Joseph Hamill

A dynamical systems approach to lower extremity running injuries.

UNLABELLED In this paper, we are presenting an alternative approach to the investigation of lower extremity coupling referred to as a dynamical systems approach. In this approach, we calculate the phase angle of each segment and joint angle. Pairing the key segment/joint motions, we use phase angles to determine the continuous relative phase and the variability of the continuous relative phase. Data from two studies illustrate the efficacy of the dynamical systems approach. Individuals who were asymptomatic, even though they may have anatomical aberrant structural problems (i.e. high Q-angle vs low Q-angle) showed no differences in the pattern of the continuous relative phase or in the variability of the continuous phase. However, differences in the variability of the continuous relative phase were apparent in comparing individuals who were symptomatic with patellofemoral pain with non-injured individuals. Patellofemoral pain individuals showed less variability in the continuous relative phase of the lower extremity couplings than did the healthy subjects. We hypothesize that the lower variability of the couplings in the symptomatic individuals indicates repeatable joint actions within a very narrow range. RELEVANCE We claim that the traditional view of the variability of disordered movement is not tenable and suggest that there is a functional role for variability in lower extremity segment coupling during locomotion. While the methods described in this paper cannot determine a cause of the injury, they may be useful in the detection and treatment of running injuries.

Arch structure and injury patterns in runners

OBJECTIVE The purpose of this study was to determine if high-arched and low-arched runners exhibit different injury patterns. DESIGN Non-randomized, two-group injury survey. BACKGROUND Running-related injuries are thought to be related, in part, to lower extremity structure. High-arched and low-arched runners with their different bony architecture may exhibit very different lower extremity mechanics and, consequently, different injury patterns. It was hypothesized that high-arched runners will exhibit a greater incidence of lateral injuries, skeletal injuries and knee injuries while low-arched runners will show a greater incidence of medial injuries, soft tissue injuries and foot injuries. METHODS Twenty high-arched and 20 low-arched runners were included in this study. Running-related injuries were recorded and divided into injury patterns of medial/lateral, bony/soft tissue and knee/foot and ankle for both high-arched and low-arched runners. A chi(2) analysis was then employed in an attempt to associate injury patterns with arch structure. RESULTS High-arched runners reported a greater incidence of ankle injuries, bony injuries and lateral injuries. Low-arched runners exhibited more knee injuries, soft tissue injuries and medial injuries. CONCLUSIONS Based on these results, high and low arch structure is associated with different injury patterns in runners. Relevance. Different injury patterns are present in individuals with extreme high arches when compared to those with extremely low arches. These relationships may lead to improved treatment and intervention strategies for runners based on their predisposing foot structure.

The force-driven harmonic oscillator as a model for human locomotion

Abstract The study was conducted to determine whether the preferred frequency of locomotion was predictable as the least amount of energy required to drive a harmonic oscillator. Subjects were instructed to walk at a preferred rate under conditions where their ankles were unloaded and bilaterally loaded. These results were compared to the frequency which was predicted from the formula for a force-driven harmonic oscillator. The length of a simple pendulum equivalent of the lower extremity (thigh, shank, foot, and added mass) was used to approximate the length of the oscillator for prediction purposes. Results indicated that a constant of 2 applied to the gravitational constant of the period prediction formula provided a more accurate representation of the actual frequency. Similar results have been found in the walking gait of quadrupeds of widely varying sizes (Kugler and Turvey 1987).

Proximal and Distal Influences on Hip and Knee Kinematics in Runners With Patellofemoral Pain During a Prolonged Run

