Muscle Activation During Single-Legged Squat Is Affected by Position of the Nonstance Limb.

CONTEXT: The single-legged squat (SLS) is appropriate for targeting activation, strengthening, and neuromuscular retraining of the gluteus maximus, gluteus medius, and quadriceps. However, the effects of different nonstance-limb positions on muscle activity have not been fully evaluated. OBJECTIVE: To compare the muscle activity of selected stance-limb hip muscles during the SLS using 3 nonstance-limb positions: in front (SLS-Front), in the middle (SLS-Middle), and in back (SLS-Back). DESIGN: Controlled laboratory study. SETTING: Biomechanics laboratory. PATIENTS OR OTHER PARTICIPANTS: A total of 17 healthy adults (8 men, 9 women; age = 22.6 ± 3.6 years, height = 173.3 ± 10.7 cm, mass = 71.2 ± 11.0 kg) participated. MAIN OUTCOME MEASURE(S): Surface electromyographic data of the gluteus maximus, gluteus medius, lateral hamstrings, medial hamstrings, rectus femoris, and tensor fascia lata (TFL) as well as kinetic data of the hip and knee were collected while participants performed the 3 SLS tasks. Mean muscle-activation levels during the descent and ascent phases for the selected hip muscles and hip and knee kinetics in all 3 planes were compared for the 3 tasks. Each variable of interest was analyzed using a separate linear regression model with a generalized estimating equations correction. RESULTS: Muscle-activation levels of the gluteus maximus, gluteus medius, medial hamstrings, rectus femoris, and TFL for the stance limb during descent (P ≤ .04) and the medial hamstrings and TFL during ascent (P ≤ .002) were different among the SLS tasks. The greatest number of differences occurred between SLS-Front and SLS-Back. During descent, gluteal muscle activity was greater in SLS-Front (P ≤ .03) and SLS-Middle (P = .03) than in SLS-Back. For both phases, TFL activity was greater during SLS-Front than during both SLS-Middle and SLS-Back (P ≤ .006). Kinetic differences at the hip and knee between SLS tasks were also observed (P values ≤ .02). CONCLUSIONS: The 3 SLS tasks had different muscle-activation and kinetic profiles. Clinicians and researchers can vary nonstance-limb position during the SLS to manipulate muscle-activation levels and tailor the exercise to assist with goals at different stages of rehabilitation.

Individuals With Pre-arthritic Hip Pain Walk With Hip Motion Alterations Common in Individuals With Hip OA.

Background: Individuals with hip osteoarthritis (OA) commonly walk with less hip extension compared to individuals without hip OA. This alteration is often attributed to walking speed, structural limitation, and/or hip pain. It is unclear if individuals who are at increased risk for future OA (i.e., individuals with pre-arthritic hip disease [PAHD]) also walk with decreased hip extension. Objectives: (1) Determine if individuals with PAHD exhibit less hip extension compared to individuals without hip pain during walking, and (2) investigate potential reasons for these motion alterations. Methods: Adolescent and adult individuals with PAHD and healthy controls without hip pain were recruited for the study. Kinematic data were collected while walking on a treadmill at three walking speeds: preferred, fast (25% faster than preferred), and prescribed (1.25 m/s). Peak hip extension, peak hip flexion, and hip excursion were calculated for each speed. Linear regression analyses were used to examine the effects of group, sex, side, and their interactions. Results: Individuals with PAHD had 2.9° less peak hip extension compared to individuals in the Control group (p = 0.014) when walking at their preferred speed. At the prescribed speed, the PAHD group walked with 2.7° less hip extension than the Control group (p = 0.022). Given the persistence of the finding despite walking at the same speed, differences in preferred speed are unlikely the reason for the reduced hip extension. At the fast speed, both groups increased their hip extension, hip flexion, and hip excursion by similar amounts. Hip extension was less in the PAHD group compared to the Control group (p = 0.008) with no significant group-by-task interaction (p = 0.206). Within the PAHD group, hip angles and excursions were similar between individuals reporting pain and individuals reporting no pain. Conclusions: The results of this study indicate that kinematic alterations common in individuals with hip OA exist early in the continuum of hip disease and are present in individuals with PAHD. The reduced hip extension during walking is not explained by speed, structural limitation, or current pain.

Hip and Trunk Muscle Activity and Mechanics During Walking With and Without Unilateral Weight.

