Muscle activity of leg muscles during unipedal stance on therapy devices with different stability properties

• We measured upper and lower leg muscle activity during unipedal balancing tasks.
• We compared balance training devices with different stability and surface structure.
• Relative muscle activity increases with decreasing training device stability.
• Lower extremity muscles are affected differently by training device stability.
• Training intensity can be gradually increased with different training devices.

ObjectivesTo test the hypotheses that less stable therapy devices require greater muscle activity and that lower leg muscles will have greater increases in muscle activity with less stable therapy devices than upper leg muscles.DesignCross-sectional laboratory study.SettingLaboratory setting.ParticipantsTwenty-five healthy subjects.Main outcome measuresElectromyographic activity of four lower (gastrocnemius medialis, soleus, tibialis anterior, peroneus longus) and four upper leg muscles (vastus medialis and lateralis, biceps femoris, semitendinosus) during unipedal quiet barefoot stance on the dominant leg on a flat rigid surface and on five therapy devices with varying stability properties.ResultsMuscle activity during unipedal stance differed significantly between therapy devices (P < 0.001). The order from lowest to highest relative muscle activity matched the order from most to least stable therapy device. There was no significant interaction between muscle location (lower versus upper leg) and therapy device (P = 0.985). Magnitudes of additional relative muscle activity for the respective therapy devices differed substantially among lower extremity muscles.ConclusionsThe therapy devices offer a progressive increase in training intensity, and thus may be useful for incremental training programs in physiotherapeutic practice and sports training programs.