Approximately 1.6 million new cases of cancer were expected to be diagnosed in the United States in 2014. Of these cancer diagnoses, it was estimated that nearly 300,000 were breast cancer [1
]. While the prognosis of breast cancer is improving, there is an estimated 2.9 million breast cancer survivors (BCS) left to deal with the numerous adverse side effects caused by the cancer itself and/or the cancer related treatments [2
]. Previous studies suggest that BCS encounter an array of detrimental physical changes resulting from the treatments for breast cancer [3
]. Studies have also shown that these physical changes can lead to a decreased level of physical functioning and have a negative impact on the quality of life (QOL) of the individual [6
The detrimental effects of cancer and cancer related treatment on the physical function and QOL of BCS vary in magnitude and longevity [10
]. Ganz et al
. (2004) reported that BCS experience significant decrements in their perceived physical function at the cessation of their primary treatment for breast cancer [11
]. Unfortunately, there has also been research that shows these negative effects on QOL and physical function extend far into survivorship, even though the primary treatments for cancer have been long finished [12
]. Specifically, Simonavice et al
. (2011) found that 17 months after the completion of primary treatment for breast cancer, BCS exhibited 21% lower strength for chest press and 23% lower strength for leg extension compared to age-matched healthy physically inactive women. Similarly, in this same study the authors found that BCS reported an 11% lower subjective physical function as measured via the Short Form-36 Health Survey (SF-36) and demonstrated lower objective physical function scores that were approaching significance compared to age-matched healthy physically inactive controls [13
]. The fact that individuals have conquered breast cancer only to remain suffering from decreased physical abilities and QOL warrants the implementation of interventions aimed to correct these deficits.
Over the past several years, researchers have investigated the effects of various exercise modalities and intensities on QOL in cancer patients and survivors. According to a recent meta-analysis, there are numerous studies that have indicated resistance training (RT) interventions can successfully improve QOL among cancer patients and survivors [14
]. Despite these findings, there are also reports that indicate resistance exercise interventions fail to elicit any positive QOL changes in cancer patients and survivors [15
]. This inconsistency in the research warrants further investigation to examine the effects of resistance exercise on QOL in cancer patients and survivors. Furthermore, of the studies examined, physical function is often measured from subcategories within QOL questionnaires (i.e
., Short Form Health Survey and Functional Assessment of Cancer Therapy—General). To date there has only been one study examining the efficacy of resistance training exercise to increase objective physical function in cancer survivors. Jankowski et al
. (2008) implemented the Continuous Scale Physical Functional Performance (CS-PFP) test in a group of older cancer survivors and found that components of the CS-PFP were significantly higher compared to the control group after a resistance training exercise intervention [17
]. The void in literature examining the efficacy of resistance training to increase the objective physical function of cancer patients and survivors demonstrates the need for further research utilizing objective assessments of physical function. Furthermore, the CS-PFP test has been utilized as a tool to establish thresholds for independent living in the elderly population [18
]. Obtaining a CS-PFP score for cancer survivors could possibly provide the information necessary to ensure that they maintain an adequate physical function capacity that will allow them to maintain their independent living status.
Studies reporting the negative physical and psychological changes that BCS encounter, and the lack of studies investigating non-pharmacological approaches to combat these negative changes, warrant an investigation of interventions to improve the conditions of this population. Thus, the purpose of the present investigation was to determine the efficacy of resistance exercise training on improving physical function, measured objectively, and subjective physical function and QOL in BCS. It was hypothesized that BCS would demonstrate improvements in both objective and subjective physical function as well as QOL in response to a six-month resistance training program.
The present study investigated the efficacy of resistance training in improving the physical function and QOL in a sample of BCS. All of the women had high adherence to the resistance training sessions (96%). The women demonstrated significant improvements in total function and all subcomponents of the CS-PFP, thus the hypothesis that a resistance training intervention would improve objection function in BCS was supported. No changes were reported for subjective levels of physical or mental QOL, measured via the SF-36 Health Survey; thus the hypothesis that a resistance training intervention would improve QOL and subjection function in BCS was rejected.
Women participating in the study showed excellent capabilities to improve objective physical function; however, the same cannot be said for the subjective levels of physical function or for QOL. To date the present study was the first to implement the CS-PFP test among BCS for an assessment of objective physical function. Results showed that the participants increased total function by 12%. While there are no studies examining BCS to which the results of the present study can be compared, Jankowski et al
. (2008) implemented the CS-PFP in a group of older cancer survivors (cancer type not specified) and found that after four months of RT, both upper body and lower body strength components of the CS-PFP were significantly higher as compared to the control group [17
]. Total physical function was not accounted for by Jankowski et al.
