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Edward C. Frederick

Elite biathletes now ski using skating techniques in place of the more traditional diagonal stride. Because of the more extreme flexion and extension of the trunk with these new techniques, it has become necessary to reevaluate the method of rifle carriage. This paper describes a model which evaluates the incremental mechanical power required to move the additional weight of the rifle through defined angular flexions and extensions of the trunk. By combining this model with actual observations of typical kinematics of trunk flexion, we can generate realistic estimates of the energy cost of rifle carriage. This approach is also used to evaluate the energy consequences of reduced rifle mass and of different rifle carriage strategies while moving with ski skating techniques. These results show that rotational kinetic energy changes are a minor part of the overall energy cost of rifle carriage, and that changes in the horizontal velocity of the rifle are the greatest source of increased cost of transport. The largest reductions in this cost, however, would come from reducing rifle mass because both potential and kinetic energies are affected. Additional but secondary reductions can be obtained by placing the rifle center of mass opposite the lumbosacral joint, thereby reducing horizontal and vertical excursions of the rifle.

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Glenn M. Street and Edward C. Frederick

This paper describes a system that was developed to measure ski pole and roller-ski reaction forces in three dimensions during roller-ski skating. Uni-axial force transducers mounted in the right and left ski poles measure axial loading of the poles. Six transducers in one roller-ski measure biaxial loads beneath the foot. A remote computer stores the amplified transducer signals transmitted from the skier through 100 m cables. Three-dimensional video-graphy determines the orientations of the poles and roller-ski in order to resolve the resultant poling and skating forces into three components. Calibration data suggest that the resolution of the force measurement system is ±3 to 9% of the actual poling and skating forces, respectively. Sample data are presented from a VI skating trial during roller-skiing. These data provide the first glimpse at the major functions of the upper and lower body during roller-ski skating and show how the tool could be used to examine the size and effectiveness of skier-generated forces.

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Edward C. Frederick and John L. Hagy

Nine subjects (6 males, 3 females) ranging in body mass from 90.9 to 45.5 kg ran repeated trials across a force platform while being filmed at 50 fps. The subjects ran five barefooted trials at each of three speeds: 3.35, 3.83, and 4.47 m · s−1. Force data were collected on-line and analyzed for the magnitude and temporal characteristics of the initial impact (Fz1) peak and the active (Fz2) peak of vertical ground reaction force (VGRF). Multiple regression and correlation analysis were used to study the relationship between the magnitudes of these kinetic data and kinematic and anthropometric data taken from the film and from measurements of the subjects. The results support the general conclusion that speed and, indirectly, body mass are significant effectors of the magnitudes of Fz1. In addition, other factors that correlate significantly with Fz1 are reciprocal ponderal index (RPI) and stature; half-stride length, step length, leg length, and vertical hip excursion during a half-stride cycle; and hip offset, contact angle, and dorsiflexion angle at contact. Body mass correlates highly with Fz2 (r = 0.95). Other significant factors correlating with Fz2 are RPI, stature, vertical hip excursion, dorsiflexion angle, hip offset, half-stride length, and step length. These data support earlier findings that speed and the effective mass of the leg at contact are important effectors of the magnitude of Fzl. In addition, the kinematic and anthropometric parameters that contribute significantly to the variability in Fzl and F are generally cross-correlated with body size and/or running speed.

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Benno M. Nigg, Edward C. Frederick, Michael R. Hawes and Simon M. Luethi

Pain, discomfort, and/or injuries in tennis can be influenced by the individual movement pattern and the external and/or internal boundary conditions. The influence of external boundary conditions on the occurrence of short-term pain was studied in a prospective study with 229 subjects. The boundary conditions investigated were shoe, temperature, type and length of game and subjective assessment of comfort, sole grip, and lateral stability Pain was reported by 40% of the 171 subjects included in the final analysis. It was frequently reported in the first two playing sessions but less frequently afterward. Discomfort was the dominant type of pain, accounting for 71.6% of all reported cases. The foot was the major site of pain (85%). The boundary conditions influencing pain were found to be the shoe (the more flexible shoe 1 had less pain than the suffer shoe 2), the type of game (competitive more than recreational), and the length of the game (longer playing sessions with more pain). Subjective assessment of comfort, sole grip, and lateral support also showed differences for the pain/no pain groups. Subjects who complained about these aspects were more frequently in the pain groups. The results show that the occurrence of pain in tennis can be influenced by various external boundary conditions.

