HengJu Lee - Academia.edu (original) (raw)
Papers by HengJu Lee
Journal of Biomechanics, 2007
Journal of Biomechanics, 2007
Journal of Athletic Training, 2014
Context: Plyometric exercise has been recommended to prevent lower limb injury, but its feasibili... more Context: Plyometric exercise has been recommended to prevent lower limb injury, but its feasibility in and effects on those with functional ankle instability (FAI) are unclear. Objective: To investigate the effect of integrated plyometric and balance training in participants with FAI during a single-legged drop landing and single-legged standing position. Design: Randomized controlled clinical trial. Setting: University motion-analysis laboratory. Patients or Other Participants: Thirty athletes with FAI were divided into 3 groups: plyometric group (8 men, 2 women, age = 23.20 ± 2.82 years; 10 unstable ankles), plyometric-balance (integrated)–training group (8 men, 2 women, age = 23.80 ± 4.13 years; 10 unstable ankles), and control group (7 men, 3 women, age = 23.50 ± 3.00 years; 10 unstable ankles). Intervention(s): A 6-week plyometric-training program versus a 6-week integrated-training program. Main Outcome Measure(s): Postural sway during single-legged standing with eyes open and...
Clinical Biomechanics, 2005
The need to identify functional impairment following a brain injury is critical to prevent re-inj... more The need to identify functional impairment following a brain injury is critical to prevent re-injury during the period of recovery. While many neuropsychological tests have been developed to assess cognitive performance, relatively little information on gait and dynamic stability is available on motor task performance for young adults following concussion. This study was performed to investigate the effect of divided attention following concussion on various gait variables. It was hypothesized that, when compared to uninjured controls, concussed subjects would demonstrate deficits in maintenance of dynamic stability. Ten subjects with Grade 2 concussion completed testing within 48 h of injury as well as 10 age-, height-, weight-, and activity-matched controls. The gait protocol consisted of level walking under two conditions: (1) undivided attention (single-task) and (2) while simultaneously completing simple mental tasks (dual-task). Whole-body motion data were collected using a six-camera motion analysis system. A 13-segment biomechanical model was used to compute whole body center of mass motion and velocity. Walking with a concurrent cognitive task resulted in significant changes in gait and center of mass measurements for both groups. Concussed subjects were found to be able to conservatively adjust their whole body center of mass motion to maintain dynamic stability while walking without divided attention. However, while walking with divided attention, subjects with concussion demonstrated a significantly greater medio-lateral center of mass sway. These data suggest that the ability to control and maintain stability in the frontal plane during walking is diminished under divided attention in individuals following a concussion.
Archives of Physical Medicine and Rehabilitation, 2006
Objective: To define a parameter that quantifies balance control during gait and better identifie... more Objective: To define a parameter that quantifies balance control during gait and better identifies elderly people who are at a higher risk of falling. Design: Controlled study. Setting: University research laboratory. Participants: Twelve elderly patients (mean age, 76.9Ϯ6y) with complaints of imbalance during walking, or with a history of falls, and 12 matched healthy elderly adults. Interventions: Not applicable. Main Outcome Measures: Temporal-distance gait parameters (gait velocity, stride length, step width); and sagittal and frontal center of mass (COM) and center of pressure (COP) inclination angles. Results: Elderly patients demonstrated a significantly greater medial, but a significantly smaller anterior, inclination angle than their matched controls during both unobstructed and obstructed gait. The medial COM-COP inclination angle was not affected by the gait velocity in the healthy elderly. When the 2 groups were compared at a similar gait velocity (Ϸ1m/s), the elderly patients still had a significantly greater medial COM-COP inclination angle than did the controls. Conclusions: Instantaneous COM-COP inclination angles during walking provide information about the ability to control COM position in relation to the corresponding COP. The medial COM-COP inclination angle may be a sensitive measure of gait stability in the elderly.
