Association of Hip and Trunk Strength With Three-Dimensional Trunk, Hip, and Knee Kinematics During a Single-Leg Drop Vertical Jump

Abstract

Martinez, AF, Lessi, GC, Carvalho, C, and Serrao, FV. Association of hip and trunk strength with three-dimensional trunk, hip, and knee kinematics during a single-leg drop vertical jump. J Strength Cond Res 32(7): 1902–1908, 2018—Kinematic changes have been correlated with different lower-limb injuries. Movement is influenced by multiple factors and strength is one of the contributors that can influence it. Thus, the aim of this study was to evaluate the correlation among trunk and hip isometric strength with trunk and lower-limb kinematics during a single-leg drop vertical jump. Twenty-three healthy recreational female athletes aged between 18 and 35 years underwent isometric evaluation of hip abductor, hip extensor, and lateral trunk muscle strength and 3-dimensional trunk and lower-limb kinematics during a single-leg drop vertical jump. Pearson's correlation coefficients (r) were calculated to establish the association among hip and trunk strength and trunk, hip, and knee kinematics. As result, no significant correlations were found between the peak and movement excursion values of kinematic and hip and trunk isometric strength data. The lack of correlation between isometric strength and kinematics in healthy female athletes indicates that intervention programs should not be focused solely on strength exercises to influence the movement pattern during single-landing activities.

Introduction

From the lower extremity joints, the knee sustains the highest percentage of injuries, particularly among physically active subjects (²⁸). In sports requiring pivoting and jumping, women are 2 to 8 times more likely than men to have noncontact anterior cruciate ligament (ACL) injury (¹⁴). In addition, the incidence rate of patellofemoral pain (PFP) in women is 2.2 times greater than in men (⁹).

Poor dynamic control of the trunk, hip, and knee may be related to ACL rupture and PFP (^11,37). Some studies observed similar kinematic changes correlated with these injuries. Alentorn-Geli et al. (¹) indicated that decreased trunk flexion during a landing-jump can increase the risk of noncontact ACL injury in soccer players, and Teng and Powers (³³) showed that running with trunk extension can increase knee internal extensor moment and patellofemoral stress. Furthermore, excessive ipsilateral trunk lean has been observed during single-leg squat (²⁴) and stepping tasks (²²) in PFP subjects. This movement is also a component of the ACL injury mechanism in female athletes during landing (¹⁶). The excessive dynamic valgus—a combination of hip internal rotation and adduction with knee abduction and lateral rotation (³⁸)—during a drop vertical jump was observed by Hewett et al. (¹⁵) as an ACL injury predictor in female athletes. Besides that, an increase in the magnitude of dynamic valgus components, such as hip adduction and internal rotation, and knee abduction was observed in subjects with PFP during single-leg squats (²⁴), running (^31,35), and a step-down maneuver (^22,31).

The movement is influenced by multiple factors, and one of them is strength. Previous studies have evaluated the association between trunk and hip muscle strength and trunk and lower-limb kinematics during weight-bearing activities in healthy subjects, but the results are inconsistent. The strength of the hip extensor, hip external rotators, and lateral trunk muscles were correlated with a knee frontal plane projection angle (FPPA) during single-leg squats (³²), but not during step down (²). However, in both tasks, correlation between the hip abductor strength and FPPA were found in 2D analysis. Similarly, Teng and Powers (³⁴) evaluated the association between isometric hip extensor strength and trunk position in the sagittal plane during running and found that the greatest isometric hip extensor strength correlated with increased trunk flexion.

One reason for equivocal findings regarding the association between trunk and hip muscle strength and specific trunk and lower-limb movement may be the low demand of the tasks assessed in these studies. It is expected that in higher demanding tasks, as well as landing-jumping tasks, this association is more evident. The single-leg jump test may impose a greater demand on the neuromuscular system. Assessing a task with similar demand in harmful movements, as the single-leg drop vertical jump (SLDVJ) could help in understanding the kinematics changes that occur during this kind of task.

