Muscular strength and endurance in cancer survivors

Muscular Strength and Endurance

Resistance exercise training has been effective in improving muscular strength and endurance in cancer survivors,with the majority of research being in those with breast cancer,prostate cancer,and head and neck cancer.Muscular strength has been measured as 1-repetition maximum (1RM) or 6- to 7-repetition maximum to estimate 1RM. Muscular endurance has been measured as the number of repetitions of a certain weight in a set time. Assessing baseline muscular strength and endurance is important for developing the most appropriate and effective prescription for cancer survivors.

Research studies with cancer survivors have used a variety of resistance prescriptions,as follows:

• Frequency: One to five sessions per week (primarily two or three)
• Number of exercises: Varied numbers involving large muscle groups (primarily five to nine)
• Sets: One to three sets
• Repetitions: 8 to 12 reps
• Intensity: 25 to 85% of 1RM
• Duration of program: 3 to 52 weeks

The 2010 ACSM roundtable guidelines for resistance training exercise for cancer survivors are also consistent with the 2008 U.S. DHHS “Physical Activity Guidelines for Americans.”Cancer survivors are encouraged to meet the U.S. DHHS guidelines of two or three weekly sessions that include exercises for the major muscle groups,as able.

Strong evidence of the benefit of resistance training has been reported in breast cancer and prostate survivors during and following cancer treatment.1 The role of resistance training following surgery for breast cancer has been controversial; traditionally, practitioners have advised people not to lift more than 10 pounds (4.5 kg) and to limit repetitive upper-extremity activities. These limitations were aimed at reducing the risk of developing upper-extremity lymphedema, swelling that can affect the arm and trunk following breast cancer surgery and treatment. Results from recent research have suggested that progressive resistance training improves muscular strength, muscular endurance, and functional ability, without increasing the risk of developing upper-extremity lymphedema or exacerbating preexisting lymphedema.

Schmitz and colleaguesstudied breast cancer survivors with preexisting lymphedema. The exercise group had an increase in strength, measured as 1RM, of 29.4% for the bench press (versus 4.1% in controls) and 32.5% for the leg press (versus 7.6% in controls). The exercise group reported a significant improvement in lymphedema symptoms. Also, exacerbations of lymphedema were nominal in the exercise group, which also had fewer exacerbations compared to the control group. The key message stressed in this study was adhering to proper form and progressing the exercises slowly. To achieve this, the study included supervision by trained instructors for the first 13 weeks. Also, the intensity started low and progressed slowly by the smallest increment to reduce the risks of worsening lymphedema. In addition, participants wore compression sleeves during their resistance exercise sessions, and symptoms of worsening lymphedema (i.e., swelling, feelings of heaviness) were closely monitored.

Resistance training has also been encouraged for prostate cancer survivors undergoing androgen deprivation therapy, which lowers testosterone levels. The treatment-associated reduction in muscle mass and muscle strength can compromise physical function, particularly in older men.In a study that compared a 12-week resistance training program and a usual care group during ADT treatment, the exercise group had a significant increase in upper- and lower-body muscular strength (1RM) and endurance (number of repetitions of 70% 1RM) compared to the control group, 36 with an 11% improvement in 1RM chest press (versus 1% in controls) and 37% improvement in the 1RM leg press (versus 7% in controls).

Resistance training has also been studied in head and neck cancer survivors. Resistance training in this population may be particularly important because of the associated shoulder dysfunction, which is a well-recognized complication of the neck dissection surgeries commonly used. The shoulder dysfunction is due to damage to or resection of the spinal accessory nerves and surrounding muscles, such as the trapezius muscle. A small randomized controlled trial compared a 12-week standard care program that included range-of-motion, stretching, and shoulder-strengthening exercises with elastic resistance bands with a 12-week progressive resistance program based on individual baseline strength testing. Both groups improved muscular strength and endurance, but the individualized, progressive program resulted in greater improvements in 1RM for the seated row (37% versus 15% in the standard care group) and the chest press (45% versus 24% in the standard care group).

Timing

The majority of resistance training programs for people with cancer have been undertaken following cancer treatment and have reported benefits.However, research on the benefits of resistance training during chemotherapy treatment is limited. During chemotherapy, an improvement in strength was reported in breast cancer survivors who were randomized to a resistance exercise program compared to those randomized to an aerobic exercise program or control group (the only group to maintain their usual lifestyle).In addition, the resistance group in this study also had a better chemotherapy completion rate than the aerobic exercise or control group did. A better chemotherapy completion rate means that people were more likely to receive their prescribed chemotherapy dose on schedule, instead of experiencing the delays commonly seen with chemotherapy. A better chemotherapy completion rate is an outcome that may be of particular interest to the clinical oncology community (i.e., oncologists) because delivery of the prescribed chemotherapy dose is linked to improved clinical outcomes. Improvements in upper- and lower-body strength were also noted in prostate cancer survivors who took part in a resistance program during radiation therapyand during androgen deprivation therapy.

Specificity of Training

As with aerobic interventions, issues with specificity also exist for resistance interventions. Baseline testing has not been used universally. A generic approach to prescribing resistance exercise that does not take baseline strength into account may result in an exercise prescription that is too easy (and therefore results in less improvement) or too hard (limiting improvement and possibility increasing the risk of injury).

The 1-repetition maximum (1RM) test has been employed during recent exercise studies with breast, prostate, and head and neck cancer survivors to determine the appropriate exercise prescription for program.This information has then been used to develop an exercise prescription in a variety of ways. The initial intensity for head and neck cancer survivors was set at 25 to 30% of 1RM and progressed to 60 to 70% of 1RM. The protocol included both double- and single-limb (arm) exercises, because strength was disproportionally reduced on the treatment side as a result of surgery or radiation.32 This study included both men and women, making an individualized approach even more important than in studies of a single sex. For breast cancer survivors with or without lymphedema, the goal of the program by Schmitz and colleagues35 was to progress slowly to avoid acute injury to the arm. Damage to the arm has been suggested as a risk factor for lymphedema (see chapter 6). The authors did not set an upper limit for resistance.

Supervision is another key feature in achieving specificity of resistance training. Supervision initially or for the entire study can ensure that clients use proper form and an appropriate progression. Home-based programs are more difficult to monitor for proper form or appropriate progression of resistance, which may limit clients' gains in strength and endurance.

Finally, adherence and compliance to the prescribed intensity and progression have not been well documented in the literature, which limits the ability to determine the overall expected effect of resistance programs for cancer survivors. Further research is needed to continue the development of feasible and effective resistance programs for cancer survivors.

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