Med Sci Sport Exercise, 2009
Gait Posture, Dec 1, 2005
Skeletal muscle strength is known to decline with age. Although lower extremity (LE) muscle stren... more Skeletal muscle strength is known to decline with age. Although lower extremity (LE) muscle strength is critical to maintaining dynamic stability, few studies have investigated lower extremity muscle challenge during activities of daily living. The purpose of this study was to investigate the effects of age and obstructed gait on relative lower extremity muscular challenge, with respect to available joint strength. Fifteen healthy young and fifteen healthy older adults were asked to walk over level ground and step over obstacles. Pre-amplified surface electrodes were used to measure bilateral muscular activation of the gluteus medius (GM), vastus lateralis (VL), and gastrocnemius (GA). Muscle activation signals were normalized to peak magnitudes collected during maximal manual muscle testing (MMT). Normalized magnitudes were analyzed during the double-support phase for gluteus medius and vastus lateralis and during the single-support phase for gastrocnemius. A two-factor ANOVA was used to test for age group effect, with repeated measure of obstacle height. In general, older adults demonstrated greater relative activation levels compared to young adults. Gluteus medius activity was significantly greater in the elderly as compared to young during periods of double-support (weight transfer). Increased obstacle height resulted in greater relative activation in all muscles, confirming the increased challenge to the musculo-skeletal system. While healthy elderly adults were able to successfully negotiate obstacles of different heights during walking, their muscular strength capacity was significantly lower than young adults, resulting in relatively higher muscular demands. The resulting potential for muscular fatigue during locomotion may place individuals at higher risk for trips and/or falls.
Journal of Strength and Conditioning Research, 2012
The purpose of this study was to investigate the effects of 8-week whole-body vibration (WBV) tra... more The purpose of this study was to investigate the effects of 8-week whole-body vibration (WBV) training on running economy (RE) and power performance. Twenty-four male collegiate athletes were recruited and randomly assigned to experimental (WBV) and placebo (PL) groups. The WBV subjects performed semisquat vibration training (30 Hz, ±1-2 mm, 3 times per week), whereas PL subjects performed identical training without vibration. The isometric maximum voluntary contraction tests were used to evaluate maximal isometric force (F(max)) and rate of force development (RFD) of lower extremities, before and after the intervention, and RE was measured on a level treadmill at 3 velocities (2.68, 3.13, and 3.58 m·s(-1)). The F(max) of the lower leg (plantar flexion, from 80.8 ± 24.5 to 99.0 ± 33.9 N·m, p < 0.05, η(2) = 0.567; dorsiflexion, from 38.1 ± 6.5 to 43.0 ± 7.7 N·m, p < 0.05), and the RFD of 0-200 milliseconds during plantar flexion (from 186.0 ± 69.2 to 264.6 ± 87.2 N·m·s(-1), p < 0.05, η(2) = 0.184) were significantly increased in the WBV group after training. The averaged RE values for the 3 running velocities were significantly improved after WBV training (pretraining vs. posttraining, 4.31 ± 0.33 vs. 4.65 ± 0.34 m·ml(-1)·kg(-1), p = 0.001, η(2) = 0.654); however, no significant differences were found in the PL group (pretraining vs. posttraining, 4.18 ± 0.26 vs. 4.26 ± 0.44 m·ml(-1)·kg(-1), p = 0.476). The WBV training significantly improved RE at selected speeds (∼5.0-8.5%, p < 0.05). These results indicated that short-term WBV training could be an effective stimulus to enhance RE and lower extremity power performance in competitive athletes.
Journal of Biomechanics, Feb 1, 2007
Stair negotiation is among the most challenging and hazardous types of locomotion for older peopl... more Stair negotiation is among the most challenging and hazardous types of locomotion for older people. However, the effect of aging on balance control during stair negotiation has not been investigated. Instantaneous inclination angles between the center of mass (CoM) and center of pressure (CoP) have been reported to detect gait instability effectively in the elderly. The purpose of this study was to compare the CoM-CoP inclination angles between 12 healthy elderly and 13 healthy young adults when performing stair ascent (SA) and descent (SD) on a three-step staircase. Whole body motion data were collected with an eight-camera motion analysis system. Four force plates were mounted on the floor as well as the first two steps to measure ground reaction forces. No significant group differences were detected in any of the temporal-distance gait measures and CoM-CoP inclination angles during SA and SD. Compared to the floor-to-stair transition phase, both groups demonstrated a significantly greater CoM-CoP medial inclination angle while ascending the stairs. However, a significant reduction in medial inclination was only detected in young adults when transferring from SD to level ground walking. Elderly adults were found to demonstrate a significantly greater medial inclination angle during the stair-to-floor transition phase when compared to young adults. Age-related degenerations in the elderly could compromise their ability to regulate body sway during the stair-to-floor transition, which may subsequently increase the risk of falling.
