh circumferences of the EX subjects did not change over time, but thigh skinfold thickness decreased at 24 months (p =.045; Table 3). This suggests that the thigh muscle mass of the EX subjects increased during training, but there were no changes for the CO subjects.


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  		Table 2. Baseline Physical Characteristics of the Subjects Based on Gender.

 

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  		Table 3. Mobility and Relative Strength Responses of Older Diabetic Adults During a 24-Month Resistive-Training Intervention.

 
Since the training response patterns were similar for both absolute (1RM) and relative (1RM/BW) strength, and support of body weight is important for mobility tasks, 1RM/BW values were used in this study. Relative strength expressions normalized the data for body weight, as baseline strength values for the EX and CO groups were not different for any of the variables, except the CO group had higher hip flexor values. Repeated measures ANOVA analyses revealed significant (p >.001) group and time effects for all individual muscle groups. Scheffé post hoc tests showed that the EX group experienced a significant increase (average of 31.4%; Figures 1A and B) in trunk and lower extremity strength following the first 6 months of training, and the increased strength was maintained for the duration of the 24-month training intervention (Table 3). For the CO group, there was no change from baseline in 1RM strength for any of the muscle groups, except hip flexors strength was higher than baseline at 18 months.



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  		Figure 1. A, Changes in trunk strength (kg/body weight in kg) during 24 months of resistive training for older adults with diabetes. Trunk is the mean of hip flexors and hip extensors. Strength values for months 6 through 24 are different than baseline at p <.001, but are not different from each other. B, Changes in lower extremity strength (kg/body weight in kg) during 24 months of resistive training for older adults with diabetes. Lower extremity strength is the average of knee extensors, knee flexors, and plantar flexion. Strength values for months 6 through 24 are different than baseline at p <.001, but are not different from each other

 
The only individual mobility test with a significant time and group effect was downstairs. Downstairs mobility performance improved (p =.031) only at 6 months for the EX group. There was a trend toward improvement for upstairs, TUG, and the walk test for the EX group. There were no changes for any of the individual mobility tasks for the CO group, except downstairs performance was poorer (p =.034) at 24 months compared with baseline (Table 3).

Repeated measures ANOVAs showed significant time and group effects in percent change for composite strength and mobility. The illustration in Figure 2A shows that strength for the EX subjects increased 31.4% following the first 6 months of training, and remained between 36% and 39% above baseline and was significantly greater than the CO group (p <.001) for the duration of the training intervention. Based on post hoc assessments, the mobility task performance of the EX subjects improved 8.6% at 6 months (p =.032) and 9.8% at 12 months (p =.031), and was significantly better than the CO group during these time periods. Mobility performance declined gradually for the remainder of the training intervention, but remained 4.6% above baseline and 8.2% better than the CO group at the conclusion of training. The CO group mobility had decreased to 3.6% below baseline (Figure 2B).



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  		Figure 2. A, Percent change in composite strength during the 24-month training intervention. Composite strength is the mean of hip flexors, hip extensors, knee extensors, knee flexors, and plantar flexors muscle groups. There was a significant group and time effect as exercise percent change in strength was greater than baseline and control strength at p <.001 from months 6 through 24. B, Percent change in mobility during the 24-month training intervention. Mobility is the average time required to complete the walk, timed up and go, upstairs, and downstairs tests. There was a significant group and time effect as exercise changes in mobility were greater than baseline and control mobility (p <.01) at months 6 and 12

 

   DISCUSSION
Top
 Abstract
 Methods
 Results
 Discussion
References
 
Results from this study demonstrate that a 24-month moderate-intensity resistive-training intervention improves strength and mobility in older adults with diabetes for the duration of the training intervention. The response patterns for mobility and strength in this study were different from each other, but relatively similar to respective patterns observed elsewhere (26,27,28). In a 5-year community based study that included strength training, the authors reported that strength increased during the first 12 months and stabilized from 12 to 24 months. Physical performance in the 5-year study increased the first 2 to 3 years, and declined gradually until the conclusion of the study (28). Strength in the present study increased during the first 6 months, stabilized, and remained constant at the elevated level for the remaining 18 months. Mobility increased during the initial 6 months in the present study and remained above baseline, although it declined from 12 months until the end of the study.

Compared with other studies in the literature, the baseline strength of the muscle groups in this study indicates that the subjects had relatively good muscular fitness (12). In this study 1RM/BW strength was used for the analyses. Strength expressed as 1RM/BW has been shown to enhance walking speed in older disabled women, and this expression for strength was more sensitive in detecting changes in mobility (17).

The 31.4% increase in relative strength during the 6-month assessment is less than increases observed in other studies with nondiabetic subjects for lower extremity strength (12,29,30,31). Since similar training protocols were used in the different studies, the smaller strength gains in the present study may be related to a reduced muscular response in the older diabetic or the change in the training protocol. Subjects were required to train 3 times a week during the first 6 months, but were given the option of training 2 or 3 days a week for the remainder of the training intervention. From months 6–24, the subjects trained an average of 2.6 days a week, as 12 subjects continued to train 3 days a week. However, there were no differences between strength or mobility values from training 2 or 3 days a week in this study. This is consistent with results reported elsewhere that strength training 1, 2, or 3 days a week has no effect on the rate of strength gains in older adults (32).

The finding in this study for individual mobility tasks, which shows that walking downstairs improved following 6 months of strength training, is consistent with findings reported in the literature (17,33,34). Strength has not only been associated with improved stair climbing activities, but has been shown to account for 73% of variance in descending stairs (35).

Mixed results were observed in this study for the TUG and walk tests compared with other studied in the literature. The TUG test has been shown to improved following 4 months of strength training in older healthy adults. Subjects in that study improved 5.2% as their time decreased from 7.7 seconds to 7.3 seconds following training (12). However, similar findings in this study, where the walk test did not improve following resistive training, have been reported elsewhere (12).

In summary, these results demonstrate that a 24-month resistive-training program increases strength, and that the strength gains are retained for the duration of the training intervention in older adults with diabetes. Mobility also increases during the first 6 months and remains above baseline for the duration of training. These results support the hypothesis that a 24-month strength-training intervention improves both mobility and strength in older adults with diabetes, and mobility benefits are retained for the duration of the training intervention. These data suggest that a resistive-training program can improve strength and mobility in older adults with diabetes, thus potentially reducing the rate of mobility loss in this population. Further research is needed to validate and build upon our findings.


   Acknowledgments
 
Contract project number E721-4RA from the VA Medical Rehabilitation Research and Development supported this study. Special thanks to Dr. Joe Ouslander for his insightful review of this manuscript.

Address Correspondence to L. Jerome Brandon, PhD, Department of Kinesiology and Health, Georgia State University, Atlanta, GA 30303. E-mail: hprljb{at}langate.gsu.edu

Received October 14, 2002

Accepted December 20, 2002


   References
Top
 Abstract
 Methods
 Results
 Discussion
 References
 

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