Background: Inversion ankle sprains are among the most frequently encountered injuries in and outside of sport. Altered feedback from joint damage and/or edema may negatively affect dynamic stabilization, thereby increasing the patients' susceptibility to further injury. In order to understand better how the sensorimotor system responds to the presence of ankle edema during a functional task, further examination is warranted. Objective: To quantify muscle activation in the peroneal, tibialis anterior, and soleus musculature as well as to determine ankle joint peak torque, peak power, and root mean square (RMS) power during a closed kinetic chain activity following artificial ankle effusion. Design: Dependent variables were compared within subjects across time intervals and between groups. Setting: All data were collected in the biomechanics laboratory. Participants: Subjects were 20 healthy, neurologically sound volunteers (age 21.9 ± 2.1 y, height 174.5 ± 9.3 cm, mass 79.3 ± 15.9 kg) with no lower extremity injuries. Interventions: Subjects were prepared for surface electrodes on the peroneus longus (PL), tibialis anterior (TA), soleus (Sol), and medial malleolus (ground). Anthropometric measures for the lower extremity were recorded for use by the Omnikinetic closed chain dynamometer. Measurements were taken prior to ankle effusion (baseline), immediately following effusion (post), and again at 30 minutes. Main Outcome Measurements: Testing consisted of 6 repetitions at 35% of 1-repetition max and a constant speed of 1.5 Hz. Separate two-way MANOVAs with repeated measures on time intervals were used to detect differences between groups (effusion and control) over time for torque, power, and RMS power and for peak and average EMG. Results: An overall time × group interaction was detected for EMG (F 4,72 = 3.878; P = 0.007) and kinetic variables (F 6,70 = 5.55; P = 0.0001). Average and peak PL EMG decreased immediately following effusion (Sidak's; P = 0.048), and average EMG remained depressed 30 minutes following effusion (Sidak's; P = 0.02). Immediately posteffusion, a decrease in ankle torque was detected (Sidak's; P = 0.007). No differences in TA or Sol EMG, power, or RMS power were detected (P > 0.05). Conclusions: Decreases in ankle plantarflexion torque and PL EMG indicate that a neuromuscular deficit exists in the presence of edema that could increase the susceptibility for further ankle injury. Inversion ankle sprains are among the most frequently encountered injuries in and outside of sport. It has been estimated that 23,000 to 27,000 ankle sprains are sustained daily in the United States, 1,2 with about 40% of these injuries resulting in chronic symptoms. 3,4 The high incidence of residual dysfunction following ankle sprains has impelled investigators to examine the contributing factors leading to this chronic instability. Damage to mechanoreceptors within the lateral ankle ligaments and throughout the joint capsule following injury has been hypothesized to interrupt neurologic feedback mechanisms, resulting in ankle instability. 3,5,6 Mechanoreceptors may also be affected by the edema that accumulates following ankle sprains. 7,8 Edema may alter the neural signaling and negatively affect dynamic stabilization, thereby increasing the patients' susceptibility to further injury. Experimentally induced ankle joint effusions have been shown to result in a facilitation of the soleus, peroneal, and tibialis anterior motoneuron (MN) pools. 7,8 The facilitated H-reflex reflects a state change within the MN pool but does not necessarily equate to changes in functional strength or performance. During voluntary activity, descending tonic spinal activity may override the facilitation seen in the MN pools when the effusion is present. 9 To understand better how the sensorimotor system responds to the presence of ankle edema during a functional task, further examination is warranted. Therefore, the purpose of this investigation was to quantify muscle activation in the peroneal, tibialis anterior, and soleus musculature as well as to determine ankle joint peak torque, peak power, and root mean square (RMS) power during a closed kinetic chain activity.
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