Evidence for exercise as an efficacious strategy to improve aerobic capacity of breast cancer survivors (BCS) has come largely from intervention studies conducted in laboratory settings. There is an increasing need to translate to community-type settings, but the efficacy of those interventions using gold standard evaluation is not well-established.

To investigate whether similar improvement in aerobic capacity (maximal oxygen consumption [VO₂]) measured with gold standard testing can be achieved through a community-based setting in BCS.

A peak cardiopulmonary exercise test (VO_2peak), 6-min walk test (6MWT), and timed up and go test (TUG) were assessed pre- and post-16 wk of progressive intensity aerobic and strength training exercise at a community center.

The sample consisted of 31 early BCS (< 1 year since treatment completion) and 15 controls (CTLs). Both groups significantly improved VO_2peak (+1.2 mL/kg/min; P = 0.030), 6MWT (+35 meters; P < 0.001), and TUG (-0.44 s; P < 0.01) following training. Both groups improved peak cycling power during the cardiopulmonary exercise test with BCS improving by +10 watts more than the CTLs (P = 0.020). Average exercise attendance was 71% (34 of 48 possible days), but compliant days averaged only 60% of total days for aerobic, and < 40% for strength in both groups.

Community-based exercise programs can be an effective strategy to improve aerobic capacity and physical function for early-stage BCS but potentially not to the same extent observed in laboratory-based randomized controlled trials. Further research is needed to explore barriers and facilitators of exercise engagement in community-based centers to maximize training benefits for adults with cancer.

Cardiorespiratory fitness describes the ability to use oxygen to produce energy for physical work and can be quantified as aerobic capacity (maximal oxygen consumption [VO₂]; mL O₂/kg/min) using the gold standard maximal cardiopulmonary exercise testing (CPET). Breast cancer survivors (BCS) have substantially impaired aerobic capacities[1,2], with a decline in VO₂ similar to that experienced with a 10 year increase in age, which can be attributed to both cancer treatment-related toxicities and increased sedentary lifestyle habits[3,4]. This impairment places BCS at substantial risk of death from cardiovascular (CV) disease and loss of functional independence[5]. Fortunately, exercise is a known promoter of CV health in the general population[6] and is an effective strategy for improving aerobic capacity in BCS during and post-treatment[7-9].

Multiple well-designed and controlled exercise intervention trials have demonstrated the benefits of aerobic and strength training exercise on aerobic capacity and other physical function outcomes, resulting in the development of exercise prescription guidelines for adults with cancer[10]. Guidelines were recently updated in 2019 and recommend at least 30 min of moderate intensity aerobic exercise at least 3 d/wk, and at least 2 d/wk of strength training for people with cancer[11]. Participation in exercise interventions reflecting these guidelines have demonstrated increases in aerobic capacity by 2.3-2.9 mL/kg/min (approximately 10%-15%)[7,9,12]. However, these changes in aerobic capacity have been observed primarily from interventions in highly controlled laboratory randomized controlled trials (RCTs), and the efficacy of this “trial-proven” exercise prescription delivered through real-world settings such as community-based centers has not been well-studied[13]. These settings likely differ from laboratory settings because they may be more relaxed environments with the opportunity for increased socialization between participants, and may provide additional flexibility in terms of training modes and session attendance (ATT) than what laboratory-controlled trials may provide or allow, regardless that the intention to improve fitness and quality of life may be the same. Of the limited work available on evaluating outcomes in community-based settings, cardiorespiratory fitness appears to be maintained or improved but has not been evaluated using direct, gold standard exercise testing methods (i.e. maximal CPET)[14-17]. Instead, alternative indicators of functional capacity such as the 6-min walk test (6MWT), and the timed up and go (TUG) test have been used, which may offer improved utility and feasibility in clinical/community-based centers. As exercise is increasingly recommended to survivors, and as interventions transition from highly controlled laboratory based settings to more practical venues like community-based centers, it is important to precisely evaluate whether similar cardiorespiratory fitness benefits can still be achieved to properly support and accommodate a large volume of cancer survivors in need of improving or even maintaining their overall health, physical function, and quality of life through participation in regular exercise[13,18].

Exercise programming for cancer survivors is a well-recognized challenge in exercise oncology[19-21] because survivors frequently require tailored exercise accommodations based on cancer-related treatments and associated side effects. Oncology-trained staff in community-based settings may be uniquely positioned to modify workouts, but these necessary adjustments have the potential to significantly impact exercise engagement[20,22]. Therefore, collecting and reporting exercise efficacy, ATT, and compliance in community-based intervention studies will improve understanding of how patients engage in these settings and how exercise engagement may relate to physical fitness and health outcomes[23-25].

