A dynamic finite element model of a shod running footstrike was developed and driven with 6 degree of freedom foot segment kinematics determined from a motion capture running trial. Quadratic tetrahedral elements were used to mesh the footwear components with material models determined from appropriate mechanical tests. Model outputs were compared with experimental high-speed video (HSV) footage, vertical ground reaction force (GRF), and center of pressure (COP) excursion to determine whether such an approach is appropriate for the development of athletic footwear. Although unquantified, good visual agreement to the HSV footage was observed but significant discrepancies were found between the model and experimental GRF and COP readings (9% and 61% of model readings outside of the mean experimental reading ± 2 standard deviations, respectively). Model output was also found to be highly sensitive to input kinematics with a 120% increase in maximum GRF observed when translating the force platform 2 mm vertically. While representing an alternative approach to existing dynamic finite element footstrike models, loading highly representative of an experimental trial was not found to be achievable when employing exclusively kinematic boundary conditions. This significantly limits the usefulness of employing such an approach in the footwear development process.
Iain Hannah, Andy Harland, Dan Price, Heiko Schlarb and Tim Lucas
Simo Ihalainen, Vesa Linnamo, Kaisu Mononen and Sami Kuitunen
To describe the long-term changes in shooting technique in relation to competition performances in elite air-rifle shooters.
Seventeen elite shooters completed simulated air-rifle shooting-competition series in 3 consecutive seasons, participating on 15 ± 7 testing occasions. Shooting score and aiming-point-trajectory variables were obtained with an optoelectronic shooting device, and postural-balance variables were measured with force platform. Shooters’ competition results were collected from all international and national competitions during the 3-y period.
Mean test score, stability of hold, aiming accuracy, cleanness of triggering, and postural balance improved during the 3-y period (ANOVA, time, P < .05−.01). Seasonal mean test results in stability of hold (R = −.70, P = .000) and cleanness of triggering (R = −.75, P = .000) were related to competition performances. Changes in stability of hold (R = −.61, P = .000) and cleanness of triggering (R = −.39, P = .022) were also related to the changes in competition performances. Postural balance in shooting direction was more related to cleanness of triggering (R = .57, P = .000), whereas balance in cross-shooting direction was more related to stability of hold (R = .70, P = .000).
The shooting-technique testing used in the current study seems to be a valid and useful tool for long-term performance assessment. Stability of hold, cleanness of triggering, and postural balance can be further developed even at the elite level, resulting in improved competition performances.
Paavo V. Komi
To understand cross-country (X-C) siding it is important to record and identity forces of skis and poles separately and together. They both contribute to the forward progression, but their functional significance may be more complex than that of the ground reaction forces in running and walking. This report presents two methods to record forces on skis and poles during normal X-C skiing. A long force-platform system with four rows of 6-m long plates is placed under the snow track for recording of Fz and Fy forces of each ski and pole separately. This system is suitable especially for the study of diagonal technique under more strict experimental conditions. The second system consists of small lightweight Fz and Fy component force plates which are installed under the boot and binding. These plates can be easily changed from one ski to another, and telemetric recording allows free skiing over long distances and with different skiing techniques, including skating. The presentation emphasizes the integrated use of either system together with simultaneous cinematographic and electromyographic recordings.
Timothy J. Suchomel and Christopher J. Sole
The force-production characteristics of 3 weight-lifting derivatives were examined by comparing the force–time curves of each exercise. Sixteen resistance-trained men performed repetitions of the hang power clean (HPC), jump shrug (JS), and hang high pull (HHP) on a force platform at several relative loads. Relative peak force (PFRel), relative impulse (IMPRel), peak rate of force development (PRFD), and time-normalized force–time curves of each exercise were compared. The JS produced greater PFRel than the HPC (P < .001, d = 1.38) and HHP (P < .001, d = 1.14), while there was no difference between the HPC and HHP (P = .338, d = 0.26). Similarly, the JS produced greater IMPRel than the HPC (P < .001, d = 0.52) and HHP (P = .019, d = 0.36). The HHP also produced greater IMPRel than the HPC (P = .040, d = 0.18). Finally, the JS produced greater PRFD than the HPC (P < .001, d = 0.73) and HHP (P = .001, d = 0.47), while there was no difference between the HPC and HHP (P = .192, d = 0.22). The HPC, JS, and HHP force–time profiles were similar during the first 75–80% of the movement; however, the JS produced markedly different force–time characteristics in the final 20–25% of the movement. The JS produced superior force-production characteristics, namely PFRel, IMPRel, and PRFD, as well as a unique force–time profile, compared with the HPC and HHP across several loads.
This article is a contribution to the experience of testing motor fitness and exploring the EUROFIT test in young children. In the age group 5–7 years, the motor fitness tests showed strong dependency on age and a small dependence on sex. Body weight and height did not appear to have any impact on the test variables for this age group. The reliability test showed significant difference between test and retest in the plate tapping test only. The reproducibility was low in bent arm hang and flamingo balance, with coefficients of variation of 67%. Modest validity of the flamingo balance test and the standing broad jump test was confirmed with correlations of 0.43 and 0.52, respectively, by laboratory testing on a force platform. Factor analyses extracted 3 components, which explained 62% of the total variance, but no single component could explain general motor fitness. The EUROFIT Motor Fitness Test appeared to be applicable also in young children, but the reproducibility of two test items was questionable. Modification of test items was suggested to fit this age group.
