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Saunders N. Whittlesey and Joseph Hamill

An alternative to the Iterative Newton-Euler or linked segment model was developed to compute lower extremity joint moments using the mechanics of the double pendulum. The double pendulum model equations were applied to both the swing and stance phases of locomotion. Both the Iterative Newton-Euler and double pendulum models computed virtually identical joint moment data over the entire stride cycle. The double pendulum equations, however, also included terms for other mechanical factors acting on limb segments, namely hip acceleration and segment angular velocities and accelerations Thus, the exact manners in which the lower extremity segments interacted with each other could be quantified throughout the gait cycle. The linear acceleration of the hip and the angular acceleration of the thigh played comparable roles to muscular actions during both swing and stance.

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Joseph Hamill, Michael Murphy and Donald Sussman

The mechanics of moving along a curved path suggest that runners must change their body positions and thus adjust their lower extremity function as they accomplish a track turn. The purpose of the present study was to investigate the changes in the kinetics and kinematics of the lower extremity as runners proceed around the turn of a 400-m track (radius 31.5 m). Five skilled runners served as subjects in the study and were required to perform 10 trials in three conditions, running at 6.31 m/s plus or minus 5% (4:15 min/mile pace). The right and left limbs on a track turn and the right limb on the straightaway were evaluated using ground reaction force data and kinematic data from high-speed film. Statistical analysis of the 18 ground reaction force variables and 4 kinematic variables suggested that the right and left limbs at the midpoint of the track turn were asymmetrical and that most of the differences occurred in the first portion of the footfall Significant differences were found in the touchdown angle, maximum pronation angle, all mediolateral variables, and in the vertical variables describing the collision phase of the footfall (p < .05). The data suggest that the etiologies of injuries to the right and left lower extremity differ, with right foot injuries being of the impact type and left leg injuries being of the overpronation type.

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Kristian M. O'Connor and Joseph Hamill

Roads are generally designed with a camber to facilitate drainage. Running on a cambered road has been suggested as a potential cause of injury. Two possible mechanisms are mediolateral control and impact shock. The purpose of this study was to investigate the effect of a cambered surface on rearfoot motion and impact shock. Twelve runners ran at 3.83 m/s on both a flat and a cambered surface with the left side raised for all of them. Selected rearfoot kinematic and tibial acceleration measures were evaluated using a 2 × 2 repeated-measures ANOVA. The touchdown angle was less supinated on the left (high) side than on the right (low) side on the cambered surface. Maximum pronation was greater on the left (high) high side than on the right (low) side, as was total rearfoot motion. Maximum velocity of pronation was greater under the left (high) limb than under the right (low) limb while running on the cambered road. Time to maximum pronation did not differ, nor were there differences in peak acceleration or time to peak acceleration. The results of this study suggest that running on a cambered road caused changes in rearfoot motion kinematics that may predispose an individual to injury. Also, since the impact shock did not change with changes in rearfoot motion, perhaps the role of pronation on shock attenuation should be reexamined.

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Pedro Rodrigues, Trampas TenBroek and Joseph Hamill

“Excessive” pronation is often implicated as a risk factor for anterior knee pain (AKP). The amount deemed excessive is typically calculated using the means and standard deviations reported in the literature. However, when using this method, few studies find an association between pronation and AKP. An alternative method of defining excessive pronation is to use the joints’ available range of motion (ROM). The purposes of this study were to (1) evaluate pronation in the context of the joints’ ROM and (2) compare this method to traditional pronation variables in healthy and injured runners. Thirty-six runners (19 healthy, 17 AKP) had their passive pronation ROM measured using a custom-built device and a motion capture system. Dynamic pronation angles during running were captured and compared with the available ROM. In addition, traditional pronation variables were evaluated. No significant differences in traditional pronation variables were noted between healthy and injured runners. In contrast, injured runners used significantly more of their available ROM, maintaining a 4.21° eversion buffer, whereas healthy runners maintained a 7.25° buffer (P = .03, ES = 0.77). Defining excessive pronation in the context of the joints’ available ROM may be a better method of defining excessive pronation and distinguishing those at risk for injury.

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Joseph Hamill, Graham E. Caldwell and Timothy R. Derrick

Researchers must be cognizant of the frequency content of analog signals that they are collecting. Knowing the frequency content allows the researcher to determine the minimum sampling frequency of the data (Nyquist critical frequency), ensuring that the digital data will have all of the frequency characteristics of the original signal. The Nyquist critical frequency is 2 times greater than the highest frequency in the signal. When sampled at a rate above the Nyquist, the digital data will contain all of the frequency characteristics of the original signal but may not present a correct time-series representation of the signal. In this paper, an algorithm known as Shannon's Sampling Theorem is presented that correctly reconstructs the time-series profile of any signal sampled above the Nyquist critical frequency. This method is superior to polynomial or spline interpolation techniques in that it can reconstruct peak values found in the original signal but missing from the sampled data time-series.

