Lynda Read

Asymmetries in ground reaction force patterns in normal human gait

The purpose of this study was to propose a measure of symmetry/asymmetry for normal human gait and to quantify symmetries/asymmetries of normal human gait for selected gait variables using a force platform. Sixty-two subjects performed ten gait trials each, stepping on the force platform five times with each leg. From these gait trials a symmetry index was calculated for 34 gait variables. The upper and lower limits of normal gait were calculated such that 95% of all symmetry indices obtained from this subject population fell within these limits. Upper and lower limits were found to vary from +/- 4% to over +/- 13,000%. Extremely high percentages were found for variables which had absolute magnitudes close to zero and/or variables which occurred at distinctly different instants during the gait cycle. The results of these variables need to be interpreted with caution.

A method for inverse dynamic analysis using accelerometry

A method was developed to calculate total resultant force and moment on a body segment, in three dimensions, from accelerometer data. The method was applied for an analysis of intersegmental loading at the hip joint during the single support phase of working and running, using four triaxial accelerometers mounted on the upper body. Results were compared to a conventional analysis using simultaneously recorded kinematics and ground reaction forces. The loading patterns obtained by both methods were similar, but the accelerometry method systematically underestimated the intersegmental force and moment at the hip by about 20%. This could be explained by the inertial and gravitational forces originating from the swing leg which were neglected in the analysis. In addition, the accelerometry analysis was not not reliable during the impact phase of running, when the upper body and accelerometers did not behave as a rigid body. For applications where these limitations are acceptable, the accelerometry method has the advantage that it does not require a gait laboratory environment and can be used for field studies with a completely body-mounted recording system. The method does not require differentiation or integration, and therefore provided the possibility of real-time inverse dynamics analysis.

Effect of viscoelastic shoe insoles on vertical impact forces in heel-toe running

The purposes of this study were: 1) to compare the impact forces in running using running shoes with con ventional insoles to the impact forces using running shoes with four different viscoelastic insoles, 2) to discuss possible effects of the viscoelastic insoles on lower leg kinematics, and 3) to explain the force and kinematic results using a mechanical model. Kinetic and kinematic data were collected for 14 subjects running heel-toe at an average speed of 4 m/s. The results showed that the four tested viscoelastic insoles did not differ in variables describing the vertical impact forces (vertical force peak, time of occurrence of vertical force peak, maximum vertical loading rate) compared to the conventional insoles furnished in running shoes. Fur thermore, the viscoelastic insoles did not influence ki nematic variables of the lower extremities in a system atic way.

Anterior Cruciate Ligament Forces in Alpine Skiing

The purpose of this study was to estimate cruciate ligament forces in Alpine skiing during a movement that has been associated with anterior cruciate ligament (ACL) tears. Resultant knee joint forces and moments were obtained from two skiers during a World Cup Downhill race using an inverse dynamics approach and a 2-D bilaterally symmetric system model. It was found that ACL forces were typically small for both skiers throughout the movement analyzed because quadriceps forces prevented anterior displacement of the tibia relative to the femur at the knee joint angles observed. However, for about 10 ms, loading conditions in the knee joint of Subject 2 (who displayed poor form) were such that large ACL forces may have been present. These particular loading conditions were never observed in Subject 1, who displayed good form. Since neither of the skiers was injured, it is not possible to draw firm conclusions about isolated ACL tears in Alpine skiing from the data at hand.