# Changes in Body Mass and Movement Strategy Maintain Jump Height Immediately after Soccer Match
## 4 Discussion  
The purpose of this study was to monitor soccer-match-induced changes in body mass alongside select CMJ strategy and outcome variables among adult male soccer players. It was hypothesized that both body mass and countermovement depth would be reduced post-match but jump height would remain unchanged. Based on the study results (Table 3), all three hypotheses were accepted. In the present study, post-match body mass was 2% lower than pre-match, which supports previous findings [17]. Although this may be considered a small reduction in body mass, a 1.7% variability in body mass across CMJ trials resulted in a 4.5 cm deviation in the total (peak center of mass displacement relative to standing) jump height [30]. Being acutely lighter would lead to increased jump height if the same or a greater net propulsive impulse was applied. This is because the take-off velocity that determines jump height is equal to the net propulsive impulse divided by body mass [16]. However, the jump height did not change post-match in the present study (Table 3), which supports previous studies involving the pre- and post-match CMJ testing of male soccer players [11; 12]. This is because the jump momentum, which is equal in number to the propulsive net impulse [25], was significantly reduced post-match (Table 3). In effect, the reduced propulsive net impulse (the jump momentum in Table 3), when divided by the lighter body mass, led to the same 2.72 m\(\cdot\)s\({}^{-1}\) take-off velocity (not shown in Table 3) and the 0.38 m jump height attainment post-match. The influence of body mass fluctuations on CMJ height following a  
Figure 1: Individual changes in body mass (**left**), jump momentum (**middle**), and countermovement depth (**right**). \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Jump Variables** & **Pre-Match** & **Post-Match** & **Mean Difference \({}^{*}\)** & \(p\) & \(g\) \\ \hline Body Mass (kg) & 79.8 \(\pm\) 6.6 & 78.2 \(\pm\) 6.5 & 1.62 & \textless{}0.001 \({}^{\dagger}\) & 1.66 \\ Jump Height (m) & 0.38 \(\pm\) 0.04 & 0.38 \(\pm\) 0.03 & \textless{}0.01 & 0.924 & 0.03 \\ Jump Momentum (kg\(\cdot\)m\(\cdot\)s\({}^{-1}\)) & 217.4 \(\pm\) 20.2 & 212.7 \(\pm\) 19.4 & 4.66 & 0.049 \({}^{\dagger}\) & 0.56 \\ Time to Take-off (s) & 0.81 \(\pm\) 0.16 & 0.84 \(\pm\) 0.19 & 0.03 & 0.303 & 0.28 \\ Unweighting Phase Time (s) & 0.36 \(\pm\) 0.06 ** & 0.40 \(\pm\) 0.08 ** & 0.01 & 0.091 & 0.31 \\ Braking Phase Time (s) & 0.17 \(\pm\) 0.04 & 0.18 \(\pm\) 0.05 & \textless{}0.01 & 0.640 & 0.12 \\ Propulsive Phase Time (s) & 0.25 \(\pm\) 0.05 & 0.25 \(\pm\) 0.04 & \textless{}0.01 & 0.459 & 0.20 \\ RSImod & 0.49 \(\pm\) 0.10 & 0.47 \(\pm\) 0.12 & 0.01 & 0.457 & 0.20 \\ CM Depth (m) & 0.32 \(\pm\) 0.07 & 0.30 \(\pm\) 0.06 & 0.02 & 0.016 \({}^{\dagger}\) & 0.72 \\ \hline \hline \end{tabular}
\begin{tabular}{c} Key: m = meters; s = seconds; kg = kilograms; m\(\cdot\)s\({}^{-1}\) = meters per second; \(p\) = significance, set at 0.05; \(g\) = Hedges effect size; CM = countermovement; RSImod = modified reactive strength index. \({}^{\dagger}\) denotes statistically significant difference (\(p\leq 0.05\)). \({}^{*}\) denotes the median difference is presented for unweighting phase time. ** Median \(\pm\) interquartile range.  
\end{table} 
Table 3: Pre- and post-match countermovement jump performance of the soccer players. soccer match had not been explored previously, to the authors' knowledge. The present results, which showed an acute reduction in body mass, may partially explain why CMJ height has sometimes not been sensitive for detecting NMF induced by soccer match play within the scientific literature [11; 12]. Previous reductions in body mass following soccer match play were attributed to water loss or glycogen depletion [17]. Specifically, fatigue towards the end of a soccer match has been suggested to be related to depleted glycogen stores within some muscle fibers [31].