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Joseph Hamill, Patty S. Freedson, Priscilla M. Clarkson and Barry Braun

This study involved an 8-day protocol to determine the effects of delayed-onset muscle soreness (DOMS) on the mechanics of the lower extremity and on oxygen consumption during level running. On Day 1 the subjects, 10 healthy female recreational runners, were administered a treadmill max V̇O2 test. They completed a 30-min downhill run on Day 3 to induce muscle soreness. On Days 2, 5, and 8 they completed a 15-min level run at a speed corresponding to 80% of V̇O2max. Subsequent to each run the subjects completed a muscle soreness questionnaire and a blood sample was taken for creatine kinase (CK) analysis. Data analysis revealed statistically significant between-day differences for perceived muscle soreness and CK activity. However, metabolic cost was not different between days. There were significant differences between days in maximum ankle support dorsiflexion and plantar flexion and maximum knee flexion during both support and swing. None of the global parameters describing the total stride produced significant differences between Days 2 and 5. Therefore DOMS appeared to have little effect on V̇O2 and a small effect on the kinematics of the lower extremity.

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Carrie A. Laughton, Irene McClay Davis and Joseph Hamill

The main purpose of this study was to investigate the effects of both strike pattern (forefoot vs. rearfoot strike pattern) and orthotic intervention on shock to the lower extremity. Semi-rigid orthotic devices were manufactured for 15 injury-free recreational runners. Tibial accelerometry, ground reaction force, and 3D kinematic data were collected on their right leg in four conditions: forefoot strike (FFS) and rearfoot strike (RFS) with and without orthotics. Two-way repeated-measures analysis of variance tests were used to assess the effects of strike pattern and orthotic intervention on tibial acceleration; angular excursions of the ankle and knee; ground reaction force (GRF) vertical and anteroposterior peaks and load rates; and ankle, knee, and leg stiffness. There was a significant increase in tibial acceleration for the FFS pattern compared to the RFS pattern. This may be explained in part by the significantly greater peak vertical GRF, peak anteroposterior GRF, anteroposterior GRF load rates, knee stiffness, and leg stiffness found in the FFS pattern compared to the RFS pattern. Tibial acceleration and rearfoot eversion excursions were similar between the orthotic and no-orthotic conditions. Knee flexion excursion and average GRF vertical load rates were significantly decreased while dorsiflexion excursion and knee stiffness were significantly increased in the orthotic condition. No significant interactions were found between strike pattern and orthotic condition for any variables assessed.

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Joseph Hamill, Mark D. Ricard and Dennis M. Golden

A study was undertaken to investigate the changes in total body angular momentum about a transverse axis through the center of mass that occurred as the rotational requirement in the four categories of nontwisting platform dives was increased. Three skilled subjects were filmed performing dives in the pike position, with increases in rotation in each of the four categories. Angular momentum was calculated from the initiation of the dive until the diver reached the peak of his trajectory after takeoff. In all categories of dives, the constant, flight phase total body angular momentum increased as a function of rotational requirement. Increases in the angular momentum at takeoff due to increases in the rotational requirement ranged from a factor of 3.61 times in the forward category of dives to 1.52 times in the inward category. It was found that the remote contribution of angular momentum contributed from 81 to 89% of the total body angular momentum. The trunk accounted for 80 to 90% of the local contribution. In all categories of dives except the forward 1/2 pike somersault, the remote percent contribution of the arms was the largest of all segments, ranging from 38 to 74% of the total angular momentum.

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Timothy R. Derrick, Graham E. Caldwell and Joseph Hamill

A modified mass-spring-damper model was used to simulate the vertical ground reaction forces of a human runner as stride length was altered. Spring stiffness values were selected by an optimizing routine that altered model parameters to match the model ground reaction force curve to a runner’s actual ground reaction force curve. A mass in series with a spring was used to simulate the behavior of body structures that produce the active portion of the ground reaction force. A second mass in series with a spring-damper system was used to simulate the behavior of those components that cause the impact portion of the ground reaction force. The stiffness of the active spring showed a 51% decrease as subjects increased their stride length. The stiffness value of the impact spring showed a trend opposite that of the active spring, increasing by 20% as strides lengthened. It appears that the impact stiffness plays a role in preventing the support leg from collapsing in response to the increased contact velocities seen in the longer strides.

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Joseph Hamill, Jeffrey M. Haddad and William J. McDermott

Variability is a critical aspect of a dynamical systems analysis. Because there are a number of numerical techniques that can be used in such an analysis, the calculation of variability has several issues that must be addressed. The purpose of this paper is to present a variety of quantitative methods for investigating variability from a dynamical systems perspective. The paper is divided into two major sections covering discrete and continuous methods. Each of these sections is subdivided into two sections. Within discrete methods, we discuss, first, the calculation of the discrete relative phase from a time-series history of two parameters and, second, the use of return maps. Using continuous methods, we present procedures for using angle-angle plots in the evaluation of relative phase. We then discuss the use of phase plots in the calculation of the continuous relative phase. Each of these methods presents unique problems for the researcher and the method to be used is determined by the nature of the question asked.