The purpose of this study was to evaluate the correlation among isometric strength of hip extensors, hip abductors and the lateral trunk muscles, and trunk, hip, and knee kinematics (movement excursion and peak values) during the SLDVJ. It was hypothesized that greater hip abductor and extensor muscle isometric strength would be associated with higher hip abduction and lower ipsilateral trunk lean, hip internal rotation, and knee abduction. In addition, it was hypothesized that greater hip extensor muscle isometric strength would be associated with greater trunk, hip, and knee flexion. Finally, it was hypothesized that greater lateral trunk muscle isometric strength would be associated with higher hip abduction and lower ipsilateral trunk lean and knee abduction. Knowledge of the precise association between hip and trunk muscle strength and the trunk, hip, and knee kinematics (movement excursion and peak values) during SLDVJ would help to develop an optimal prevention program for ACL injury and PFP in female athletes.

Methods

Experimental Approach to the Problem

Cross-sectional analysis of female recreational athletes involving in jump tasks was used. Jump task (SLDVJ task) kinematics and isometric strength test of hip abductors, hip extensors, and trunk lateral muscles were evaluated. A correlation analysis was used to identify possible associations between the kinematic and strength variables.

Subjects

We recruited 23 female recreational athletes aged between 18 and 35 years (Table 1) who practiced different physical activities, at least one involving jump tasks (handball, volleyball, or soccer). The sample size calculation was performed using G*Power software (Version 3.1.9.2; Kiel University, Germany) for correlation data. Thus, we used a significance level of α = 0.05, β = 0.2 as parameters for correlation analyses and estimated r = 0.5 for a moderate-to-good correlation (²⁷), which resulted in a sample size of 23 participants. The recreational athletes were women who practiced physical activity at least 3 times a week (⁵), and the activity level was evaluated using the short form of the International Physical Activity Questionnaire (^10,26).

Potential participants were screened by a licensed physical therapist, who evaluated the following inclusion criteria: recreational athletes in sports with jump activity who did not have any injuries in the lumbar spine or lower limbs over the last 12 months, had no pain or injury that makes evaluation impossible, and had no neurological vestibular or visual disorders that prevented participation (^18,19). All participants signed a written informed consent form, and the study was approved by the São Carlos Federal University's Ethics Committee for Human Investigations.

Procedures

The dominant leg was assessed, which was determined by asking the participant which leg she would use to kick a ball as far as possible (¹³). The isometric strength of the lateral trunk muscles was assessed on the opposite side to the dominant lower limb. The kinematics and isometric strength evaluations were performed on 2 separate days with a maximum of 5 days' difference between them, and the evaluation order was randomly selected. All the participants wore a T-shirt, shorts, and athletic shoes (Asics Gel-Equation 5) provided by the examiner.

Kinematic Assessment

For the kinematic assessment, the subjects were instructed to perform an SLDVJ. To perform the SLDVJ, the participants were positioned on a 31-cm box (^18,19) and were instructed to fold their arms across their chest (^18,19) so as not to obstruct the pelvis markers; step off the box without jumping up, stepping down or losing balance; and land on the dominant leg. Immediately after the initial contact, the participants performed a maximal effort single-leg vertical jump (^18,19). No verbal or visual clues were given on landing techniques at any time (^18,19). Five validated trials of the SLDVJ were considered for analysis. A valid trial was considered when the subject landed without losing balance, with arms in the correct position, and without touching the ground with the nonassessed leg (^18,19).

