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Daniel J. Petit, John D. Willson and Joaquin A. Barrios

Efforts to compare different surface marker configurations in 3-dimensional motion analysis are warranted as more complex and custom marker sets become more common. At the knee, different markers can been used to represent the proximal shank. Often, two anatomical markers are placed over the femoral condyles, with their midpoint defining both the distal thigh and proximal shank segment ends. However, two additional markers placed over the tibial plateaus have been used to define the proximal shank end. For this experiment, simultaneous data for both proximal shank configurations were independently collected at two separate laboratories by different investigators, with one laboratory capturing a walking population and the other a running population. Common discrete knee joint variables were then compared between marker sets in each population. Using the augmented marker set, peak knee flexion after weight acceptance was less (1.2−1.7°, P < .02) and peak knee adduction was greater (0.7−1.4°, P < .001) in both data sets. Similarly, the calculated peak knee flexion moment was less by 15–20% and internal rotation moment was greater by 11–18% (P < .001). These results suggest that the calculation of knee joint mechanics are influenced by the proximal shank’s segment endpoint definition, independent of dynamic task, investigator, laboratory environment, and population in this study.

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Sharon H. Thompson, Alan J. Case and Roger G. Sargent

Group exercise instructors are at particular risk for performance-related injuries because many teach multiple classes each day where they repetitively demonstrate exercise moves. To assess performance-related injuries, a paper-pencil survey was mailed to 1000 randomly selected American Council on Exercise certified group exercise instructors. Questionnaire respondents included 386 professionally certified female instructors from 48 states. Most injuries reported (77%) were of the lower extremity (feet, knee, calf, thigh, shin, ankle, hip). Less than one-fourth of the injuries (23%) were of the trunk or upper body (shoulder, arm, back). The three most commonly reported injury sites were the foot (13.1%), knee (12.5%), and back (9.5%). The three most common types of injury reported were general inflammation (20.7%), muscle strain or sprains (19.6%), and stress fractures (16.8%). Two independent variables were significantly associated with rates of injuries: obligatory exercise scores (p = .0028), and reports of a past eating disorder (p = .0007). Group exercise instructors are at particular risk for injury to the lower body. Those instructors with exercise and eating-related disorders are especially prone to activity-related injuries.

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Filipe Conceição, Mark A. King, Maurice R. Yeadon, Martin G.C. Lewis and Stephanie E. Forrester

This study aimed to determine whether subject-specific individual muscle models for the ankle plantar flexors could be obtained from single joint isometric and isovelocity maximum torque measurements in combination with a model of plantar flexion. Maximum plantar flexion torque measurements were taken on one subject at six knee angles spanning full flexion to full extension. A planar three-segment (foot, shank and thigh), two-muscle (soleus and gastrocnemius) model of plantar flexion was developed. Seven parameters per muscle were determined by minimizing a weighted root mean square difference (wRMSD) between the model output and the experimental torque data. Valid individual muscle models were obtained using experimental data from only two knee angles giving a wRMSD score of 16 N m, with values ranging from 11 to 17 N m for each of the six knee angles. The robustness of the methodology was confirmed through repeating the optimization with perturbed experimental torques (±20%) and segment lengths (±10%) resulting in wRMSD scores of between 13 and 20 N m. Hence, good representations of maximum torque can be achieved from subject-specific individual muscle models determined from single joint maximum torque measurements. The proposed methodology could be applied to muscle-driven models of human movement with the potential to improve their validity.

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John H. Hollman, Robert H. Deusinger, Linda R. Van Dillen, Dequan Zou, Scott D. Minor, Matthew J. Matava and Jack R. Engsberg

Context:

Analyses of the path of instant center of rotation (PICR) can be used to infer joint-surface rolling and sliding motion (arthrokinematics). Previous PICR research has not quantified arthrokinematics during weight-bearing (WB) movement conditions or studied the association of muscle activity with arthrokinematics.

Objective:

To examine tibiofemoral arthrokinematics and thigh-muscle EMG during WB and non-weight-bearing (NWB) movement.

Design:

2 x 9 repeated-measures experiment.

Setting:

Laboratory.

Participants:

11 healthy adults (mean age 24 years).

Main Outcome Measures:

Tibiofemoral percentage rolling arthrokinematics and quadriceps: hamstring EMG activity.

Results:

WB percentage rolling (76.0% ± 4.7%) exceeded that of NWB (57.5% ± 1.8%) through terminal knee extension (F 8,80 = 8.99, P < .001). Quadriceps:hamstring EMG ratios accounted for 45.1% and 34.7% of the variance in arthrokinematics throughout the WB and NWB movement conditions, respectively (P < .001).

Conclusions:

More joint-surface rolling occurs through terminal knee extension during WB movement and is associated with an increase in hamstring activity.

