Background/Objectives:A number of recent studies dealing with the relationship between the effects of high body mass (BM) and fat mass (FM) on bone mass and strength exhibit a range of contrasting variations in their findings. These diverse findings have led to an ongoing controversy as to whether high BM and FM positively or negatively affect bone mass and strength. Excessive FM and the associated low-grade inflammation might overturn the higher mechanical stimulus arising from a higher BM. Therefore, we aimed at quantifying the functional muscle-bone unit in premenopausal women with markedly diverging body composition.Subjects/Methods:Sixty-four young women with BMs ranging from 50 to 113 kg and body fat percentages between 20.7% and 51.8% underwent jumping mechanography and peripheral quantitative computed tomography measurements. Maximum voluntary ground reaction force during multiple one-legged hopping (F m1LH), as well as bone characteristics at 4, 14 and 38% of tibia length, were determined. Body composition was assessed by dual-energy X-ray absorptiometry, and serum inflammatory markers were analyzed from blood samples.Results:F m1LH predicted volumetric bone mineral content at the 14% site by 48.7%. Women with high body fat percentage had significantly higher F m1LH, significantly lower relative bone mass, relative bone strength and relative bone area, as well as higher serum inflammatory markers in comparison to women with lower body fat percentage.Conclusions:In conclusion, high body fat percentage was associated with lower relative bone mass and strength despite normal habitual muscle force in premenopausal women, indicating that high body fat percentage compromised the functional muscle-bone unit in these individuals.