EMG signal amplitude assessment during abdominal bracing and hollowing

Motor pattern re-education is often used by clinicians as part of treatment regimens for chronic low back pain. Such programmes are often validated by the analysis of the electromyographical (EMG) signal from specific muscles. Independent muscles are often compared using the raw amplitude of the EMG signal or comparing the ratio of the amplitudes of two muscles. Statistical inferences from these derived data may depend on minimizing the sources of error when manipulating the EMG signal profile data. This is particularly true for amplitude normalization procedures, their reliability and the subsequent derivation of amplitude ratios. The purpose of the study was first to examine the reliability of five amplitude normalized procedures and second to examine the sensitivity of raw versus ratio amplitude comparisons during two different abdominal muscle exercises. The study demonstrated that maximal effort amplitude normalization techniques reduce the sensitivity of raw data comparisons, but had little influence on the sensitivity of the ratio data in differentiating the two movement patterns. It was concluded that using the EMG signal profile to identify pathological movement strategies, in association with regional pain syndromes, needs special attention to the reliability and validity of the derived variables.