C. Roger James, Barry T. Bates and Janet S. Dufek
The purposes of this study were to (a) present a theoretical model to explain the methods by which individuals accommodate impact force in response to increases in an applied stressor, (b) use the model and a correlation procedure to classify a sample of individuals based on their observed response patterns, and (c) statistically evaluate the classification process. Ten participants performed landings from three heights while video and force platform data were being collected. Magnitudes of impact-force characteristics from ground reaction force and lower extremity joint moments were evaluated relative to changes in landing momentum. Correlation between impact force and landing momentum was used to classify participant responses into either a positive or negative biomechanical strategy, as defined by the model. Positive and negative groups were compared using the Mann-Whitney U test. Results indicated that all responses fit within the categories defined by the model. Some individuals preferred positive strategies while others preferred negative ones depending on the specific variable. Only one participant consistently exhibited the negative strategy for all variables. Positive and negative groups were determined to be statistically different, p ≤ 0.05, for 61% of the comparisons, suggesting actual differences between groups. The proposed model appeared robust and accounted for all responses in the current experiment. The model should be evaluated further using landing and other impact activities; it should be refined and used to help researchers understand individual impact-response strategies in order to identify those who may be at risk for impact related injuries.
Erik B. Simonsen, Morten B. Svendsen, Andreas Nørreslet, Henrik K. Baldvinsson, Thomas Heilskov-Hansen, Peter K. Larsen, Tine Alkjær and Marius Henriksen
The aim of the study was to investigate the distribution of net joint moments in the lower extremities during walking on high-heeled shoes compared with barefooted walking at identical speed. Fourteen female subjects walked at 4 km/h across three force platforms while they were filmed by five digital video cameras operating at 50 frames/second. Both barefooted walking and walking on high-heeled shoes (heel height: 9 cm) were recorded. Net joint moments were calculated by 3D inverse dynamics. EMG was recorded from eight leg muscles. The knee extensor moment peak in the first half of the stance phase was doubled when walking on high heels. The knee joint angle showed that high-heeled walking caused the subjects to flex the knee joint significantly more in the first half of the stance phase. In the frontal plane a significant increase was observed in the knee joint abductor moment and the hip joint abductor moment. Several EMG parameters increased significantly when walking on high-heels. The results indicate a large increase in bone-on-bone forces in the knee joint directly caused by the increased knee joint extensor moment during high-heeled walking, which may explain the observed higher incidence of osteoarthritis in the knee joint in women as compared with men.
Benno M. Nigg and H. Alexander Bahlsen
The purpose of this study was to determine the influence of lateral heel flare on pronation, external impact forces, and takeoff supination for different midsole constructions. Data were collected using force platforms and high-speed film cameras. Fourteen male subjects participated in the study, running heel-toe at a speed of 4 m/s. The analysis of kinetic and kinematic variables showed that changes in lateral heel flare of 16°, 0°, and a rounded heel can be used to influence initial pronation during heel-toe running. It could be shown that changes in lateral heel flare do not have a relevant influence on changes in total and/or maximal pronation. Changes in lateral heel flare do have an effect on vertical impact force peaks if the midsole is relatively hard but not if the midsole is relatively soft. Based on the present study, a running shoe with a relatively hard midsole material and a neutral flare would have low initial pronation values and low vertical impact force peaks.
Thomas A. Haugen, Espen Tønnessen and Stephen Seiler
To compare sprint and countermovement-jump (CMJ) performance among competitive soccer players as a function of performance level, field position, and age. In addition, the authors wanted to quantify the evolution of these physical characteristics among professional players over a 15-y period.
939 athletes (22.1 ± 4.3 y), including national-team players, tested 40-m sprint with electronic timing and CMJ on a force platform at the Norwegian Olympic Training Center between 1995 and 2010.
National-team and 1st-division players were faster (P < .05) than 2nd-division (1.0–1.4%), 3rd- to 5th-division (3.0–3.8%), junior national-team (1.7–2.2%), and junior players (2.8–3.7%). Forwards were faster than defenders (1.4%), midfielders (2.5%), and goalkeepers (3.2%) over 0–20 m (P < .001). Midfielders jumped ~2.0 cm lower than the other playing positions (P < .05). Sprinting velocity peaked in the age range 20–28 y and declined significantly thereafter (P < .05). Players from 2006–2010 had 1–2% faster 0–20 m and peak velocity than players from the 1995–1999 and 2000–2005 epochs, whereas no differences in CMJ performance were observed.
This study provides effect-magnitude estimates for the influence of performance level, position, and age on sprint and CMJ performance in soccer. While CMJ performance has remained stable over the time, there has been a small but positive development in sprinting velocity among professional players.
Melvin R. Ramey and Keith R. Williams
Ground reaction forces were obtained for the three phases of the triple jump for four collegiate triple jumpers, two men and two women. A single force platform was used, which thereby required the subjects to execute three separate jumps to produce a single triple jump record. The vertical force records for each phase showed two peaks having magnitudes in the range of 7 to 12 times body weight (BW) and 3.3 to 5 BW, respectively. These magnitudes are substantially higher than has been reported by others for distance running, sprinting, and in some cases other jumps. The maximum horizontal forces act to decrease the velocity of the mass center, but to different degrees for the different subjects. The data show that for any phase of the jump there is considerable variability in the timing and magnitudes of the force records among the different subjects although general patterns are similar. The results suggest that the use of mean force data from a number of subjects may conceal important differences between the way individuals execute the jump.