# Lower Limb Muscle Activation in Young Adults Walking in Water and on Land
## 2 Materials and Methods
### Procedures  
Participants attended two separate sessions at a movement research clinic. In the initial session, they became familiar with the study protocol. During the familiarization process, participants underwent anthropometric measurements, including height, weight, and the determination of leg dominance. Leg dominance was assessed by asking participants which leg they preferred to kick a ball [30]. Additionally, participants practiced walking on the aquatic treadmill to acquaint themselves with the equipment and walking conditions. The aquatic treadmill familiarization consisted of walking for 4 min at a moderate 2.5 mph pace. During the aquatic walking, participants were given the following standard verbal instructions: \"Walk as you normally would on land. Try to keep one foot in contact with the ground at all times, and try not to bounce or float between steps. You may walk with your arms at your sides, but do not use your arms to swim forward.\" All practice trials were monitored by a member of the research team, with augmented feedback provided if necessary. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Sex** & \(n\) & **Age (years)** & **Height (cm)** & **Body Mass (kg)** \\ \hline Collapsed & 38 & 22.6 (2.2) & 172.5 (8.5) & 72.4 (14.9) \\ Female & 18 & 21.7 (1.8) & 167.6 (6.9) & 65.4 (12.9) \\ Male & 20 & 23.4 (2.2) & 177.0 (7.2) & 78.8 (14.0) \\ \hline \hline \end{tabular} Data are reported as mean (SD).  
\end{table} 
Table 1: Participant characteristics. Participants then attended an experimental session scheduled for at least 24 h after familiarization. Upon arrival, participants underwent surface electromyography (sEMG) preparation. This involved gently shaving and cleaning the designated sEMG sites with an alcohol swab. Subsequently, adhesive waterproof electrodes (Cometa Mini Wave, Cometa SRL, Milan, Italy) were carefully positioned over the tibialis anterior (TA) and gastrocnemius medialis (GM) muscles of their dominant leg, adhering to established guidelines from the Surface Electromyography for Non-Invasive Assessment of Muscles (SENIAM) project [31]. Once the electrode placement was completed, adhesive waterproof tape was used to further secure the electrodes, minimizing any potential movement artifacts during the study. In the experimental protocol, participants walked for 2 min at both 2.5 mph and 3.5 mph, with the order of speeds randomized, both on land and in water. For a supplementary analysis, participants walked for an additional 2 min in water at 3.5 mph with 75% water jet resistance applied to the anterior torso. The supplementary bout of water walking was performed after the completion of the 2.5 mph and 3.5 mph walking conditions. Walk speeds were determined from existing literature, which indicates that the average preferred walk-run transition speed for young adults falls within the range of approximately 4.25-4.70 mph [32]. sEMG data were collected during walking at a sampling rate of 2000 Hz [29]. Video data of participants' lower legs and feet were captured at 100 Hz using an underwater camera (Miquus Underwater, Qualisys AB, Sweden) and time-synchronized with sEMG data. Land walking was performed on an instrumented treadmill (Tandem Treadmill, AMTI, Watertown, MA, USA), and walking in water was performed on an adjustable-depth aquatic treadmill (2000 Series, HydroWox, Middletown, PA, USA). The water temperature was maintained at 29.5 \({}^{\circ}\)C \(\pm\) 0.2 \({}^{\circ}\)C, which is considered thermoneutral for aquatic exercise [33]. Participants walked in the water while submerged to the level of the xiphoid process. Participants performed land walking first to prevent movement of the electrodes while drying off and also to negate the potential impact of thermoregulation on muscle activation. A 5 min rest period was provided between land and water walks. An additional 2 min rest time was provided before participants underwent the supplemental water walking with jet resistance condition.