ORIGINAL STUDIES, REVIEWS, AND SCHOLARLY DIALOG THYROID FUNCTION AND DYSFUNCTION Effects of Physical Activity on Body Composition and Fatigue Perception in Patients on Thyrotropin-Suppressive Therapy for Differentiated Thyroid Carcinoma Patrı ´cia dos Santos Viga ´ rio, 1,2 Dhia ˜ nah Santini de Oliveira Chachamovitz, 1 Mo ˆ nica Fabı ´ola Nogueira Cordeiro, 1 Patrı ´cia de Fa ´ tima dos Santos Teixeira, 1 Carmen Lu ´ cia Natividade de Castro, 3 Fa ´ tima Palha de Oliveira, 2 and Ma ´ rio Vaisman 1 Background: Subclinical thyrotoxicosis (scTox) may be associated with alterations in body composition and fatigue that can be possibly reversed with physical activity. The aim of the present study was to evaluate whether the systematic practice of physical activity improves lower extremity muscle mass and fatigue per- ception in patients with scTox. Materials and Methods: We studied 36 patients (2 men) with median age of 48.0 (43.0–51.0) years, body mass index of 27.4 (22.1–30.2) kg/m 2 , thyrotropin <0.4 mU/L, and free thyroxine between 0.8 and 1.9 ng/dL and 48 control subjects (C group; 7 men). Patients were randomly divided in two groups according to the adherence to the exercise training: scTox-Tr (n ¼ 19)—patients who adhered to the exercise intervention and scTox-Sed (n ¼ 17)—patients who did not adhere to it. The C group did not participate in the randomization. The exercise training was supervised by a physical education instructor, and it was composed of 60 minutes of aerobic activity and stretching exercises, twice a week, during 12 weeks. In both groups, body composition was assessed (anthropometric method), and the Chalder Fatigue Scale was determined at baseline and after 3 months of intervention (scTox-Tr group) or observation (scTox-Sed group). Results: At baseline, patients with scTox had lower muscle mass and mid-thigh girth and more fatigue on the Chalder Fatigue Scale than euthyroid control subjects. The scTox-Tr group had an increase in muscle mass, reduction in the variables reflecting whole body fat, and lesser perception of fatigue during the exercise training period ( p  0.05 for these parameters at the start and end of the exercise training period). Conclusions: scTox is associated with lower muscle mass and mid-thigh girth and more fatigue. Physical activity training can partially ameliorate these characteristics. More studies are needed to determine what training program would be optimum, both in terms of beneficial effects and for avoiding potential adverse responses. Introduction D ifferentiated thyroid carcinoma (DTC) accounts for 90% of all thyroid malignancies (1). In the last decades, there has been an increase in the incidence of DTC, possibly as a result of improved diagnostic methods and their more widespread use. Thyroid nodules are very common, though only about 5%–10% of them are malignant. The conventional treatment for DTC consists of total or partial thyroidectomy, often followed by ablation of the thyroid remnants with 131-I. Following these procedures, patients require levothyroxine (LT 4 ) treatment (2), and currently most are given doses that suppress serum thyrotropin (TSH). Therefore, LT 4 treatment in patients with a history of DTC is a common cause of so- called subclinical hyperthyroidism (subclinical thyrotoxicosis [scTox]), which is characterized by serum TSH concentrations that are low with normal serum free T4 (FT 4 ) and free triio- dothyronine concentrations (3). Epidemiological data indicate a wide variation in the prevalence of scTox, from less than 1% to about 16%. Among other things, it is influenced by gender, the underlying disease, age, the assignment for what the lower limit of the normal range for TSH is, and the methods used to measure serum TSH concentrations (4–6). Cardio- vascular, neuromuscular, and psychological alterations have been described in scTox, and many clinical parameters have been evaluated (7). 1 Endocrine and 3 Rehabilitation Clinics, University Hospital Clementino Fraga Filho; 2 Exercise Physiology Laboratory, Physical Education School; Federal University of Rio de Janeiro, Rio de Janeiro, Brazil. THYROID Volume 21, Number 7, 2011 ª Mary Ann Liebert, Inc. DOI: 10.1089/thy.2010.0052 695