The reference value used for normalization (the denominator), called the normalization factor, should be processed in an identical manner as the task EMG. Each data point is divided by the peak value recorded from an isometric maximal voluntary contraction of the same muscle. The third method of normalization is maximum voluntary contraction (MVC). Both PDM and MDM produce good reliability between sessions and between subjects, reduce inter-subject variability by 12–72% in comparison to un-normalized EMG and give a representation of coordinated muscle activity by indicating the period at which the muscle is most active. For the mean dynamic method (MDM), each data-point of the processed EMG signal is divided by an average of both quiet and active periods during the gait cycle. The peak dynamic method (PDM) expresses EMG data from a muscle as a ratio of the peak value acquired from the same muscle during gait. ĭifferent methods of normalization have been introduced and are in current practice, each with advantages and limitations related to inter-subject variability and the clinical interpretation of muscle activity. Normalization of the EMG signal reduces the negative impact of the aforementioned variables and facilitates the comparison of EMG across muscles, between subjects, or between days for the same subject. The EMG signal amplitude and frequency components are affected by many factors: electrode placement and orientation, subcutaneous fat thickness, muscle fiber type, and crosstalk from nearby muscles. Surface electromyography (EMG) has been used for decades to evaluate neuromuscular responses during a range of activities, in non-pathological subjects and to investigate alterations due to pathology and rehabilitation. Ethics: REC for Wales/Cardiff and Vale UHB.Ĭompeting interests: The authors have declared that no competing interests exist. Data collection support was from NISCHR CRC. All interested readers may contact Cheryl Clearly ( to request access to the underlying data.įunding: Funding was received from Arthritis Research UK, EPSRC, Arthrex and the Higher Committee for Education Development in Iraq (HCED). This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.ĭata Availability: Due to current ethical approval restrictions on use of the data for projects undertaken within the Arthritis Research UK Biomechanics and Bioengineering Centre, this cannot be made publicly available. Received: JAccepted: MaPublished: April 3, 2017Ĭopyright: © 2017 Ghazwan et al. Where MVC testing is not possible, *PDM is the next preferred option.Ĭitation: Ghazwan A, Forrest SM, Holt CA, Whatling GM (2017) Can activities of daily living contribute to EMG normalization for gait analysis? PLoS ONE 12(4):Įditor: Vera Bril, University of Toronto, CANADA It was concluded that **PDM and *PDM were reliable, **PDM mirrored MVC and thus could be used as an alternative to MVC for subjects who are unable to provide the required effort for MVC testing. root mean square difference and absolute difference were both around 0.08 for Vastus medialis to about 4 for Medial gastrocnemius. Both MVC and **PDM, and to some extent *PDM, demonstrated good-to-excellent relative amplitude’s matching i.e.
Coefficient of variability showed a similar trend to Variance Ratio, ranging from 0.60–1.25 for **PDM and 1.97–3.92 for MVC. **PDM showed excellent reliability across subjects in comparison to MVC, where variance ratio ranged from 0.43–0.99 for **PDM and 0.79–1.08 for MVC. Intra- and inter-individual variability were calculated to determine reliability and similarity to MCV. EMG data recorded from knee flexion-extension muscles in 10 control subjects during the stance phase of the gait cycle were examined by adopting different approaches of normalization: MVC, Mean and Peak Dynamic during gait cycles, (MDM and PDM, respectively), Peak Dynamic during activities of daily living (ADLs), (*PDM), and a combination of ADLs and MVC(**PDM).
This study aims to examine alternative methods of normalization that effectively reflect muscle activity as compared to Maximal Voluntary Contraction (MVC).