Pelvic drop is caused by decreased hip abductor muscle activity and is associated with lower-extremity injury. Hip abductor strengthening exercises are well established; however, no standard method exists to increase hip abductor activity during functional activities. The purpose of this research was to study the effects of walking with a unilateral weight. A total of 26 healthy adults walked on an instrumented treadmill with and without handheld weight (15%-20% body weight). Muscle activity, kinematic, and kinetic data were collected using surface electromyography, motion capture, and force plates, respectively. Average hip and trunk muscle activity, hip, pelvic, and trunk angles, and peak internal hip moments during stance were compared for each side (contralateral/ipsilateral to the weight) between conditions (unweighted/weighted) using a generalized linear model with generalized estimating equation correction. Interactions between condition and side were observed for muscle activity, frontal plane pelvic and trunk angles, and frontal plane hip moments (P ≤ .003). Compared with the unweighted condition, the weighted condition had higher hip abductor activity contralateral to the weight (P < .001), while no change was found ipsilateral to the weight (P ≥ .790). Similar changes were found for kinematic and kinetic variables. Walking with a unilateral weight may be a therapeutic option to increase functional hip abductor activity.

Effects of Cognitive Over Postural Demands on Upright Standing Among Young Adults.

A growing body of research has shown that static stance control (e.g., body sway) is influenced by cognitive demands (CD), an effect that may be related to competition for limited central resources. Measures of stance control have also been impacted by postural demands (PD) (e.g., stable vs. unstable stances). However, less is known of any possible interactions between PD and CD on static stance control in populations with intact balance control and ample cognitive resources, like young healthy adults. In this study, among the same participants, we factorially compared the impact of PD with and without CD on static stance control. Thirty-four healthy young adults wore inertial measurement units (IMU) while completing static stance tasks for 30 seconds in three different PD positions: feet apart, feet together, and tandem feet. After completing these tasks alone, participants performed these tasks with CD by concurrently completing verbal serial seven subtractions from a randomly selected three-digit number. For two dependent measures, path length and jerk, there were main effects of CD and PD but no interaction effect between these factors. For all other stance control parameters, there was only a PD main effect. Thus, adding a cognitive demand to postural demands, while standing upright, may have an independent impact on stance control, but CD does not seem to interact with PD. These results suggest that young healthy adults may be less sensitive to simple PD and CD due to their greater inherent balance control and available cognitive resources. Future work might explore more complex PD and CD combinations to determine the boundaries under which young adults' resources are taxed.

Females and males use different hip and knee mechanics in response to symmetric military-relevant loads.

The purpose of this study was to determine if females and males use different hip and knee mechanics when walking with standardized military-relevant symmetric loads. Fifteen females and fifteen males walked on a treadmill for 2-min at a constant speed under three symmetric load conditions (unloaded: 1.71 kg, medium: 15 kg, heavy: 26 kg). Kinematic and kinetics of the hip and knee were calculated in the sagittal and frontal planes of the dominant limb. In females, hip abduction moments (normalized to total mass) and sagittal knee excursion decreased with increased load (p ≤ 0.024). In males, hip frontal excursion and adduction angle increased with load (p ≤ 0.003). Females had greater peak hip adduction angle than males in the unloaded and medium load conditions (p ≤ 0.036). Across sex, sagittal hip and knee excursion, peak knee extension angle, and peak hip and knee flexion angles increased with increased load (p ≤ 0.005). When normalized to body mass, all peak joint moments increased with each load (p ≤ 0.016) except peak hip adduction moment. When normalized to total mass, peak hip adduction moment and knee flexion, extension, and adduction moments decreased with each load (p < 0.001). While hip frontal plane kinetic alterations to load were only noted in females, kinematic changes were noted in males at the hip and females at the knee. Differences in strategies may increase the risk of hip and knee injuries in females compared to males. This study noted load and sex effects that were previously undetected, highlighting the importance of using military-relevant standardized loads and investigating frontal plane adaptations.

Kinematic variability and local dynamic stability of gait in individuals with hip pain and a history of developmental dysplasia.

BACKGROUND: Individuals with developmental dysplasia of the hip (DDH) often report hip pain and exhibit gait adaptations. Previous studies in this patient population have focused on average kinematic and acceleration measures during gait, but have not examined variability. RESEARCH QUESTION: Do individuals with hip pain and DDH have altered kinematic variability or local dynamic stability (LDS) compared to individuals without hip pain? METHODS: Twelve individuals with hip pain and DDH and 12 matched controls walked for two minutes on a treadmill at three speeds: preferred, fast (25% faster than preferred), and prescribed (1.25 m/s). Kinematic variability of spatiotemporal measures, joint and segment angles, and LDS of the trunk were calculated for each speed. RESULTS: At the prescribed speed, individuals with hip pain and DDH had more kinematic variability than controls at the hip, pelvis, and trunk as well as greater variability in spatiotemporal measures. LDS was not different between groups. Kinematic variability of the joints decreased and LDS of the trunk increased (i.e., increased gait stability) with increased speed. SIGNIFICANCE: Individuals with hip pain and DDH had greater kinematic variability compared to individuals without hip pain when walking at the same prescribed speed, indicating either an adaptation to pain or reduced neuromuscular control. LDS of the trunk was not different between groups, suggesting that hip pain does not affect overall gait stability. Kinematic variability and LDS were affected by walking speed, but in different ways, emphasizing that these measures quantify different aspects of walking behavior.

