The aim of this prospective case-control study was to clarify whether pink paddling influences the quality of life and any lymphoedema - quantified by arm circumference measurements.
Discussion of patient characteristics
Apart from the BMI - which was significantly higher in the controls - there were no significant differences regarding the medical history and personal data of the PG and CG. The fact that the average participant in the CG was overweight (average BMI = 26.3 kg/m2) may be due to their general lack of interest in exercise. Most interestingly the literature describes that an increased BMI is associated with an increased risk of developing postoperative lymphoedema [1, 35–38].
This could also explain the possibly slightly (not significantly) higher frequency of lymphoedema in the control group (25% controls vs. 21% patients at T1, 16% controls vs. 4% patients at T2).
As in the publication by Brown et al. 2004 [22], lymphoedema was defined in the present study as a difference in arm circumference between affected and non-affected arm of at least 2 cm. According to this definition, a seasonal decrease in lymphoedema could be observed over time, which was more pronounced in the PG than in the CG (17% versus 9% difference).
At the beginning of the study, the paddlers reported significantly less pain in the affected arm and back as well as a significantly lower feeling of tightness from the surgical scar than the controls. The CG therefore suffered from subjectively more symptoms than the PG.
Reis et al. [39] were able to confirm in 2018 the effects of physical activity on pain in BCS observed in this study. For example, patients who exercised three times a week had significantly lower absolute pain levels and intensities and significantly lower levels of impairment due to pain in everyday life than the control group without physical activity. The mobility of the arms as well as the strength of both arms increased significantly in the sports group - in contrast to the control group.
Discussion of the quality of life
One of the major limitations of the study is, that the patients were not randomly assigned to each group. The paddle group was pre-existing. Before the start of the paddling season, they had no training within 6 months prior to the measurements (during wintertime). Therefore, the effects of both groups are comparable.
At the beginning, the PG started with a significantly better physical health status (SF 36, p = 0.029) - in contrast to the CG - and maintained it over the entire season. The physical health of the CG significantly decreased over time (SF36, p = 0.045). This could be due to the overall lower level of physical activity and the lack of opportunities to increase performance over time. Kendall et al. [40] found similar conclusion: patients who were physically active after being diagnosed with cancer, achieved a higher quality of life on the physical cumulative scale in SF36.
Regarding the mental summary scale of the SF36, there were no significant differences in the present study group.
This also corresponds with the available literature [41, 42]: with increasing disease-free survival, the quality of life of breast cancer patients approaches that of the healthy reference population, independent of interventions or rehabilitation measures.
In the evaluation of the EORTC QOL C30, the results also indicate that no improvement of HRQoL can be achieved without sports intervention. Thus, only the PG achieved a significant increase in the subscale of global health.
Role functioning was already significantly higher in the PG than in the CG at the beginning of the study. This could be explained by participation in team sports with the assumption of certain roles and functions within the group that existed before the study began.
The present study showed that the CG suffered significantly more from fatigue than the PG. This result has already been shown by Kessels et al. 2018 [43] for physical activity in general and Ray et al. [18] specifically for dragon boat paddling: regular physical activity has a positive effect on cancer-associated fatigue in cancer survivors.
Iacorossi et al. 2019 [44] were also able to determine this result in a similar setting through a singular evaluation of EORTC: The PP achieved a better HRQoL in the "operational and symptoms areas" than the CG, but the authors did not mention the time of measurement in their publication.
Overall, it can be stated that the developments in HRQoL identified in this study and the results of EORTC QLQ C30 and SF 36 fit into the existing knowledge of the effects of physical activity on BCS.
Discussion of arm circumference measurements
Whether the affected or unaffected arm, whether before or after training - the measured arm circumference decreased significantly in the PG over time. Thus, no negative effect of dragon boat training on a possibly pre-existing BCRL could be observed.
Iacorossi et al. 2019 [44] came to a similar conclusion regarding the influence of PP on lymphoedema incidence. In the Italian study, measurements of the arms were taken once at the beginning and end of the study. In contrast to the present study, neither the progression over the training season nor possible differences due to individual training sessions were recorded. Looking at the two time points, a decrease in lymphedema was observed in the Italian paddling group at the end of the study, as arm circumferences had decreased at almost all measurement points by the end of the study.
The decrease in arm circumference, also visible in the control group but less pronounced, could also be due to muscle atrophy caused by increased rest.
The fact that the number of removed lymph nodes has a clear influence on the arm circumference is shown both in the present study and in the literature. In women with AXLND, the measured arm circumference was greater in all positions, but significance was only achieved in the middle hand (p = 0.024).
Haid et al. [45] were able to show in their publication that patients with AXLND suffer significantly more frequently from restricted movement, lymphoedema and loss of sensitivity compared to SNLB alone. Helms et al. [46], Tsai et al. [47], Kilbreath et al. [48] and Bromham et al. came to similar conclusions in their 2017 review [49].
In the present study, adjuvant radiotherapy was not a significant factor in the development of BCRL. However, many recent studies show that radiotherapy to the breast and thoracic wall and lymphatic drainage system are relevant risk factors for the development of arm lymphoedema [38, 47, 48, 50].