An Electromyography analysis of lower limb muscles for different locomotion activities

An Electromyography analysis of lower limb muscles for different locomotion activities

Jeevika, Amit Srivastava and R.P.Tewari

Motilal Nehru National Institute of Technology, Allahabad -211004, INDIA

Abstract

In this study, surface electromyography (EMG) signals of the Gastrocnemius, Tibialis anterior and Soleus muscles were recorded on various subject during their daily life activities such as walk ing and stair ascent and decent. The lower- limb muscle activities have been studied to enable power-assist robotic systems to estimate human lower-limb muscle activities based on muscle electromyographic (EMG) signals. The results from study will be used to estimate the muscle activation patterns and also be used to design the lower- limb exosk eleton assistive robotic systems for physically weak persons.

1. Introduction

   The lower-limb motions are very important for the human daily activities, such as walking, stair ascent and decent. It is sometimes painful and tiring for physically weak persons (elderly, disabled, and injured persons) obese persons and women during pregnancy to perform daily activit ies. Previous studies show that walking speed affects the amp litude of muscle activity. Stair loco motion, being a common functional activity of daily liv ing, has been used in the rehabilitation of the lower e xtre mity as a motor performance test [1] Several studies were performed to investigate normal human stair ascent and descent [2][3][4]. Available literatures have shown that stair locomotion places higher loads on the joints of the lower limb than level walking does, with la rger ranges of motion [5][6][7], and muscle e fforts [8]. In modern society, it is important that physically weak persons are able to take care of themselves during daily activities. It is also important that such persons use their own body functions properly to keep them healthy and fit. In such cases power assisted robotic systems are very useful to assist physically wea k persons daily life activit ies. The EM G signals are important informat ion for powe r-assist robotic systems to understand how the person intends to move. [9]

   Therefore, it is important to find out and establish the relationships between the human lowe r-limb motions and related muscles activities during daily life activities. Lo wer-limb muscles may adapt to changes according various locomotion activities. These adaptations are muscle-specific. The rhythmic move ments of lower limb muscles during daily activit ies can be studied with tools like electro myography (EM G). In this study, surface electro myography (EM G) signals of the Gastrocnemius, Tibia lis Anterior and Soleus muscles were recorded on various subject walked over ground with different walking speed and on stairs with norma l speed. A result from this study will be helpful in developing suitable assistive devices for physically weak persons who are unable to wa lk like norma l hu man subjects.

2. Methodology

   Six hea lthy volunteers between the 20-30 years of age were participated in this study. The volunteers reported not having any kind of musculoskeletal or neuromuscular proble m in lowe r e xt re mity that restricts the range of lower e xt re mity motion, which might ma ke the walking painful. Part icipants were e xc luded if they had chronic ankle or knee problems. The subjects were instructed first to wa lk with their norma l speed and then with two self selected speeds, i.e. slow speed and fast speed on level ground. After that subjects were asked to walk over stairs at norma l speed.

   Surface EM G (BIOPAC Inc., USA) was used to

   measure the activity of Gastrocnemious, Soleus and Tibia lis Anterior muscles. The BIOPA C system comprised an MP150 data acquisition system. EM G signals were recorded, stored and analyzed offline using AcqKnowledge software version 4.1. After cleaning the skin with isopropyl alcohol, surface EM G recording electrodes were placed on Gastrocnemious, Soleus and Tibialis Anterior muscles sites. All electrodes were taped to the skin to reduce movement artifacts and rema ined in place

   throughout the study.[10] The Surface EM G data were recorded at a sampling rate of 1000 Hz. Partic ipants carried out three repetitions of walking task under each of five conditions; normal walk, fast walk, slow wa lk, stair ascent and stair decent.

