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EMG in the transtibial amputee
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Atrophy of the amputated limb thigh musculature is commonly observed in the transtibial amputee. The purpose of this investigation was to determine the relationship between this observed atrophy, and muscle activation patterns which occur during common daily activities. The tasks investigated were level walking, stair ascent, stair descent, rising and sitting. Ten active unilateral transtibial amputee (TTA) subjects and ten able-bodied (AB) subjects participated in the study. Surface electrodes were used to record EMG activity of the quadriceps and hamstrings muscles, as the subject completed the set tasks. The peak amplitude EMG was analysed and compared between limbs for each activity.
The AB subjects displayed symmetry of muscle activation in all activities. In level walking the TTA subjects also demonstrated similar peak quadriceps activation between amputated and sound limbs. Postural compensations and altered thigh muscle activity were observed in stair ambulation. Although variations occurred, the peak muscle activation in the amputated limb was not significantly different to the sound limb.
During the activities of rising and sitting, the peak activation in the amputated limb quadriceps was substantially reduced in comparison to the sound limb (p<0.001). This result may be due to the decreased lever arm of the tibial remnant, or to limitations of the prosthetic socket. The inability to flex the knee past ninety degrees, or pain at the anterodistal tibia due to pressure on the socket, will result in the transfer of most body weight to the sound limb during rising. The activities of rising and sitting are involved in the maintenance of normal strength in the AB individual. The sound limb dominance displayed by the TTA during these activities results in a reduced activation of the amputated limb quadriceps. A lack of sufficient muscle stimulation leads to disuse atrophy of the affected muscles.
Although gait is an important functional requirement for the transtibial amputee, it is vital that other common activities are considered during prosthesis design and manufacture.
