OBJECTIVE: To examine issues of EMG asymmetry and repeatability in populations with LBP and populations without LBPin 3 separate studies.
STUDY DESIGN: Three separate experimental research studies.
METHODS: Study 1 examined the intraclass correlation of the EMG signal of the paraspinal musculature at L3 on 3 separate days during quiet stance with use of 3 different normalization techniques: percent maximum voluntary contraction, percent submaximal voluntary contraction, and percent averaged submaximal contractions. Study 2 used a population with chronic LBP to compare the bilateral asymmetry of paraspinal musculature in segments exhibiting pain with segments not exhibiting pain during quiet stance. A 1-way analysis of variance was used to compare differences between asymmetry scores in the pain and nonpain groups. In study 3, persons with LBP and persons in the control group had the dynamic asymmetry of paraspinal musculature compared during forward bending. A cross-correlation coefficient assessing bilateral muscle activity was calculated for each subject and differences between groups were evaluated using a 1-way analysis of variance.
RESULTS: Study 1: Subjects showed excellent repeatability (ICC > 0.75) regardless of the normalization technique. Study 2: During quiet stance no differences were found in bilateral asymmetry between painful and nonpainful motion segments. Study 3: No differences existed in bilateral dynamic symmetry for the upper erector spinae; however, differences between groups did exist for the lower erector spinae.
CONCLUSION: Repeatability of the EMG signal during quiet stance is acceptable; however, bilateral asymmetry may not be a definitive indicator of dysfunction.
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