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THE EFFECTS OF DISUSE FROM LOWER LIMB IMMOBILIZATION ON PROPRIOCEPTION: A PRELIMINARY STUDY

Abstract

Claire M. Smith1, JoCarol E. Shields1, Rob J, MacLennan1, Shawn M. Reese1, Alex A. Olmos1, Jason M. DeFreitas1

1Oklahoma State University, Stillwater, Oklahoma

While many studies have examined the motor deficits that arise from disuse, such as muscle atrophy and weakness, very little is known in regards to sensory deficits. PURPOSE: The purpose of this preliminary trial was to examine the effects of 2-weeks of left leg immobilization on proprioception using tendon taps (TT) and a reactive leg drop (RLD). METHODS: Ten healthy subjects (18-39 yrs) volunteered to participate in this preliminary study, but only 4 (2 males and 2 females) completed the protocol in full due to the difficulty of the intervention. For the disuse intervention, each participant was fitted for a brace on their left leg, and crutches were used for mobility for 2 consecutive weeks. Proprioceptive measures were taken before and after the immobilization period via TT and RLD. During the TT, while the participant performed the Jendrassik maneuver, a reflex hammer was used to hit the patellar tendon to evoke a knee jerk reflex. During the RLD, participants sat in a chair with their knee fully extended to 180° and relaxed while the leg’s weight was supported by an investigator. While the participant performed the Jendrassik maneuver, the investigator would drop the leg at random intervals. The participant was instructed to kick the leg back to full extension once they felt their leg begin to fall. In the RLD, poor proprioception and sensorimotor integration is shown by a larger leg drop (a greater change in knee angle). An electrogoniometer was attached to the knee for both measures to acquire joint angle. Percent change (Δ) and Cohen’s d were used to assess the mean effects of disuse from the underpowered, preliminary data. RESULTS: There was a decrease in TT reflex magnitude in both the immobilized left leg (Δ = -38%, d = -1.33 ) and the right leg (Δ = -16.7%, d = -0.53 ). There was an improvement in the RLD knee angle (less of a drop) from pre to post in both legs, likely due to a familiarization effect. However, the immobilized left leg (Δ = 15%, d = 0.58 ) did not improve as much as the right leg (Δ = 37%, d = 0.65). CONCLUSION: Our exploratory analysis suggests that there is a decrease in stretch reflexes and a reduced improvement in leg drop angle after 2-weeks of lower-limb disuse. While the reduced reflex in the immobilized leg was hypothesized, the decreased reflex in the right leg, as well as the improved RLD’s were unexpected.

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