The present study found that heavyweight collegiate Sumo wrestlers could have approximately 10 % higher total BMC compared to middleweight Sumo wrestlers (Table 2). Moreover, the highest value of total BMC was 4.16 kg (2.9 % BMC to 143.6 body weight kg) in the present study. According to the previous study in healthy Japanese adults, mean and 95th percentiles of total BMC was 2.5 kg and about 3.1kg for the age group of 20-29 (140 males, mean body weight: 65.6 kg) using DXA (QDR-2000, Hologic Inc.)9, which is the same product as the present study. In addition, according to the previous study on competitive athletes, the mean total BMC is 4.32 kg in collegiate American football players (33 males, mean age: 22.3 years, mean bodyweight: 97.7 kg) using the same product DXA (Hologic-WI, Hologic Inc.)10. On the other hand, the inverse relationship between body weight and BMC percentage was observed in the present study (Figure 1). When the regression equation is applied in the case of having 200 kg body weight, BMC percentage and BMC would be 1.4% and 2.76 kg, respectively. Based on the present and previous studies, it is indicated that total BMC is not easily increased in response to larger body weight, and the upper limit of total BMC in humans with 150 kg bodyweight might be around 5.0 kg.
It has been well documented that weight-bearing physical activity has a positive effect on BMD8,12. In fact, an elite male soccer player (age 21.0 years, body weight: 77.8 kg, total BMD: 1.23 g/cm2) has approximately 10% higher value than controls (age 24.3 years, body weight: 76.5 kg, total BMD: 1.12 g/cm2) in case of using DXA (QDR-1000, Hologic Inc.)13. The above-mentioned previous study in healthy Japanese adults reported that the mean total BMD was 1.12 g/cm2 for the age group of 20-299. Compared to this BMD value of the previous study, middle (body weight: 98.1 kg, total BMD: 1.28 g/cm2) and heavy (body weight: 130.4 kg, total BMD: 1.33 g/cm2) weight Sumo wrestlers in the present study has about 15 % higher total BMD (The highest value of total BMD was 1.59 g/cm2). Moreover, there were significant correlations between body weight and total BMD in all subjects. As predicted from regression analysis in the case of 200 kg body weight, the calculated total BMD was 1.42 g/cm2. Although the recent study reported that the collegiate American football player with 135.5 kg mean body weight had the mean and max values of 1.63 and 2.11 g/cm2 total BMD using iDXA (Prodigy GE Healthcare Lunar)11, it was speculated that the upper limit of total BMD in human with 150 kg bodyweight might be around 1.60 g/cm2 when using DXA manufactured by Hologic Inc.
In the present study, BMD in legs is significantly different between middle and heavyweight Sumo wrestlers, but not in arms. (Table 2). In addition, although BMD in arms was not correlated with body weight, fat mass, and LSTM, BMD in legs was significantly related to body weight and LSTM (Table 3). These results suggested that BMD in the legs might receive a larger load and mechanical stress through daily living and exercise compared to the BMD in arms. Especially, it is speculated that the specific Sumo wrestling training such as stamping with a heavy body mass is more effective for the BMD in legs.
Sumo wrestlers have large masses of SM, liver, kidneys, and heart6,7. Similarly, this study found that Sumo wrestlers had a greater BMC and BMD from the comparison of previous studies, although the present study was a lack of controls. On the other side, the present study indicates that BMC and BMD might not sharply elevate among even heavyweight athletes.