The aim of this paper was to compare the effect of different optimization methods and different k... more The aim of this paper was to compare the effect of different optimization methods and different knee joint degrees of freedom (DOF) on muscle force predictions during a single legged hop. Nineteen subjects performed single-legged hopping manoeuvres and subjectspecific musculoskeletal models were developed to predict muscle forces during the movement. Muscle forces were predicted using static optimization (SO) and computed muscle control (CMC) methods using either 1 or 3 DOF knee joint models. All sagittal and transverse plane joint angles calculated using inverse kinematics or CMC in a 1 DOF or 3 DOF knee were well-matched (RMS error < 3 o). Biarticular muscles (hamstrings, rectus femoris and gastrocnemius) showed more differences in muscle force profiles when comparing between the different muscle prediction approaches where these muscles showed larger time delays for many of the comparisons. The muscle force magnitudes of vasti, gluteus maximus and gluteus medius were not greatly influenced by the choice of muscle force prediction method with low normalized root mean squared errors (< 48%) observed in most comparisons. We conclude that SO and CMC can be used to predict lower-limb muscle co-contraction during hopping movements. However, care must be taken in interpreting the magnitude of force predicted in the biarticular muscles and the soleus, especially when using a 1 DOF knee. Despite this limitation, given that SO is a more robust and computationally efficient method for predicting muscle forces than CMC, we suggest that SO can be used in conjunction with musculoskeletal models that have a 1 or 3 DOF knee joint to study the relative differences and the role of muscles during hopping activities in future studies.
The human biceps femoris long head is susceptible to injury, especially when sprinting. The poten... more The human biceps femoris long head is susceptible to injury, especially when sprinting. The potential mechanical action of this muscle at a critical stage in the stride cycle was evaluated by calculating three-dimensional lines-of-action and moment arms about the hip and knee joints in vivo. Axial magnetic resonance images of the right lower-limb (pelvis to proximal tibia) were recorded from four participants under two conditions: a reference pose, with the lower-limb in the anatomical position and the hamstrings relaxed; and a terminal swing pose, with the hip and knee joints flexed to mimic the lower-limb orientation during the terminal swing phase of sprinting and the hamstrings isometrically activated. Images were used to segment biceps femoris long head and the relevant bones. The musculotendon path and joint coordinate systems were defined from which lines-of-action and moment arms were computed. Biceps femoris long head displayed hip extensor and adductor moment arms as well as knee flexor, abductor and external-rotator moment arms. Sagittal-plane moment arms were largest, whereas transverse-plane moment arms were smallest. Moment arms remained consistent in polarity across all participants and testing conditions, except in the transverse-plane about the hip. For the terminal swing pose compared to the reference pose, sagittal-plane moment arms for biceps femoris long head increased by 19.9% to 48.9% about the hip and 42.3% to 93.9% about the knee. Biceps femoris long head has the potential to cause hip extension and adduction as well as knee flexion during the terminal swing phase of sprinting.
The aim of this paper was to compare the effect of different optimisation methods and different k... more The aim of this paper was to compare the effect of different optimisation methods and different knee joint degrees of freedom (DOF) on muscle force predictions during a single legged hop. Nineteen subjects performed single-legged hopping manoeuvres and subject-specific musculoskeletal models were developed to predict muscle forces during the movement. Muscle forces were predicted using static optimisation (SO) and computed muscle control (CMC) methods using either 1 or 3 DOF knee joint models. All sagittal and transverse plane joint angles calculated using inverse kinematics or CMC in a 1 DOF or 3 DOF knee were well-matched (RMS error<3°). Biarticular muscles (hamstrings, rectus femoris and gastrocnemius) showed more differences in muscle force profiles when comparing between the different muscle prediction approaches where these muscles showed larger time delays for many of the comparisons. The muscle force magnitudes of vasti, gluteus maximus and gluteus medius were not greatly...
The human biceps femoris long head is susceptible to injury, especially when sprinting. The poten... more The human biceps femoris long head is susceptible to injury, especially when sprinting. The potential mechanical action of this muscle at a critical stage in the stride cycle was evaluated by calculating three-dimensional lines-of-action and moment arms about the hip and knee joints in vivo. Axial magnetic resonance images of the right lower-limb (pelvis to proximal tibia) were recorded from four participants under two conditions: a reference pose, with the lower-limb in the anatomical position and the hamstrings relaxed; and a terminal swing pose, with the hip and knee joints flexed to mimic the lower-limb orientation during the terminal swing phase of sprinting and the hamstrings isometrically activated. Images were used to segment biceps femoris long head and the relevant bones. The musculotendon path and joint coordinate systems were defined from which lines-of-action and moment arms were computed. Biceps femoris long head displayed hip extensor and adductor moment arms as well as knee flexor, abductor and external-rotator moment arms. Sagittal-plane moment arms were largest, whereas transverse-plane moment arms were smallest. Moment arms remained consistent in polarity across all participants and testing conditions, except in the transverse-plane about the hip. For the terminal swing pose compared to the reference pose, sagittal-plane moment arms for biceps femoris long head increased by 19.9% to 48.9% about the hip and 42.3% to 93.9% about the knee. Biceps femoris long head has the potential to cause hip extension and adduction as well as knee flexion during the terminal swing phase of sprinting.
