INTRODUCTION:

Walking is the most basic form of human activity performed for mobility. Also, walking refers to the consecutive and repetitive movement of each body segment to move the whole body gradually in a specific direction at a desired speed¹. As the form of transport from one place to another, walking is the most ubiquitous among human activities and can be mastered with little conscious effort².

Gait patterns can vary with social psychological factors such as lifestyle and conscious attitude and individual physical characteristics. At an individual level, walking is related to good health when done correctly, but walking abnormalities can affect the body structure. Researchers therefore stress the importance of proper walking³. Although it is obvious that walking can benefit people in today's busy society, abnormal gait can cause adverse effects throughout the body. Hence, having a proper walking posture is very important^4,5. Abnormal gait patterns can affect many parts of the body including joints, muscles and even brain, in addition to the adverse effects on postural balance. Furthermore, the shockwaves generated when the foot hits the ground are not properly absorbed during abnormal walking, causing excessive fatigue to the musculoskeletal system, which may lead to the onset of injury^6,7. While walking, FPA , in particular toe-out angle, is related to many symptoms of the musculoskeletal system^8-11. The foot angle or the degree of toe-out represents the angle between the line of progression and the long axis of the foot¹². While walking, the range of 7° to 15° is considered normal^1,13. Many studies have focused on identifying mechanisms related to gait variables using kinematics and biomechanical analysis methods to analyze the relationship between gait patterns and various conditions and characteristics related to human gait. Lin et al. (2001) reported a greater knee adduction moment during toe-in gait in 48 subjects in their 10s in comparison with those found during normal and toe-out gait¹⁴.Guo et al. (2007) reported that the first peak knee adduction moment was increased but the second peak knee adduction moment was much reduced in 10 patients with osteoarthritis (OA) who walked and climbed stairs with self-selected walking posture and 15° toe-out, facilitating their mobility¹⁵.Simic et al. (2013) reported that changes in knee moments were influenced by parameters of knee load during toe-in and toe-out walking in their study Involving 22 patients with medial knee OA¹⁶.

There have been previous studies on foot angles, as briefly discussed above, that investigated the effects of changing the FPA during walking on lower extremity joint load and knee adduction moment under different foot angle magnitudes. However, studies addressing the muscular activity based on surface EMG responses, which is commonly used for clinical gait analysis^1,17, are currently lacking. Therefore, this study aimed to analyze the effects of changing the FPA on the activity of the TA and GCM muscles and provide basic data regarding gait analysis.

2. MATERIALS AND METHODS:

2.1. Study design:

In this study, the independent variable is FPA, and the dependent variables are changes in muscular activity over ankle muscles. The primary research design method used was the same group design.

2.2. Subjects:

This study was conducted with 21 male and female students of N University in Chungnam, Korea. Those who had neither ankle injury nor medical history of impaired nerve and musculoskeletal system with a normal gait pattern defined as the FPA range of 7° to 15°. The purpose and methods of the study were explained to the participant and informed consent was obtained according to the principles of the Declaration of Helsinki. The subjects in this study are 21 healthy university students (9 males and 12 females) in their 20s, who are attending N University in Chungnam, Korea, Physical characteristics of the subjects, are summarized in Table 1.

Table 1: Physical Characteristics of subjects

	Mean±SD
Age(yrs)	20.52±0.75
Height(cm)	166.76±9.20
Weight(kg)	66.25±15.39

2.3. Assessment instruments

In this study, a metronome app installed on smartphone was used to enable subjects to maintain a consistent speed while walking on the treadmill (Sky Life 5300, Korea). Wireless EMG electrodes (Free EMG, BTS/Italy) were used to measure muscular activity. During the screening process, a goniometer (baseline, APSUN/Korea) was used to measure FPA when potential subjects walked three steps on the prepared papers. Subjects were instructed to walk by maintaining the pre-determined FPA magnitudes that were distinguished from each other by colors of the tape attached. A tape ruler (Fitting tape ruler, Fine Trade/ Korea) was used to measure step length. A body composition analyzer for professional use was used to assess general characteristics of subjects.

