THE EFFECT OF LOWER EXTREMITY LIMB ALIGNMENT ON MUSCULAR ACTIVATION PATTERNS

Abstract

1402 Excessive navicular drop (ND) and quadriceps angle (QA) have been implicated as potential risk factors in ACL injury. This study determined if these static measures influence muscular response times and activation patterns following lower extremity perturbation in a functional, single leg weight bearing stance. Subjects with Q-angles <14 deg (Q1; n=17) were compared to those >20 deg (Q2; n=17) and subjects with navicular drop <5 mm (ND1; n=14) were compared to those >9 mm (ND2; n=14). A lower extremity perturbation device was designed to produce a forward and either internal rotation (IR) or external rotation (ER) moment of the trunk and femur relative to the weight bearing tibia. During perturbation, EMG recorded (in msec) long latency reflex times (LLRT) for the medial and lateral quadriceps (MQ, LQ), hamstring (MH, LH) and gastrocnemius muscles (MG, LG). Alpha for all analyses was set at p<.05. For QA, differences in LLRT were noted between Q1 and Q2 for IR. LLRT for Q2 were slower for LH (80 vs. 69) and faster for LG (51 vs. 58). This resulted in longer response delays between LG and LH (29 vs. 11) and shorter delays between LH and LQ (12 vs. 24) in Q2 compared to Q1. No differences were found for ER. For ND, ND2 demonstrated faster LLRT for MQ (94 vs. 85), LH (75 vs. 62), MH (64 vs. 54) and LG (62 vs. 55) for ER only. The LH was slower than the MH in both groups resulting in a 21 msec difference between LH in ND1 and MH in ND2. Response delays were shorter between LG and LH (7 vs. 13) and longer between LH and LQ (28 vs. 20) for ND2. Compared to the lateral side, there was essentially no delay between MG and MH firing (<5 msec) and much longer delays between MH and MQ (30 msec) for both groups. These findings suggest that limb alignment may influence neuromuscular timing and activation patterns. Further study is warranted to determine what effect this influence may have on dynamic joint stabilization. Supported by NATA REF Grant #0397-A007