To perform the kinematic analysis, a 6-camera, 3-dimensional motion-analysis system (Vicon Motion Systems Ltd., Oxford, United Kingdom) was used. All the kinematic data were collected at a sampling rate of 250 Hz. For data acquisition, we used Nexus System 2.1.1 software (Vicon Motion Systems Ltd.) and 3D Motion Monitor Software (Innovative Sports Training, Chicago, IL, USA). The same researcher positioned 32 reflective markers (14-mm diameter) in each volunteer on the following anatomic landmarks: jugular notch, seventh cervical vertebra spinous process, tenth thoracic vertebra spinous process, both acromion, anterior superior iliac spine and posterior superior iliac spine bilaterally, first sacral, both greater trochanter, anterolateral of the thigh (on both thighs but at different heights), both medial and lateral femoral condyles, both tibial tuberosities, anterolateral of the leg (on both legs but at different heights), both medial and lateral malleoli, immediately over both second metatarsal heads on the shoe, immediately over both calcaneus on the shoe, and at a lateral side of the foot on the shoe (on both feet but at different distances immediately over the fifth metatarsal head on the right foot and fifth metatarsal base on the left foot). The reflective markers at different heights or distances were used to differentiate the 2 sides (right and left thigh, leg, or foot) for the system. After this preparation, each participant was positioned inside the assessment area staying in a neutral position and with her arms crossed over the trunk (^18,19) looking forward. A static measurement was performed to align the subject with the global coordinate system and to act as a reference for further analysis.

A priory study was conducted to determine the test-retest reliability of the kinematics measurements. For this, 10 subjects were evaluated on 2 separate days with 2–5 days between them. The intraclass correlation coefficient (ICC3,1) and the standard error of measurement (considering peak values) were, respectively, 0.95 and 3.2° for hip flexion, 0.89 and 1.79° for hip internal rotation, 0.85 and 1.27° for hip abduction, 0.89 and 1.64° for knee flexion, 0,81 and 1.28° for knee abduction, 0.94 and 3.48º for trunk flexion, and 0.89 and 2.55° for ipsilateral trunk lean.

Isometric Strength Assessment

Isometric strength assessment was made by a handheld dynamometer (Lafayette Instruments, Lafayette, IN, USA) for the following muscle groups: hip abductors, hip extensors, and lateral trunk muscles. Inelastic straps were used to stabilize the participants and the dynamometer. This stabilization was used to eliminate the tester strength external influence on evaluation. The evaluation order was randomly selected.

For maximal voluntary isometric strength (MVIS) evaluation of the hip abductors, the participants were positioned as described by Nakagawa et al. (²⁴) and as shown in Figure 1A. The participants stayed in lateral decubitus with the dominant leg up and in neutral position supported by pillows (⁶). An adjustable inelastic strap was placed around the examination table and proximal to the iliac crest to stabilize the hip, and the dynamometer was positioned over the femoral condyle with a second strap positioned over the dynamometer and around the table resisting the abduction. The researcher instructed the participant to “push trying to move your leg up” with maximal effort and offered encouraging words during the test (²⁴).

Figure 1.: Test position for the evaluation of hip abductor strength (A), hip extensor strength (B), and trunk lateral muscles strength (C).

For the MVIS evaluation of the extensors hip, the participants were positioned as described by Scattone Silva et al. (³⁰) and Nakagawa et al. (²⁴) (Figure 1B). The participants were positioned in the prone position, lying with the dominant leg at 90° knee flexion and the hip in neutral position. The first strap was positioned around the volunteer's pelvis, and the examination table to stabilize the hip. The dynamometer was positioned immediately proximal the popliteal fossa, and a second strap was positioned over the dynamometer and the examination table. The researcher asked the participants to “push trying to move your foot toward the ceiling” with maximal effort and offered encouraging words during the test (³⁰).

For MVIS evaluation of the lateral trunk muscles, we used the side bridge test. The participants were positioned as described by McGill et al. (²⁰) (Figure 1C). Participants were positioned in lateral decubitus with the nondominant side down. The dynamometer was positioned on the iliac crest, and a strap was positioned over the dynamometer and around the examination table. The researcher asked the participant to “make every effort to lift their hip from the examination table” and used encouraging words during the test (²³).

