An a priori power analysis was performed to determine the sample size for adequate statistical power. The anticipated effect sizes for this study were conservatively estimated. The study used the intent to treat (ITT) (8) principle of retaining all participants randomized into the prehabilitation group regardless of their adherence with the prehabilitation intervention. Participants lost to follow-up would be replaced through oversampling to maintain a sufficient sample size to ensure adequate statistical power. The standard method of determining sample size between treatments with covariance correction for baseline scores within a repeated measures model used the following formula (23):
A conservative r2 between pretest and posttest means was estimated to be 0.5 (level of correlation) for each variable being studied to estimate sample size. These sample size estimates are based on obtaining statistical power (1 − β) of 0.80 for the analysis of each dependent variable with an overall α = 0.05. Under these assumptions, the sample needed in each group to complete the posttest to yield approximately 80% power is presented in Table 2. Therefore, it was estimated that by enrolling 40 subjects and using the ITT principle, anticipating a 25% dropout the proposed final sample of 30 subjects (n = 15 per study group) will have at least 80% power to detect a clinically significant effect of the treatments on the principle dependent variables.
The individuals in the prehabilitation group were introduced to an exercise program that was based on the constructs of the SCT. Table 3 dislays how the SCT concepts were applied within the exercise intervention program (13). These concepts included the appropriate skills, knowledge and adequate incentives to perform a given behavior, and confidence in one’s ability to take action to overcome barriers needed for successful outcomes. The construct of self-efficacy was targeted by using strategies from the SCT that include: (a) setting incremental goals, (b) behavioral contracting (committing to a formal contract), (c) monitoring, and (d) reinforcement (feedback from self-monitoring or record keeping). Observational learning occurred as the participants learn through the experiences of credible others (professional trainers) rather than through their own experience. Finally, the use of reinforcements (using motivation) to change behavior was done by having the participants meet with the a member of the research team once a week to reinforce his or her good progress and help maintain his or her good exercise behavior.
The prehabilitation treatment group was given a prehabilitation training booklet, which explained all 5 components of the prehabilitation training program, including warm-up, resistance exercises, flexibility exercises, step training, and a cool down. Components of this training program have been demonstrated to improve performance of functional tasks, knee pain, or the markers of rehabilitation among older adults (31). The prehabilitation training booklet was based on previous guidelines for older adult exercise programs (28).
One of the critical components of any exercise training program is the principle of specificity. This principle of training stipulates that the more closely the training mimics the evaluation method, the greater the improvement in the evaluation method as a result of the training (11).
Participants were requested to complete the prehabilitation training protocol 3 times per week, once per week under the supervision of the project staff at the University’s Physical Therapy Clinic and 2 times per week without supervision at home. All 3 prescribed sessions included the same warm-up, resistance exercises, flexibility exercises, step training, and a cool down. This method of partially supervising the exercise intervention has previously resulted in acceptable adherence by older participants without making unreasonable demands on their time commitment to the supervised exercise sessions (28,29,31). Participants in this group were taught how to record each session of prehabilitation training in an exercise log.
A session of prehabilitation training included approximately 5 minutes of warming up, 15 minutes of resistance training exercises, 15 minutes of flexibility exercises, 10 minutes of step training, and 5 minutes of cool down exercises. The warm-up consisted of unweighted leg joint movements to increase blood flow to the muscles of the legs, trunk, and arms. Following the warm-up, participants completed 8 dynamic muscle strengthening exercises with elastic resistance, including squats, ankle dorsi/plantar, hamstring flexion, bicep curls, triceps extensions, chest press, and seated row. During the first training week, each participant performed 1 set of 10 repetitions of each strengthening exercise using an elastic band with sufficient resistance to produce “moderate” fatigue after the final repetition. Individual training progressed under the supervision of the researcher until weeks 7 and 8, during which each participant performed 1 or 2 sets of 10 repetitions of each exercise using an elastic band with sufficient resistance to produce “moderate” fatigue after the final repetition with a 2-minute rest between sets (approximately 20 minutes).
After completion of the resistance training exercises, within each session of prehabilitation, participants completed 6 flexibility exercises. Over the entire duration of the 8-week prehabilitation training program, the flexibility exercises included 2 repetitions of static stretching for 20 seconds for each flexibility exercise. The flexibility exercises emphasized knee extension/flexion, hip flexion/extension, trunk extension/flexion, and shoulder flexion/extension/rotation. After completion of the flexibility exercises, participants completed 3 step-training exercises. These step-training exercises included going up and down a single step forward and then sideways to the left and right. During the first week of the prehabilitation program, participants completed 8 repetitions of each of the step exercise using a 2- or 3-inch step. The number of repetitions and the height of the step of each of these step exercises were increased over the 8-week prehabilitation intervention. During the eighth week of the prehabilitation program, participants completed 20 repetitions of each of the step exercises using a 4- or 7-inch step. The cool-down consisted of 5 minutes of unweighted leg joint movements of the muscles of the legs, trunk, and arms. If the participant was unable to complete the initial level of training or was unable to progress at any week in the 8-week training schedule, an individualized training program was developed for him or her, consistent with that participant’s ability level. This individualized prehabilitation training program strived to have the individual achieve the same level of training for all 5 components as prescribed in the prehabilitation exercise booklet. The number of repetitions and sets for all components of the prehabilitation program was recorded in the exercise log.
