This trial studies how well strength training works in improving bone health, pain, and quality of life in patients with multiple myeloma. Weekly physical activity may improve bone recovery, reduce pain, and increase quality of life in patients with multiple myeloma.

PRIMARY OBJECTIVES:

• I. To assess the feasibility of a 6 month, twice weekly supervised strength training intervention in patients with multiple myeloma. (Cohort 1)
• II. To assess the feasibility of a 6 month behavioral intervention to prompt an increase in weekly physical activity in patient with multiple myeloma. (Cohort 2)

SECONDARY OBJECTIVES:

I. To assess the adherence rate of patients during a 6 month intervention program.

II. To assess the eligibility and recruitment rate for the trial among patients with multiple myeloma.

EXPLORATORY OBJECTIVES:

I. Comparison of disease activity parameters, physical activity level, clinical symptoms, medication, psycho-oncological parameters before, during and after intervention.

II. Determine factors that may influence a persons' willingness to participate in the trial.

III. Investigate "immune fitness" by frequencies and function of immune cell subsets in peripheral blood.

OUTLINE: Patients are assigned to 1 of 2 cohorts.

COHRT 1 (STRENGTH TRAINING): Patients receive a Fitbit to track their physical activity, and complete an in-person personalized and supervised full-body strength training program over 1 hour twice weekly (BID) up to 52 sessions for 6 months.

COHORT 2 (BEHAVIORAL INTERVENTION): Patients receive a Fitbit to track their physical activity, and complete an unsupervised walking program daily at home, increasing physical activity stepwise weekly, for 6 months.

After completion of study, patients are followed up every 3 months for 1 year.

Inclusion Criteria:

• Have an Eastern Cooperative Oncology Group (ECOG) performance status of 0 - 1
• Have a diagnosis of multiple myeloma
• Show no signs of comorbidities, myeloma symptoms, or treatment side effects that would put them in danger when participating in the study according to the physician's discretion
• Are able to understand and follow assessment and training procedures
• Participant or legal representative must understand the investigational nature of this study and sign an Independent Ethics Committee/Institutional Review Board approved written informed consent form prior to receiving any study related procedure

Exclusion Criteria:

• Current and symptomatic pathological fracture(s) or severely advanced instability of the musculo-skeletal system
• Acute bone instability as assessed by whole body low-dose computed tomography and evaluated by an experienced neuro- and spine surgeon
• Major comorbidities that would cause danger to the patient when participating in the study. Examples are cardiac or pulmonary and infectious diseases that would have a risk of progression if the patient took part in the study
• Unwilling or unable to follow protocol requirements
• Any condition which in the investigator's opinion deems the participant an unsuitable candidate to take part in study intervention (comorbidities, myeloma symptoms, treatment side effects)