DEFINING LOWER EXTREMITY DOMINANCE: THE RELATIONSHIP BETWEEN PREFERRED LOWER EXTREMITY AND TWO FUNCTIONAL TASKS

Abstract

Background

A commonly utilized operational definition of lower extremity (LE) dominance assumes the LE with which a participant prefers to kick a ball with is the same preferred LE a participant would choose for a unilateral landing task.

Hypothesis/Purpose

The purpose of this study was to determine the relationship between the preferred lower extremity (LE) when performing a unilateral landing and kicking task. The authors hypothesized a strong correlation between the LE the participant chose for the landing task and the LE the participant chose for the kicking task would be evident.

Study Design

Repeated measures.

Methods

A convenience sample of 50 (age = 21.9 ± 0.9 years; sex = 27 female; 23 male; height = 170.6 ± 10.8 cm; weight = 73.3 ± 18.3 kg) healthy, recreationally active college aged students performed two tasks (kicking a ball; unilateral drop jump landing) in a counterbalanced order.

Results

Thirty-three participants kicked and landed with their right LE; 14 kicked with the right and landed on their left; two kicked and landed with their left and one participant kicked with their left and landed on their right LE. The Phi Coefficient (ϕ = 0.18; p = 0.18) indicated little to no relationship between the preferred LE for kicking a ball and landing from a drop jump. Similarly, the Chi-squared statistic revealed no differences between observed and expected frequencies (χ2 = 1.76; p = 0.23).

Discussion

When studying anterior cruciate ligament injury mechanisms in the laboratory, most investigators examine characteristics of the dominant LE. Dominance is frequently defined by which LE the individual kicks a ball with. The majority of ACL injuries however occur to the landing or plant LE. Hence, LE limb selection based on this approach may be flawed.

Conclusion

A significant relationship was not evident between the preferred LE for kicking a ball and a unilateral landing in a group of healthy recreationally active college aged students. The data suggests the preferred LE for kicking a ball and a unilateral landing task is not necessarily the same.

Level of Evidence

Level 3

INTRODUCTION

Investigations into anterior cruciate ligament (ACL) injury risk factors have been at the forefront of the sports and orthopedic community. This line of research has developed as ACL injuries remain common,^1-5 costly,⁶ and present a considerable sex bias.^3-4,7-8 Despite advances in surgical and rehabilitation techniques, ACL injuries frequently lead to knee osteoarthritis.⁹ Prevention of ACL injuries has the potential to benefit thousands of individuals and reduce considerable health care costs.

Strategies to prevent ACL injuries require a precise understanding of the injury mechanism. ACL injuries occur more frequently with non-contact mechanisms.^1,4 Epidemiological data reveals non-contact ACL injuries occur more frequently during single LE deceleration activities such as cutting, pivoting or landing from a jump.¹⁰ As such, unilateral landing tasks are commonly utilized to study non-contact anterior cruciate ligament risk factors.^11-12

Investigation of unilateral landing tasks often examines data from the participant's dominant LE. LE dominance is frequently operationally defined as the LE the participant prefers to kick a ball with.^13-16 The majority of ACL injuries however occur to the landing, or plant LE.^15,17 The manner in which lower extremity dominance has traditionally been defined in studies and in the orthopedic literature hence may be problematic. The commonly utilized operational definition of limb dominance assumes that the LE with which the participant prefers to kick a ball with is the same preferred LE a participant would choose for a unilateral landing task. Given the epidemiological data and injury rates, it is apparent that choosing the appropriate LE for testing is imperative.

To date, the authors were unable to identify any studies that examined the relationship between the preferred kicking LE and preferred unilateral landing LE. The purpose of this study was to determine the relationship between the preferred lower extremity (LE) when performing a unilateral landing and kicking task. The authors hypothesized a strong correlation between the LE chosen for each task would be evident.

METHODS

Participants

An a priori power analysis for correlation (α₁ = .05), using a medium effect size (r = .4) revealed a sample size of 37 subjects was required to achieve a power of .80. Subsequently, a convenience sample of 50 healthy, recreationally active, college-aged students was recruited. Inclusion criteria included no history of lower extremity surgery and no lower extremity injury within the prior six months, which necessitated the use of crutches for more than a day. In addition, participants were excluded from the study if they were unable to perform the drop vertical jump task or kicking a ball without pain.

Design

This investigation utilized a repeated measures counterbalanced design. Specifically, the order in which subjects were instructed to perform the two tasks was alternated from one subject to the next. All data acquisition took place in the Kristen McMaster Human Movement Laboratory and each participant followed identical procedures. Upon participant arrival to the laboratory, inclusion and exclusion criteria were reviewed to ensure eligibility. Prior to any data collection, participants provided written consent to participate in this University Institutional Review Board approved study.

