Influence of Foot Position on Lower Extremity Muscle Activation Casey Darling University of North Dakota

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2012 Influence of Foot Position on Lower Extremity Muscle Activation Casey Darling University of North Dakota

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INFLUENCE OF FOOT POSITION ON LOWER EXTREMITY MUSCLE ACTIVATION

Casey Darling Bachelor of Science in Athletic Training University of North Dakota, 2006

A Scholarly Project Submitted to the Graduate Faculty of the Department of Physical Therapy School of Medicine University of North Dakota

in partial fulfillment of the requirements for the degree of

Doctor of Physical Therapy

Grand Forks, North Dakota May, 2012 i

This Scholarly Project, submitted by Casey Darling in partial fulfillment of the requirements for the degree of Doctor of Physical Therapy from the University of North Dakota, has been read by the Advisor and Chairperson of Physical Therapy under whom the work has been done and is hereby approved.

______(Graduate School Advisor)

______(Chairperson, Physical Therapy)

PERMISSION

Title Influence of Foot Position on Lower Extremity Muscle Activation

Department Physical Therapy

Degree Doctor of Physical Therapy

In presenting this Scholarly Project in partial fulfillment of the requirements for a graduate degree from the University of North Dakota, I agree that the Department of Physical Therapy shall make it freely available for inspection. I further agree that permission for extensive copying for scholarly purposes may be granted by the professor who supervised my work or, in his absence, by the Chairperson of the department. It is understood that any copying or publication or other use of this Scholarly Project or part thereof for financial gain shall not be allowed without my written permission. It is also understood that due recognition shall be given to me and the University of North Dakota in any scholarly use which may be made of any material in this Scholarly Project.

Signature ______

Date ______

iii

TABLE OF CONTENTS

LIST OF TABLES ...... v

ABSTRACT ...... vi

CHAPTER

I. INTRODUCTION ...... 1

II. METHODS ...... 8

III. RESULTS ...... 11

IV. DISCUSSION ...... 20

REFERENCES ...... 22

LIST OF TABLES

Table Page

1. Friedman’s Test for All Muscles Tested...... 13

2-1. ANOVA for Tibialis Anterior...... 13

2-2. ANOVA for Lateral Gastrocnemius...... 14

2-3. ANOVA for Rectus Femoris...... 14

2-4. ANOVA for Biceps Femoris...... 15

2-5. ANOVA for Gluteus Medius...... 15

2-6. ANOVA for Gluteus Maximus...... 16

3-1. Mauchly’s Test for Tibialis Anterior...... 16

3-2. Mauchly’s Test for Lateral Gastrocnemius...... 17

3-3. Mauchly’s Test for Rectus Femoris...... 17

3-4. Mauchly’s Test for Biceps Femoris...... 18

3-5. Mauchly’s Test for Gluteus Medius...... 18

3-6. Mauchly’s Test for Gluteus Maximus...... 19 v

ABSTRACT

The anterior cruciate ligament (ACL) in the knee is often sprained or torn in

injuries resulting from jumping, cutting, or hyperextension of the knee. When the knee is put under a valgus, varus, or rotatory stress it can put strain on the ACL. Lower

extremity motor control can help control the amount of varus and valgus stress on the

knee. Lower extremity muscle control is involved with preventing this stress and

resulting injuries. This study was performed to determine whether the position of the

foot (neutral, supination, and pronation) has an effect on lower extremity muscle activity

during single-leg squats.

Six muscles were measured with EMG while the subjects performed single-leg

squats with the foot in various subtalar positions. The muscles measured were gluteus

maximus, gluteus medius, biceps femoris, rectus femoris, lateral gastrocnemius, and

tibialis anterior.

The study produced significant differences in EMG activity for the gluteus

maximus, lateral gastrocnemius, and biceps femoris. However, more research needs to

be performed to prove if foot position has significant influence on lower extremity

muscle activity and how it affects the ACL.

CHAPTER I

INTRODUCTION AND LITERATURE REVIEW

The anterior cruciate ligament (ACL) in the knee is often sprained or torn in

injuries resulting from jumping, cutting, or hyperextension of the knee. This is especially

true in athletic individuals who put themselves in these situations more often than

sedentary people. When the knee is put under a valgus, varus, or rotatory stress (which

occurs during athletic activity) it can put strain on the ACL. Lower extremity motor

control can help control the amount of varus and valgus stress on the knee. It has been

suggested in research1,2 that lower extremity muscle control is involved with preventing this stress and resulting injuries. This study was performed to determine whether the position of the foot (neutral, supination, and pronation) has an effect on lower extremity muscle activity during single-leg squats.