Gait Alterations in Femoroacetabular Impingement Syndrome Differ by Sex.

Background Femoroacetabular impingement (FAI) syndrome may affect gait kinematics differently between males and females. Objectives To investigate whether individuals with FAI syndrome have different hip and pelvic motion during gait, at their preferred speed and a prescribed speed, compared to individuals of the same sex without pain. Methods Twenty-one participants (11 males and 10 females) with FAI syndrome and 41 participants (19 males and 22 females) without hip pain were included in this case-control laboratory study. There were no differences between the 2 groups in age, body mass index, and activity score. Kinematic data for all participants were collected while walking at a preferred speed and at 1.25 m/s. For sex and walking speed, linear regression analyses were used to examine the effect of group and the interaction of group by limb. Results At both speeds, males with FAI syndrome walked with more than 6° less peak hip extension (P≤.018), 5° greater anterior pelvic tilt (P≤.020), and 5° less posterior pelvic tilt (P≤.018) compared to males without hip pain. Females with FAI syndrome walked with 2° less hip extension (P≤.012) and at least 3° more hip adduction (P<.001) in the more painful hip than in the less painful hip at both speeds. Conclusion Males and females with FAI syndrome have different gait alterations when compared to a same-sex comparison group. In males, differences were between groups. In females with FAI syndrome, differences were between the more painful and the less painful limb. J Orthop Sports Phys Ther 2018;48(8):649-658. Epub 22 May 2018. doi:10.2519/jospt.2018.7913.

Kinematic Differences During Single-Leg Step-Down Between Individuals With Femoroacetabular Impingement Syndrome and Individuals Without Hip Pain.

Study Design Controlled laboratory study, case-control design. Background Despite recognition that femoroacetabular impingement syndrome (FAIS) is a movement-related disorder, few studies have examined dynamic unilateral tasks in individuals with FAIS. Objectives To determine whether movements of the pelvis and lower extremities in individuals with FAIS differ from those in individuals without hip pain during a single-leg step-down, and to analyze kinematic differences between male and female participants within groups. Methods Individuals with FAIS and individuals without hip pain performed a single-leg step-down while kinematic data were collected. Kinematics were evaluated at 60° of knee flexion. A linear regression analysis assessed the main effects of group, sex, and side, and the interaction of sex by group. Results Twenty individuals with FAIS and 40 individuals without hip pain participated. Individuals with FAIS performed the step-down with greater hip flexion (4.9°; 95% confidence interval [CI]: 0.5°, 9.2°) and anterior pelvic tilt (4.1°; 95% CI: 0.9°, 7.3°) than individuals without hip pain. Across groups, female participants performed the task with more hip flexion (6.1°; 95% CI: 1.7°, 10.4°), hip adduction (4.8°; 95% CI: 2.2°, 7.4°), anterior pelvic tilt (5.8°; 95% CI: 2.6°, 9.0°), pelvic drop (1.4°; 95% CI: 0.3°, 2.5°), and thigh adduction (2.7°; 95% CI: 1.3°, 4.2°) than male participants. Conclusion The results of this study suggest that individuals with FAIS have alterations in pelvic motion during a dynamic unilateral task. The noted altered movement patterns in the FAIS group may contribute to the development of hip pain and may be due to impairments that are modifiable through rehabilitation. J Orthop Sports Phys Ther 2018;48(4):270-279. Epub 6 Mar 2018. doi:10.2519/jospt.2018.7794.

The Human Pelvis: Variation in Structure and Function During Gait.

The shift to habitual bipedalism 4-6 million years ago in the hominin lineage created a morphologically and functionally different human pelvis compared to our closest living relatives, the chimpanzees. Evolutionary changes to the shape of the pelvis were necessary for the transition to habitual bipedalism in humans. These changes in the bony anatomy resulted in an altered role of muscle function, influencing bipedal gait. Additionally, there are normal sex-specific variations in the pelvis as well as abnormal variations in the acetabulum. During gait, the pelvis moves in the three planes to produce smooth and efficient motion. Subtle sex-specific differences in these motions may facilitate economical gait despite differences in pelvic structure. The motions of the pelvis and hip may also be altered in the presence of abnormal acetabular structure, especially with acetabular dysplasia. Anat Rec, 300:633-642, 2017. © 2017 Wiley Periodicals, Inc.

Changes in Gait with Anteriorly Added Mass: A Pregnancy Simulation Study.

