# Lower Limb Muscle Activation in Young Adults Walking in Water and on Land
## 1 Introduction
However, the study did not find a significant difference in TA activation when expressed as a percentage of maximal voluntary contraction between the two environments. It is important to note that in the study, muscle activation measures were derived by averaging data from 10 full stride cycles without separately analyzing the swing and stance phases. Additionally, it is important to consider that findings from investigations focusing on muscle activation during running may not directly apply to walking gait. For instance, during the swing phase of running, the knee and hip exhibit greater flexion to minimize the moment arm of the leg, facilitating a faster swing phase. This altered posture may lead to reduced drag forces opposing dorsiflexion, which contrasts with the more fully extended leg position typically observed during the swing phase of walking. The observation of greater TA activation during running at matched stride rates and speeds does, however, reflect a current need for investigation into TA activation during walking performed in water and on land at matched speeds. Moreover, there is a scarcity of research on plantar flexor (i.e., gastrocnemius) activation, and, to our knowledge, no prior study has provided insights into muscle co-activation (Co-A) between the TA and medial gastrocnemius (GM) during walking in water. Improving the ability to dorsiflex the foot involves either enhancing TA activation or minimizing GM Co-A. Consequently, it is crucial to assess the activation of both muscles. To our knowledge, no study has compared distal leg muscle activation patterns during both the stance and swing phases of gait between aquatic and land treadmill walking. This represents a notable gap in the current literature. The purpose of this study was to compare stride kinematics and surface electromyography (sEMG) of the TA and GM in young adults performing aquatic and land treadmill walking at matched speeds. We hypothesized that (1) TA activation would be greater when walking in water than on land at matched speeds, attributed to increased fluid drag opposing the forward movement of the distal lower limb. We anticipated (2) no significant differences in the magnitude of TA activation between walking environments during the stance phase at matched speeds. Additionally, we hypothesized that (3) GM activation would be greater during aquatic walking than on land during the stance phase. This expectation stemmed from the assumption that the GM would play a more substantial role in propelling the body forward in the presence of increased fluid drag. However, we also anticipated (4) no significant difference in GM activation between environments during the swing phase. Given the relationship between relative velocity and fluid drag, we further hypothesized that (5) observed differences in muscle activation magnitude between aquatic and land walking would be more pronounced at the 3.5 mph speed condition than the 2.5 mph speed condition. The findings of this study may offer valuable insights into how the aquatic environment influences the activation of muscles spanning the ankle joint during walking and provide supporting evidence for including aquatic exercise as a component of treatment for foot drop.