Anatomy and Physiology

The ACL is a 3-piece twisted ligament that attaches to the distal posterior femur and proximal anterior tibia. It serves to prevent the tibia from moving anteriorly on the femur and also stabilizes the tibia against excessive internal rotation and serves as a

secondary restraint for valgus or varus stress with collateral ligament damage. The

ligament is tight when the knee is in extension and works with the thigh muscles to

stabilize the knee joint.3 An intact ACL resists forces up to 2500 N before failing.4

These forces include resisting knee hyperextension, cutting, and accelerating/decelerating activities. It is highly probable that ACL injuries are more likely to occur during multi- planar rather than single-planar mechanisms of injury.5 ACL tears can be treated

conservatively in the older or inactive population, but are usually surgically repaired in an

active individual regardless of age. The surgery involves replacing the sprained or ruptured ligament with either an allograft or autograft by tunneling through the bone and securing it in place. The surgery usually requires a somewhat lengthy (about 6 months) rehabilitation to return to prior level of function. This length of recovery is vastly improved compared to 20 or 30 years ago, when tearing an ACL meant the end of any athletic career. Advances in medicine have resulted in patients returning to both professional and recreational sports, usually with no recurrence or injury.

Problems

An ACL tear and the resulting surgery and rehabilitation can cause many

hardships for an individual and his or her family including financial, social, and

functional problems. Advances in health care have greatly reduced the amount of time

and severity of functional disability caused by these injuries, but the cost has increased

greatly. A conservative estimate of the average cost of an ACL tear, including repair and

rehabilitation, is $17,000 to $25,000 per injury.1 This cost can also be in addition to the

loss of participation in entire sports seasons, decreased scholarship funding for 2 prospective college athletes, lowered academic performance, possible long term disability, and a significantly greater risk of developing osteoarthritis.6

An ACL tear usually involves trauma to more anatomical structures in the knee than the single ligament alone. Joint capsules, menisci, additional ligaments, and joint surface cartilage can all be damaged from stress or shearing forces. When these structures are damaged, it can lead to instability and poor arthrokinematics. This can result in bone on bone contact during weight bearing and lead to osteoarthritis and possibly the need for total joint arthroplasty in the future.

Incidence

ACL injuries are common in all levels of athletics as well as in the active population. In the United States, an estimated 80,000 to 100,000 ACLs are repaired each year. In the general population, the ACL tear ratio of females to males is 9:17 and female athletes are 4 to 6 times more likely to sustain an ACL injury than males. The number of

ACL injuries found in females has greatly increased over the past couple of decades.

This is possibly due to Title IX of the Education Amendments of 19728 which states that

“No person in the United States shall, on the basis of sex, be excluded from participation in, be denied the benefits of, or be subjected to discrimination under any education program or activity receiving Federal financial assistance…” This law increased the opportunities for females to be involved with many different sports. The number of males involved in high school athletics has remained steady (3.8 million), but the involvement of females has increased from 0.3 to 3 million.9

Causes

The reasons as to why the female population is more susceptible to ACL injuries than males has been debated and researched much in the literature. The real mechanism is most likely multi-factorial10 and may include extrinsic (physical and visual

perturbations, bracing, and shoe-surface interaction) and intrinsic (anatomic, hormonal,

neuromuscular, and biomechanical differences between genders) variables.2

Anatomical differences between genders such as a wider pelvis, underdeveloped

musculature, increased genu valgum and tibial torsion can all put a female at a

disadvantage when it comes to being susceptible to ACL injuries. While in a single-leg

squat position, women have been shown to assume a position with increased dorsiflexion,

pronation, hip adduction, hip flexion, hip external rotation, and less trunk lateral flexion

than men.11 When combined, weakness and malalignment of the lower extremity can

produce instability in the knee that is exploited during activities such as jumping and

landing (especially forward jumping as opposed to drop jumping),12 cutting, and other activities that increase rotation on the joint.13 It is during these non-contact activities that

most ACL injuries occur.