STUDY DESIGN Cross-sectional experimental laboratory study. OBJECTIVES To investigate the relationships between hip strength and hip kinematics, and between arch structure and knee kinematics during prolonged treadmill running in runners with and without patellofemoral pain syndrome (PFPS). BACKGROUND Hip weakness can lead to excessive femoral motions that adversely affect patellofemoral joint mechanics. Similarly, foot mechanics, which are influenced by foot structure, are also known to influence patellofemoral joint mechanics. Thus, proximal and distal factors should be considered when studying individuals with PFPS. METHODS AND MEASURES Twenty recreational runners with PFPS (5 male, 15 female) and 20 matched uninjured runners participated in the study. Hip abduction and hip external rotation isometric strength measurements were collected before and after a prolonged run, while the arch height index was recorded on all runners before the run. Lower extremity kinematic data were collected at the beginning and end of the run. Two-way repeated-measures analyses of variance (ANOVAs) were used for analysis. RESULTS Both groups displayed decreases in hip abductor and external rotator strengths at the end of the run. The PFPS group displayed significantly lower hip abduction strength [(kg x cm)/body mass] compared to controls (PFPS group: begin 15.3, end 13.5; uninjured group: begin 17.3, end 15.4). At the end of the run, the level of association between hip abduction strength and the peak hip adduction angle for the PFPS group was statistically significant, indicating a strong relationship (r = -0.74). No other associations with hip strength were observed in either group. Arch height did not differ between groups and no significant association was observed between arch height and peak knee adduction angle during running. CONCLUSIONS Runners with PFPS displayed weaker hip abductor muscles that were associated with an increase in hip adduction during running. This relationship became more pronounced at the end of the run. LEVEL OF EVIDENCE Therapy, level 5.

Predicting the minimal energy costs of human walking

Preferred stride frequency (PSF) of human walking has been shown to be predictable as the resonant frequency of a force-drive harmonic oscillator (FDHO). The purpose of this study was to determine whether walking at the PSF and FDHO leads to minimal metabolic and mechanical costs. Subjects walked on a level treadmill at the PSF, FDHO, and frequencies above and below. Effects of stride length (SL) and speed (S) were assessed by two conditions, one in which SL was constant and the other in which S was constant. The predictability of PSF from resonance was replicated. Walking at the PSF and FDHO frequencies resulted in metabolic costs which were not significantly different (P greater than 0.05). A U-shaped oxygen consumption curve was observed with the minimum at the PSF and FDHO conditions when S was constant. A two-component curve in which a breakpoint was observed was found in the SL constant condition. A significant increase in metabolic cost was observed above the PSF/FDHO (P less than 0.01). Internal work (power) values were not significantly different between walking frequencies for the S constant condition. In the SL constant condition, internal work values showed linear increases as frequency increased. It was concluded that PSF of walking arises from the interface of the resonance properties of the limbs as oscillators and the tendency of biological systems to self-optimize.

Energy absorption of impacts during running at various stride lengths

PURPOSE The foot-ground impact experienced during running produces a shock wave that is transmitted through the human skeletal system. This shock wave is attenuated by deformation of the ground/shoe as well as deformation of biological tissues in the body. The goal of this study was to investigate the locus of energy absorption during the impact phase of the running cycle. METHODS Running speed (3.83 m x s[-1]) was kept constant across five stride length conditions: preferred stride length (PSL), +10% of PSL, -10% of PSL, +20% of PSL, and -20% of PSL. Transfer functions were generated from accelerometers attached to the leg and head of ten male runners. A rigid body model was used to estimate the net energy absorbed at the hip, knee, and ankle joints. RESULTS There was an increasing degree of shock attenuation as stride length increased. The energy absorbed during the impact portion of the running cycle also increased with stride length. Muscles that cross the knee joint showed the greatest adjustment in response to increased shock. CONCLUSION It was postulated that the increased perpendicular distance from the line of action of the resultant ground reaction force to the knee joint center played a role in this increased energy absorption.

Energetic Cost and Stability during Human Walking at the Preferred Stride Frequency

Abstract The possibility that preferred modes of locomotion emerge from dynamical and optimality constraints and the energetic and dynamical constraints on preferred and predicted walking frequency are explored in this article. Participants were required to walk on a treadmill at their preferred frequency, at a frequency predicted as the resonance of a hybrid pendulum-spring model of the legs, and at frequencies ±15%, ±25%, ±35% of the predicted frequency. Walking at the preferred and predicted frequencies resulted in minimal metabolic costs and maximal stability of the head and joint actions. Mechanical energy conservation was constant across conditions. The head was more stable than the joints. The joints appeared to be in service of the head in maintaining a stable trajectory. The major findings of this study suggest a complementary relationship between energetic (physiological) and stability constraints in the adoption of a preferred frequency of walking. Multiple subsystems may be involved in constra...