2.4. Experiment methods:

2.4.1. EMG electrode placement:

Prior to electrode placement, the skin zone was cleaned with alcohol to minimize resistance. To measure muscle activity, EMG electrodes were positioned over the TA and GCM muscles of the subjects who consented to participate in the experiment. A surface electrode was positioned over the intersection of the line that is four fingers below the tibial tuberosity and the line that is one finger below the spine of the tibia. Another surface electrode was positioned between the anterior and medial zone of the Achilles tendon in the distal portion of the gastrocnemius muscle belly¹⁷.

2.4.2. Experimental Procedures:

To identify general characteristics of subjects signed the informed consent form for the experiment; an automatic anthropometer and an in body composition analyzer were used. After measuring FPA of potential subjects walking three steps on the prepared paper, those who had a normal gait pattern were selected. At week 1, EMG electrodes were attached to the TA and GCM muscles of subjects to measure MVC. At week 2, to measure RMS, subjects were instructed to walk with a toe-in gait pattern for 5 minutes by maintaining the 10° FPA marked with tape (marked as -10°) with EMG electrodes attached on their muscles. At week 3, RMS was measured in the same way while subjects were walking with a normal gait pattern at the marked 10° angle. At week 4, subjects walked with a toe-out gait pattern at the marked 30° and RMS was measured. Each trial was performed on the walking track measuring 5.5m x 3.7m on which each angle (-10°, 10°, 30°) was marked with tape.

2.5. Statistical analysis:

Data were analyzed using SPSS version 18.0 software. The Kolmogorov-Smirnov test was used to check the normality, and data were normally distributed. Multivariate analysis of variance was used to determine the effect of changing the FPA on the activity of the TA and GCM muscles, and Tukey’s test was used for post-hoc analysis. A 𝑎=.05 is considered to be statistically significant.

3. RESULTS AND DISCUSSION:

3.1. Comparison of muscle activity of the right and left TA under different FPA:

Based on analysis results, the changes in muscle activity of the TA on the right and left side were statistically significant among the three FPA. Post hoc analysis revealed statistically significant differences in muscle activity in the right and left TA between –10° toe-in and 10° normal gait and between 10% normal gait and 30° toe-out (p<.05)as shown in table2.

Table 2, Comparison of muscle activity of the right and left TA under different FPA

				(unit: %MVC)
Muscle	FPA	M±SD	F	p	post-hoc
	-10°	48.63±8.12	5.404	0.007	1>2, 2<3
Left TA	10°	37.92±14.21
	30°	46.99±10.94
	-10°	45.16±5.42	8.528	0.001	1>2, 2<3
Right TA	10°	37.64±4.98
	30°	44.23±8.34

*Expressed as p<0.05, 1=-10, 2=10, 3=30, TA: tibialis anterior, FPA: Foot progression angle

3.2. Comparison of muscle activity of the right and left GCM under different FPA:

Based on analysis results, the changes in muscle activity of the GCM on the right and left side were statistically significant among the three FPA. Post-hoc analysis revealed statistically significant differences in muscle activity of the right and left GCM between –10° toe-in and 10° normal gait and between 10% normal gait and 30° toe-out (p<.05)as shown in table3.

Table 3. Comparison of muscle activity of the right and left GCM under different FPA

				(unit: %MVC)
Muscle	FPA	M±SD	F	p	post-hoc
	-10°	44.63±3.48
Left GCM	10°	34.42±15.86	6.653	0.002	1>2, 2<3
	30°	43.91±6.58
	-10°	54.05±11.70
Right GCM	10°	36.83±12.84	10.234	0.000	1>2, 2<3
	30°	49.87±13.96

*Expressed as p<0.05, 1=-10, 2=10, 3=30, GCM: gastrocnemius, FPA: Foot progression angle

