Skeletal muscle mass in female athletes: the average and the extremes

Objectives: To examine the absolute and relative skeletal muscle mass (SM) in female athletes and to discuss the potential upper limit of whole-body muscle mass between large sized female and male athletes.
Methods: Forty-five female athletes and forty-five recreationally active females (control) had muscle thickness measured by ultrasound at nine sites on the anterior and posterior aspects of the body. SM was estimated from an ultrasound-derived prediction equation. Body fat percentage and fat-free mass (FFM) were calculated from ultrasound measured subcutaneous fat thickness. To eliminate fat-free component of adipose tissue (FFAT), we calculated FFM minus FFAT (FFM-FFAT). 
Results: FFM, FFM-FFAT, and muscle mass were markedly higher in athletes. Fat Mass was similar (Athlete: 14.9 kg vs Control: 12.9 kg [median value]). The large-sized female athletes had approximately 9 to 11 kg FFAT which corresponds to about 10% to 15% of FFM. Seven of the female athletes had more than 60?kg of FFM-FFAT, the largest of whom had 77.0 kg of FFM-FFAT. SM increased in a parabolic fashion reaching a value of 35 kg SM beyond 100 kg body mass. Only one of the athletes had a SM index of more than 13 kg/m².
Conclusions: Female athletes had much greater muscle mass than controls. In large-sized female athletes, the influence of FFAT needs to be considered when interpreting their FFM. In addition, the largest SM index in female athletes was 13.2 kg/m², which was approximately 77% of that observed with the largest male athlete ever recorded. This difference appears similar to that observed in nonathletes.