Shock attenuation and stride frequency during running

Abstract Human locomotion has been modeled as a force-driven harmonic oscillator (FDHO). The minimum forcing function in locomotion has been shown to occur at the resonant frequency of the FDHO and results in the suggestion that oxygen cost may be considered an optimality criterion for locomotion. The purposes of this study were twofold: first, to determine the relationship between stride frequency and shock attenuation, and second, to determine whether shock attenuation may also be considered an optimality criterion. Ten healthy young adult males served as subjects in this study. Each subjects preferred running speed and preferred stride frequency (PSF) were determined. In addition to the PSF, they ran at stride frequencies corresponding to −20%, −10%, +10%, and +20% of the PSF at the preferred running speed. Metabolic data as well as leg and head acceleration data were collected during a steady state run at each of the stride frequency conditions. The metabolic data produced a U-shaped curve hypothesized by the FDHO model. Spectral analysis on the leg and head acceleration data were used to develop transfer functions for each of the stride frequency conditions. Analysis of the transfer function indicated that there was a gain at the low frequencies and an attenuation at the higher frequencies. The transfer function at the higher frequencies indicated that the impact shock signal was attenuated as it passed through the body. However, the transfer functions appeared to vary according to the amount of shock input to the system with the result that the head accelerations remained constant. It would appear that impact (high frequency) shock attenuation increases with stride frequency and thus does not fit the FDHO model as an optimization criterion. At all stride frequencies, regardless of the impact shock, head accelerations were maintained at a constant level.

Biomechanical and Anatomic Factors Associated with a History of Plantar Fasciitis in Female Runners

Objective:To compare selected structural and biomechanical factors between female runners with a history of plantar fasciitis and healthy control subjects. Design:Cross-sectional. Setting:University of Delaware Motion Analysis Laboratory, Newark, Delaware; and University of Massachusetts Biomechanics Laboratory, Amherst, Massachusetts. Participants:Twenty-five female runners with a history of plantar fasciitis were recruited for this study. A group of 25 age- and mileage-matched runners with no history of plantar fasciitis served as control subjects. Interventions:The independent variable was whether or not subjects had a history of plantar fasciitis. Main Outcome Measures:Subjects ran overground while kinematic and kinetic data were recorded using a motion capture system and force plate. Rearfoot kinematic variables of interest included peak dorsiflexion, peak eversion, time to peak eversion along with eversion excursion. Vertical ground reaction force variables included impact peak and the maximum instantaneous load rate. Structural measures were taken for calcaneal valgus and arch index during standing and passive ankle dorsiflexion range of motion. Results:A significantly greater maximum instantaneous load rate was found in the plantar fasciitis group along with an increased ankle dorsiflexion range of motion compared with the control group. The plantar fasciitis group had a lower arch index compared with control subjects, but calcaneal valgus was similar between groups. No differences in rearfoot kinematics were found between groups. Conclusion:These data indicate that a history of plantar fasciitis in runners may be associated with greater vertical ground reaction force load rates and a lower medial longitudinal arch of the foot.

Biomechanical predictors of retrospective tibial stress fractures in runners

Both kinematics and kinetics of the lower limb have been shown separately to be related with a history of tibial stress fractures (TSFs) in female runners. However, it is likely that these factors interact together to increase the risk of a TSF. This study was conducted to determine which combination of kinematic and kinetic factors are the best predictors of retrospective TSF in female distance runners. Total 30 female runners who had previously sustained a TSF were recruited, along with an age and mileage matched control group (n=30). Subjects ran overground at 3.7m/s while kinematic and kinetic data were recorded. Five trials from each subject were used for data analysis and ensemble means were calculated for both groups. The kinematic variables of peak hip adduction (HADD), peak knee internal rotation (KIR) and knee adduction (KADD), peak rearfoot eversion (RFEV) were entered into a binary logistic regression along with the kinetic variables of vertical instantaneous load rate (VILR) and absolute free moment (FM). The variables HADD, FM and RFEV were able to correctly predict a history of TSF in 83% of cases. Increases in HADD, FM and RFEV (odds ratios of 1.29, 1.37 and 1.18) were associated with an elevated risk of having a history of TSF. The addition of VILR, KIR and KADD did not improve the ability to predict previous injury. Based on these results, HADD, FM and RFEV appear to be the most important of the variables of interest in terms of predicting retrospective TSF in female runners.