# Lower Limb Muscle Activation in Young Adults Walking in Water and on Land
## 1 Introduction  
Foot drop, prevalent in various neurological disorders, significantly heightens the risk of falls and diminishes individuals' physical independence [1, 2, 3, 4]. This condition, marked by a decreased capacity to dorsiflex the foot during walking, results in a dragging or slapping motion of the foot against the ground. Foot drop is typically attributed toweakness in ankle dorsiflexors or over-activation in ankle plantar flexors [3]. Consequently, individuals affected by foot drop often exhibit slower walking speeds and encounter challenges navigating uneven terrain like stairs [2; 3; 4]. Compensatory mechanisms, such as hyper-flexion of the knee and hip joints (e.g., \"steppage gait\" and \"hip hiking\"), can lead to improper skeletal loading and injury over time [5; 6]. Furthermore, a foot drop may restrict activities of daily living, contributing to a decline in functional independence and overall quality of life [1]. Footnote 1: [[https://www.sds.org/](https://www.sds.org/)]([https://www.sds.org/](https://www.sds.org/))  
Footnote 2: [[https://www.sds.org/](https://www.sds.org/)]([https://www.sds.org/](https://www.sds.org/))  
Footnote 3: [[https://www.sds.org/](https://www.sds.org/)]([https://www.sds.org/](https://www.sds.org/))  
Footnote 4: [[https://www.sds.org/](https://www.sds.org/)]([https://www.sds.org/](https://www.sds.org/))  
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disease, prior research supports aquatic exercise as an effective intervention for addressing motor symptoms in individuals with various other neurological diseases, including stroke, multiple sclerosis, dementia, and cerebral palsy [22]. In essence, water provides a secure environment for individuals with limited mobility to exercise with increased confidence. Moreover, the heightened drag forces associated with walking in water may demand increased voluntary activation of the TA compared to walking on land. In both aquatic and dry land environments, fluid drag forces act on the body to impede movement. However, the density of the fluid, in this case, water, significantly influences the magnitude of the fluid drag force. Given the higher density of water compared to air, an individual experiences greater resistance to motion in water than on land [23]. Additionally, fluid drag force intensifies with the relative velocity of the object in the fluid. During the swing phase of the walking stride cycle, the foot attains a higher linear velocity relative to more proximal lower-extremity body segments, akin to the tip of a windmill. This elevated velocity increases fluid drag, particularly at the anterior foot and ankle. Consequently, walking on an aquatic treadmill should necessitate greater TA activation to overcome heightened drag forces at the distal lower limb and lift the toes before foot strikes. Further, as indicated by [PERSON] et al. [14], the repetitive activation of lower-limb muscles during exercises that demand heightened TA activation may enhance neural control of the ankle by strengthening corticospinal connections. Results from previous studies examining differences in TA muscle activation between aquatic and land treadmill gaits are mixed. For instance, in studies where walking in water was performed at slower speeds compared to land or at self-selected speeds, no significant differences in peak or average TA activation have been reported [24; 25; 26; 27]. In a study by [PERSON] et al. [28] investigating running gait while controlling for stride rate across participants, significantly greater TA activation was observed for running in water than on land, with deeper water immersion depths also leading to greater activation. However, it is noteworthy that a significant difference was observed only in the left leg, with no differences noted in the right leg. Moreover, [PERSON] et al. [29] observed an increase in the absolute duration of activity and total TA activation between water and land running at matched speeds.