Objective To explore limb coordination patterns and energy flow strategies during the sit-to-stand(STS)transition in individuals with patellofemoral pain(PFP),so as to provide a theoretical evidence for the pathogenesis of PFP and subsequent formulation of treatment and rehabilitation strategies for PFP patients.Methods A totoal of 36 participants was recruited for the STS test.They were divided into the unilateral PFP group(unilateral group),bilateral PFP group(bilateral group),and control group,based on the number of limbs affected by PFP.An infrared motion capture system and a three-dimensioanl force plate were used for motion capture.Visual 3D and Matlab software were used to calculate the trunk and pelvis angles,angular velocities,linear velocities,and proximal and distal joint forces.Additionally,the angles,torques,and joint forces of the hip,knee,and ankle joints,along with the angular and linear velocities of the thigh and shank,were computed.Coupling angles was used to represent coordination patterns via vector coding;the segmental net energy integration method was used to calculate energy flow within segments at each stage.Results For the coordination pattern at frontal plane,the proximal coordination mode frequency of the pelvis-hip coordination in the flexion momentum phase(FMP)was higher in unilateral group than that in bilateral group(P=0.024).In the momentum transfer phase(MTP),the frequency of in-phase coordination in the trunk-pelvis coordination was higher in unilateral group than that in bilateral group(P=0.023),while the frequency of distal coordination was higher in control group than in that in unilateral group(P=0.032).For the knee-ankle coordination pattern,the frequency of distal coordination in control group was lower than that in unilateral and bilateral groups(P=0.025,P=0.005).In segmental energy flow,during the FMP,the energy output from the pelvis during extension phase(MP)was higher in bilateral group than that in control group(P=0.021).Conclusions PFP affects energy flow patterns and coordination patterns at frontal plane during the STS transition.Individuals in unilateral group may engage in lateral pelvic and ankle movements as a dynamic compensation for patellofemoral joint pressure,whereas individuals in bilateral group appear to increase pelvic region energy output and employ a more complex whole-body coordination pattern to compensate for functional deficits in the knee caused by PFP.

BACKGROUND:The stiffness of muscle fibers and tendons within skeletal muscles is regulated by the neuromuscular system and remains variable.However,observing the mechanical properties of muscle fibers and tendons during complex multi-joint movements is challenging,and the real-time variation patterns of their stiffness are not yet clear.OBJECTIVE:Taking the open-access simulation data of triceps surae at different running speeds and gait phases as an example,to explore the real-time stiffness change rules of muscle fiber stiffness and tendon stiffness.METHODS:OpenSim simulation results of muscle fiber activation,length,velocity parameters,and tendon length parameters of the triceps surae in five long-distance runners at different running speeds were collected from the Website of Stanford University.The instantaneous slope of the force-length relationship curve of muscle fibers and tendons in the Hill-Zajac muscle model used in the simulation was extracted as the real-time stiffness of the triceps surae muscle fibers and tendons.The temporal changes of stiffness indicators of muscle fibers and tendons during gait were analyzed.RESULTS AND CONCLUSION:The regulation of muscle fiber activation-length-velocity status and tendon strain resulted in the stiffness of muscle fibers and tendons changing in the same trend as the applied force.Compared with lower running speeds,the stiffness of the gastrocnemius muscle fibers was higher in the early support phase at higher running speeds(P ≤ 0.01),and the tendon stiffness of the medial head of the gastrocnemius was higher in the early support phase(P≤ 0.02).The stiffness of the gastrocnemius muscle fibers and tendons was lower from the mid-support to the mid-swing phase(P≤ 0.03),and the stiffness of the soleus muscle fibers was higher during the support phase(P ≤ 0.02).Under all running speeds,the stiffness of the triceps surae muscle fibers and tendons showed a trend of being higher during the support phase than during the pre-swing phase(P ≤ 0.03),and the stiffness of the gastrocnemius muscle fibers and tendons increased again in the late swing phase(P ≤ 0.05).These findings indicate that increasing running speed can increase the stiffness of triceps surae muscle fibers and tendons during the stance phase;when running speed and gait phase change,gastrocnemius and soleus muscles have different patterns of muscle fiber and tendon stiffness changes,whereas gastrocnemius can increase its muscle fiber stiffness and tendon stiffness in the late swing phase through pre-activation phenomenon.

