SPORT EQUIPMENT - ENERGY AND PERFORMANCE

Over the past 30 years, sport scientists and sport equipment manufacturers have investigated ways of improving athletic equipment to enhance performance. The result is equipment that is stronger, lighter, more durable and more pleasant to use. Consequently, sport performances are faster, higher, longer and more accurate than they used to be. In fact every world record in sport which was set before 1980 has been broken an indication for the recent developments in athletic ability and improvements in athletic equipment

THE INFLUENCE OF GROUND CONTROL FOOTWEAR ON KNEE JOINT MOMENTS DURING RUNNING

Subjects who developed patellofemoral pain syndrome during running had higher internal knee abduction and external rotation moments than asymptomatic subjects (Stefanyshyn et al., in press). Footwear can significantly influence joint moments at the knee and ankle (Mündermann et al., 2003). Therefore, it was speculated that footwear could be developed specifically to reduce knee joint moments, primarily in the transverse and frontal planes. New prototypes were developed to allow the foot to displace both in a medial-lateral and anterior-posterior direction relative to the outsole. The purpose of this study was to determine if the prototype footwear allowing relative movement between the foot and outsole would reduce three-dimensional knee joint moments during running

OPTIMIZING MUSCULOSKELETAL PROPERTIES OF SPRINTERS

INTRODUCTION In sprinting events, a strong start is a major component of high-level performance. Coaches and sprinters have personal preferences on starting position and subsequent lower extremity joint angles, however there is little research on optimal start position. As the hip extensors are a key contributor to sprint performance [1], the purpose of this study was to determine the effects of altering the joint moment about the hip by manipulating hip and knee angles on block start performance. METHODS Four male sprinters (mean 100 m time 11.30 s ± 0.55 s) were recruited for this study. First, athletes performed maximal effort isometric hip extensions on a Biodex dynamometer. Hip extensor strength was tested at 90-140° of hip flexion for the front hip and 70-130° of hip flexion for the rear hip (10° increments for both). Due to biarticular muscles crossing both the hip and knee joint, the knee angle was also accounted for. Each set of hip extensor strength tests were performed at three knee angles per leg (tested in three sessions): (i) the self-selected knee angle, and the self-selected knee angle plus 10° of knee (ii) flexion and (iii) extension. Optimal joint angles were determined based on assessing the hip joint moment as a function of hip and knee angle. Participants then performed sprint starts in four positions: (i) a self-selected (control) position, (ii) a position in which only the front leg hip and knee angles were adjusted based on strength test data, (iii) a position in which only the rear leg angles were adjusted, and (iv) a position in which angles for both legs were adjusted. Five sprint starts were performed for each position. Sprint blocks were cut in half and secured to two force plates embedded in the floor to measure forces separately for each leg (2400 Hz). Kinematic data was collected using a 3D motion capture system (240 Hz). The main outcome variable for assessing performance was the total horizontal propulsive impulse, computed using Kintrak. As this was a pilot study with four subjects, no statistical analysis was performed. RESULTS Three of four athletes increased their horizontal propulsive impulse by 3.9% (9 Ns) on average compared to the control position when optimizing the front leg angles. Two of these 3 athletes also increased performance (to a lesser extent) when the angles of both legs were optimized. All athletes decreased performance when only the rear leg angle was optimized.DISCUSSION AND CONCLUSIONS Optimizing the hip and knee angles of the front leg in the starting blocks resulted in improved performance in three of the four athletes tested, while optimizing the rear leg resulted in a decrease in performance for all athletes. Previous research has shown that the front leg contributes a greater impulse during the sprint start than the rear leg [2]. As a result, we speculate that the increase in impulse from optimizing the rear leg did not compensate for the impulse lost as a result of changing the front leg. A distinguishing factor of the athlete that did not have an increased impulse when the front leg position was optimized was that he generated a much greater impulse from his rear leg when in the self-selected position. This decrease in horizontal propulsive impulse from the rear leg caused the athletes net horizontal propulsive impulse to decrease. The results of this study suggest that optimizing the sprint block positons to maximize hip extension torque based on the front leg hip torque-angle relationship is a feasible way to improve sprint start performance. Future research could assess other performance measures such as sprint times, or investigate the effect of optimizing other joint angles

Effect of Relative Marker Movement on the Calculation of the Foot Torsion Axis Using a Combined Cardan Angle and Helical Axis Approach

