## 4 Discussion  
It should be highlighted that, during the measurement of the highest workload, horses walking on a WT at fetlock-depth with an AR mode and at carpal-depth with and without AR achieved higher HR, LAC, and CK values than horses following a similar protocol on a DT. During each training session, HR and LAC reached levels previously \begin{table}
\begin{tabular}{c c c c c c c c} \hline  & \begin{tabular}{c} **Time** \\ **Point** \\ \end{tabular} & **DT Session** & \begin{tabular}{c} **Fellock-Depth** \\ **WT Session** \\ \end{tabular} & \begin{tabular}{c} **Fellock-Depth** \\ **WT +AR Session** \\ \end{tabular} & \begin{tabular}{c} **Carpal-Depth** \\ **Session** \\ \end{tabular} & \
\begin{tabular}{c} **Carpal-Depth** \\ **WT +AR Session** \\ \end{tabular} &
\begin{tabular}{c} **p-Value** \\ **p-Value** \\ \end{tabular} \\ \hline CK & before & 204 (79–279) a & 180 (127–240) a & 203 (89–275) a & 157 (103–263) a & 155 (109–222) a & \(p\) = 0.06 \\ (U/L) & 0 min & 214 (116–282) a,bX & 267 (167–397) b,bY & 276 (176–361) bY & 249 (200–388) b,bX & 270 (170–440) bY & \(p\) = 0.05 \\ norm: 90-565 & 30 min & 243 (181–545) ab & 234 (137–479) ab & 232 (133–471) ab & 250 (183–420) ab & 275 (109–448) ab & \(p\) = 0.79 \\ U/L & 24 h & 260 (169–482) b & 220 (117–348) ab & 248 (140–346) ab & 231 (117–367) ab & 241 (116–334) ab & \(p\) = 0.08 \\ \(p\)-value & \(p\) = 0.001 & \(p\) = 0.003 & \(p\) = 0.02 & \(p\) = 0.002 & \(p\) = 0.0002 & \(p\) \(<\) 0.001 \\ above N/m: & & & 0 & 0 & 0 & 0 & \\ \hline AST & before & 292 (194–394) a & 262 (214–362) a & 301 (210–373) & 281 (206–421) & 280 (189–298) a & \(p\) = 0.31 \\ (U/L) & 0 min & 317 (272–423) b & 332 (267–415) b & 311 (262–449) & 309 (248–440) & 348 (272–486) b & \(p\) = 0.16 \\ norm: & 30 min & 347 (290–425) b & 357 (274–443) b & 342 (254–245) & 317 (240–444) & 383 (239–492) b & \(p\) = 0.06 \\
1-450 U/L & 24 h & 326 (297–393) ab & 390 (293–450) b & 316 (256–429) & 311 (275–436) & 393 (266–482) b & \(p\) = 0.12 \\ \(p\)-value & \(p\) = 0.005 & \(p\) = 0.001 & \(p\) = 0.42 & \(p\) = 0.09 & \(p\) = 0.001 \\ above N/n: & & & 0 & 0 & 5/3 & \\ \hline LDH & before & 380 (292–489) & 329 (214–502) a & 440 (230–505) & 352 (260–471) & 423 (324–581) b & \(p\) = 0.06 \\ (U/L) & 0 min & 431 (241–708) bX & 424 (246–599) ab,bX & 398 (236–497) Y & 397 (234–705) bX & 482 (335-816) b & \(p\) = 0.001 \\ norm: & 30 min & 398 (224–718) bX & 506 (316–646) bX & 402 (213–603) Y & 411 (240–725) bX & 494 (292–691) bX & \(p\) = 0.002 \\
0.1–639 U/L & 24 h & 415 (227–493) bX & 495 (250–719) bX & 327 (227–559) bX & 388 (295–517) bX & 455 (291–629) bX & \(p\) = 0.007 \\ \(p\)-value & \(p\) = 0.05 & \(p\) = 0.0008 & \(p\) = 0.026 & \(p\) = 0.23 & \(p\) = 0.006 \\ above N/n: & & & 2/1 & 3/3 & & \\ \hline \end{tabular}
\end{table} 
Table 3: Creatine phosphokinase (CK), aspartate aminotransferase (AST), and lactate dehydrogenase (LDH) measured during the following treadmill exercise sessions: dry treadmill (DT) session, water treadmill (WT) session at fetlock-depth water, WT session at fetlock-depth water with artificial river (AR) mode, WT session at carpal-depth water, and WT session at carpal-depth water with AR mode. Data are presented as median and ranges (minimum and maximum values). reported for WT exercise at greater water depths [2; 20; 21; 22; 23; 26; 30], while CK activity remained within the normal range for all horses [28]. These findings support our hypothesis that incorporating AR into WT exercise increases the horse's energy expenditure and workload. This observation aligns with previous research showing that the high degree of resistance created by water increases workload without adding concussive forces [2; 36]. However, to date, a high degree of water resistance has primarily been achieved by increasing water depth [2; 23; 26; 4] or by increasing the treadmill belt speed [22; 23; 26]. The current study demonstrates that increasing water resistance can also be achieved by introducing a water counterflow.