Athletic Training and Sports Health Care

Original Research 

The Influence of Step Direction and Step Height on Lower Extremity Joint Kinematics During Step-Down Tasks

Jennifer Thorpe, MS, ATC, CSCS; Phil Oblak, ATC; Jennifer Earl-Boehm, PhD, ATC

Abstract

Purpose:

To investigate differences in lower extremity joint angles between a forward (FSD) and lateral (LSD) step-down task at different heights (4 and 6 inches).

Methods:

Eighteen healthy adults performed four variations of the step-down task while hip, knee, and ankle kinematics were measured. A two-way repeated measures analysis of variance was performed.

Results:

There was a significant interaction and main effect for step direction and height for knee external rotation and ankle dorsiflexion angle (P < .05). Participants exhibited greater hip adduction, knee flexion, knee adduction, and ankle dorsiflexion during performance of the FSD than the LSD at the 4- and 6-inch height. For each step direction, participants demonstrated greater hip flexion, hip adduction, knee flexion, knee adduction, and ankle dorsiflexion during performance of the task at the 6-inch height.

Conclusions:

The FSD requires greater movement of the lower extremity than the LSD and increasing step height increases the biomechanical demands of the lower extremity.

[Athletic Training & Sports Health Care. 20XX;XX(X):XX–XX.]

Abstract

Purpose:

To investigate differences in lower extremity joint angles between a forward (FSD) and lateral (LSD) step-down task at different heights (4 and 6 inches).

Methods:

Eighteen healthy adults performed four variations of the step-down task while hip, knee, and ankle kinematics were measured. A two-way repeated measures analysis of variance was performed.

Results:

There was a significant interaction and main effect for step direction and height for knee external rotation and ankle dorsiflexion angle (P < .05). Participants exhibited greater hip adduction, knee flexion, knee adduction, and ankle dorsiflexion during performance of the FSD than the LSD at the 4- and 6-inch height. For each step direction, participants demonstrated greater hip flexion, hip adduction, knee flexion, knee adduction, and ankle dorsiflexion during performance of the task at the 6-inch height.

Conclusions:

The FSD requires greater movement of the lower extremity than the LSD and increasing step height increases the biomechanical demands of the lower extremity.

[Athletic Training & Sports Health Care. 20XX;XX(X):XX–XX.]

A common exercise approach used for lower extremity injury is to replicate weight-bearing activities of daily living to improve muscle strength and quality of movement. One such activity, the single-leg step-down task, is used for rehabilitation of many lower extremity injuries, including anterior cruciate ligament injuries and patellofemoral pain.1 The single-leg step-down task and squat have been used in research studies to assess quality of lower extremity motion and are promoted to screen for lower extremity injury risk.2,3 Clinicians use several variations of this task, including changing the step direction (forward or lateral direction) or the step height. It is assumed that these variations are biomechanically different and thus challenge the lower extremity in different ways, although little empirical evidence supports this assumption.

Few studies have examined the biomechanical differences between forward (FSD) and lateral (LSD) step-down tasks (Figure 1). Chinkulprasert et al4 identified that patellofemoral joint stress was greater during the FSD task compared to the LSD task performed from a step height adjusted based on height to achieve a knee flexion angle of 45°, but did not report any three-dimensional kinematic differences between the two exercises.4 Lopes Ferreira et al5 compared three-dimensional kinematics of the trunk, pelvis, and hip and two-dimensional motion of the knee, ankle, and foot during performance of the FSD and LSD tasks in women with patellofemoral pain and healthy controls. The joint angles for each task were analyzed with the Movement Deviation Profile, which was used to quantify motion across tasks. The LSD task was better than the FSD task in differentiating between groups, but the authors did not specify the height used for the step-down tasks.5

Performance of the forward and lateral step-down tasks at the 6-inch height.

Figure 1.

Performance of the forward and lateral step-down tasks at the 6-inch height.