These effects could be due to decreased motor control of the lower extremities

and also poor positioning in space resulting in additional stress on the ACL. The bony

structure of the female pelvis and alignment is not easily or feasibly modified, but

strength, proprioception, and motor control can be improved through proper education, cueing, and exercises. Also, a female may have a natural amount of valgus in her knees,

but controlling additional valgus during physical activity is something that should be

stressed in young athletes to hopefully help prevent some of these injuries. Females, when jumping, are “significantly more likely to have poor technique due to landing with less hip and knee flexion at initial contact, more knee valgus with wider landing stance, and less flexion displacement over the entire landing” compared to males.14 During

cutting maneuvers, they also use less hip flexion and more hip external rotation which

results in a smaller hip flexion moment compared to male athletes.15 These factors can all

put a female athlete at risk for ligament tears.

Women also have greater laxity of ligaments in general than men. There has been

research to see whether this is a result of hormonal influence, especially during the

menstrual cycle: however it is as yet inconclusive as taking samples of sex hormone profiles can be inconsistent.16 Some research suggests the use of oral contraceptives have

not been shown to increase the incidence of ACL tears, but that women in the pre-

ovulatory phase of the menstrual cycle are at a greater risk of ACL rupture than women

in the post-ovulatory phase.17 Still, other research concludes that due to the wide intra

and inter-variability in women’s menstrual cycles, it is difficult to determine which phase

a woman is actually in, making the research on the injuries inaccurate.18 It is evident that

more research needs to be done in this area to determine if hormones indeed do have an

effect on the incidence of ACL injuries.

Women tend to have different neuromuscular characteristics than men, including

the decreased ability to generate muscular force, decreased dynamic stabilization of the

knee, and slower muscle activation and force generation. Women also have the tendency 5

to activate the quadriceps instead of the hamstrings or the gastrocnemius in dynamic situations.4 Contracting the quadriceps actually contributes to an anterior translation of the tibia on the femur, which places stress on the ACL and increases the risk of a non- contact ACL injury.19 Using better control of the hamstrings and gastrocnemius/soleus can help to control the anterior translation of the tibia, especially in dynamic situations.

Since most ACL injuries occur in non-contact situations, decreased

neuromuscular control can contribute to an increased risk for ACL injury. “Female

athletes who have poor landing mechanics are at an increased risk for ACL injury and are

more likely to benefit from neuromuscular training targeted to these risk factors.”20

Altering these poor mechanics can result in a decrease in the load on the knee which can result in a decreased anterior cruciate ligament injury risk.21 Neuromuscular control is

inherited but also can be practiced and enhanced. In a study by Zebis et al,22

“neuromuscular training increased EMG activity for the medial hamstring muscles,

thereby decreasing the risk of dynamic valgus.” Learning how to jump and land with

proper mechanics could possibly have a positive effect on the number of ACL injuries we

see today by decreasing the peak tibial shear force and loading placed on the ligament.23

Screening and targeting the “high risk” female athletes is the more difficult part.

One way to screen for at-risk athletes is to use EMG to determine which athletes have

decreased EMG preactivity of the semitendonosis and increased EMG preactivity of the

vastus lateralis during side cutting.24 However, this is not feasible for most athletes or health care providers due to time and monetary constraints.

Having a dysfunction to a distal lower extremity joint or muscle can also lead to problems in more proximal joints. According to a study by Kulig et al,25 women with

posterior tibial tendon dysfunction were found to have decreased strength, endurance, and

torque in hip extensor and abductor muscles when compared to an age-matched control

group. The body works together as a unit and when a distal joint or muscle is impaired or dysfunctional, it affects the rest of the extremity and most likely the contralateral extremity as well through compensation or poor mechanics while weight bearing.

It has also been hypothesized that excessive pronation, or navicular drop, can

result in an increased risk for ACL injuries,26 although this has been debated.27 Adding a

5o medial post has been shown to significantly decrease knee valgus and ankle

pronation/eversion during a drop jump both at initial contact and at maximum value.28

This is in agreement with another study by Eng and Pierrynowski29 that showed that

providing proper foot mechanics through orthotics produced beneficial changes in transverse and frontal plane motion of the knee and the foot during walking and running.

There needs to be additional research performed to determine whether or not poor foot positioning such as pronation or supination leads to impaired lower extremity motor control or muscle activity.

CHAPTER II

METHODS

Subjects who participated in this study volunteered their time and received no compensation. They were both male and female between the ages of 18 and 30. Subjects were excluded if they were pregnant, had an acute injury to a lower extremity, or if they

could not perform a single-leg squat. Subjects were educated about the procedures of the

study and each read and signed an informed consent document. If they had any questions

regarding the study, they were answered by the researchers. All of the research was

conducted in the research laboratory located in the UND Physical Therapy Department

within the School of Medicine and Health Sciences.

