Benno M. Nigg

Effect of skin movement on the analysis of skeletal knee joint motion during running

It is not known how well skin markers represent the skeletal knee joint motion during running. Hence the purpose of this investigation was to compare the skin marker derived tibiofemoral motion with the skeletal tibiofemoral motion during running. In addition to skin markers attached to the shank and thigh, triads of reflective markers were attached to bone pins inserted into the tibia and femur. Three-dimensional kinematics of the stance phase of five running trials were recorded for three subjects using high-speed cine cameras (200 Hz). The knee motion was expressed in terms of Cardan angles calculated from both the external and skeletal markers. Good agreement was present between the skin and bone marker based knee flexion/extension. For abduction/adduction and internal/external knee rotation, the difference between skeletal and external motion was large compared to the amplitude of these motions. Average errors relative to the range of motion during running stance were 21% for flexion/extension, 63% for internal/external rotation, and 70% for abduction/adduction. The errors were highly subject dependent preventing the realization of a successful correction algorithm. It was concluded that knee rotations other than flexion/extension may be affected with substantial errors when using skin markers.

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.

The role of impact forces and foot pronation: a new paradigm.

ObjectiveThis article discusses the possible association between impact forces and foot pronation and the development of running-related injuries, and proposes a new paradigm for impact forces and foot pronation. Data SourcesThe article is based on a critical analysis of the literature on heel–toe running addressing kinematics, kinetics, resultant joint movements and forces, muscle activity, subject and material characteristics, epidemiology, and biologic reactions. However, this paper is not a review of the literature but rather an attempt to replace the established concepts of impact forces and movement control with a new paradigm that would allow explaining some of the current contradictions in this topic of research. Study SelectionThe analysis included all papers published on this topic over the last 25 years. For the last few years, it concentrated on papers expressing critical concerns on the established concepts of impact and movement control. Data ExtractionAn attempt was made to find indications in the various publications to support or reject the current concept of impact forces and movement control. Furthermore, the results of the available studies were searched for indications expanding the current understanding of impact forces and movement control in running. Data SynthesisData were synthesized revealing contradictions in the experimental results and the established concepts. Based on the contradictions in the existing research publications, a new paradigm was proposed. ConclusionTheoretical, experimental, and epidemiological evidence on impact forces showed that one cannot conclude that impact forces are important factors in the development of chronic and/or acute running-related injuries. A new paradigm for impact forces during running proposes that impact forces are input signals that produce muscle tuning shortly before the next contact with the ground to minimize soft tissue vibration and/or reduce joint and tendon loading. Muscle tuning might affect fatigue, comfort, work, and performance. Experimental evidence suggests that the concept of “aligning the skeleton” with shoes, inserts, and orthotics should be reconsidered. They produce only small, not systematic, and subject-specific changes of foot and leg movement. A new paradigm for movement control for the lower extremities proposes that forces acting on the foot during the stance phase act as an input signal producing a muscle reaction. The cost function used in this adaptation process is to maintain a preferred joint movement path for a given movement task. If an intervention counteracts the preferred movement path, muscle activity must be increased. An optimal shoe, insert, or orthotic reduces muscle activity. Thus, shoes, inserts, and orthotics affect general muscle activity and, therefore, fatigue, comfort, work, and performance. The two proposed paradigms suggest that the locomotor system use a similar strategy for “impact” and “movement control.” In both cases the locomotor system keeps the general kinematic and kinetic situations similar for a given task. The proposed muscle tuning reaction to impact loading affects the muscle activation before ground contact. The proposed muscle adaptation to provide a constant joint movement pattern affects the muscle activation during ground contact. However, further experimental and theoretical studies are needed to support or reject the proposed paradigms.

The influence of running velocity and midsole hardness on external impact forces in heel-toe running

The purpose of this study was to investigate the influence of midsole hardness and running velocity on external impact forces in heel-toe running. Fourteen subjects were assessed with a force platform and high speed film while running at speeds of 3, 4, 5 and 6 m s-1. The result showed that running velocity does influence external impact force peaks (linear connection) and that midsole hardness does not influence magnitude and loading rate of the external vertical impact forces. Changes in kinematic and kinetic data can be used to explain this result mechanically. However, the neuromuscular control mechanisms to keep external impact forces constant are not known.