ObjectiveTo determine whether people with patellofemoral (PF) joint osteoarthritis (OA) ascend an... more ObjectiveTo determine whether people with patellofemoral (PF) joint osteoarthritis (OA) ascend and descend stairs with different PF joint loading, knee joint moments, lower limb kinematics, and muscle forces compared to healthy people.MethodsWe recruited 17 participants with isolated PF joint OA, 13 participants with concurrent PF joint OA and tibiofemoral (TF) joint OA, and 21 age‐matched controls. Joint kinematics and ground reaction forces were measured while participants ascended and descended stairs at a self‐selected speed. Musculoskeletal computer modeling was used to determine lower limb muscle forces and the PF joint reaction force, and these parameters were compared between groups by analysis of variance.ResultsCompared to their healthy counterparts, participants with isolated PF joint OA and participants with concurrent PF and TF joint OA ascended and descended stairs with lower knee extension moments, lower quadriceps muscle forces, lower PF joint reaction forces, and in...
Stair ambulation is more physically demanding than level walking because it requires the lower-li... more Stair ambulation is more physically demanding than level walking because it requires the lower-limb muscles to generate greater net joint moments. Although lower-limb joint kinematics and kinetics during stair ambulation have been extensively studied, relatively little is known about how the lower-limb muscles accelerate the whole-body center of mass (COM) during stair ascent and descent. The aim of the current study was to evaluate differences in muscle contributions to COM accelerations between level walking and stair ambulation in 15 healthy adults. Three-dimensional quantitative gait analysis and musculoskeletal modeling were used to calculate the contributions of the individual lower-limb muscles to the vertical, fore-aft and mediolateral accelerations of the COM (support, progression, and balance, respectively) during level walking, stair ascent and stair descent. Muscles that contribute most significantly to the acceleration of the COM during level walking (hip, knee, and ankle extensors) also dominate during stair ambulation, but with noticeable differences in coordination. In stair ascent, gluteus maximus accelerates the body forward during the first half of stance and soleus accelerates the body backward during the second half of stance, opposite to the functions displayed by these muscles in level walking. In stair descent, vasti generates backward and medial accelerations of the COM during the second half of stance, whereas it contributes minimally during this period in level walking. Gluteus medius performs similarly in controlling mediolateral balance during level walking and stair ambulation. Differences in lowerlimb muscular coordination exist between stair ambulation and level walking, and our results have implications for interventions aimed at preventing stair-related falls.
The aim of this paper was to compare the effect of different optimization methods and different k... more The aim of this paper was to compare the effect of different optimization methods and different knee joint degrees of freedom (DOF) on muscle force predictions during a single legged hop. Nineteen subjects performed single-legged hopping manoeuvres and subjectspecific musculoskeletal models were developed to predict muscle forces during the movement. Muscle forces were predicted using static optimization (SO) and computed muscle control (CMC) methods using either 1 or 3 DOF knee joint models. All sagittal and transverse plane joint angles calculated using inverse kinematics or CMC in a 1 DOF or 3 DOF knee were well-matched (RMS error < 3 o). Biarticular muscles (hamstrings, rectus femoris and gastrocnemius) showed more differences in muscle force profiles when comparing between the different muscle prediction approaches where these muscles showed larger time delays for many of the comparisons. The muscle force magnitudes of vasti, gluteus maximus and gluteus medius were not greatly influenced by the choice of muscle force prediction method with low normalized root mean squared errors (< 48%) observed in most comparisons. We conclude that SO and CMC can be used to predict lower-limb muscle co-contraction during hopping movements. However, care must be taken in interpreting the magnitude of force predicted in the biarticular muscles and the soleus, especially when using a 1 DOF knee. Despite this limitation, given that SO is a more robust and computationally efficient method for predicting muscle forces than CMC, we suggest that SO can be used in conjunction with musculoskeletal models that have a 1 or 3 DOF knee joint to study the relative differences and the role of muscles during hopping activities in future studies.
The human biceps femoris long head is susceptible to injury, especially when sprinting. The poten... more The human biceps femoris long head is susceptible to injury, especially when sprinting. The potential mechanical action of this muscle at a critical stage in the stride cycle was evaluated by calculating three-dimensional lines-of-action and moment arms about the hip and knee joints in vivo. Axial magnetic resonance images of the right lower-limb (pelvis to proximal tibia) were recorded from four participants under two conditions: a reference pose, with the lower-limb in the anatomical position and the hamstrings relaxed; and a terminal swing pose, with the hip and knee joints flexed to mimic the lower-limb orientation during the terminal swing phase of sprinting and the hamstrings isometrically activated. Images were used to segment biceps femoris long head and the relevant bones. The musculotendon path and joint coordinate systems were defined from which lines-of-action and moment arms were computed. Biceps femoris long head displayed hip extensor and adductor moment arms as well as knee flexor, abductor and external-rotator moment arms. Sagittal-plane moment arms were largest, whereas transverse-plane moment arms were smallest. Moment arms remained consistent in polarity across all participants and testing conditions, except in the transverse-plane about the hip. For the terminal swing pose compared to the reference pose, sagittal-plane moment arms for biceps femoris long head increased by 19.9% to 48.9% about the hip and 42.3% to 93.9% about the knee. Biceps femoris long head has the potential to cause hip extension and adduction as well as knee flexion during the terminal swing phase of sprinting.
