In our breast cancer survivors cohort, all participants had
2 risk factors for CVD not related to treatment and 77% of this group had low cardiorespiratory fitness measured by VO2max
despite a normal LVEF at time of study. These results suggest that they are at a higher risk of breast cancer and cardiovasular mortality (Blair et al. 1996
; Blair et al. 1995
; Peel et al. 2009
). Our results are similar to three earlier reports in breast cancer survivors, (one of which women had controlled hypertension), suggesting the majority of women with non-treatment related CVD risk factors have a lower VO2max
compared to healthy women even with a concomitant normal LVEF (Jones et al. 2012
; Jones et al. 2007b
; Tolentino et al. 2010
). Our study differs from the earlier studies since we used a similar VO2max
protocol (Balke protocol) to the standardized treadmill test used for determining normative values (ACSM 2009
) and we reported pre- and post-treatment LVEF.
Collectively, the double impact from the effects of lifestyle changes and breast cancer adjuvant treatment may increase the risk for late-onset
CVD. Despite this knowledge, there is not a current stratification tool to accurately assess increased risk of CVD morbidity and mortality in breast cancer survivors. For example, sub-clinical cardiac dysfunction may go unnoticed until more overt symptoms occur and still remain undetected by a resting echocardiogram (ECHO) (Cardinale et al. 2004
; Civelli et al. 2006
). However, exercise tests may be more sensitive than resting tests in identifying cardiac dysfunction in long-term survivors (Gottdiener et al. 1981
; Klewer et al. 1992
; Weesner et al. 1991
). Therefore, exercise testing may serve as an important clinical tool for identifying breast cancer survivors who are asymptomatic, but at increased risk for the development of CVD. Furthermore, cardiorespiratory exercise testing can provide an objective evaluation of cardiorespiratory fitness, reducing the variability found in self-reported activity measures by 70-80% (Blair & Church 2004
Sub-maximal exercise testing with VO2
measured at the anaerobic threshold has shown good correlation with maximal exercise testing in individuals where a maximum test would be difficult because of disability or de-conditioning including those with congestive heart failure, stroke, or undergoing bone marrow transplant (Carlson et al. 2006
; Eng et al. 2004
; Kemps et al. 2008
). To our knowledge, this is the first study to investigate the association between maximal and submaximal cardiorespiratory fitness testing in breast cancer survivors. We found that submaximal VO2
endpoints were highly correlated with VO2max
, indicating that submaximal testing can be a good measure of cardiorespiratory fitness in breast cancer survivors. Our study produced similar results when comparing submaximal VO2
at anaerobic threshold and 85% age predicted maximum heart rate to VO2max
, suggesting that submaximal testing can be used as a surrogate for VO2max
testing in breast cancer survivors.
The submaximal VO2
at 85% age predicted maximum heart rate was used because this predetermined endpoint can be performed without expensive gas analysis equipment and can be more feasible than measuring anaerobic threshold when a large number of patients or subjects need to be tested. Submaximal VO2
endpoint at 85% age predicted maximum heart rate had a similar group mean heart rate and VO2
compared to the anaerobic threshold endpoint. This is important to note since anaerobic threshold is a helpful indicator for determining fitness level and for measuring the effect of exercise training (Casaburi 1994
; Casaburi et al. 1991
). Overall, the submaximal VO2
endpoint at 85% age predicted maximum heart rate showed the highest correlation to actual measured VO2max
, as seen in Figure
. Our findings suggest using the speed and grade at the 85% age predicted maximum heart rate endpoint during a submaximal test for predicting VO2
and objectively measuring cardiorespiratory fitness for breast cancer survivors, especially when repeated measures are required for assessing improvement after an exercise intervention. Our results support the use of a submaximal cardiorespiratory test as an objective measure of fitness that can be used for breast cancer survivors. Furthermore, this study suggests that a submaximal cardiorespiratory test using a modified Balke protocol with an endpoint set at 85% age predicted maximum heart rate can be performed when the equipment and personnel needed to conduct directly measured oxygen uptake via indirect calorimetry are not available. A validation study to design an accurate predictive model for extrapolating VO2max
from a submaximal testing end point at the 85% age predicted maximum heart rate endpoint.
We are unaware of previous studies that have used an Arc trainer with decreased load bearing force as an exercise testing modality to examine cardiorespiratory fitness in breast cancer survivors, many of whom have age-related or aromatase inhibitor induced arthalgia and may prefer alternate forms of testing. Turner et al. showed that VO2max
and time to attain VO2max
were similar when comparing results between testing modalities including an Arc trainer and a treadmill in healthy adults (Turner et al. 2010
). During our study three participants were unable to complete testing on the Arc trainer due to their inability to coordinate the movement between the lower and upper limbs simultaneously. Also, the Arc trainer produced significantly lower VO2
and heart rate at anaerobic threshold versus the treadmill submaximal test (Table
). Overall, we suggest that the benefit of using an Arc trainer does not outweigh difficulty with performing the required coordinated movements and lack of standard testing protocol. Also, It is important to note that there were no breast cancer survivors in our study that could not complete testing on the treadmill due to joint or muscle pain.
This is the first study to investigate the association between the gold standard for cardiorespiratory fitness (VO2max
) to submaximal VO2
tests in breast cancer survivors who had been treated with adjuvant therapy. The findings from this study indicate that breast cancer survivors with
2 CVD risk factors had low cardiorespiratory fitness and submaximal testing on the treadmill is a feasible, objective measure of fitness that can be used in breast cancer survivors. Limitations of this study include the small sample size (n
30), lack of racial diversity, and lack of non-cancer controls.
Future research should focus on using a high-risk breast cancer control group with
2 CVD risk factors to compare maximal and sub-maximal VO2
measures. In addition, novel approaches should be made to improve cardiorespiratory fitness during sustainable exercise interventions for breast cancer survivors.
All work described within this manuscript complies with United States and institutional regulations for the protection of human subjects.