During pregnancy, the female body experiences structural changes, such as weight gain. As pregnancy advances, most of the additional mass is concentrated anteriorly on the lower trunk. The purpose of this study is to analyze kinematic and kinetic changes when load is added anteriorly to the trunk, simulating a physical change experienced during pregnancy. Twenty healthy females walked on a treadmill while wearing a custom made pseudo-pregnancy sac (1 kg) under 3 load conditions: sac-only condition, 10-lb condition (4.535 kg added anteriorly), and 20-lb condition (9.07 kg added anteriorly), used to simulate pregnancy in the second trimester and at full-term pregnancy, respectively. The increase in anterior mass resulted in kinematic changes at the knee, hip, pelvis, and trunk in the sagittal and frontal planes. In addition, ankle, knee, and hip joint moments normalized to baseline mass increased with increased load; however, these moments decreased when normalized to total mass. These kinematic and kinetic changes may suggest that women modify gait biomechanics to reduce the effect of added load. Furthermore, the increase in joint moments increases stress on the musculoskeletal system and may contribute to musculoskeletal pain.

Differences in Lower Extremity and Trunk Kinematics between Single Leg Squat and Step Down Tasks.

The single leg squat and single leg step down are two commonly used functional tasks to assess movement patterns. It is unknown how kinematics compare between these tasks. The purpose of this study was to identify kinematic differences in the lower extremity, pelvis and trunk between the single leg squat and the step down. Fourteen healthy individuals participated in this research and performed the functional tasks while kinematic data were collected for the trunk, pelvis, and lower extremities using a motion capture system. For the single leg squat task, the participant was instructed to squat as low as possible. For the step down task, the participant was instructed to stand on top of a box, slowly lower him/herself until the non-stance heel touched the ground, and return to standing. This was done from two different heights (16 cm and 24 cm). The kinematics were evaluated at peak knee flexion as well as at 60° of knee flexion. Pearson correlation coefficients (r) between the angles at those two time points were also calculated to better understand the relationship between each task. The tasks resulted in kinematics differences at the knee, hip, pelvis, and trunk at both time points. The single leg squat was performed with less hip adduction (p ≤ 0.003), but more hip external rotation and knee abduction (p ≤ 0.030), than the step down tasks at 60° of knee flexion. These differences were maintained at peak knee flexion except hip external rotation was only significant in the 24 cm step down task (p ≤ 0.029). While there were multiple differences between the two step heights at peak knee flexion, the only difference at 60° of knee flexion was in trunk flexion (p < 0.001). Angles at the knee and hip had a moderate to excellent correlation (r = 0.51-0.98), but less consistently so at the pelvis and trunk (r = 0.21-0.96). The differences in movement patterns between the single leg squat and the step down should be considered when selecting a single leg task for evaluation or treatment. The high correlation of knee and hip angles between the three tasks indicates that similar information about knee and hip kinematics was gained from each of these tasks, while pelvis and trunk angles were less well predicted.

Use of body armor protection with fighting load impacts soldier performance and kinematics.

The purpose of this evaluation was to examine how increasing body armor protection with and without a fighting load impacted soldiers' performance and mobility. Thirteen male soldiers performed one performance (repeated 30-m rushing) and three mobility tasks (walk, walk over and walk under) with three different body armor configurations and an anterior fighting load. Increasing body armor protection, decreased soldier performance, as individual and total 30-m rush times were significantly longer with greater protection. While increasing body armor protection had no impact on mobility, i.e. significant effect on trunk and lower limb biomechanics, during the walk and walk over tasks, greater protection did significantly decrease maximum trunk flexion during the walk under task. Adding fighting load may negatively impact soldier mobility, as greater maximum trunk extension was evident during the walk and walk over tasks, and decreased maximum trunk flexion exhibited during the walk under task with the fighting load.

Location of minimum foot clearance on the shoe and with respect to the obstacle changes with locomotor task.

Minimum foot clearance (MFC) as it relates to trips and falls has been extensively studied across many locomotor tasks, but examination of this body of research yields several studies with conflicting results and a wide range of MFCs within tasks. While there are several factors that may affect the MFC variability across studies (populations studied, environmental conditions, etc.), one aspect of the discrepancies in the literature may be the result of different placements of shoe markers and/or MFC calculation methods. A marker on the toe is often used, but may only quantify one aspect of how the foot actually clears the trip hazard. The purpose of this study was to determine the location on the shoe where MFC occurs during locomotor tasks with the highest risk of tripping. Ten young adults performed three trials of locomotor tasks which included overground walking, obstacle crossing, level change and stair negotiation. Clearance was calculated for 72 points on each shoe, including those most commonly used in past research. The location of the overall MFC on the shoe sole differed both between limbs and across locomotor tasks. Additionally, the region of the obstacle, step or stair over which the MFC occurred varied both within and across task. Use of this 3D MFC methodology provided further insight into which portions of the shoe may come closest to the tripping hazard. Future research should examine whether the location and value of the MFC changes between different populations, or with environmental modifications.