Objective To explore limb coordination patterns and energy flow strategies during the sit-to-stand(STS)transition in individuals with patellofemoral pain(PFP),so as to provide a theoretical evidence for the pathogenesis of PFP and subsequent formulation of treatment and rehabilitation strategies for PFP patients.Methods A totoal of 36 participants was recruited for the STS test.They were divided into the unilateral PFP group(unilateral group),bilateral PFP group(bilateral group),and control group,based on the number of limbs affected by PFP.An infrared motion capture system and a three-dimensioanl force plate were used for motion capture.Visual 3D and Matlab software were used to calculate the trunk and pelvis angles,angular velocities,linear velocities,and proximal and distal joint forces.Additionally,the angles,torques,and joint forces of the hip,knee,and ankle joints,along with the angular and linear velocities of the thigh and shank,were computed.Coupling angles was used to represent coordination patterns via vector coding;the segmental net energy integration method was used to calculate energy flow within segments at each stage.Results For the coordination pattern at frontal plane,the proximal coordination mode frequency of the pelvis-hip coordination in the flexion momentum phase(FMP)was higher in unilateral group than that in bilateral group(P=0.024).In the momentum transfer phase(MTP),the frequency of in-phase coordination in the trunk-pelvis coordination was higher in unilateral group than that in bilateral group(P=0.023),while the frequency of distal coordination was higher in control group than in that in unilateral group(P=0.032).For the knee-ankle coordination pattern,the frequency of distal coordination in control group was lower than that in unilateral and bilateral groups(P=0.025,P=0.005).In segmental energy flow,during the FMP,the energy output from the pelvis during extension phase(MP)was higher in bilateral group than that in control group(P=0.021).Conclusions PFP affects energy flow patterns and coordination patterns at frontal plane during the STS transition.Individuals in unilateral group may engage in lateral pelvic and ankle movements as a dynamic compensation for patellofemoral joint pressure,whereas individuals in bilateral group appear to increase pelvic region energy output and employ a more complex whole-body coordination pattern to compensate for functional deficits in the knee caused by PFP.

BACKGROUND:The stiffness of muscle fibers and tendons within skeletal muscles is regulated by the neuromuscular system and remains variable.However,observing the mechanical properties of muscle fibers and tendons during complex multi-joint movements is challenging,and the real-time variation patterns of their stiffness are not yet clear.OBJECTIVE:Taking the open-access simulation data of triceps surae at different running speeds and gait phases as an example,to explore the real-time stiffness change rules of muscle fiber stiffness and tendon stiffness.METHODS:OpenSim simulation results of muscle fiber activation,length,velocity parameters,and tendon length parameters of the triceps surae in five long-distance runners at different running speeds were collected from the Website of Stanford University.The instantaneous slope of the force-length relationship curve of muscle fibers and tendons in the Hill-Zajac muscle model used in the simulation was extracted as the real-time stiffness of the triceps surae muscle fibers and tendons.The temporal changes of stiffness indicators of muscle fibers and tendons during gait were analyzed.RESULTS AND CONCLUSION:The regulation of muscle fiber activation-length-velocity status and tendon strain resulted in the stiffness of muscle fibers and tendons changing in the same trend as the applied force.Compared with lower running speeds,the stiffness of the gastrocnemius muscle fibers was higher in the early support phase at higher running speeds(P ≤ 0.01),and the tendon stiffness of the medial head of the gastrocnemius was higher in the early support phase(P≤ 0.02).The stiffness of the gastrocnemius muscle fibers and tendons was lower from the mid-support to the mid-swing phase(P≤ 0.03),and the stiffness of the soleus muscle fibers was higher during the support phase(P ≤ 0.02).Under all running speeds,the stiffness of the triceps surae muscle fibers and tendons showed a trend of being higher during the support phase than during the pre-swing phase(P ≤ 0.03),and the stiffness of the gastrocnemius muscle fibers and tendons increased again in the late swing phase(P ≤ 0.05).These findings indicate that increasing running speed can increase the stiffness of triceps surae muscle fibers and tendons during the stance phase;when running speed and gait phase change,gastrocnemius and soleus muscles have different patterns of muscle fiber and tendon stiffness changes,whereas gastrocnemius can increase its muscle fiber stiffness and tendon stiffness in the late swing phase through pre-activation phenomenon.