Journal of Biomechanics, 2007
Journal of Biomechanics, 2007
Journal of Athletic Training, 2014
Context: Plyometric exercise has been recommended to prevent lower limb injury, but its feasibili... more Context: Plyometric exercise has been recommended to prevent lower limb injury, but its feasibility in and effects on those with functional ankle instability (FAI) are unclear. Objective: To investigate the effect of integrated plyometric and balance training in participants with FAI during a single-legged drop landing and single-legged standing position. Design: Randomized controlled clinical trial. Setting: University motion-analysis laboratory. Patients or Other Participants: Thirty athletes with FAI were divided into 3 groups: plyometric group (8 men, 2 women, age = 23.20 ± 2.82 years; 10 unstable ankles), plyometric-balance (integrated)–training group (8 men, 2 women, age = 23.80 ± 4.13 years; 10 unstable ankles), and control group (7 men, 3 women, age = 23.50 ± 3.00 years; 10 unstable ankles). Intervention(s): A 6-week plyometric-training program versus a 6-week integrated-training program. Main Outcome Measure(s): Postural sway during single-legged standing with eyes open and...
Clinical Biomechanics, 2005
The need to identify functional impairment following a brain injury is critical to prevent re-inj... more The need to identify functional impairment following a brain injury is critical to prevent re-injury during the period of recovery. While many neuropsychological tests have been developed to assess cognitive performance, relatively little information on gait and dynamic stability is available on motor task performance for young adults following concussion. This study was performed to investigate the effect of divided attention following concussion on various gait variables. It was hypothesized that, when compared to uninjured controls, concussed subjects would demonstrate deficits in maintenance of dynamic stability. Ten subjects with Grade 2 concussion completed testing within 48 h of injury as well as 10 age-, height-, weight-, and activity-matched controls. The gait protocol consisted of level walking under two conditions: (1) undivided attention (single-task) and (2) while simultaneously completing simple mental tasks (dual-task). Whole-body motion data were collected using a six-camera motion analysis system. A 13-segment biomechanical model was used to compute whole body center of mass motion and velocity. Walking with a concurrent cognitive task resulted in significant changes in gait and center of mass measurements for both groups. Concussed subjects were found to be able to conservatively adjust their whole body center of mass motion to maintain dynamic stability while walking without divided attention. However, while walking with divided attention, subjects with concussion demonstrated a significantly greater medio-lateral center of mass sway. These data suggest that the ability to control and maintain stability in the frontal plane during walking is diminished under divided attention in individuals following a concussion.
Archives of Physical Medicine and Rehabilitation, 2006
Objective: To define a parameter that quantifies balance control during gait and better identifie... more Objective: To define a parameter that quantifies balance control during gait and better identifies elderly people who are at a higher risk of falling. Design: Controlled study. Setting: University research laboratory. Participants: Twelve elderly patients (mean age, 76.9Ϯ6y) with complaints of imbalance during walking, or with a history of falls, and 12 matched healthy elderly adults. Interventions: Not applicable. Main Outcome Measures: Temporal-distance gait parameters (gait velocity, stride length, step width); and sagittal and frontal center of mass (COM) and center of pressure (COP) inclination angles. Results: Elderly patients demonstrated a significantly greater medial, but a significantly smaller anterior, inclination angle than their matched controls during both unobstructed and obstructed gait. The medial COM-COP inclination angle was not affected by the gait velocity in the healthy elderly. When the 2 groups were compared at a similar gait velocity (Ϸ1m/s), the elderly patients still had a significantly greater medial COM-COP inclination angle than did the controls. Conclusions: Instantaneous COM-COP inclination angles during walking provide information about the ability to control COM position in relation to the corresponding COP. The medial COM-COP inclination angle may be a sensitive measure of gait stability in the elderly.