The two main movements occurring between the forefoot and rearfoot segment of a human foot are flexion at the metatarsophalangeal joints and torsion in the midfoot. The location of the torsion axis within the foot is currently unknown. The purpose of this study was to develop a method based on Cardan angles and the finite helical axis approach to calculate the torsion axis without the effect of flexion. As the finite helical axis method is susceptible to error due to noise with small helical rotations, a minimal amount of rotation was defined in order to accurately determine the torsion axis location. Using simulation, the location of the axis based on data containing noise was compared to the axis location of data without noise with a one-sample t-test and Fisher's combined probability score. When using only data with helical rotation of seven degrees or more, the location of the torsion axis based on the data with noise was within 0.2 mm of the reference location. Therefore, the proposed method allowed an accurate calculation of the foot torsion axis location

Effect of shoe inserts on kinematics, center of pressure, and leg joint moments during running

The purposes of this project were to assess the effect of four different shoe inserts on the path of the center of pressure (COP), to quantify the effect of these inserts on selected knee joint moments during running, and to assess the potential of COP data to predict the effects of inserts/orthotics on knee joint moments.; Kinematics for the lower extremities, resultant ankle and knee joint moments, and the path of the COP were collected from the right foot of 15 male subjects while running heel-toe with five different shoe inserts (full or half with 4.5-mm postings).; Individual movement changes with respect to the neutral insert condition were typically small and not systematic. Significant changes for the path of the COP were registered only for the full lateral insert condition with an average shift toward the lateral side. The mediolateral shift of the COP was not consistent for the full medial and the two half-shoe inserts. The subject-specific reactions to the inserts' intervention in the corresponding knee joint moments were typically not consistent. Compared with the neutral insert condition, subjects showed increases or decreases of the knee joint moments. The correlation between the individual COP shifts and the resultant knee joint moment was generally small.; The results of this study showed that subject-specific reactions to the tested inserts were often not as expected. Additionally, reactions were not consistent between the subjects. This result suggests that the prescription of inserts and/or orthotics is a difficult task and that methods must be developed to test and assess these effects. Such methods, however, are not currently available

Immediate Effects of Foot Orthoses Consistent Immediate Effects of Foot Orthoses on Comfort and Lower Extremity Kinematics, Kinetics, and Muscle Activity

In order to accommodate patients to new foot orthoses over time, two steps are required: The first is to obtain a baseline reading of the immediate effects across several weeks to ensure consistency. The second step is to look at changes with progressively longer wear periods similar to what occurs in general practice. This study addressed the first step. The purpose of this study was to determine whether the baseline reading of the immediate effects of foot orthoses on comfort and lower extremity kinematics, kinetics, and muscle activity is consistent between days. Participants were 21 recreational runners who volunteered for the study. Three orthotic conditions (posting, custom-molding, posting and custom-molding) were compared to a control (flat) insert. Lower extremity kinematic, kinetic, and EMG data were collected for 108 trials per participant and condition in 9 sessions for each person for running at 4 m/s. Comfort for all orthotic conditions was assessed in each session using a visual analog scale. Statistically significant session effects were detected using repeated-measures ANOVA (α = .05). Three of the 93 variables had a significant session effect. A significant interaction between orthotic condition and session was observed for 6 of the 93 variables. The results of this study showed that the effects of foot orthoses on comfort, lower extremity kinematics, kinetics, and muscle activity are consistent across a 3-week period when the wear time for each condition is restricted. Thus, foot orthoses lead to immediate changes in comfort, kinematics, kinetics, and muscle activity with limited use. These immediate effects of foot orthoses on comfort, kinematics, kinetics, and muscle activity are consistent between days

LOWER EXTREMITY KINEMATICS OF SKI MOTION ON HILLS

This research study aimed to collect thre- dimensional joint angles of the lower extremity during a basic ski motion in order to provide more quantitative teaching guide-lines for ski instructors. Eleven infrared cameras were placed to cover the capture volume of three different stopping movements (e.g. “Pflug Fahren”) on hills. Six ski instructors participated in the test. Three trials of each stop were selected for comparison. Based on the results, skiers tended to use the edge of the ski and maintain a wider “V” shape at the shortest stop distance (e.g. 2m) compared to the other stops. Also, each skier had to invert the foot with a less flexed and more abducted knee and hip position as the stopping distance was decreased. This information will be useful for the development of more objective teaching guide-lines for beginner skiers

Mechanical energy contributions of the lower extremity joints to athletic performance

Bibliography: p. 108-119

ATHLETE - EQUIPMENT INTERACTION

The purpose of this research is to understand how to match an athlete to a piece of athletic equipment. Individual athlete characteristics require specific equipment parameters to optimize performance. Similarly individual movement patterns can be matched to equipment characteristics to help prevent injury. The athlete and equipment form a biomechanical system influenced by biomechanical principles such as the force-length and force-velocity relationship of skeletal muscle. By understanding the athlete-equipment interaction, sport equipment can be tuned to individual athletes to maximize performance and minimize injury