When the subjects arrived for the study, they completed a form addressing any

history of injury/surgery and also the stage of their menstrual cycle (if applicable). Their

dominant plant leg was found by having them kick a stationary soft soccer ball 3 times.

Whichever leg they used to plant for kicking the majority of the kicks was deemed the

dominant leg and this leg was used for measurement during the study.12

The leg was prepped for electromyography (EMG) electrodes in 7 areas (6 EMG

sites and 1 ground) by shaving (if necessary, to reduce impedance), using fine sandpaper

to gently abrade the skin, and cleaned with rubbing alcohol. The head of the fibula was

8 used as the ground site. The 6 muscles measured by EMG were: gluteus medius

(electrodes placed 1/3 of the distance from the iliac crest to the greater trochanter), gluteus maximus (midpoint from the inferior lateral angle of the sacrum to the greater trochanter), rectus femoris (midpoint between ASIS and superior pole of the patella), biceps femoris (midpoint between ischial tuberosity and lateral femoral condyle), anterior tibialis (1/3 of the distance from the inferior pole of the patella to the distal point of the lateral malleolus), and lateral gastrocnemius (1/3 of the distance from the fibular head to the distal posterior calcaneus).

Two disposable, self-adhesive electrodes were placed over each prepared area a finger-width apart and connected to the EMG recording device, which sent the data wirelessly to the computer containing the software used to analyze the data. Impedance was checked for each set of electrodes by using a Noraxon ® Electrode Impedance

Checker (Noraxon, Scottsdale, AZ). If the resistance was less than 50,000 ohms, it was deemed acceptable for our study. If resistance was at over 50,000 ohms, the electrodes were placed closer together and checked again. Each subject performed 4 to 5 practice squats to make sure each set of electrodes was picking up data and being sent to the computer correctly. An electronic goniometer was placed at the lateral knee joint to monitor the joint position of the knee during the squats.

EMG data was collected for the 6 muscles while the subject performed barefoot single-leg squats and returned to standing erect. The squats were performed with the foot in 5 different positions. The foot positions included flat or neutral ground, 5 and 10 degrees of medial incline (supination), and 5 and 10 degrees of lateral incline (pronation). 9

The incline was achieved by standing on an inclined wood platform covered with a

pillowcase for sanitary reasons. The neutral ground squats were also performed on a

wood platform with no inclination. Five squats were performed in each position (for a total of 25 squats) with a metronome cueing the subject to complete one squat every 2 seconds. The order in which the foot positions were selected was through random selection by each subject drawing cards. Following data collection, the electrodes were

removed and the areas were cleaned with rubbing alcohol to remove any residue of the

gel.

There was minimal risk for injury to the subjects in this research project. There was a slight risk of a fall or loss of balance, but each subject was spotted while squatting and the angle of supination/pronation was not extreme. The muscle activity required for this squat is not more than walking on uneven ground and required only moderate effort.

The electrodes also had the possibility of creating a transient skin reaction which would subside naturally.

CHAPTER III

RESULTS

Muscle activation of the lateral gastrocnemius, rectus femoris, biceps femoris,

gluteus medius, gluteus maximus, and tibialis anterior was monitored and recorded during a single-leg squat in 5 foot positions. A percent of the maximal voluntary contraction (%MVC) was found by comparing muscle activation to the maximal voluntary contraction (MVC) value determined by taking the average MVC values of participants in the preceding study. The mean and standard deviation for each foot position are listed in Tables 2.1 to 2.6, Friedman’s Test is listed in Table 1, and

Mauchly’s is presented in Tables 3.1 to 3.6. Friedman’s Test was run due to the study violating assumptions of a normal distribution. The post hoc tests were performed on muscles found to be significant to study the interaction between foot positions.

Tibialis Anterior, Rectus Femoris, and Gluteus Medius

Muscle activity of the tibialis anterior, rectus femoris, and gluteus medius was not statistically significant between foot positions according to Friedman’s.

