Abstract
The relationship between muscle strength and bone mineral content (BMC) and bone mineral density (BMD) is supposed from the assumption of the mechanical stress influence on bone tissue metabolism. However, the direct relationship is not well established in younger men, since the enhancement of force able to produce effective changes in bone health, still needs to be further studied. This study aimed to analyze the influence of muscle strength on BMC and BMD in undergraduate students. Thirty six men (24.9 ± 8.6 y/o) were evaluated for regional and whole-body composition by dual energy X-ray absorptiometry (DXA). One repetition maximum tests (1RM) were assessed on flat bench-press (BP), lat-pull down (LPD), leg-curl (LC), knee extension (KE), and leg-press 45° (LP45) exercises. Linear regression modelled the relationships of BMD and BMC to the regional body composition and 1RM values. Measurements of dispersion and error (R2adj and standard error of estimate (SEE)) were tested, setting ρ at ≤0.05. The BMD mean value for whole-body was 1.12±0.09 g/cm2 and BMC attained 2477.9 ± 379.2 g. The regional lean mass (LM) in upper-limbs (UL) (= 6.80±1.21 kg) was related to BMC and BMD for UL (R2adj = 0.74, p<0.01, SEE = 31.0 g and R2adj = 0.63, SEE = 0.08 g/cm2), and LM in lower-limbs (LL) (= 19.13±2.50 kg) related to BMC and BMD for LL (R2adj = 0.68, p<0,01, SEE = 99.3 g and R2adj = 0.50, SEE = 0.20 g/cm2). The 1RM in BP was related to BMD (R2adj = 0.51, SEE = 0.09 g/cm2), which was the strongest relationship among values of 1RM for men; but, 1RM on LPD was related to BMC (R2adj = 0.47, p<0.01, SEE = 44.6 g), and LC was related to both BMC (R2adj = 0.36, p<0.01, SEE = 142.0 g) and BMD (R2adj = 0.29, p<0.01, SEE = 0.23 g/cm2). Hence, 1RM for multi-joint exercises is relevant to BMC and BMD in young men, strengthening the relationship between force and LM, and suggesting both to parametrizes bone mineral health.
Highlights
The mineral content of bone tissue (BMC) is a component of the body composition, providing the fat-free mass (FFM) when associated with the lean mass (LM) [1, 2, 3, 4]
Having analyzed the association between aging and the reduction of physical activities, bone mineral content (BMC) and FFM, Proctor et al [7] reported that from 20 to 80 years of age there is a tendency of physical activity reduction, ranging between 34–38% both for women and men, in association to the reductions of FFM (18–17%) and fat mass (FM) (16–30%)
The study by Lee et al [1] contributed to supporting this association, concluding that FFM is a significant and independent determinant to the whole-body and regional bone mineral mass, reporting low but significant coefficients of variance (R2 < 0.5, p < 0,01) to the association between appendicular mass (Kg) and the total pelvic and forearm Bone mineral density (BMD)
Summary
The mineral content of bone tissue (BMC) is a component of the body composition, providing the fat-free mass (FFM) when associated with the lean mass (LM) (musculature and viscera) [1, 2, 3, 4]. The study by Lee et al [1] contributed to supporting this association, concluding that FFM is a significant and independent determinant to the whole-body and regional bone mineral mass, reporting low but significant coefficients of variance (R2 < 0.5, p < 0,01) to the association between appendicular mass (Kg) and the total pelvic and forearm BMD These associations among body composition and mineral bone mass were observed in the study of Makovey et al [3] with both genders, from different age ranges. According to these authors, FFM and body FM positively influence BMC with explanatory potential of 52% between the FFM and BMC and of 20% between the body FM and BMC. The explanations to these associations are the neuromuscular system’s integrity as a mechanical factor, which acts as a regulator of osteogenic activity, and the fat’s influence over estrogen secretion as a humoral factor on the regulation of the osteoblast activities [1, 3]
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