(2008). The baseline values for the women from the present study were seemingly higher for the upper body strength component (63.5 ± 16.3 units) as compared to the baseline values from Jankowski and colleagues (59 ± 29 units). Similarly, for the lower body strength component, the women from the present study had higher baseline values (58.5 ± 14.9 units) compared to Jankowski and colleagues (45 ± 16 units). These discrepancies are likely due to the older population (71 ± 5 years) with which Jankowski and colleagues studied, as compared to the present study where the sample population was younger (64 ± 7 years). Although time effects were not reported by Jankowski et al
. (2008), pre-to-post differences were calculated to be +20% for the upper body strength component and +11% for the lower body strength component [17
]. These improvements are similar to the results of the present study. Another study reported that a resistance training intervention significantly improved six-minute walking distance in a sample of BCS [25
]. The six-minute walk test is essentially the “endurance” component of the CS-PFP. Thus, these results are in agreement with the 12% improvement in the endurance component of the CS-PFP test as seen respectively for the participants of the present study. While there is no minimum clinically importance difference established for the CS-PFP test, the improvements in CS-PFP from the present study were significantly correlated with improvements in the participants’ upper and lower body strength, as measured by 1RM assessments.
Although, there is a lack of literature in which to compare the CS-PFP results of the present study with cancer survivor populations, the results found align with published data in other female chronic diseased populations. Kingsley and colleagues (2005) reported that 12 weeks of resistance training in women with fibromyalgia, resulted in a 14% increase in total CS-PFP function [26
]. Whereas, Brochu et al
. (2002) reported an even larger improvement (+24%) in total function in a group of older, disabled women with coronary heart disease after six months of resistance training [27
]. These results in combination with the +12% increase in total CS-PFP function experienced in the present study tout the effectiveness of resistance training to improve objective physical function.
The ability for BCS to increase physical function is especially important given the fact that after the completion of cancer treatments, BCS have significantly (p
= 0.08) lower physical function scores as compared to healthy age-matched women who were physically inactive [9
]. It should also be noted that while the baseline values from the present study for total function (65.5 ± 12.1 units) mimicked those of the BCS baseline values for total function (66.1 ± 13.8 units) from Simonavice and colleagues, the six-month values from the present study for total function (73.6 ± 12.2 units) more closely mirrored the baseline results from the healthy controls (75.1 ± 13.0 units) from Simonavice and colleagues [9
]. These results imply that resistance training is an effective way to improve the physical functional status of BCS to that of healthy women. Additionally, it should be highlighted that in the present study at baseline, six participants achieved a CS-PFP score that fell below the threshold score of 57 units, which is needed for independent living [18
]. At the six-month mark, only two participants had a score that remained below the threshold score of 57 units, indicating that the intervention was able to bring four BCS above the functional threshold needed for successful independent living. The two BCS that remained under the 57 unit functional threshold were still able to make improvements from baseline to three months and then able to maintain their heightened score from three months to six months. Specifically, the two BCS scored 36 units and 45 units at baseline and were both able to increase their scores to 50 units by three months and maintain a score of 50 at six months, demonstrating an 11% and 39% increase in total function, respectively.
The significant correlations that were found between both upper and lower body strength and total CS-PFP function are similar to that found in previous studies investigating strength and function. While the present study is unique in that CS-PFP was used to assess objective function in BCS, previous studies have assessed function using other modalities in older adult populations. Fukagawa et al
. (1995) found that lower body strength was significantly related to lower body function as measured with chair stands in a group of elderly individuals [28
]. These results are similar to those found with Chandler et al
. (1998) who found that lower extremity strength was significantly related to chair stand performance and gait speed in older adults [29
]. While the relationship between upper body strength and function is less clearly defined in past literature compared to lower body strength, Foldvari et al
. (2000) found a significant relationship between upper body strength and subjective self-reported function in elderly women [30
]. These findings are consistent with the results of the present study which indicated a significant relationship between upper body strength and function as measured by total CS-PFP. The relationship between upper body strength and function is especially important in BCS because of the high incidences of upper body morbidities that accompany a breast cancer diagnosis. Specifically, Hayes et al
. (2012) state that 10%–64% of BCS report upper body morbidities from six months to three years after diagnosis [31
]. These morbidities in combination with the severity of the cancer and cancer-related treatments dispose BCS to a loss of upper body function [32
]. The results of the present study are encouraging in that if BCS can improve their upper body strength during recovery from a breast cancer diagnosis, it is likely that physical function will also be favorably affected.
