Testosterone Levels in Athletes at Rest and Exhaustion: Effects of Calcium Supplementation Vedat Cinar & Abdulkerim Kasim Baltaci & Rasim Mogulkoc & Mehmet Kilic Received: 23 November 2008 / Accepted: 8 December 2008 / Published online: 20 December 2008 # Humana Press Inc. 2008 Abstract The effects of 4 weeks of calcium supplementation on free- and total testosterone levels were established in active and sedentary adult males at rest and exhaustion. Thirty healthy male athletes were equally divided into three study groups, as follows: Group 1— non-exercising subjects receiving 35 mg calcium/kg body weight; Group 2—subjects receiving 35 mg calcium/kg body weight undergoing training routines for 90 min/day, 5 days a week and Group 3—subjects undergoing training routines for 90 min/day, 5 days a week. The testosterone levels were determined before and after supplementation, at rest and following a hard training routine. The plasma free- and total testosterone levels increased at exhaustion before and after supplementation relative to resting values (p <0.05). This was also true when active subjects were compared to inactive subjects (p <0.05). Our results show that training results in increased testosterone levels in athletes and that the increase is greater if accompanied by calcium supplementation, which may be useful for increasing overall athletic performance. Keywords Exercise . Calcium supplementation . Free and total testosterone . Athletes Introduction Exercise changes homeostasis by physical stress. The autonomous nervous system and hypothalamus–pituitary–adrenal axis also participate in this response and assist in the preservation of homeostasis and physical fitness [1]. Biol Trace Elem Res (2009) 129:65–69 DOI 10.1007/s12011-008-8294-5 V. Cinar (*) Karaman High School of Physical Education and Sport, Selcuk University, Karaman, Turkey e-mail: bsyovedat@yahoo.com.tr A. K. Baltaci : R. Mogulkoc Department of Physiology, Meram Medical School, Selcuk University, Konya, Turkey M. Kilic High School of Physical Education and Sport, Selcuk University, Konya, Turkey