Lateral Gastrocnemius

Muscle activity of the lateral gastrocnemius was found to be statistically significant with changing foot position (P=.014). According to the post hoc analysis

there was a significant difference in lateral gastrocnemius muscle activity between the

following positions: neutral foot position and 5 degrees pronation (P=.050); 5 degrees supination and 10 degrees pronation (P=.035); 10 degrees supination and 5 degrees pronation (P=.020); 10 degrees supination and 10 degrees pronation (P=.035).

Biceps Femoris

Muscle activity of the biceps femoris was found to be statistically significant with changing foot position (P=.046) According to the post hoc analysis there was a significant difference in biceps femoris muscle activity between the following positions: neutral foot position and 5 degrees pronation (P=.010); neutral foot position and 10 degrees pronation (P=.008).

Gluteus Maximus

Muscle activity of the gluteus maximus was found to be statistically significant with changing foot position (P=.000) According to the post hoc analysis there was a

significant difference in gluteus maximus muscle activity between the following

positions: neutral foot position and 5 degrees supination (P=.021); neutral and 10 degrees

supination (P=.023); neutral and 5 degrees pronation (P=.002); neutral and 10 degrees

pronation (P=.001); 5 degrees supination and 10 degrees pronation (P=.003); 5 degrees

pronation and 10 degrees pronation (P=.036).

Table 1. Friedman’s Test for All Muscles Tested

Muscle N Chi-square df P (significance)

Anterior tib 10 2.240 4 0.692

Lateral Gastroc 10 12.560 4 0.014

Rectus Femoris 10 5.246 4 0.263

Biceps Femoris 10 9.680 4 0.046

Glut Medius 10 6.080 4 0.193

Glut Max 10 22.814 4 < .001

Friedman’s Test showing significance of muscle activity compared to %MVC for each muscle. Muscles found to be significant were the lateral gastrocnemius, biceps femoris, and gluteus maximus.

Tables 2: RM ANOVA data – mean and standard deviation for each muscle in each position.

Table 2 – 1. ANOVA for Tibialis Anterior

Muscle – position Mean Std. Deviation

Ant tib – std 62.4500 11.05976

Ant tib - sup5 55.1500 17.38162

Ant tib – sup10 58.2500 10.97788

Ant tib – pron5 60.3500 14.35752

Ant tib – pron10 64.9200 19.27686

Mean and standard deviation values for RM ANOVA of the tibialis anterior in each foot position. The mean is expressed as %MVC.

Table 2-2. ANOVA for Lateral Gastrocnemius

Muscle – Position Mean Std. Deviation

Lat gastroc – std 74.1600 7.02032

Lat gastroc – sup5 76.9700 22.38859

Lat gastroc – sup10 74.2200 13.29969

Lat gastroc – pron5 82.9200 11.43871

Lat gastroc – pron10 88.4900 20.72038

Mean and standard deviation values for RM ANOVA of the lateral gastrocnemius in each foot position. The mean is expressed as %MVC.

Table 2-3. ANOVA for Rectus Femoris

Muscle – Position Mean Std. Deviation

Rectus Femoris – std 66.8400 8.87170

Rectus Femoris – sup5 74.1200 31.97064

Rectus Femoris – sup10 72.4800 31.55605

Rectus Femoris – pron5 70.9500 28.14227

Rectus Femoris – pron10 70.1200 33.81334

Mean and standard deviation values for RM ANOVA of the rectus femoris in each foot position. The mean is expressed as %MVC.

Table 2-4. ANOVA for Biceps Femoris

Muscle – Position Mean Std. Deviation

Biceps Femoris – std 68.4000 7.14967

Biceps Femoris – sup5 76.4000 26.53446

Biceps Femoris – sup10 87.6900 29.47422

Biceps Femoris – pron5 81.8100 16.66890

Biceps Femoris – pron10 87.1100 20.43828

Mean and standard deviation values for RM ANOVA of the biceps femoris in each foot position. The mean is expressed as %MVC.

Table 2-5. ANOVA for Gluteus Medius

Muscle - position Mean Std. Deviation

Glut med - std 75.7300 8.27500

Glut med – sup5 82.0200 18.36572

Glut med – sup10 85.8000 17.67251

Glut med – pron5 86.9100 13.53903

Glut med – pron10 88.7400 14.33575

Mean and standard deviation values for RM ANOVA of the gluteus medius in each foot position. The mean is expressed as %MVC.