Self-efficacy to exercise and OEE were measured by using the SEE scale (19) and the OEE scale, respectively (27). The 9-item SEE demonstrated reliability and validity (14,22). This instrument asked participants to indicate how confident (ranging from 0 [not very confident] to10 [very confident]) they were in their ability to exercise 3 times per week for 20 minutes if (sample items): the weather was bothering them; they felt pain when exercising; and they felt tired. An average of the items was calculated, with higher values indicating greater SEE.
The OEE scale, which has demonstrated evidence of reliability and validity (27), asks individuals to identify expected positive outcomes of engaging in exercise. Sample items from the 9-item OEE include: makes me feel better physically, makes my mood better in general, makes my muscles stronger, and gives me a sense of personal accomplishment. Item responses were based on a 5-point Likert scale ranging from 1 (strongly agree) to 5 (strongly disagree). The scale is scored by adding the responses to obtain the total score and dividing by the number of items.
This study used the ITT (8) principle of retaining all subjects randomized into the prehabilitation group regardless of their adherence with the prehabilitation intervention. Repeated measures analysis of variance (RM-ANOVA) was used to determine the main effects of group (control vs. treatment), time (T1 vs. T2 vs. T3 vs. T4), and the interaction of group and time on the outcome variables. If significant main or interaction effects were detected with the RM-ANOVA, post hoc comparisons were conducted between the means using the Bonferroni (1) post hoc tests. These post hoc comparisons compensate to maintain the overall for Type 1 error at 0.05 (21).
Because of missing data during time 3 (T3), a secondary analysis was performed while excluding T3 data. This secondary analysis consisted of RM-ANOVAs being developed for each outcome variable while examining the effect of group (PRE vs. CON) and time over the remaining 3 data collection points (T1, T2, and T4). Although the attrition at T3 was higher than expected (50%), the attrition rate for T3 did not limit the results of the study. For all models, statistical significance was established as a p value < 0.05.
Demographic characteristics of the sample are shown in Table 4. Comparisons between the 2 study groups indicated no differences.
Self-efficacy for Exercise
Hypothesis 1 was evaluated using a RM-ANOVA, which included the within-factor time points (T1, T2, T3, and T4) and the between-group factor (PRE vs CON). The interaction of group and time was also evaluated. The dependent variable in this model was SEE. The time effect was nonsignificant, Wilks’ Lamda = 0.89, F(3,15) = 0.606, p = 0.62. The between-group comparisons were also nonsignificant, F(1,17) = 0.034, p = 0.86. There was no significant interaction effect on SEE, Wilks’ Lamda = 0.87, F(3,15) = 0.784, p = 0.52. However, the observed power for the main effect of time test was only 0.62 for time and 0.52 for the interaction between time and group. Neither the PRE group nor the CON group had a significant change in their SEE over the 4 data collection points of the study as seen in Figure 2.
A secondary analysis of SEE was performed because there were a high number of study participants (PRE 5, CON 6) who did not complete data collection at T3. To maximize statistical power, a secondary analysis of the SEE data was completed, excluding T3 data. There were several reasons for this loss of T3 data. Those reasons included (a) extended inpatient rehabilitation by 3 PRE and 4 CON subjects along with (b) medical complications like infections (1 PRE and 2 CON) and (c) cold symptoms causing one PRE to miss because of inability to leave their home. This resulted in a sample of 31 (n = 15 CON and n = 16 PRE) participants being evaluated.
This analysis examined the main effects of time (T1, T2, and T4) and group (PRE vs CON) and the group × time interaction. The effect of time remained nonsignificant for SEE, Wilks’ Lamda = 0.97, F(2,27) = 0.430, p = 0.655. There was no significant interaction effect on SEE, Wilks’ Lamda = 0.96, F(2,27) = 0.537, p = 0.590. The observed power for this test was 0.113 for time and 0.130 for time × group. The between-group comparison was also nonsignificant, F(1,28) = 0.549, p = 0.465.
Outcome Expectations for Exercise
The evaluation of hypothesis 2 used a similar statistical model as above to determine significant differences in OEE within the sample over the duration of the study. There was a nonsignificant effect of time on OEE, Wilks’ Lamda = 0.72, F(3,15) = 2.06, p = 0.146.
There was no significant interaction effect on OEE, Wilks’ Lamda = 0.97, F(3,15) = 0.142, p = 0.933. The observed power for this test was 0.430 for time and 0.071 for time × group interaction. The between-groups comparison was nonsignificant, F(1,17) = 0.187, p = 0.069, although there was a trend toward significance. Whether significance will be reached when the sample size is increased is unclear but likely.