Participants performed the two tasks (kicking a ball; unilateral drop jump landing) in a counterbalanced, alternating order. For the kicking task, participants were asked to kick a stationary soccer ball at a target five meters away using their preferred lower extremity. The participants completed five trials of this activity. The LE the participant chose to kick the ball with three out of the five trials was defined as their preferred kicking LE. For the landing task, the participants were instructed to stand on a 40cm (15.7 inches) high platform. Participants then were asked to step off of the platform, land with both LEs, immediately jump as high as they were able in a vertical direction and land then on their preferred LE. The participants completed five trials of this activity. The LE the participant chose to land on during three out of the five trials was visually determined by the investigator and defined as their preferred landing LE.

Statistical analysis was completed using commercially available software (SPSS v21, Armonk, New York, USA). Specific analyses included: 1) Standard descriptive statistics of subject characteristics (height, weight, sex, age); 2) Formulation of a 2x2 contingency table for the kicking and landing tasks by side (right, left); 3) Phi-coefficient was used to determine the strength of the relationship between the landing and kicking tasks and the 4) Chi-Square analysis was used to determine if the two dichotomous variables were associated (test of independence).

RESULTS

Fifty healthy, recreationally active, college-aged students (age = 21.9 ± 0.9 years; sex = 27 female; 23 male; mass = 73.3 ± 18.4 kg; height = 170.6 ± 10.8 cm) participated. Thirty-three participants kicked and landed with their right LE; 14 kicked with the right and landed on their left; two kicked and landed with their left and one participant kicked with their left and landed on their right LE (Table 1). The Phi Coefficient (ϕ = 0.18; p = 0.18) indicated little to no relationship between the LE with which a participant kicked a ball and performed a unilateral landing. Likewise, the Chi-square statistic revealed both observed and expected frequencies were not different (χ2 = 1.76; p = 0.23).

Table 1.

.2×2 Contingency table showing frequency of preferred lower extremity for kicking and landing tasks (n = 50).

DISCUSSION

The purpose of this investigation was to determine the relationship between the preferred LE for a unilateral landing task and for a kicking task. In contrast to the hypothesis, the results indicated that there was no significant relationship between the two functional tasks.

There is little discrepancy in the literature when defining upper extremity dominance.^18-19 Defining lower extremity dominance is less clear. Previous investigations have provided clear definitions for LE dominance²⁰ while others have utilized a battery of tests.²¹ Additional investigations have utilized the stance or weight-bearing LE for kicking a ball¹² or the preferred single LE for landing task.²² The most common LE dominance operational definition however, involves the preferred LE for kicking a ball.^13-16

Epidemiological evidence on ACL injuries contrasts with the rationale for LE selection in the majority of investigations. Data shows ACL injuries occur more frequently with a unilateral landing²³ during a non-contact mechanism^1,4 and do not occur as frequently to the kicking LE¹⁷. The utilization of a consistent and task specific LE selection therefore, is essential for application of any research finding.

Prior work in dancers has suggested level of expertise may affect the preferred LE utilized for skill performance even where bilateralism is expected.²⁴ While this study did not recruit participants from competitive sport teams or other populations with elevated knee injury risk, the sample was active and healthy. Expectations of possible knee injury risk from this sample although not profound, were not unreasonable. Because of this, research with a competitive athlete population would be indicated for improved application of findings.

The authors believe that this study is the first to examine the relationship between the preferred LE for unilateral landing and for kicking a ball. The results of this study show that the leg one prefers to kick a ball with and the leg one prefers to perform a unilateral landing task with are not necessarily the same. Given this, previous injury risk identification investigations may have obtained results from the LE less likely to be injured as a result. The authors however acknowledge the data are only generalizable to a similar population of healthy college aged individuals. Future study should examine whether the results of this study would hold true in a population of collegiate athletes from various sports (e.g. basketball, volleyball, soccer) where LE injury risk is heightened and preferred lower extremity may be sport specific.

CONCLUSIONS

The results of this study indicate that the lower extremity one chooses to kick a ball with has little to no relationship to the limb one chooses to land on. The authors encourage future investigations which explore lower extremity kinematics and kinetics at foot contact to consider an operational definition of LE dominance that examines the preferred single LE for landing. The authors feel that information from this study improves clarity for operationally defining LE dominance. Further, the results of this study provide a basis from which future study can determine if LE dominance is associated with the side on which non-contact ACL injury occurs. Clinicians and investigators alike are encouraged to be cognizant how they operationally define lower extremity dominance. This notion is particularly relevant during screenings which attempt to identify and quantify lower extremity injury risk.