Direct dynamics simulation of the impact phase in heel-toe running

The influence of muscle activation, position and velocities of body segments at touchdown and surface properties on impact forces during heel-toe running was investigated using a direct dynamics simulation technique. The runner was represented by a two-dimensional four- (rigid body) segment musculo-skeletal model. Incorporated into the muscle model were activation dynamics, force-length and force-velocity characteristics of seven major muscle groups of the lower extremities: mm. glutei, hamstrings, m. rectus femoris, mm. vasti, m. gastrocnemius, m. soleus and m. tibialis anterior. The vertical force-deformation characteristics of heel, shoe and ground were modeled by a non-linear visco-elastic element. The maximum of a typical simulated impact force was 1.6 times body weight. The influence of muscle activation was examined by generating muscle stimulation combinations which produce the same (experimentally determined) resultant joint moments at heelstrike. Simulated impact peak forces with these different combinations of muscle stimulation levels varied less than 10%. Without this restriction on initial joint moments, muscle activation had potentially a much larger effect on impact force. Impact peak force was to a great extent influenced by plantar flexion (85 N per degree of change in foot angle) and vertical velocity of the heel (212 N per 0.1 m s-1 change in velocity) at touchdown. Initial knee flexion (68 N per degree of change in leg angle) also played a role in the absorption of impact. Increased surface stiffness resulted in higher impact peak forces (60 N mm-1 decrease in deformation).(ABSTRACT TRUNCATED AT 250 WORDS)

The influence of foot positioning on ankle sprains

The goal of this study was to examine the influence of changes in foot positioning at touch-down on ankle sprain occurrence. Muscle model driven computer simulations of 10 subjects performing the landing phase of a side-shuffle movement were performed. The relative subtalar joint and talocural joint angles at touchdown were varied, and each subject-specific simulation was exposed to a set of perturbed floor conditions. The touchdown subtalar joint angle was not found to have a considerable influence on sprain occurrence, while increased touchdown plantar flexion caused increased ankle sprain occurrences. Increased touchdown plantar flexion may be the mechanism which causes ankles with a history of ankle sprains to have an increased susceptibility to subsequent sprains. This finding may also reveal a mechanism by which taping of a sprained ankle or the application of an ankle brace leads to decreased ankle sprain susceptibility.

Shoe inserts and orthotics for sport and physical activities.

The purposes of this paper were to discuss the perceived benefits of inserts and orthotics for sport activities and to propose a new concept for inserts and orthotics. There is evidence that inserts or orthotics reduce or prevent movement-related injuries. However, there is limited knowledge about the specific functioning an orthotic or insert provides. The same orthotic or insert is often proposed for different problems. Changes in skeletal movement due to inserts or orthotics seem to be small and not systematic. Based on the results of a study using bone pins, one may question the idea that a major function of orthotics or inserts consists in aligning the skeleton. Impact cushioning with shoe inserts or orthotics is typically below 10%. Such small reductions might not be important for injury reduction. It has been suggested that changes in material properties might produce adjustments in the muscular response of the locomotor system. The foot has various sensors to detect input signals with subject specific thresholds. Subjects with similar sensitivity threshold levels seem to respond in their movement pattern in a similar way. Comfort is an important variable. From a biomechanical point of view, comfort may be related to fit, additional stabilizing muscle work, fatigue, and damping of soft tissue vibrations. Based on the presented evidence, the concept of minimizing muscle work is proposed when using orthotics or inserts. A force signal acts as an input variable on the shoe. The shoe sole acts as a first filter, the insert or orthotic as a second filter, the plantar surface of the foot as a third filter for the force input signal. The filtered information is transferred to the central nervous system that provides a subject specific dynamic response. The subject performs the movement for the task at hand. For a given movement task, the skeleton has a preferred path. If an intervention supports/counteracts the preferred movement path, muscle activity can/must be reduced/increased. Based on this concept, an optimal insert or orthotic would reduce muscle activity, feel comfortable, and should increase performance.

Effects of arch height of the foot on angular motion of the lower extremities in running.