The primary aim of this study was to evaluate the impact of a community-based exercise program on change in aerobic capacity in women with breast cancer measured using the gold standard CPET. A secondary aim was to evaluate if changes in aerobic capacity in the community-based setting differ between women with and without cancer. A third aim evaluated how exercise engagement (ATT and compliance) relates to changes in aerobic capacity. For the primary aim, we hypothesized that aerobic capacity would significantly improve following community-based training. For the second and third aims, we hypothesized that women in both groups would benefit similarly from the community-based protocol and that the observed changes in aerobic capacity would be directly related to training ATT and compliance.

This study used a parallel-group, pre-post design. Two groups (one BCS, one non-cancer control [CTL]) of women were engaged in an identical supervised exercise evaluation and intervention at Get REAL and Heel (GRH), an established, community-based exercise facility for cancer survivors in Chapel Hill, North Carolina that has offered exercise training reflective of recommended guidelines to cancer survivors for the past 10 years. This study leveraged an associated exercise oncology lab with gold standard testing capacity to evaluate the existing community-based program as it has currently operated. For data collection, two consecutive visits to the Exercise Oncology Research Laboratory of the UNC Department of Exercise and Sport Science occurred prior to (pre-intervention) and immediately following (post-intervention) the 16-wk exercise program. Outcomes evaluated included peak aerobic capacity (VO_2peak), the 6MWT, and the TUG test. Patient demographics and cancer-specific clinical data were extracted from the UNC Health Care electronic medical record by the research team. The study (NCT03760536) was approved by the Protocol Review Committee of the UNC Lineberger Comprehensive Cancer Center and the UNC Institutional Review Board. All participants provided written informed consent.

Thirty-five women with breast cancer were enrolled, of which 31 completed all study assessments. Twenty-one non-cancer CTLs were enrolled, of which 15 completed all study assessments (Figure 1). Those who did not complete post-testing were excluded from the analyses due to missing data but were otherwise very similar to women with complete data. At baseline (Table 2), BCS participants were taller (P = 0.035) and had worse TUG performance (P < 0.01) than CTL participants.

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Figure 1 Recruitment and retention.

Aerobic capacity between participants

There was no significant time x group interaction for VO_2peak but women in both the BCS and CTL groups had significantly improved aerobic capacity by approximately 1.2 mL O₂/kg/min (95%confidence interval [CI]: 0.15-2.27, Cohen’s d = 0.36; P = 0.03) from pre- to post-testing (Figure 2A).

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Figure 2 Maximal testing results (standard error bars). A: Aerobic capacity; B: Peak Power; C: Time to Exhaustion in breast cancer survivors and controls before and after 16-wk of training. ^aP < 0.05 for time; ^cP < 0.05 for group time interaction.

Participation in community-based exercise training reflective of recommended guidelines increased aerobic capacity in women with breast cancer in our study, but not to the extent observed in laboratory RCT settings. The 1.2 mL O₂/kg/min (+6%) improvement following community-based training is less than the 2.3-2.9 mL/kg/min (approximately 10%-15%) improvement reported in recent meta-analyses; however, the latter interventions were completed in laboratory RCT settings[7,9,12]. Changes in VO_2peak following training in non-RCT settings have been only minimally evaluated using gold standard methodology[13] in contrast to alternatives such as submaximal VO_2peak testing, 6MWT, and/or TUG[14,16,17,30] but have nonetheless supported beneficial changes. However, while the transition of interventions from laboratory settings to community settings is increasing[13,31,32], it is important to evaluate outcomes with gold standard testing to ensure survivors are receiving effective intervention in this newer setting. While the aerobic capacity improvement in our study may be small, substantial decline in aerobic capacity is a known manifestation of cancer survivorship[1,3,33]. Therefore, maintenance or even slight improvement is encouraging especially in conjunction with the observed improvements in peak cycling power and cycling endurance. Furthermore, while functional capacity (6MWT and TUG) of BCS in our study is not equivalent to non-cancer population norms[34], it reflects improvement commonly observed for women with breast cancer[35], which is of clinical relevance[28,29] and underscores the beneficial impact of exercise for demands of daily life.

