Mass affects lower extremity muscle activity patterns in children's gait.

Overweight children demonstrate biomechanical differences during gait; however it is not known if these differences occur within active or passive tissue. The purpose of this study was to examine differences in lower extremity muscle activation patterns of children with different body mass during three walking speeds. Twenty children (8-12 years) were recruited and classified as overweight (OW), normal-weight (NW), or underweight (UW). Electromyography was recorded for vastus lateralis, semitendinosus, gastrocnemius, and tibialis anterior while participants walked on a treadmill at slow (SP), self-selected (SSP), and fast (FP) speeds. Differences in group and walking speed were analyzed for duration of muscle activation (presented as a percentage of stride, stance, or swing phases). Compared to OW, UW experienced greater duration of vastus lateralis and tibialis anterior activation during the swing phase. OW had greater duration of gastrocnemius activation during stride than UW. Increased walking speed resulted in greater duration of vastus lateralis activation for all groups. NW also exhibited greater duration of tibialis anterior activation at faster walking speeds. During FP, OW had greater duration of gastrocnemius activity during stance, but lower duration during swing. These findings are consistent with the idea that children with greater mass adopt a more passive gait strategy during swing to maximize energy recovery. Increased duration of gastrocnemius activity during stance also provides greater stability and stronger propulsion, which corroborates previous research. These findings help to understand the neuromuscular mechanisms associated with previous biomechanical findings in children's gait.