The LSD task is reported more frequently in the literature than the FSD task for the assessment of movement quality. Piva et al6 used the LSD task from a 20-cm height (7.87 inches) to assess two-dimensional visual quality of movement in participants with patellofemoral pain and identified that only 22% of the sample exhibited good quality motion. Another study examined the relationship between kinematics of the lower extremity and movement quality during performance of the LSD task from a 15-cm height (5.91 inches) in healthy controls.7 Participants with moderate quality of movement during the LSD task displayed greater peak knee external rotation than those with a good quality of movement.7 These findings suggest that the LSD task may be able to differentiate movement quality and kinematics in individuals with patellofemoral pain and in healthy controls. However, it is unclear how step height may influence these findings.

One study examined differences in FSD kinematics from two different heights: 16 cm (6.29 inches) and 24 cm (9.45 inches).8 When comparing kinematics at the time of peak knee flexion, the FSD task at 24 cm produced significantly greater knee flexion, hip flexion, hip adduction, and hip internal rotation than when performed at the 16-cm height.8 However, when the tasks were compared at 60° of knee flexion, there were no significant differences in hip or knee kinematics across tasks.8 These findings support that altering step height can influence kinematics at the point of peak knee flexion, but not at 60° of knee flexion. When using the step-down task for assessing movement quality and comparing between the FSD and LSD tasks, it may be desirable to focus on the movement at 60° of knee flexion for standardization of the motion.

Although there is some evidence supporting biomechanical differences between the LSD and FSD tasks, further research is warranted to determine how altering the step direction and the step height may influence lower extremity kinematics. Therefore, the purpose of this study was to investigate the differences in three-dimensional lower extremity kinematics between the FSD and LSD tasks and between different step heights in healthy individuals. Based on previous literature and clinical experience, the authors hypothesized that the FSD task would lead to greater hip, knee, and ankle angles than the LSD task, and that a higher step height would lead to greater hip, knee, and ankle angles than a lower height.

Methods

Participants

Eighteen healthy, physically active participants between 18 and 35 years old (10 women and 8 men, mean age: 22.94 ± 2.90 years, mean height: 175.12 ± 9.42 cm, mean body mass: 75.36 ± 16.88 kg) participated in this study. Inclusion criteria were healthy, moderately physically active adults between 18 and 35 years old. Participants were excluded if they reported any current lower extremity injuries or surgery to the lower extremity. Prior to participation, each participant provided written informed consent as approved by the university's institutional review board, and then completed a health history questionnaire and International Physical Activity Questionnaire Short Form (IPAQ) to ensure that the minimum physical activity level for all participants was moderate.

Instrumentation and Equipment

During the performance of the step-down tasks, participants wore laboratory-provided footwear to maintain consistency between participants and shorts and a short-sleeved shirt to allow for proper anatomical placement of the reflective markers. Three-dimensional lower extremity kinematic data were recorded using a 10-camera motion capture system (Motion Analysis Eagle; Motion Analysis Corporation). Thirty-two anatomical reflective markers (12.7-mm spheres) were affixed over the trunk and lower extremity landmarks bilaterally to establish joint centers and anatomical axes. A plastic cluster of four markers was attached to the posterior trunk and bilaterally on the lateral aspect of the thighs and shins, and on the back of the heels (Figure 2).9 Prior to kinematic data collection, a standing calibration trial was conducted to define segment coordinates. Joint angles were calculated using a joint coordinate system approach.10

Placement of reflective markers for three-dimensional joint motion analysis.

Figure 2.

Placement of reflective markers for three-dimensional joint motion analysis.

Procedures

Prior to performance of the step-down task, participants were instructed to warm up for 5 minutes on a treadmill at a brisk walking pace, which was set to each participant's desired speed. After the participant completed the warm up, trials of both step-down tasks (FSD and LSD) were performed from a box height of 10.2 cm (4 inches) and repeated from a box height of 15.2 cm (6 inches), which were selected to align with the box heights typically used in clinical practice. The exercise protocol used for these tasks was similar to the protocol used in a previous study.4 For each step-down exercise, the dominant foot remained on the step throughout each trial, whereas the contralateral foot moved between the floor and the step.4 Prior to each trial, the non-dominant foot rested on the floor and the dominant foot remained on the step. After being given a cue that the trial was about to begin, the participant elevated the non-dominant foot off the floor by extending the dominant leg into full knee extension to assume the starting position. At this point, participants were full weight-bearing on the dominant limb and were allowed as much time as needed to regain their balance following the ascent. After reestablishing their balance in the upright position, participants were instructed to cross their arms across their chest to minimize any compensatory motion to maintain balance during each trial.