The lack of QOL improvement for the BCS in the present study was inconsistent with most previous literature investigating QOL changes in cancer survivors after an exercise intervention. Many studies have reported that following resistance training interventions of various durations, intensities, and volumes have produced significant improvements in QOL in BCS [33
]. The difference between these previous studies and the present study is the type of subjective questionnaire utilized. The Functional Assessment of Cancer Therapy-General (FACT-G) or the Functional Assessment of Cancer Therapy-Breast (FACT-B) were the most commonly used survey tools assessing QOL among the studies reviewed. The present study implemented the Short Form-36 Health Survey (SF-36). The lack of significant improvement for QOL in the present study suggests that the FACT-B and FACT-G may address more specific questions regarding the impact that cancer and cancer-related treatments may have on QOL and thus may be more sensitive to detecting QOL changes within BCS. Despite the inconsistencies of the present QOL results with those previously published in cancer survivors populations, the lack of significant findings for improvement in the SF-36 QOL components in the present study are similar to that found in various studies with older and chronic diseased populations. Ades and Meyers (2003) reported no improvements in the physical function QOL component of the SF-36 after a six-month resistance training intervention with older female cardiac patients [23
]. Similarly, Barrett and Smerdely (2002) reported no significant improvement in the physical function QOL component of the SF-36 after a ten-week resistance training intervention with older individuals [36
]. The baseline scores from the participants of the present study for physical function QOL component were 82.6 ± 13.6, which are notably higher than previous studies, such as Ades and Meyers, who reported a baseline score of 59 ± 20 or Barrett and Smerdely, who reported baseline scores of 71 ± 18. The higher baseline scores for the SF-36 components reported in the present study could have increased the difficulty to detect significant changes over time. Despite the fact that neither the physical nor mental QOL scores were changed over the course of the six-month intervention, the fact remains that all the BCS from the present study significantly improved physical function, as measured objectively via the CS-PFP. Also noteworthy is the fact the present study failed to show any significant correlations between the percent changes of function measured subjectively via the SF-36 and objectively measured via the CS-PFP. These results emphasize the importance of objective measures of physical function in the BCS population.
The present study had several limitations that may have hindered the ability to accurately interpret the results. The present study had a seemingly smaller sample size than other studies of similar design, which may have hindered the obtainment of statistical significance for some of the variables assessed. Another limitation of the current study was a lack of a true control group, which may have lessened the magnitude of the results reported. Lastly, the usage of the SF-36 QOL instrument may not have been sensitive enough to accurately represent the physical and mental changes that BCS experienced over the course of the intervention. In fact, previous literature suggests that self-reported questionnaires, such as the SF-36, are not sensitive enough to allow individuals to accurately report subtle changes in physical function that may be clinically relevant [23
In conclusion, our findings indicate that a resistance training intervention of moderate intensity was well tolerated among BCS. All women displayed high levels of adherence to the attendance of exercise sessions and reported no adverse physical incidences as a result of the intervention. With the exception of upper body flexibility, the women improved all other subcomponents, as well as total function, measured via the CS-PFP. It is also noteworthy that at the end of the six-month intervention, upper and lower body strength as well as objective physical function measures were increased to levels that mimicked those achieved by healthy inactive post-menopausal women. This implies that a resistance training intervention is capable of helping BCS achieve similar levels of strength and function that they may have had prior to their diagnosis and treatment of breast cancer. Also noteworthy is the fact that the participants of the present study were able to make the aforementioned gains from a light to moderate intensity resistance training intervention (52%–69% 1RM). The efficacy of a light to moderate intensity resistance training program should be emphasized among health care practitioners and can possibly motivate cancer survivors to begin a more conservative resistance training program who are hesitant to begin strenuous activity. The present study was unable to detect any changes in QOL among the participants; however, from the literature reviewed, the QOL assessment tool may have not been the best choice for the BCS population. Furthermore, the significant gains in objective levels of physical function that the participants achieved should be more heavily considered as opposed to the subjective assessment of QOL, as it provides a more accurate depiction of their true physical capacities and physical well-being.