The goal of this clinical trial is to determine if a weight bearing exercise intervention can improve body composition and bone health in adolescents and adults with Thalassemia.

The main questions it aims to answer are:

• Does participation in a 12-week weight bearing exercise intervention change total body lean mass and percentage body fat (as assessed by DXA) in adolescents and adults with Thalassemia?
• Does participation in a 12-week weight bearing exercise intervention change muscle function (assessed by hand grip strength, sit to stand and vertical jump) and endurance (assessed by the 6 minute walk test) in adolescents and adults with Thalassemia?
• Does participation in a 36 week weight bearing exercise intervention (30 min/day; 5x/week) change bone mineral density as assessed by DXA in adolescents and adults with Thalassemia?

Researchers will compare participants' change in body composition, muscle mass, and muscle function during a "Usual Activity" period (12 weeks) with an exercise intervention (Period 1: 12 weeks) to see if exercise can improve body composition and muscle function.

The intervention will then be extended an additional 24 weeks for a total of 36 weeks of exercise (Period 2) to explore the change in bone mineral density between between "Usual Activity" and "Exercise Intervention" (Period 2) in individuals with Thalassemia.

During the intervention period, participants will engage in a self-directed exercise regime of either weight bearing aerobic exercise or strength training exercises (30 min/day; 5x/week).

Inclusion Criteria:

• Age: 14 - 40 years
• BMD Z-score at any skeletal site < -1.0
• Diagnosed with thalassemia (any genotype, regardless of transfusion dependency)
• Vitamin D (25-Hydroxy) drawn within the previous 12 months >20 ng/mL
• English speaking, able to consent

Exclusion Criteria:

• Patients who self-identify as 'exercisers' e.g. routinely exercise for minimum of 45 min/day, 5x/week
• Pregnant (unable to conduct bone density measurements in pregnant females)
• Hypogonadal, must be on replacement sex hormone therapy for min of 6 months
• Cardiac T2* by Magnetic Resonance Imaging of <20 ms (e.g. evidence of cardiac iron overload)
• Recent long bone or vertebral fracture (within the last 6 months)
• Cognitive impairment limiting ability to understand instructions during orientation
• Other conditions known to influence bone health or body composition as determined by the investigator
• Patients at risk for cardiovascular disease yet have not received a routine cardiology assessment within the previous 12 months
• Bone medication (e.g. Zometa, Prolia, Forteo) use in previous 2 years