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Simon M. Luethi, Edward C. Frederick, Michael R. Hawes and Benno M. Nigg

The purpose of this study was to analyze the influence of footwear on the kinematics and the mechanical load on the lower extremities during fast lateral movements in tennis. The method used was a prospective study. Two types of tennis shoes were randomly distributed among 229 tennis players. The subjects were measured before starting a 3-month test period. The study showed that the kinematics of the lower extremities and internal load conditions during fast lateral movements in tennis are highly influenced by the type of shoe worn. The results further suggest that a prospective biomechanical analysis can be used to establish assumptions concerning the etiology of pain and injuries in sports related activities.

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Trampas M. TenBroek, Pedro A. Rodrigues, Edward C. Frederick and Joseph Hamill

The purpose of this study was to: (1) investigate how kinematic patterns are adjusted while running in footwear with THIN, MEDIUM, and THICK midsole thicknesses and (2) determine if these patterns are adjusted over time during a sustained run in footwear of different thicknesses. Ten male heel-toe runners performed treadmill runs in specially constructed footwear (THIN, MEDIUM, and THICK midsoles) on separate days. Standard lower extremity kinematics and acceleration at the tibia and head were captured. Time epochs were created using data from every 5 minutes of the run. Repeated-measures ANOVA was used (P < .05) to determine differences across footwear and time. At touchdown, kinematics were similar for the THIN and MEDIUM conditions distal to the knee, whereas only the THIN condition was isolated above the knee. No runners displayed midfoot or forefoot strike patterns in any condition. Peak accelerations were slightly increased with THIN and MEDIUM footwear as was eversion, as well as tibial and thigh internal rotation. It appears that participants may have been anticipating, very early in their run, a suitable kinematic pattern based on both the length of the run and the footwear condition.

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Edward C. Frederick, Jeremy J. Determan, Saunders N. Whittlesey and Joseph Hamill

Seven top amateur or professional skateboarders (BW = 713 N ± 83 N) performed Ollie maneuvers onto and off an elevated wooden platform (45.7 cm high). We recorded ground reaction force (GRF) data for three Ollie Up (OU) and Ollie Down (OD) trials per participant. The vertical GRF (VGRF) during the OU has a characteristic propulsive peak (M = 2.22 body weight [BW] ± 0.22) resulting from rapidly rotating the tail of the board into the ground to propel the skater and board up and forward. The anterior-posterior (A-P) GRF also shows a pronounced peak (M = 0.05 ± 0.01 BW) corresponding with this propulsive VGRF peak. The initial phase of landing in the OD shows an impact peak in VGRF rising during the first 30 to 80 ms to a mean of 4.74 ± 0.46 BW. These impact peaks are higher than expected given the relatively short drop of 45.7 cm and crouched body position. But we observed that our participants intentionally affected a firm landing to stabilize the landing position; and the Ollie off the platform raised the center of mass, also contributing to higher forces.

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Bastiaan Breine, Philippe Malcolm, Veerle Segers, Joeri Gerlo, Rud Derie, Todd Pataky, Edward C. Frederick and Dirk De Clercq

In running, foot contact patterns (rear-, mid-, or forefoot contact) influence impact intensity and initial ankle and foot kinematics. The aim of the study was to compare impact intensity and its spatial distribution under the foot between different foot contact patterns. Forty-nine subjects ran at 3.2 m·s−1 over a level runway while ground reaction forces (GRF) and shoe-surface pressures were recorded and foot contact pattern was determined. A 4-zone footmask (forefoot, midfoot, medial and lateral rearfoot) assessed the spatial distribution of the vertical GRF under the foot. We calculated peak vertical instantaneous loading rate of the GRF (VILR) per foot zone as the impact intensity measure. Midfoot contact patterns were shown to have the lowest, and atypical rearfoot contact patterns the highest impact intensities, respectively. The greatest local impact intensity was mainly situated under the rear- and midfoot for the typical rearfoot contact patterns, under the midfoot for the atypical rearfoot contact patterns, and under the mid- and forefoot for the midfoot contact patterns. These findings indicate that different foot contact patterns could benefit from cushioning in different shoe zones.

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Irene S. McClay, John R. Robinson, Thomas P. Andriacchi, Edward C Frederick, Ted Gross, Philip Martin, Gordon Valiant, Keith R. Williams and Peter R. Cavanagh

Basketball is a sport that involves multiple impacts with the ground through a variety of moves such as running Jumping, and cutting. Repetitive impacts have been associated with stress-related injuries in other sports such as running. The purpose of this investigation was to gain an understanding of the typical stresses the body experiences during common basketball moves. To this end, the ground reaction forces from 24 players from five professional basketball teams were studied. In addition, a game analysis was performed to determine the frequency of selected moves. These data indicated that certain common movements, such as jump landings and shuffling, resulted in absolute and relative forces much greater than many of those reported previously in studies of other sports. These movements were also identified in a companion paper as being associated with large angular excursions and velocities. Findings are discussed with respect to injury risks, and suggestions for future study are made.