Participants began the trial by slowly lowering their non-dominant foot to the floor with the heel of their foot. When the heel touched the floor, participants returned to the starting position. A metronome set at 60 beats per minute maintained the pace of the descent and ascent (1 second down, 1 second up). After several practice trials, participants performed three sets of five repetitions of the FSD and LSD tasks from the 4- and 6-inch box heights (Figure 1). Step direction and step height were randomized across participants. A 1-minute rest period was given to the participants between each set.

Data and Statistical Analysis

Joint angle data collected from the step-down task trials were filtered using a 4th order Butterworth filter with a cutoff frequency of 12 Hz. The segment coordinate systems for the laboratory set-up in this study followed the right-hand convention. The x-axis was aligned in the medial-lateral direction, the y-axis was aligned in the anterior-posterior direction, and the z-axis was aligned in the vertical direction.10 The middle three repetitions of each set were analyzed to account for any compensatory movements that may have been used to maintain balance for the first and last repetitions. Sagittal, frontal, and transverse hip and knee plane joint angles and sagittal plane ankle joint angles at the time of peak knee flexion were calculated using Visual3D biomechanical modeling software (C-Motion, Inc). The independent variables were step direction (FSD and LSD) and step height (4 and 6 inches). The dependent variables were joint angles at peak knee flexion for hip flexion, hip adduction, hip internal rotation, knee flexion, knee adduction, knee external rotation, and ankle dorsiflexion. A two-way repeated measures analysis of variance was performed using SPSS software (IBM Corporation) to identify differences in the kinematic dependent variables between step-down task direction and height. The level of significance was set at a P value of less than .05. Effect sizes (Cohen's d) were also calculated for each step-down variation.

Results

Mean joint angles and standard deviations for all three planes of motion at the hip and knee and the sagittal plane for the ankle are included in Figure 3 for both step directions and heights.

(A) Hip flexion angles for each variation of the step-down task. A significant main effect was found for step height (P ≤ .05). (B) Hip adduction angles for each variation of the step-down task. A significant main effect was found for both step direction and step height (P ≤ .05). (C) Hip internal rotation angle for each variation of the step-down task. (D) Knee flexion angles for each variation of the step-down task. A significant main effect was found for both step direction and step height (P ≤ .05). (E) Knee adduction angles for each variation of the step-down task. A significant main effect was found for both step direction and step height (P ≤ .05). (F) Knee external rotation angles for each variation of the step-down task. A significant main effect was found for both step direction and step height (P ≤ .05). (G). Ankle dorsiflexion angles for each variation of the step-down task. A significant main effect was found for both step direction and step height (P ≤ .05). Note: For ease of graphical representation, absolute values of joint angle measures were used in D and F. FSD = forward step-down; LSD = lateral step-down

Figure 3.

(A) Hip flexion angles for each variation of the step-down task. A significant main effect was found for step height (P ≤ .05). (B) Hip adduction angles for each variation of the step-down task. A significant main effect was found for both step direction and step height (P ≤ .05). (C) Hip internal rotation angle for each variation of the step-down task. (D) Knee flexion angles for each variation of the step-down task. A significant main effect was found for both step direction and step height (P ≤ .05). (E) Knee adduction angles for each variation of the step-down task. A significant main effect was found for both step direction and step height (P ≤ .05). (F) Knee external rotation angles for each variation of the step-down task. A significant main effect was found for both step direction and step height (P ≤ .05). (G). Ankle dorsiflexion angles for each variation of the step-down task. A significant main effect was found for both step direction and step height (P ≤ .05). Note: For ease of graphical representation, absolute values of joint angle measures were used in D and F. FSD = forward step-down; LSD = lateral step-down