The secondary analysis of OEE excluding T3 indicted a similar pattern as the initial analysis; only this time there was a significant effect of time on OEE, Wilks’ Lamda = 0.709, F(2,27) = 5.75, p = 0.008. There was no significant interaction effect on OEE, Wilks’ Lamda = 0.986, F(2,27) = 0.199, p = 0.821. The observed power for this test was 0.828 for time and 0.078 for time × group interaction. Although time was significant, between-group comparison was not F(1,28) = 0.604, p = 0.443. Post hoc analysis, using the Bonferroni correction method indicated that the groups significantly declined between T2 and T4. Additional planned comparisons using T-tests (independent and paired samples) looked at between groups and within group changes over time. These tests indicated no significant differences. The PRE and CON groups did not significantly change their OEE over the 3 data collection points of the study as seen in Figure 3.
The purpose of this study was to assess whether knee OA patients, scheduled for TKA, who participated in guided exercise before TKA had higher SEE and higher OEE than those who do not. The findings indicated no significant effect of the time, group, or group × time on self-efficacy, which is not in support of our hypothesis. However, it is interesting to observe in Figure 2 that the SEE of the PRE seemed to be consistently maintained over the study, and actually trended upward after their TKA at T3 and T4, but did not increase to a significant difference. This trend was not observed in the CON group; the SEE of the CON demonstrated a downward trend before and after their TKA and only trended upward at T3 to T4 after starting into their rehabilitation. These trends observed among the PRE and CON groups are similar to previous studies that have shown an increase in SEE in patients who participated in exercise (10,25). Other researchers have found that exercise interventions with knee OA patients after TKA resulted in improvements in these measures of self-efficacy (15). Although speculative, it is possible that with a larger sample size, this discernible trend for self-efficacy may have reached statistical significance but future investigations are needed to support this premise.
Regarding the variable OEE, our findings showed a significant time effect. The PRE and CON groups changed in their OEE between T2 and T4 (Figure 3). The CON group declined between T1 and T2 but improved at T4 as the PRE group maintained OEE scores at T2. The PRE group did not significantly change but steadily maintained their scores at T2 and improved their OEE scores from T1 to T4 over the course of the study. The PRE group had higher OEE scores than the CON group at T4, but the scores were not significantly different. Data presented in Figure 3 showed that the OEE of the PRE was maintained or trended upward while the OEE of the CON demonstrated lower scores than the PRE at T2 and T4.
Even though OEE scores of the PRE group did not increase significantly, they trended in the hypothesized direction of higher outcome expectations at T2, before their TKA, and remained higher than their baseline values after their TKA at T4. The CON groups’ OEE scores decreased before their TKA and improved only slightly after their TKA. This increase of OEE at T4 for the CON group may be attributable to their participation in formal postoperative rehabilitation after their TKA, which may have positively influenced their expectations of the outcomes of their participation in exercise.
Outcome expectations, as described by the SCT, are beliefs that carrying out a specific behavior will lead to a desired outcome. This outcome expectation might be what the PRE group perceived to be the benefits of exercise (e.g., improving muscle strength, improved function, or feeling good in general). Through the exercise intervention, the PRE participants may have come to realize the value of the benefits of performing exercise and changing their behavior choices. As they may have realized and/or perceived results (e.g., better functioning and improved strength) because of the exercise program, they may have begun to change their outcome expectations. This interpretation of the findings supports the SCT with the PRE group having “past performance accomplishments, and a mastery of skills.”
In summary, the outcomes of this study have revealed that preoperative exercise did not have an effect on SEE. The study did, however, demonstrate some evidence, although limited, that outcome expectations may be positively influenced through a prehabilitation exercise program. A limitation of this study is the relatively small sample size; therefore, future studies are encouraged to examine a larger group of participants to increase the statistical power of the analysis. Despite this limitation, major strengths of this study include using a randomized controlled trial design and examining the role that prehabilitation may have on psychological outcomes that, in turn, may be associated with postoperative exercise capacity and functional outcomes. It was not within the scope of the present study to examine the influence of prehabilitation-induced changes in psychological parameters (e.g., self-efficacy and outcome expectations) on postoperative outcomes, such as functional ability. Given that previous work demonstrates an influence of prehabilitation on postoperative functioning, along with the fact that the present study suggests that prehabilitation may influence outcome expectations, a logical next step would be to see if prehabilitation-induced changes in outcome expectations is linked with postoperative physical functioning. It would also be informative if future studies examined whether a preoperative exercise intervention could influence a patient’s length of rehabilitation, lower cost of healthcare services, expedite return to work time, and improve overall quality of life. Additionally, future research assessing the participant’s perceptions of the benefits of the prehabilitation exercises would be useful. Furthermore, additional research considering dispositional tendencies and perceptions of confidence in the physical therapist are warranted. Finally, research testing specific strategies to enhance self-perception of confidence and strategies to improve outcome expectations are needed.
This study indicates that a prehabilitation exercise program performed by patients with knee OA before TKA may enhance their OEE after the surgery. Enhancing these perceptions is hypothesized to increase the likelihood that the patient will actively engage in their prescribed rehabilitation program and continue to exercise after formal rehabilitation.
This study was supported by the Bellarmine Fellowship Fund and Hygenic Research Fund.
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Keywords:Copyright © 2014 by the National Strength & Conditioning Association.
Social Cognitive Theory; preoperative exercise; motivation