Before the test, 3 submaximal and 1 maximal trials were made to familiarize the subject with the test (²⁴). In all evaluations, we recorded the peak value (in kilograms) during 5 seconds. There was a 2-minute rest between each trial. For statistical analysis, we considered the average of 3 repetitions that show variability less than 10% on average. When a difference greater than 10% occurred between trials, a fourth trial was performed (⁷). The results of the all trials (kg) were transformed into Newtons (strength [N] = strength [kg] × 9.81) and normalized by body mass (normalized strength [N·kg⁻¹] = strength [N] ÷ body mass [kg]) (¹⁷).

A priori study was conducted to determine the test-retest reliability of the isometric strength measurements. For this, 10 subjects were evaluated on 2 separate days with 2–5 days between them. The ICC3,1 and the standard error of measurements were, respectively, 0.93 and 0.22 N·kg⁻¹ for hip abductors, 0.98 and 0.45 N·kg⁻¹ for lateral trunk muscles, and 0.96 and 0.36 N·kg⁻¹ for hip extensors.

Data Reduction

Kinematic data were processed using 3D Motion Monitor Software (Innovative Sports Training). The Euler angles were calculated using the joint coordinate system definitions that were recommended by the International Society of Biomechanics (³⁶) relative to the static standing trial. The trunk flexion and ipsilateral trunk lean were evaluated as the angle between the segment and the global coordinate system (laboratory coordinate system). Lower-limb kinematics was calculated as the motion of the distal segment relative to the proximal reference. The ankle and knee joint centers were defined as the midpoint between the medial and lateral malleoli and the medial and lateral epicondyles, respectively. The hip center was estimated using Bell's method (⁴). The kinematic data were filtered by a second-order zero-lag Butterworth 12-Hz low-pass filter. Analysis for determining the kinematic variables was performed by a custom program in Matlab (MathWorks, Natick, MA, USA). The kinematic variables of interest included the peak angles and the movement excursion during the landing phase. The movement excursion was defined as the angle variation between the angle at initial contact and the peak angle. The kinematic angles of interest included the following: hip flexion, hip internal rotation, hip abduction, knee flexion, knee abduction, trunk flexion, and ipsilateral trunk lean. The landing phase was from the initial contact to toe-off. The initial contact was defined as when the vertical velocity of the marker that was fixed on the second toe was zero (¹⁹) and the toe-off was determined by the knee extension peak after support phase (¹²). By convention, positive kinematic values represented flexion, abduction, internal rotation, and ipsilateral trunk lean angles.

Statistical Analyses

All statistical analyses were performed using the SPSS software, version 19 (SPSS, Inc., Chicago, IL, USA). Initially, the statistical distribution and homoscedasticity of the data were checked with the Shapiro-Wilk test and Levene's test, respectively. Pearson's correlation coefficients were calculated to evaluate the association between the kinematic data and isometric strength data. The alpha level was preset at 0.05.

Results

The demographic data are shown in Table 1, and the isometric strength and kinematic data are shown in Table 2.

Table 1.: Demographic characteristics of the subjects.

Table 2.: Kinematics and strength data of the subjects.

The results of the correlation analysis among the isometric strength data and the peak angles and among the isometric strength data and movement excursion are reported in Table 3 and Table 4, respectively. No significant correlations were found among any data during the landing phase.

Table 3.: Pearson correlation coefficients (r) and p value (p) among hip extensor, hip abductor and lateral trunk strength, and peak values of kinematic.

Table 4.: Pearson correlation coefficients (r) and p value (p) among hip extensor, hip abductor and lateral trunk strength, and excursion values of kinematic.

Discussion

The aim of this study was to evaluate the correlation between the isometric strength of the hip extensors, hip abductors and the lateral trunk muscles, and trunk, hip, and knee kinematics (movement excursion and peak values) during the SLDVJ. The hypothesis that hip muscles isometric strength is correlated to hip, knee, and trunk kinematics was not confirmed.