There were no significant interactions between step direction and height for hip flexion angle (F(1,17) = 1.794, P = .198, ŋp 2 = .095), hip adduction angle (F(1,17) = 1.984, P = .177, ŋp 2 = .105), hip internal rotation angle (F(1,17) = 2.984, P = .102, ŋp 2 = .149), knee flexion angle (F(1,17) = .572, P = .460, ŋp 2 = .033), and knee adduction angle (F(1,17) = .880, P = .002, ŋp 2 = .445). There was a significant interaction between step direction and height for knee external rotation (F(1,17) = 13.637, P = .002, ŋp 2 = .445) and ankle dorsiflexion (F(1,17) = 6.280, P = .023, ŋp 2 = .270). Due to the lack of significant interactions, main effects for direction and height were examined.

Direction (FSD versus LSD)

There was a significant main effect of step direction on participant's hip adduction angle (F(1,17) = 9.066, P = .008, ŋp 2 = .348), knee flexion angle (F(1,17) = 63.650, P < .001, ŋp 2 = .789), knee adduction angle (F(1,17) = 38.365, P <.001), knee external rotation angle (F(1,17) = 14.873, P < .001, ŋp 2 = .467), and ankle dorsiflexion (F(1,17) = 48.380, P < .001, ŋp 2 = .740). Participants exhibited greater hip adduction, knee flexion, knee adduction, and ankle dorsiflexion during performance of the FSD task than the LSD task at 4 and 6 inches. There was no significant main effect of step direction on participants' peak hip flexion angle (F(1,17) = .450, P = .511, ŋp 2 = .026) or peak hip internal rotation angle (F(1,17) = .605, P = .447, ŋp 2 = .034.

Height (4 vs 6 Inches)

There was a significant main effect of step height on participant's peak hip flexion angle (F(1,17) = 289.036, P < .001, ŋp 2 = .944), peak hip adduction angle (F(1,17) = 46.616, P < .001, ŋp 2 = .733), peak knee flexion (F(1,17) = 324.544, P < .001, ŋp 2 = .950), peak knee adduction (F(1,17) = 21.960, P < .001, ŋp 2 = .564), peak knee external rotation (F(1,17) = 46.152, P < 0.001, ŋp 2 = .731), and peak ankle dorsiflexion (F(1,17) = 75.081, P < .001, ŋp 2 = .815).

For each step direction, participants demonstrated greater hip flexion, hip adduction, knee flexion, knee adduction, and ankle dorsiflexion during performance of the task at the 6-inch height.

There was no significant main effect of height on participants' peak hip internal rotation angle (F(1,17) = 3.929, P = .379, ŋp 2 = .046.

Effect Sizes

Effect sizes were calculated to determine the size of the difference in joint angles for each step-down variation and are presented graphically in Figure 4. Although these effect sizes are large, it should be noted that they cross 0, meaning they are not statistically significant. For the 4-inch step height, there was a large effect size calculated between the LSD and FSD tasks for both knee flexion (d = −1.36 [−0.60, −2.05]) and knee adduction (d = −0.85 [−0.15, −1.51]). A large effect size was also calculated for knee flexion (d = −1.18 [−0.45, −1.86]) for the 6-inch step height between the LSD and FSD tasks.

Effect sizes for lower extremity kinematics of the (A) forward step-down (FSD) (6- vs 4-inch height), (B) lateral step-down (LSD) (6- vs 4-inch height), (C) 4-inch step-down, and (D) 6-inch step-down.

Figure 4.

Effect sizes for lower extremity kinematics of the (A) forward step-down (FSD) (6- vs 4-inch height), (B) lateral step-down (LSD) (6- vs 4-inch height), (C) 4-inch step-down, and (D) 6-inch step-down.

For the FSD task, there was a large effect size calculated between the 6- and 4-inch height for hip flexion (d = 0.95 [1.61, 0.24]) and knee flexion (d = 1.64 [2.35, 0.85]). A large effect size was also calculated for hip flexion (d = 1.17 [1.85, 0.44]) and knee flexion (d = 2.09 [2.85, 1.24]) for the LSD task.