3. Data processing

   In this study, EM G signal processing was done to determine each muscles activation profile. As it was known that raw EM G signal is a voltage that shows both positive and negative amplitude, whereas muscle activation is e xpressed as a number between 0 and 1.For this EM G signal will be rectified but before rectification re moval of low frequency noise should be done. The low frequency noise can be corrected by high-pass filtering the EM G signal. Once this is done, signal will be rectified where the absolute values of each point are taken and this will result in a rectified EM G signal. For each participant, the Rectified Va lue and Normalized value we re calculated for Gastrocnemious, Soleus and Tibialis Anterior muscles in each wa lking repetition by d ividing the EM G integra l by the contraction time interval. The EM G RV values and Normalized values of Gastrocnemious, Soleus and Tibialis Anterior muscles were then averaged over the three repetitions for each condition.

4. Result

   Data were co llected using Bio PA C MP150 acquisition system. The ma x EM G A RV value, Norma lized mean value, median value for GM, GL, SOL, TA are recorded. Fig. shows that as the walking speed increases EM G activity were increases in various muscles. GM , TA and SOL shows significant increase in EM G act ivity as walking speed increases. Data for normalized EM G value were taken and graph were plotted in MS e xcel 2007. Graph for gastrocnemius, soleus and

   Fig-1 : EMG activation of TA muscle at variable speeds

   Fig-2 : EMG activation of GM muscle at variable speeds

   Tibia lis anterior muscle EM G activation shows

   significant differences as walking speed increases. During stair ascent and decent ma ximu m EM G activation was seen in Tibia lis anterior muscle followed by gastrocnimus and soleus muscle.

   Fig-3 : EMG activation of Soleus muscle at variable speeds

   Fig-4 : EMG activation of various muscle at stair ascent and decent

5. Discussion

   A typical EM G trace showing raw and norma lized GM , SOL and TA muscle activity during various walking conditions(normal ,slow and fast) were displayed in fig.EM G activation of GM , SOL and TA muscles during stair ascent and decent were also displayed in fig . A one-way analysis of variance test (ANOVA) with repeated measures was performed to determine the effect of changes in walking speed and stair ascent and decent on activity in the tibialis anterior, soleus and gastrocnemius muscles for each subject. Max, Mean and Median values of activity of each muscle considered for the various cases. The pair wise comparisons with revealed that for GM muscle, the diffe rence between fast walk Vs norma l walk and fast walk Vs slow wa lk statistically significant (p < 0.05). Fo r SOL muscle, the difference between fast walk Vs slow walk was statistically significant (p < 0.05). For TA muscle, the difference between fast walk Vs slow walk was statistically significant (p < 0.05). It was seen that during gait cycle plantar fle xion move ment is achieved by gastrocnemius muscle and Gastrocnemius shows activity in terminal loading and in in itia l swing phase [11]. Dorsifle xion move ment is achieved by Tibialis anterior an TA activity extended over the complete swing phase, starting slightly before toe- off, a round 27% , and ending at heel contact (100%)

   [12] In this study, at the slower speeds, Gastrocnemius muscle EM G pattern showed a similar EM G act ivation during stance, but the amp litude was substantially decreased from natural speed. Similarly, at the slower speed and at faster speed, the EMG act ivation for Tib ialis anterior muscle rises at initial contact and at toe-off. A loss of EM G a mp litude of the TA and MG muscles occurred at slower speed and increase in EM G activation occurred at faster speed, which has been found in past studies. [13][14][15] [16]

   When we observe changes for muscle group during stair ascent and stair decent, significant diffe rences were seen for GM and SOL muscle. During stair ascent, Tibia lis anterior muscle shows greater activation than other muscles and during stair decent, Gastrocnemius and soleus muscle shows activation higher than other muscles.

6. Conclusion

   In this study, the lower-limb muscle act ivities during the daily lo wer-limb mot ions such as walking, stair ascending and descending motions have been studied. The relationship between the lower-limb motions and the EM G act ivation levels of various muscles which are main ly concerned with the daily lower-limb activ ities are analyzed. The biomechanica l lo wer e xt re mity model proposed in this study will estimate the muscle activation patterns and also be used to design

   the lower-limb e xoskeleton assistive robotic systems for physically weak persons.

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