Although our study did not show a significant correlation between the isometric strength of the hip muscles and the kinematic variables of the knee, hip, and trunk, some studies have confirmed this correlation. Stickler et al. (³²) found that isometric strength of hip extensors, abductors, and external rotators muscles and lateral trunk muscles was inversely correlated with FPPA during single-leg squats. Recently, Almeida et al. (²) reported that isometric strength of hip abductor muscles was inversely correlated with FPPA peak during the step-down and Teng and Powers (³⁴), who evaluated the association between isometric hip extensor strength and trunk position in the sagittal plane during running, found that the greatest isometric hip extensor strength correlated with increased trunk flexion. It should be emphasized that the differences between task methodologies may have influenced the different results. In addition, the study performed by Stickler et al. (³²) and the study by Almeida et al. (²) used a 2D kinematic analysis, which may also have caused divergences in the results.

Strength training has been observed as a possible pathway in controlling potentially harmful movement patterns (¹¹) based on possible association between the muscles with kinematic alterations cited in the literature (^2,25,32). Although these results are controversial, it is important to consider that movement control is multifactorial and may be influenced by other components such as muscle elasticity and neural and anatomical components, besides strength, and they may also influence these injurious movements (¹).

Recently, Scattone-Silva et al. (²⁹) evaluated the effects of hip extensor strengthening and landing strategy modification training (greater trunk flexion) in a subject with patellar tendinopathy. After an 8-week intervention and a 6-month follow-up, the athlete was completely asymptomatic during sports. This positive clinical outcome was accompanied by increased peak trunk flexion, increased hip extensor moment, decreased knee extensor moment, and a 26% decrease in patellar tendon force during jump landing after 8 weeks of training. In a similar study, Baldon et al. (³) evaluated the effects of a strengthening program and functional stabilization training and instruction concerning correct dynamic alignment of the lower limb in subjects with PFP. After 2 months' intervention, they concluded that the training was related to better trunk and lower-limb kinematics for this population. Both studies used movement instruction combined with the strengthening program.

Considering the findings from Scattone-Silva et al. (²⁹) and Baldon et al. (³) and the lack of correlation found in our study, it is reasonable to consider that movement instruction may play an important role in promoting an effective change in the movement pattern. Palmer et al. (²⁵) did not find a statistically significant correlation between the strengthening program or control motor program with a better lower-limb dynamic alignment in 2 different tasks (single-leg squat and single-leg landing), but they showed that the functional motor control program had better clinical outcomes (reducing 10° in dynamic knee valgus) compared with the strengthening group (reducing 5° in dynamic knee valgus). Similarly, Mizner et al. (²¹) concluded that after brief instructions and feedback during landing, female high school athletes had better alignment during landing (including less dynamic knee valgus) and the muscular strength was not predictive of this better result.

Although we did not find a correlation between the strength of the hip extensor, hip abductor and lateral trunk muscles, and the trunk, hip, and knee kinematics during SLDVJ, we assessed only the isometric strength. Considering that during landing, the muscles act eccentrically and some authors have shown different correlations when evaluating the eccentric and concentric strength (^6,8), in other populations and tasks, our results cannot be generalized. However, the isometric test was used because it is an easy and inexpensive method and can be reproduced easily in clinic practice. In addition, isometric evaluation was used because it is a reliable analysis for hip (³⁰) and trunk muscles (²³).

The authors acknowledge some limitations in this study. Only healthy women were assessed and our results cannot be used for other populations. Along the same lines, we did not evaluate the kinetics and its association with isometric strength. Another limitation, as cited, is that only the isometric strength of the trunk and hip was evaluated. Further research is required to evaluate whether an association exists among hip and trunk eccentric strength with three-dimensional trunk and lower-limb kinematics during an SLDVJ task. Despite this instruction, the eccentric strength evaluation is normally performed using an isokinetic dynamometer. Therefore, because this equipment is expensive, this factor must be taken into account for more clinical results.

Practical Applications

In healthy recreational female athletes, trunk, and hip isometric strength do not correlate with the knee, hip, and trunk kinematics during an SLDVJ. In this way, our study indicates that prevention strategies cannot be focused only on strengthening programs to influence movement patterns.