3.3. DISCUSSION:

This study was conducted to analyze the activity of the TA and GCM muscles while walking with three different gait patterns (normal, toe-in and toe-out) with the purpose of underlining the importance of proper gait and reducing the risk factors of walking abnormalities. In this study, three FPA magnitudes (-10° toe-in gait, 10° normal gait and 30° toe-out gait) were used,15 and subjects were instructed to walk the pre-determined track at constant speed for 5 minutes under each FPA magnitude. As a result, the muscle activity was significantly higher in the right and left TA during -10° toe-in, compared with that of 10° normal gait. The muscle activity of the TA on both sides was also higher during 30° toe-out than that of 10° normal gait. There was no statistical difference in muscle activity of the TA on both sides between -10° toe-in and 30° toe-out. The changes in muscle activity of the right and left GCM were similar with the TA, showing significantly higher muscle activity during -10° toe-in and 30° toe-out than that of 10° normal gait. However there was no statistical difference in muscle activity of the GCM between -10° toe-in and 30° toe-out Gait alteration strategies have drawn much attention as their effectiveness in reducing knee joint load became known. One of those strategies involves changing the FPA given that toe-in gait and toe-out gait have been reported to reduce different indices of medial knee load¹⁸. Sasaki and Neptune (2010) as well as Win by et al. (2013) reported that loading of the knee depend on not only biomechanical and kinematic variables but the strength in the muscles around the knee^19,20. In this study, the significant differences in muscle activity among normal gait, toe-in and toe-out can be attributed to increased knee loads as a result of changing the FPA. Toe-in gait is evident in children with cerebral pals while toe-out gait can occur as compensation for muscle imbalance, Achilles tendon shortening, lateral twisting of the tibia, twisting of the femur and consequently lead to changes in knee and hip function as well as feet structure if it remains untreated²¹. Toe-in gait occurs beyond the normal FPA range and induces higher levels of muscle activity than normal gait by placing more loads on the lower extremity.

Guo et al. (2007) and Simic et al. (2013) claimed that walking with the toes at an angle increased as much as 10°-15° would benefit the loading environment in the knee^15,16. Their claim appears to explain why lower levels of muscle activity occurred during 10° normal gait, compared to those found during –10° toe-in and 30° toe-out.

Neumann (2010) reported that toe-out gait where the toes turned outward can have some benefit as this pattern somehow compensates for limited ankle joint and dorsiflexsion, but it certainly increases stress on medial structures of the feet and knee joint¹³. Gait with toe-out angle of 30° appears to increase the muscle activity of the lower extremity by placing more stress on knee joints than normal gait.

Stokes et al. (1989) and White and McNair (2002) reported that proper walking helps maintain harmonized movement at the hip and active equilibrium states of muscle activity and reduce energy and accidents such as missing steps during walking^4,5. The mechanism of the onset of knee OA is known to be related to excessive joint loads. In particular, knee joint loads induced by knee joint moments for lateral movement are closely linked with OA progression and its pace^22,23. Greater muscle activity found during toe-in and toe-out gait, compared with that of normal gait, can be translated into increased muscle fatigue and loads in the knees and ankles. It is therefore important to avoid abnormal FPA during walking as a means of reducing knee-joint loads. Mastering how to walk correctly is also required to lessen the loads and fatigue placed on muscles of the lower extremity and eventually to decrease the risk of walking injuries.

This study has the following limitations: The study was limited to the sample population of university students in their 20s (N University) in Cheonan city, and a small sample size (21) was used. Since this study investigated the TA and GCM muscles only, further study is necessary to examine muscle activity in various body parts with diverse study populations. Also, it was difficult to control subject's daily activities such as workout habits and diet despite their impact on muscle activity. As subjects were instructed to walk with normal, toe-in and toe-out get pattern, there was a possibility that unnatural walking patterns have distorted the results.

In further study, study populations actually need to walk with either toe-in gait pattern or toe-out gait pattern, and kinematic variables associated with gait patterns can be analyzed with the purpose of establishing the mechanism of lower extremity injuries that occur due to gait patterns

4. CONCLUSION:

This study analyzed the effect of gait patterns under three different FPA magnitudes (10° normal gait, –10° toe-in and 30° toe-out) on muscle activity of the lower extremity in male and female university students in their 20s (N University) in Chungnam. In comparison of changes in muscle activity in the TA and GCM during walking under different FRA magnitudes, there was no significant difference during –10° toe-in and 30° toe-out. However, significantly lower activity of the right and left TA and GCM muscles was found during 10° normal gait, compared to those of –10° toe-in and 30° toe-out.

5. ACKNOWLEDGMENT:

Funding for this paper was provided by Namseoul University

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Received on 28.06.2017 Modified on 29.07.2017

Research J. Pharm. and Tech. 2017; 10(9): 3151-3155.

DOI: 10.5958/0974-360X.2017.00561.3

Analysis of Tibialis Anterior and Gastrocnemius Muscle Activity According to Toe Angle during Gait