Both women with and without breast cancer in our study demonstrated similar improvements in aerobic capacity (+1.2 mL/kg/min; P = 0.03) following the community-based exercise program. Interestingly, VO_2peak of both groups reflected that of published norms for women with breast cancer who are post-treatment (21.5 mL O₂/kg/min)[2]. For CTL participants, this is substantially lower than conventional standards[36]. Recently, our laboratory has consistently observed impaired VO_2peak in both BCS and middle-aged, sedentary women without cancer[37,38]. We speculate that this may reflect a regional fitness characteristic but warrants further investigation. In terms of training response for non-cancer populations, interventions similar to our study have generally elicited up to a 15% improvement in VO_2peak[39,40]. Therefore, the approximate 6% improvement observed in our study is also less than what is considered clinically significant in non-cancer populations[41,42]. The relatively poor compliance observed in our study indicates that prescribed training progression was not followed and may provide a partial explanation for the relatively modest improvements observed in VO2_peak. Exercise dosing and progression are important components related to the FITT principle[20,21,43] and are important factors for impacting patient physical and functional outcomes[8,11,44]. Furthermore, while ATT in our study (71%, attending about 2 of 3 training days per week) is similar to other exercise oncology interventions (approximately 70%-75%)[19,20,45], it reflects less than that recommended by national guidelines (≥ 3 d/wk, ≥ 30 min/d)[11]. It is reasonable to consider that improved exercise ATT closer to or matching the established, recommended guidelines in addition to improved compliance (which considers progressing intensity) would lead to more optimal physiological changes. However, despite modest intervention engagement, participants in our study still demonstrated positive/beneficial training adaptations which reiterates the need to investigate the fundamental question of what is the optimal training prescription for this population[9,23,43,46].

The ability to provide a community-based program that may improve physical and functional health and that survivors enjoy is paramount, especially when a survivor needs to prioritize aspects of work, life, and family around exercise[20,46]. Documenting exactly why patients missed sessions was not specifically recorded in this study but were anecdotally related to job, family, or general life obligations. Survivors also frequently expressed enjoyment with study participation and the GRH program, and many women regretted not having started their exercise journey earlier in treatment process. With respect to our generally positive findings, community-based programs such as GRH appear to have a place in cancer survivorship. Continued focus and conversations with survivors to better understand challenges around exercise compliance may help identify targets to improve engagement, and should remain a priority.

Difficulties with exercise engagement and compliance reflect the well-recognized challenges of exercise programming for clinical populations[19-21,47,48]. Based on the observations of our exercise staff and research team, participant compliance was primarily hindered by not achieving prescribed intensity, as measured by self-reported RPE. This method has the inherent weakness of subjectivity; however, it was the most feasible option in our relatively small community-based setting where, historically, heart rate monitor transmitter signals have overlapped between participants, displayed incorrectly, and caused unnecessary worry/confusion to an otherwise upbeat and positive environment. In our study, it was observed that while participants would and could complete both prescribed duration (aerobic) and volume (sets x reps, strength), there was reluctance to increase intensity (grade/speed/weight, etc.) especially in the second half of training when intensity targets increased. Strength training intensity targets were achieved less frequently than aerobic for both groups, leading to fewer strength compliant days than aerobic (Table 3), which has been observed previously in this population[20,49,50]. GRH training staff encouraged and guided participants how to safely reach more difficult intensities and no adverse events were documented during training; therefore, lack of training support, injury, or unnecessary discomfort were unlikely contributors to sub-optimal compliance, yet successfully increasing intensity remained a challenge. While participants were reminded how to contextualize and use the RPE scale, it is possible there was misunderstanding or concern from participants that reporting a higher RPE somehow suggested they were less capable of completing the prescribed exercise.

The primary limitation of our study is that it was a small, self-selected sample of mostly White women willing who were able to engage in exercise training for 4 consecutive months. This is not representative of the majority of women with breast cancer, especially younger women who may have acute family and job demands. The greatest strength of this study was the well-established, long-standing community-based exercise oncology program with veteran training staff, but we recognize that this experienced environment is difficult to replicate[13,51-53] especially in partnership with facilities capable of gold standard testing.

Future research would benefit from the inclusion of more diverse participants and from continued efforts to explore barriers and facilitators of exercise engagement. Calculation of both ATT and compliance in community-based settings similar to the methods presented in our study would improve the ability to quantify exercise load, progression, and dose responses more precisely. Heart rate monitoring in addition to self-reported RPE may also help better communicate and indicate training intensity, especially as technology for self-monitoring progresses. Directly collecting more information from participants about missed sessions and live feedback during training sessions would help provide better understanding of participant barriers, concerns, and potential limitations to engagement. These improvements would help contribute to the development of more specific future exercise prescriptions that are both suitable and effective in community-based settings. Furthermore, a third group of BCS who did not exercise for 16-wk, or who completed prescriptions with differing levels of exercise volume (days/reps/time) and/or undulating intensity progression (high vs low intensity) would help clarify specific findings from the current study and enhance future designs.

A community-based exercise program such as GRH can improve aerobic capacity and overall physical function in women with breast cancer, potentially not to the extent of an exercise oncology laboratory based RCT setting but similar to that of women without a cancer diagnosis participating in a similar program. Survivors may not meet recommended physical activity guidelines immediately, but proper training accommodations may help facilitate and encourage the integration of exercise as a daily routine. This is an important first step to life-long exercise commitment and provides the foundation to achieve recommended guidelines. Community-based venues offering exercise oncology programs have the potential to augment long term cancer care[13], will be essential for accommodating the growing number and needs of survivors[18], and should be continually evaluated as interventions are implemented in new settings.