Our study revealed a decreasing of FC in women with BC, with a mean time to perform TGlittre of 3.13 minutes. Currently, there are few studies that evaluated the FC among cancer patients. [12, 22, 23] Among the large number of tests available to evaluate FC, there is no gold standard instrument to assess it in women with BC.
Cancer treatment is associated with numerous adverse side effects, including pain, fatigue, cachexia, reduced strength and lung capacity, diminished range of motion, among others. A significant percentage of women will keep some of these symptoms for months after the end of treatments and will experience treatment-related late effects that may influence not only their quality of life, but also morbidity and mortality. [4, 6, 7, 24]
A reduction of lower limbs muscle strength and endurance, associated with compromised walking ability, have been reported in women with BC. [12, 25] In addition, Kokkonen et al.  reported poor balance, especially dynamic balance, in 78,1% of women with advanced BC. Impaired muscle strength associated to peripheral neuropathy, induced by neurotoxic chemotherapy agents, can compromise balance and disturb walking, leading to a further decline in FC. .
TGlittre was initially developed and validated to assess FC and the ability to perform ADL in patients with chronic obstructive pulmonary disease (COPD).  However, the evidence is limited about the performance in patients with other diseases such as cancer. Reis CM et al.  proposed a reference equation for TGlittre based on anthropometric and demographic variables in apparently healthy subjects. Although the reliability of the equation in women with BC cannot be established, when we applied it in our population, we found that 73.81% of women had higher values than the predicted ones, suggesting the FC compromise among our sample. In another work, Reis CM et al.  reported the shortest time to complete TGlittre of 2.03 minutes and a mean time of 2.62 minutes in healthy subjects. Similarly, Skumlien et al , found that the shortest time to perform TGlittre by healthy subjects was 2 minutes. However, it is known that FC decreases with age, and in the study of Côrrea et al.  with 10 healthy subjects with a mean age of 64 years, the mean time to complete TGlittre was 3.3 minutes. In our study, BC women were younger (59.62 ± 9.99 years) and needed 3.13 minutes to perform TGlittre, suggesting that other factors may play an important role in FC.
Kokkonen et al used six-minute walk test (6MWT) to determine functional impairment in women with advanced BC and found that FC was significantly lower compared with healthy subjects.  Comparing TGlittre and 6MWT, the last one includes only walking, which may imply a different metabolic profile compared with daily activities. In a study with heart failure patients, Almeida MP et al.  showed that TGlittre elicited higher ventilatory and cardiovascular responses than 6MWT. On the other hand, TGlittre simulates several daily activities, such as walking, sitting-standing, climbing up and down stairs and moving objects in different heights. It seems to be more representative of ADL and could reflect more faithfully real-life situations and the limitations experienced in a daily basis. Despite an overall correlation of TGlittre with 6MWD in COPD, Skumlien et al  found a substantial variability, especially in more debilitated patients, showing that TGlittre provided additional information about functional status, particularly in more disabled patients. To our knowledge, this is one of the first studies that evaluate FC in women with BC using TGlittre. We only found a published abstract by Cakmak et al , which had similar results. They evaluated fifteen BC survivors without any metastasis or active disease, that took a mean time of 3.1 minutes to complete TGlittre.
In our study, age was the only predictor of variation in TGlittre time. As previously described, FC tends to decrease with aging, due to a gradual reduction of muscle strength and oxygen uptake.  Women with cardiovascular and endocrine comorbidities spend more time to complete TGlittre. A fundamental condition for many ADL is the ability to perform mainly aerobic, i.e. oxygen-using, work. Such activities require the integrated work of the heart, lungs, and circulatory system to carry oxygen to the metabolically active muscles.  The presence of cardiovascular and some endocrine comorbidities, represented in our study by hypertension, diabetes mellitus, dyslipidemia, valvular disease, interatrial communication, arrhythmia and peripheral venous insufficiency, may compromise this mechanism and lead to the limitation of FC. Nonetheless, age was the only predictor of TGlittre variation, regardless of the presence of these comorbidities.
It is important to mention that women with BC may had the difficulty of using the backpack, due to pain caused by the catheter implantation, scars and/ or lymphedema in the upper limb caused by previous surgery. TGlittre was not initially developed to this population, and it would be interesting to report and quantify the impact of these limitations in future studies, in order to adapt it to these population characteristics.
Also, our work revealed that expiratory and inspiratory muscle strength were decreased in 24% and 14% of the patients, respectively. The analysis showed that TGlittre time was inversely correlated with MIP and MEP, suggesting generalized muscle weakness and deconditioning. This respiratory muscle impairment is considered one of the underlying mechanisms of exercise intolerance. 
We found that 35.7% of women reported fatigue, which did not correlate with TGlittre time. Fatigue is one of the symptoms most frequently reported by women with BC, with a high variability in prevalence. Besides, it is a multifactorial and subjective symptom, involving biological and psychological aspects, and the physiopathology is not completely understood. [3, 32–34] In another cross-sectional study, with 215 BC women, 72.09% were fatigued, while physically active women showed lower symptoms of fatigue and higher scores for quality of life scales, compared with sedentary ones.  Although fatigue did not correlate with TGlittre time, other studies show that feeling tired has a direct impact on functionality and compromises quality of life. [32, 33] The absence of correlation between fatigue and FC reinforces the importance of evaluating FC, which may be compromised even in the absence of self-reported fatigue.
There are limitations in this study. Firstly, it included only patients with criteria to be referred for a physical medicine and rehabilitation consult, and who wanted to participate in an exercise program, which may induce selection biases. It is possible that more vulnerable women or less motivated women may not be referred to our center, and it could overestimate FC and underestimate fatigue of this population.
Secondly, the tests used were not validated for breast cancer patients. The lack of sex and age-matched reference values of TGlittre for this population may compromise the clinical results interpretation. Since it is a relatively new test, more studies are needed to determine the reference values according age groups in healthy people. Additionally, MFIS was originally developed to assess fatigue in patients with chronic diseases, and it is not specific for this population.
Some rehabilitation needs of women with BC are still poorly recognized. Currently, exercise is recognized as a key element in cancer treatment to reduce symptoms and improve physical functioning, mood and quality of life.  In order to promote and validate physical and functional improvements during the recovery process, an adequate FC evaluation to assess the physical abilities of BC women could facilitate and optimize the development of exercise-based rehabilitation programs. Despite time-consuming, TGlittre may be a valid test to assess FC in this group of patients.