Discussion

Direction (FSD vs LSD)

The results of this study identified that the direction and height of the step-down task influence lower extremity joint kinematics. Our findings suggest that the FSD task resulted in greater hip adduction, knee flexion, knee adduction, and ankle dorsiflexion than the LSD task. These findings suggest that the FSD task is a more demanding biomechanical task than the LSD task, and it requires greater control of the limb, especially at the knee joint. When participants reach forward during the FSD task, they must maintain control to step forward and clear the edge of the step. The increase in hip adduction during the FSD task may be the result of lowering the contralateral pelvis as a compensatory action to maintain balance during the task. The average hip adduction and knee flexion angles during the FSD task reported in this study are slightly lower than those reported in previous studies, but these angles may be dependent on step height.8,11 The heights used in this study were lower than those used in the previously cited studies, but the heights reflected those that are commonly used in clinical practice.

Previous research has identified that the FSD task exercise produces greater patellofemoral joint stress than the LSD tasks, which along with the findings of this study support the idea that the FSD task is more demanding on the knee, particularly the patellofemoral joint, than the LSD task.4 Increased hip adduction during a weight-bearing task is associated with dynamic malalignment (hip adduction and hip internal rotation), which is theorized to contribute to increased patellofemoral stress.12,13 This study identified greater hip adduction angles with the FSD task than the LSD task, which is consistent with the findings of Chinkulprasert et al.4

The participants exhibited significantly greater transverse plane motion at the knee during performance of the LSD task compared to the FSD task at the 6-in height. This may have been part of a compensatory motion to stabilize the stance limb against dynamic malalignment as the opposite foot reached laterally to the ground. These findings are consistent with previous research that has identified increased transverse plane motion at the knee in individuals with moderate movement quality during the LSD task.7

The participants in this study demonstrated greater ankle dorsiflexion for the FSD task than the LSD task. Decreased ankle dorsiflexion has been associated with dynamic malalignment during a single-leg squat in asymptomatic individuals and with lower quality of movement during an LSD task in individuals with patellofemoral pain and chronic ankle instability.14–16 It is plausible that the FSD task can also be used to assess movement quality in the clinical setting, but further research is warranted to validate this approach. However, although statistically significant differences were identified between the two directions, these findings are not conclusive to suggest that these two directions are clinically different.

Height (4 vs 6 Inches)

Our results identified that performance of the step-down task from the 6-inch height resulted in greater hip flexion, hip adduction, knee flexion, and knee adduction than the 4-inch height, regardless of the direction of the movement (FSD or LSD). These findings are consistent with Lewis et al,8 who also reported increased sagittal and frontal plane motion at the hip and knee when the step-down height was increased from 16 to 24 cm. When examining our effect sizes for this study, increasing the step height influenced sagittal plane motion at the hip and knee, particularly during the LSD task. The increase in sagittal plane motion for the hip and knee is explained by the increase in distance of the motion required at the hip and knee joint to touch the opposite foot to the ground. These findings suggest that step height is an important consideration when including a step-down task in a rehabilitation intervention or movement quality assessment. Increasing the height of the step is another progression to increase the biomechanical demands of the step-down task, challenging an individual's ability to maintain adequate lower extremity control during the movement.

The increase in step height also resulted in an increase in frontal plane motion at the hip and knee, which could be the result of contralateral pelvic drop. Lewis et al8 reported that pelvic drop was consistently observed during performance of the step-down tasks. As mentioned earlier, this pelvic drop could contribute to increased sagittal plane motion of the hip and knee, leading to dynamic malalignment.12,13 Therefore, it is important for clinicians to monitor motion at the hip and knee when increasing the height of a step-down task for a patient.

Transverse motion at the knee was greater for the LSD task than the FSD task at both step heights. Although statistically significant, the large standard deviation and small differences (< 3°) are not likely to be clinically meaningful.