It has been suggested that a relationship exists between the height of the medial longitudinal arch of the foot and athletic injuries to the lower extremities. However, the functional significance of arch height in relation to injury is not well understood. The purpose of this study was to determine the influence of arch height on kinematic variables of the lower extremities that have been associated with the incidence of injury in running in an attempt to gain some insight into a functional relationship between arch height and injury. The three-dimensional kinematics of the lower extremities were measured during running for 30 subjects using high-speed video cameras. A joint coordinate system was used to calculate the three-dimensional orientation of the ankle joint complex for a single stance phase. Simple, linear regression analyses showed that arch height does not influence either maximal eversion movement or maximal internal leg rotation during running stance. However, assuming that knee pain in running can result from the transfer of foot eversion to internal rotation of the tibia, a functional relationship between arch height and injury may exist in that the transfer of foot eversion to internal leg rotation was found to increase significantly with increasing arch height. A substantial (27%), yet incomplete, amount of the variation in the transfer of movement between subjects was explained by arch height, indicating that there must be factors other than arch height that influence the kinematic coupling at the ankle joint complex. Additionally, the transfer of movement is only one factor of many associated with the etiology of knee pain in running.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of Foot Orthoses on Skeletal Motion During Running

OBJECTIVE To quantify the effects of medial foot orthoses on skeletal movements of the calcaneus and tibia during the stance phase in running. DESIGN Kinematic effects of medial foot orthoses (anterior, posterior, no support) were tested using skeletal (and shoe) markers at the calcaneus and tibia. BACKGROUND Previous studies using shoe and skin markers concluded that medially placed orthoses control/reduce foot eversion and tibial rotation. However, it is currently unknown if such orthoses also affect skeletal motion at the lower extremities. METHODS Intracortical Hofman pins with reflective marker triads were inserted under standard local anesthetic into the calcaneus and tibia of five healthy male subjects. The three-dimensional tibiocalcaneal rotations were determined using a joint coordinate system approach. Eversion (skeletal and shoe) and tibial rotation were calculated to study the foot orthoses effects. RESULTS Orthotic effects on eversion and tibial rotations were found to be small and unsystematic over all subjects. Differences between the subjects were significantly larger (p<0.01; up to 10 degrees ) than between the orthotic conditions (1-4 degrees ). Significant orthotic effects across subjects were found only for total internal tibial rotation; p<0.05). CONCLUSIONS This in vivo study showed that medially placed foot orthoses did not change tibiocalcaneal movement patterns substantially during the stance phase of running. RELEVANCE Orthoses may have only small kinematic effects on the calcaneus and tibia (measured with bone pins) as well as on the shoes (measured with shoe markers) during running of normal subjects. Present results showed that orthotic effects were subject specific and unsystematic across conditions. It is speculated that orthotic effects during the stance phase of running may be mechanical as well as proprioceptive.

Tibiofemoral and tibiocalcaneal motion during walking: external vs. skeletal markers

Abstract The purpose of this study was to determine the errors in knee (tibiofemoral) and ankle joint complex (AJC; tibiocalcaneal) rotations caused by the skin movement artefact. Intracortical bone pins were inserted into the femur, tibia, and calcaneus of five subjects. Marker triads were attached to these pins, and additionally, six skin markers to the thigh, six to the shank, and three to the shoe. For each subject three walking trials were filmed with three synchronized LOCAM cameras (50 Hz). Flexion/extension, ab/adduction, and longitudinal rotation at the tibiofemoral joint as well as plantar-/dorsiflexion, ab/adduction, and in/eversion at the AJC were calculated from both skin and bone markers during the stance phase of walking. The results showed that the errors in knee rotations were mainly caused by the thigh markers. Knee flexion/extension was generally well reflected with the use of skin markers (mean difference: 2.1°). The agreement between skin and bone marker based kinematics for ab/adduction and internal/external knee rotation ranged from good to virtually no agreement, and in some subjects, the errors exceeded the actual motion. The errors in AJC rotations were mainly caused by the markers on the shoe/foot segment. The tibiocalcaneal rotations were generally well reflected with external markers. However, tibiocalcaneal rotations derived from external markers typically exceeded the true bone motions. The results suggest that (a) knee rotations other than flexion/extension may be affected with substantial errors when using external markers, and (b) tibiocalcaneal rotations are generally well reflected with external markers, but amplitudes are overestimated.