Med Sci Sport Exercise, 2009
Gait Posture, Dec 1, 2005
Skeletal muscle strength is known to decline with age. Although lower extremity (LE) muscle stren... more Skeletal muscle strength is known to decline with age. Although lower extremity (LE) muscle strength is critical to maintaining dynamic stability, few studies have investigated lower extremity muscle challenge during activities of daily living. The purpose of this study was to investigate the effects of age and obstructed gait on relative lower extremity muscular challenge, with respect to available joint strength. Fifteen healthy young and fifteen healthy older adults were asked to walk over level ground and step over obstacles. Pre-amplified surface electrodes were used to measure bilateral muscular activation of the gluteus medius (GM), vastus lateralis (VL), and gastrocnemius (GA). Muscle activation signals were normalized to peak magnitudes collected during maximal manual muscle testing (MMT). Normalized magnitudes were analyzed during the double-support phase for gluteus medius and vastus lateralis and during the single-support phase for gastrocnemius. A two-factor ANOVA was used to test for age group effect, with repeated measure of obstacle height. In general, older adults demonstrated greater relative activation levels compared to young adults. Gluteus medius activity was significantly greater in the elderly as compared to young during periods of double-support (weight transfer). Increased obstacle height resulted in greater relative activation in all muscles, confirming the increased challenge to the musculo-skeletal system. While healthy elderly adults were able to successfully negotiate obstacles of different heights during walking, their muscular strength capacity was significantly lower than young adults, resulting in relatively higher muscular demands. The resulting potential for muscular fatigue during locomotion may place individuals at higher risk for trips and/or falls.
Journal of Strength and Conditioning Research, 2012
The purpose of this study was to investigate the effects of 8-week whole-body vibration (WBV) tra... more The purpose of this study was to investigate the effects of 8-week whole-body vibration (WBV) training on running economy (RE) and power performance. Twenty-four male collegiate athletes were recruited and randomly assigned to experimental (WBV) and placebo (PL) groups. The WBV subjects performed semisquat vibration training (30 Hz, ±1-2 mm, 3 times per week), whereas PL subjects performed identical training without vibration. The isometric maximum voluntary contraction tests were used to evaluate maximal isometric force (F(max)) and rate of force development (RFD) of lower extremities, before and after the intervention, and RE was measured on a level treadmill at 3 velocities (2.68, 3.13, and 3.58 m·s(-1)). The F(max) of the lower leg (plantar flexion, from 80.8 ± 24.5 to 99.0 ± 33.9 N·m, p < 0.05, η(2) = 0.567; dorsiflexion, from 38.1 ± 6.5 to 43.0 ± 7.7 N·m, p < 0.05), and the RFD of 0-200 milliseconds during plantar flexion (from 186.0 ± 69.2 to 264.6 ± 87.2 N·m·s(-1), p < 0.05, η(2) = 0.184) were significantly increased in the WBV group after training. The averaged RE values for the 3 running velocities were significantly improved after WBV training (pretraining vs. posttraining, 4.31 ± 0.33 vs. 4.65 ± 0.34 m·ml(-1)·kg(-1), p = 0.001, η(2) = 0.654); however, no significant differences were found in the PL group (pretraining vs. posttraining, 4.18 ± 0.26 vs. 4.26 ± 0.44 m·ml(-1)·kg(-1), p = 0.476). The WBV training significantly improved RE at selected speeds (∼5.0-8.5%, p < 0.05). These results indicated that short-term WBV training could be an effective stimulus to enhance RE and lower extremity power performance in competitive athletes.
Journal of Biomechanics, Feb 1, 2007
Stair negotiation is among the most challenging and hazardous types of locomotion for older peopl... more Stair negotiation is among the most challenging and hazardous types of locomotion for older people. However, the effect of aging on balance control during stair negotiation has not been investigated. Instantaneous inclination angles between the center of mass (CoM) and center of pressure (CoP) have been reported to detect gait instability effectively in the elderly. The purpose of this study was to compare the CoM-CoP inclination angles between 12 healthy elderly and 13 healthy young adults when performing stair ascent (SA) and descent (SD) on a three-step staircase. Whole body motion data were collected with an eight-camera motion analysis system. Four force plates were mounted on the floor as well as the first two steps to measure ground reaction forces. No significant group differences were detected in any of the temporal-distance gait measures and CoM-CoP inclination angles during SA and SD. Compared to the floor-to-stair transition phase, both groups demonstrated a significantly greater CoM-CoP medial inclination angle while ascending the stairs. However, a significant reduction in medial inclination was only detected in young adults when transferring from SD to level ground walking. Elderly adults were found to demonstrate a significantly greater medial inclination angle during the stair-to-floor transition phase when compared to young adults. Age-related degenerations in the elderly could compromise their ability to regulate body sway during the stair-to-floor transition, which may subsequently increase the risk of falling.