Sagittal plane motion at the ankle was greater at the 6-inch height than the 4-inch height. As mentioned previously, decreased ankle dorsiflexion has been associated with lower movement quality and dynamic malalignment in individuals with chronic lower extremity conditions.15,16 It is plausible that, as step height increases, a lack of ankle dorsiflexion could result in poorer control of the knee and hip during a step-down task.

Limitations

Although these findings identified some significant differences in lower extremity kinematics between direction and height of the step-down task, there are some potential limitations to this study. Healthy participants with no current lower extremity injury and no previous history of surgery to the lower extremity were recruited for this study. We based our sample size on similar studies, but we acknowledge that we had a relatively small sample size for this study.4,8 The standard deviations for our joint angle measures, particularly for transverse motion, were large. This could be attributed to multiple factors, including variability in movement patterns between individuals, and potential measurement error with our approach. Clinicians should interpret these findings with caution because they may not accurately reflect the motion in a broader population. The joint angles for these motions provide information on only one aspect of task performance. It is possible that there may be significant differences in other measures, such as muscle activation, which may also provide important applications to clinical practice. Another measure that could be examined regarding the step-down exercise is the correlation of hip strength with kinematics in each direction. Hip strength may play a significant role in the ability to control movement of the femur during a dynamic task such as a step-down. Further research is warranted to examine how variations to step height and direction may influence other aspects of muscle function, such as muscle activation.

Implications for Clinical Practice

These findings provide clinicians with guidance on how to adapt the step-down exercise in clinical practice. Our results indicate that increasing step height had a large effect on hip flexion and knee flexion angles. Independent of step height, changing the movement direction from a FSD task to an LSD task led to decreased knee flexion. When used in a rehabilitation intervention, it may be desirable to begin with the LSD task at a lower height (eg, 4 inches), and progress to the FSD task and a higher step height. This approach would allow the patient to demonstrate adequate lower extremity control before moving to a more challenging position.

These findings may differ in a population with a lower extremity injury or chronic conditions such as patellofemoral pain.2 The LSD task has been identified as a more appropriate screening tool than the FSD task to differentiate individuals with patellofemoral pain from healthy controls.5 Differences in kinematics have been identified in individuals with a meniscus tear compared to healthy controls during performance of the FSD task.17 Further research is warranted to examine potential outcomes associated with the FSD and LSD tasks at varying heights in a rehabilitation program. It is possible that variations of the step-down task could influence treatment outcomes. For example, a previous study identified that recruitment of the gluteus maximus during a single-leg squat correlated with frontal plane knee motion, suggesting that activation of the gluteus maximus during this task may modulate frontal plane motion of the knee.18 Mercer et al19 identified increased gluteus medius activation during a lateral step-up task as compared to a forward step-up task in older adults, supporting directional differences in lower extremity muscle activity during a stepping task. Step-down variations could alter the biomechanical demands in a manner that leads to increased muscle activity of the muscles primarily responsible for stabilization and movement.

Conclusion

The FSD task is more demanding than the LSD task, and it requires greater motion, particularly at the knee joint. In rehabilitation programs, clinicians may want to begin with the LSD task and progress to the FSD task as strength and balance improve. Our findings also identified that the step-down task from the 6-inch height resulted in greater sagittal plane motion at the hip, knee, and ankle and frontal plane motion at the hip and knee than the 4-inch height, regardless of the direction of the movement (FSD or LSD). Transverse motion of the knee was greater during performance of the FSD task for both the 4- and 6-inch height than the LSD task. Because increasing the height of the step for the step-down task also increases the biomechanical demands, the step-down task may be another way for clinicians to progress a patient through a rehabilitation program.

References

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Authors

From the University of Wisconsin–Milwaukee, Milwaukee, Wisconsin.

The authors have no financial or proprietary interest in the materials presented herein.

The authors thank Dr. David Bazett-Jones for his mentorship.

Correspondence: Jennifer Thorpe, MS, ATC, CSCS, 12800 N. Lake Shore Dr., Mequon, WI 53097. Email: jln@uwm.edu

Received: December 31, 2019
Accepted: August 13, 2020
Posted Online: December 15, 2020

10.3928/19425864-20201027-01

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