# The Effect of Hot Water Extract of Tilapia on Exercise Capacity in Mice
## 3 Results and Discussion
### Effects of HWET on Exercise Performance in Swimming Endurance Test  
As shown in Figure 1, the swimming times of the control, HWET-L, HWET-M, and HWET-H groups were 263.6 \(\pm\) 22.3 s, 351.8 \(\pm\) 27.0 s, 392.4 \(\pm\) 32.3 s, and 451.3 \(\pm\) 20.6 s, \begin{table}
\begin{tabular}{l c c c c} \hline  & **Control** & **HWET-L** & **HWET-M** & **HWET-H** \\ \hline Initial body weight (g) & 33.5 \(\pm\) 0.6 & 33.5 \(\pm\) 0.5 & 33.6 \(\pm\) 0.4 & 33.5 \(\pm\) 0.4 \\ Final body weight (g) & 34.3 \(\pm\) 0.6 & 35.3 \(\pm\) 1.0 & 35.0 \(\pm\) 0.6 & 34.1 \(\pm\) 0.7 \\ Food intake (g/day) & 5.45 \(\pm\) 0.15 & 5.66 \(\pm\) 0.19 & 5.49 \(\pm\) 0.14 & 5.26 \(\pm\) 0.17 \\ Muscle weight (g) & 0.30 \(\pm\) 0.01 & 0.31 \(\pm\) 0.01 & 0.29 \(\pm\) 0.01 & 0.30 \(\pm\) 0.02 \\ \hline \end{tabular} Data are presented as the mean \(\pm\) SEM for n = 10 per group. Muscle weight of forelimbs was measured 1 h after swimming endurance test.  
\end{table} 
Table 2: A summary of body weight, food intake, and skeletal muscle mass. respectively. The administration of HWET significantly enhanced the exercise capacity of the mice in a dose-dependent manner (\(p\) < 0.05). Compared to the control group, the swimming times of the HWET-L, HWET-M, and HWET-H groups increased 1.3-fold, 1.5-fold, and 1.7-fold, respectively. Previous studies showed that supplementation with branched-chain amino acids (BCAA) and taurine enhanced athletic performance by reducing exercise-induced muscle soreness and damage [30,31]. BCAA provide higher substrate bioavailability to support protein synthesis, alleviating the level of muscle damage associated with strenuous exercise. HWET is rich in protein and possesses a considerable amount of BCAA and taurine (as shown in Table 1), suggesting that this is one of the major factors in improving exercise performance. Effects of HWET on Serum Levels of Lactate, Creatine Kinase (CK), Alanine Aminotransferase (ALT), and Blood Urea Nitrogen (BLIN) in Mice  
To confirm whether orally administered HWET changes blood biochemical parameters to enhance exercise performance, blood was collected from mice 1 h after the swimming endurance test and serum samples were prepared to measure lactate, CK, BUN, glucose, and ALT levels. Lactate is the end product of anaerobic metabolism. Glycolysis produces pyruvate, which is converted into lactate under anaerobic conditions. Following high-intensity exercise over a short period, anaerobic glycolysis leads to abundant lactate accumulation in the muscle and liver [32]. Our results showed that the serum lactate concentrations in the HWET-treated groups were lower than that of the control group (Figure 2A). Significant differences can be observed in the HWET-M (1600 mg/kg/day) and HWET-H (4000 mg/kg/day) groups compared to the control group (\(p\) < 0.05). This suggests that HWET could alleviate fatigue by lowering blood lactate levels in mice. CK, also known as creatine phosphokinase (CPK), is found in skeletal muscle, the myocardium, and other organs, but the majority is in skeletal muscle, accounting for 96% of the total amount. The main function of CK is to help energy synthesis during short-term intense exercise. When the muscle is damaged, the rupture or increased permeability of the cell membrane causes a large amount of CK to be released into the blood. Therefore, the amount of CK in the blood is commonly used as an indicator to assess muscle damage following exercise [33]. As shown in Figure 2B, significant reductions in serum CK levels in the HWET-L (1319 \(\pm\) 190 IU/L), HWET-M (942 \(\pm\) 115 IU/L), and HWET-H (555 \(\pm\) 58 IU/L) groups were noted compared to the control group (2052 \(\pm\) 315 IU/L), indicating that HWET reduced exercise-induced muscle damage and fatigue. Figure 2C shows the effects  
Figure 1: Effects of HWET treatment on swimming time in ICR mice. Mice were treated with vehicle (control), 800 mg/kg (HWET-L), 1600 mg/kg (HWET-M), or 4000 mg/kg (HWET-H) of HWET once per day for 7 days, and conducted the swimming test 1 h after the last administration.