The aim of this paper was to compare the effect of different optimisation methods and different k... more The aim of this paper was to compare the effect of different optimisation methods and different knee joint degrees of freedom (DOF) on muscle force predictions during a single legged hop. Nineteen subjects performed single-legged hopping manoeuvres and subject-specific musculoskeletal models were developed to predict muscle forces during the movement. Muscle forces were predicted using static optimisation (SO) and computed muscle control (CMC) methods using either 1 or 3 DOF knee joint models. All sagittal and transverse plane joint angles calculated using inverse kinematics or CMC in a 1 DOF or 3 DOF knee were well-matched (RMS error<3°). Biarticular muscles (hamstrings, rectus femoris and gastrocnemius) showed more differences in muscle force profiles when comparing between the different muscle prediction approaches where these muscles showed larger time delays for many of the comparisons. The muscle force magnitudes of vasti, gluteus maximus and gluteus medius were not greatly...
The human biceps femoris long head is susceptible to injury, especially when sprinting. The poten... more The human biceps femoris long head is susceptible to injury, especially when sprinting. The potential mechanical action of this muscle at a critical stage in the stride cycle was evaluated by calculating three-dimensional lines-of-action and moment arms about the hip and knee joints in vivo. Axial magnetic resonance images of the right lower-limb (pelvis to proximal tibia) were recorded from four participants under two conditions: a reference pose, with the lower-limb in the anatomical position and the hamstrings relaxed; and a terminal swing pose, with the hip and knee joints flexed to mimic the lower-limb orientation during the terminal swing phase of sprinting and the hamstrings isometrically activated. Images were used to segment biceps femoris long head and the relevant bones. The musculotendon path and joint coordinate systems were defined from which lines-of-action and moment arms were computed. Biceps femoris long head displayed hip extensor and adductor moment arms as well as knee flexor, abductor and external-rotator moment arms. Sagittal-plane moment arms were largest, whereas transverse-plane moment arms were smallest. Moment arms remained consistent in polarity across all participants and testing conditions, except in the transverse-plane about the hip. For the terminal swing pose compared to the reference pose, sagittal-plane moment arms for biceps femoris long head increased by 19.9% to 48.9% about the hip and 42.3% to 93.9% about the knee. Biceps femoris long head has the potential to cause hip extension and adduction as well as knee flexion during the terminal swing phase of sprinting.
ObjectiveTo determine whether people with patellofemoral (PF) joint osteoarthritis (OA) ascend an... more ObjectiveTo determine whether people with patellofemoral (PF) joint osteoarthritis (OA) ascend and descend stairs with different PF joint loading, knee joint moments, lower limb kinematics, and muscle forces compared to healthy people.MethodsWe recruited 17 participants with isolated PF joint OA, 13 participants with concurrent PF joint OA and tibiofemoral (TF) joint OA, and 21 age‐matched controls. Joint kinematics and ground reaction forces were measured while participants ascended and descended stairs at a self‐selected speed. Musculoskeletal computer modeling was used to determine lower limb muscle forces and the PF joint reaction force, and these parameters were compared between groups by analysis of variance.ResultsCompared to their healthy counterparts, participants with isolated PF joint OA and participants with concurrent PF and TF joint OA ascended and descended stairs with lower knee extension moments, lower quadriceps muscle forces, lower PF joint reaction forces, and in...
Stair ambulation is more physically demanding than level walking because it requires the lower-li... more Stair ambulation is more physically demanding than level walking because it requires the lower-limb muscles to generate greater net joint moments. Although lower-limb joint kinematics and kinetics during stair ambulation have been extensively studied, relatively little is known about how the lower-limb muscles accelerate the whole-body center of mass (COM) during stair ascent and descent. The aim of the current study was to evaluate differences in muscle contributions to COM accelerations between level walking and stair ambulation in 15 healthy adults. Three-dimensional quantitative gait analysis and musculoskeletal modeling were used to calculate the contributions of the individual lower-limb muscles to the vertical, fore-aft and mediolateral accelerations of the COM (support, progression, and balance, respectively) during level walking, stair ascent and stair descent. Muscles that contribute most significantly to the acceleration of the COM during level walking (hip, knee, and ankle extensors) also dominate during stair ambulation, but with noticeable differences in coordination. In stair ascent, gluteus maximus accelerates the body forward during the first half of stance and soleus accelerates the body backward during the second half of stance, opposite to the functions displayed by these muscles in level walking. In stair descent, vasti generates backward and medial accelerations of the COM during the second half of stance, whereas it contributes minimally during this period in level walking. Gluteus medius performs similarly in controlling mediolateral balance during level walking and stair ambulation. Differences in lowerlimb muscular coordination exist between stair ambulation and level walking, and our results have implications for interventions aimed at preventing stair-related falls.
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Papers by Laurence Fok