Maximal Strength Training for Breast Cancer Patients Undergoing Adjuvant Treatment. Doctoral Thesis

Abstract

Objective. Breast cancer (BC) is the most frequently diagnosed type of cancer among women, with more than 2 million new cases and over 600 000 deaths annually (Bray et al., 2018), and its global incidence is steadily rising. BC patients through the cancer continuum experience complex health and psychosocial challenges. BC and anti-cancer treatment accompanied by an inactive lifestyle may further impair muscle strength and muscle force development characteristics. Historically, patients diagnosed with cancer were advises to rest and avoid vigorous activity following their diagnosis, but this dogma has changed markedly over the last 20 years as exercise oncology intervention studies have gained broad acceptance and acknowledgment. Strength training can optimally affect muscles and increased muscle strength may contribute to participation in daily activities, thus potentially improving the health-related quality of life (HRQoL). However, the optimal type, intensity and frequency of strength training, as a part of cancer care, that will most enhance muscle strength during anti-cancer treatment is yet unknown. Christensen et al. (Christensen et al., 2014) investigated newly confirmed (breast, gastric, colorectal, lung and pancreas) cancer patients and concluded that these patients had 0.9 kg lower muscle mass compared with healthy controls even before the initiation of anti-cancer treatment. Furthermore, during adjuvant chemotherapy, BC patients lost 1.3 kg lean body mass (LBM), and continued to lose LBM after therapy was completed. Ultimately, BC survivors evaluated after completion of primary therapy displayed 20–30% lower muscle strength compared with healthy counterparts. Most physical activity interventions for BC patients combine aerobic endurance training with strength training and diverse relaxation therapies, hence making it more complicated to evaluate the impact of training type. There has been a limited number of well-defined clinical trials on BC patients that include higher intensity strength training, moreover when intervention is administered during adjuvant treatment. Training intensities vary substantially across cancer studies ranging from 25–80% of one-repetition maximum (1RM), although, it has been documented that higher training intensities yield greater strength gains in young healthy individuals (Campos et al., 2002). Similarly, greater gains in muscle strength are documented with increasing intensity for cancer patients, however, these patients are likely to have some improvement even at low training intensities (Fairman et al., 2017). The common consent from clinical trials when strength training interventions were applied for cancer patients states that training programs were well tolerated, they are safe, feasible and showed strength improvements that led to improved physical functioning and improved HRQoL (Segal et al., 2003), (De Backer et al., 2007), (Battaglini et al., 2014). Recognizing that training intensity during strength training is a key factor to improve maximal muscular strength and strength related characteristics. Therefore, well-defined training methods with high intensity could also be preferable to induce greater physiological adaptations, thus contribute to faster recovery from specific cancer treatment and enhancing the completion of prescribed anti-cancer treatment.