Table 2-6. ANOVA for Gluteus Maximus

Muscle – position Mean Std. Deviation

Glut Max – std 68.6700 5.41542

Glut Max – sup5 81.7700 16.31421

Glut Max – sup10 91.9700 29.94955

Glut Max – pron5 87.2100 16.35240

Glut Max – pron10 101.4800 22.43251

Mean and standard deviation values for RM ANOVA of the gluteus maximus in each foot position. The mean is expressed as %MVC.

Tables 3: Mauchly’s Test of Sphericity (tests of within-subjects effects)

Table 3-1. Mauchly’s Test for Tibialis Anterior

Muscle – ant Type III Sum df Mean Square F Sig. (P) tib of Squares

Sphericity 566.655 4 141.664 .827 .517 assumed

Error – 6165.513 36 171.264 sphericity assumed

Mauchly’s Test of Sphericity demonstrating non-significance (P=.517)

Table 3-2. Mauchly’s Test for Lateral Gastrocnemius

Muscle – lat Type III sum df Mean square F Sig. gastroc of squares

Sphericity 1552.019 4 388.005 3.060 .029 assumed

Error - 4564.565 36 126.793 sphericity assumed

Mauchly’s Test of Sphericity demonstrating significance (P=.029)

Table 3-3. Mauchly’s Test for Rectus Femoris

Muscle – Type III Sum df Mean square F Sig. rectus femoris of Squares

Sphericity 299.593 4 74.898 .335 .853 assumed

Error – 8053.567 36 223.710 sphericity assumed

Mauchly’s Test of Sphericity demonstrating non-significance (P=.852)

Table 3-4. Mauchly’s Test for Biceps Femoris

Muscle – Type III Sum df Mean Square F Sig. biceps femoris of Squares

Sphericity 2600.867 4 650.217 2.727 .044

Assumed

Error – 8582.189 36 238.394 sphericity assumed

Mauchly’s Test of Sphericity demonstrating significance (P=.044)

Table 3-5. Mauchly’s Test for Gluteus Medius

Muscle – glut Type III sum df Mean square F Sig. med of squares

Sphericity 1063.610 4 265.903 2.695 .046 assumed

Error - 3551.358 36 98.649 sphericity assumed

Mauchly’s Test of Sphericity demonstrating significance (P=.046)

Table 3-6. Mauchly’s Test for Gluteus Maximus

Muscle- glut Type II sum df Mean square F Sig. max of squares

Sphericity 5947.152 4 1486.788 8.696 <.001 assumed

Error - 6155.176 36 170.977 sphericity assumed

Mauchly’s Test of Sphericity demonstrating significance (P=.001)

CHAPTER IV

DISCUSSION

The statistical analysis of this study did not reveal strong, significant results that

were anticipated. Most notably, the EMG activity of gluteus medius did not significantly change when foot position was altered. The same was true for tibialis anterior and rectus femoris. Significant differences were found for lateral gastrocnemius, biceps femoris, and gluteus maximus.

The most significant muscle tested was the gluteus maximus. There was a significant change in EMG activity between neutral foot position and every other foot position tested. However, gluteus maximus is not usually talked about in the literature

concerning ACL injuries. It does play a strong role in stance stability, but it has not been

proven if it has an influence on knee valgus and has no anatomical connection that would

control anterior tibial translation.

There were a number of different factors that could have influenced the validity and accuracy of this research. Perhaps the most notable reason was the small sample size used for statistical analysis (n=10). This violated the assumptions of normal distribution

and did not provide a large enough sample to portray the normal population. The small

sample size also produced very large standard deviations for every muscle tested. More

20 subjects would need to be studied and analyzed in order to provide more powerful statistical significance.

Different researchers were used for different subjects when preparing the subjects

(attaching EMG electrodes and lead wires) and operating the computer software. To provide more consistent results, the same researcher should have been used for each job throughout the study. This would have eliminated some of the learning curve for the researchers and also made the process more constant.

When analyzing data for each subject, there was a wide range in EMG activity even between different squats for the same individual in the same foot position. This could have been due to a loss of balance experienced by the subject, distractions, or lack of proper execution of a squat. In future studies, it may be beneficial to allow the subjects more practice repetitions so they can become accustomed to performing the single-leg squat activity with confidence.

Anterior cruciate ligament injuries will continue to occur in the athletic and general population. Various prevention and treatment protocols have been developed and should be followed according to evidence based practice. After analyzing the results of this research study, clearly, more research needs to be done to prove if foot position has a significant influence on lower extremity muscle activity during activity and whether this has a significant impact on ACL injuries.

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