## 4 Discussion
\begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline \multirow{2}{*}{**Variables**} & \multicolumn{2}{c}{**HWE**} & \multicolumn{2}{c}{**CON**} & \multicolumn{2}{c}{**F-value**} \\  & **Pre** & **Post** & **Pre** & **Post** & **(p5\% CD)** & **Time** & **Group** & **Interaction** \\ \hline
25-(OH) D & 14.1 \(\pm\) 7.24 & 20.5 \(\pm\) 7.81 ** & 17.3 \(\pm\) 6.37 & 19.0 \(\pm\) 5.17 & 13.559 ** & 0.158 & 4.451 * \\ (ng-mL\({}^{-1}\)) & (9.9–18.2) & (16.0 \(\pm\) 25.1) & (13.9–20.5) & (16.4–21.7) & (.319) & (0.005) & (0.133) \\ Intact PTH & 36.6 \(\pm\) 9.00 & 42.6 \(\pm\) 8.73 * & 36.5 \(\pm\) 10.18 & 38.9 \(\pm\) 8.85 & 4.447 * & 0.498 & 0.800 \\ (pg-mL\({}^{-1}\)) & (31.4–41.8) & (37.6–47.7) & (31.2–41.7) & (34.4–43.5) & (0.133) & (0.017) & (0.027) \\ OPG & 5.7 \(\pm\) 0.80 & 5.1 \(\pm\) 1.26 & 5.6 \(\pm\) 1.26 & 5.3 \(\pm\) 1.65 & 3.911 & 0.021 & 0.173 \\ (pmol-L\({}^{-1}\)) & (5.2–6.1) & (4.4–5.8) & (5.0–6.3) & (4.4–6.1) & (0.119) & (0.001) & (0.006) \\ RANKL & 286.9 \(\pm\) 178.95 & 277.8 \(\pm\) 186.06 & 199.6 \(\pm\) 108.34 & 224.5 \(\pm\) 124.01 & 0.225 & 1.868 & 1.062 \\ (pmol-L\({}^{-1}\)) & (183.6–390.3) & (170.3–325.2) & (143.9–255.3) & (160.7–288.2) & (0.008) & (0.061) & (0.035) \\ OPN & 63.2 \(\pm\) 31.97 & 50.1 \(\pm\) 37.46 * & 51.2 \(\pm\) 15.56 & 47.8 \(\pm\) 20.78 & 5.480 * & 0.622 & 1.867 \\ (ng-mL\({}^{-1}\)) & (44.7–81.6) & (28.5–71.8) & (43.2–59.2) & (37.1–58.5) & (0.159) & (0.021) & (0.060) \\ Osteocalcin & 6.8 \(\pm\) 1.46 & 7.3 \(\pm\) 1.29 & 6.9 \(\pm\) 1.69 & 6.2 \(\pm\) 1.50 * & 0.132 & 1.068 & 10.514 ** \\ (ng-mL\({}^{-1}\)) & (6.0–7.7) & (6.6–8.1) & (6.0–7.8) & (5.5–7.0) & (0.005) & (0.036) & (0.266) \\ CTX & 0.24 \(\pm\) 0.10 & 0.28 \(\pm\) 0.09 & 0.26 \(\pm\) 0.16 & 0.31 \(\pm\) 0.14 * & 8.768 ** & 0.296 & 0.018 \\ (ng-mL\({}^{-1}\)) & (0.19–0.30) & (0.23–0.34) & (0.18–0.35) & (0.23–0.38) & (0.232) & (0.010) & (0.001) \\ Calcium & 9.7 \(\pm\) 0.46 & 9.5 \(\pm\) 0.40 & 9.8 \(\pm\) 0.29 & 9.5 \(\pm\) 0.29 ** & 7.986 ** & 0.204 & 0.442 \\ (mg-dL\({}^{-1}\)) & (9.5–10.0) & (9.3–9.8) & (9.7–10.0) & (9.4–9.7) & (0.216) & (0.007) & (0.015) \\ \hline \hline \end{tabular} Values are expressed as mean \(\pm\) SD. 95% CI: 95% confidence interval, HWE: high-impact weight-bearing exercise, CON: control, PTH: parathyroid hormone, OPG: osteoproteger, RANKL: receptor activator of nuclear factor kB ligand, OPN: osteopontin, CTX: C-terminal telopeptide of type 1 collagen. Significant interaction or main effect, * \(p<\) 0.05, ** \(p<\) 0.01. Significant difference between pre- and post-tests, * \(p<\) 0.05, ** \(p<\) 0.01.  
\end{table} 
Table 4: Changes in bone metabolic markers between pre- and post-tests in middle-aged premenopausal women. impact exercise protocols lasting more than six months (duration: 30-60 min; frequency: \(\geq\)3 days/week) have been recommended for greater bone health benefits [49]. Moreover, adults might benefit from high-impact exercises, but previous studies have suggested that its effect might occur to a lesser extent than in children or adolescents [50]. In this study, the effect of four-months of high-impact weight-bearing exercise appeared to be none or small only in particular sites such as femur BMD in middle-aged premenopausal women. Biochemical bone metabolic markers indicate changes in bone metabolism more quickly than changes in BMD, which are commonly used to monitor osteoporosis [51]. Additionally, bone metabolic markers could be used to evaluate the antiresorptive agents in the clinical diagnosis of osteoporosis and osteopenia [52]. One intended therapeutic aim of the antiresorptive therapy is to decrease levels of bone metabolic markers below the average reference range for pre-menopausal women [53]. Bone metabolic markers provide important information such as the rate of bone remodeling by changing bone formation and resorption, and the evaluation of these markers has been used in previous intervention studies to identify the effectiveness of exercise [54; 55; 56].