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Ricardo Pires, Thays Falcari, Alexandre B. Campo, Bárbara C. Pulcineli, Joseph Hamill and Ulysses Fernandes Ervilha

The aim of this study is to use a support vector machine algorithm to identify and classify shod and barefoot running as well as rearfoot and forefoot landings. Ten habitually shod runners ran at self-selected speed. Thigh and leg muscle surface electromyography were recorded. Discrete wavelet transformation and fast Fourier transformation were used for the assembly of vectors for training and classification of a support vector machine. Using the fast Fourier transformation coefficients for the gastrocnemius and tibialis anterior muscles presented the best results for differentiating between rearfoot/forefoot running in the window before foot-floor contact possibly due to these muscles’ critical role in determining which part of the foot will first touch the floor. The classification rate was 76% and 67%, respectively, with a probability of being random of 0.5% and 4%, respectively. For the same terms and conditions of classification, the discrete wavelet transformation produced a reduction in the percentage of correctness of 60% and 53% with a probability of having reached these levels randomly of 15% and 35%. In conclusion, based on electromyographic signals, the use a fast Fourier transformation to train a support vector machine was a better option to differentiate running forefoot/rearfoot than to use the discrete wavelet transformation. Shod/barefoot running that could not be differentiated.

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Heidi L. Petersen, C. Ted Peterson, Manju B. Reddy, Kathy B. Hanson, James H. Swain, Rick L. Sharp and D. Lee Alekel

This study determined the effect of training on body composition, dietary intake, and iron status of eumenorrheic female collegiate swimmers (n = 18) and divers (n = 6) preseason and after 16 wk of training. Athletes trained on dryland (resistance, strength, fexibility) 3 d/wk, 1.5 h/d and in-water 6 d/wk, nine, 2-h sessions per week (6400 to 10,000 kJ/d). Body-mass index (kg/m2; P = 0.05), waist and hip circumferences (P ≤ 0.0001), whole body fat mass (P = 0.0002), and percentage body fat (P ≤ 0.0001) decreased, whereas lean mass increased (P = 0.028). Using dual-energy X-ray absorptiometry, we found no change in regional lean mass, but fat decreased at the waist (P = 0.0002), hip (P = 0.0002), and thigh (P = 0.002). Energy intake (10,061 ± 3617 kJ/d) did not change, but dietary quality improved with training, as refected by increased intakes of fber (P = 0.036), iron (P = 0.015), vitamin C (P = 0.029), vitamin B-6 (P = 0.032), and fruit (P = 0.003). Iron status improved as refected by slight increases in hemoglobin (P = 0.046) and hematocrit (P = 0.014) and decreases in serum transferrin receptor (P ≤ 0.0001). Studies are needed to further evaluate body composition and iron status in relation to dietary intake in female swimmers.

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Hans H.C.M. Savelberg, Ingrid G.L. Van de Port and Paul J.B. Willems

By manipulating trunk angle in ergometer cycling, we studied the effect of body configuration on muscle recruitment and joint kinematics. Changing trunk angle affects the length of muscles that span the hip joint. It is hypothesized that this affects the recruitment of the muscles directly involved, and as a consequence of affected joint torque distributions, also influences the recruitment of more distal muscles and the kinematics of distal joints. It was found that changing the trunk from an upright position to approximately 20 deg forward or backward affected muscle activation patterns and kinematics in the entire lower limb. The knee joint was the only joint not affected by manipulation of the lengths of hip joint muscles. Changes in trunk angle affected ankle and hip joint kinematics and the orientation of the thigh. A similar pattern has been demonstrated for muscle activity: Both the muscles that span the hip joint and those acting on the ankle joint were affected with respect to timing and amplitude of EMG. Moreover, it was found that the association between muscle activity and muscle length was adapted to manipulation of trunk angle. In all three conditions, most of the muscles that were considered displayed some eccentric activity. The ratio of eccentric to concentric activity changed with trunk angle. The present study showed that trunk angle influences muscle recruitment and (inter)muscular dynamics in the entire limb. As this will have consequences for the efficiency of cycling, body configuration should be a factor in bicycle design.

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Jenna M. Kraska, Michael W. Ramsey, G. Gregory Haff, Nate Fethke, William A. Sands, Margaret E. Stone and Michael H. Stone

Purpose:

To investigate the relationship between maximum strength and differences in jump height during weighted and unweighted (body weight) static (SJ) and countermovement jumps (CMJ).

Methods:

Sixty-three collegiate athletes (mean ± SD; age= 19.9 ± 1.3 y; body mass = 72.9 ± 19.6 kg; height = 172.8 ± 7.7 cm) performed two trials of the SJ and CMJ with 0 kg and 20 kg on a force plate; and two trials of mid-thigh isometric clean pulls in a custom rack over a force plate (1000-Hz sampling). Jump height (JH) was calculated from fight time. Force-time curve analyses determined the following: isometric peak force (IPF), isometric force (IF) at 50, 90, and 250 ms, and isometric rates of force development (IRFD). Absolute and allometric scaled forces, [absolute force/(body mass0.67)], were used in correlations.

Results:

IPF, IRFD, F50a, F50, F90, and F250 showed moderate/strong correlations with SJ and CMJ height percent decrease from 0 to 20 kg. IPFa and F250a showed weak/moderate correlations with percent height decrease. Comparing strongest (n = 6) to weakest (n = 6): t tests revealed that stronger athletes (IPFa) performed superior to weaker athletes.

Conclusion:

Data indicate the ability to produce higher peak and instantaneous forces and IRFD is related to JH and to smaller differences between weighted and unweighted jump heights. Stronger athletes jump higher and show smaller decrements in JH with load. A weighted jump may be a practical method of assessing relative strength levels.

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John H. Challis

This study examined the influence of force plate targeting, via stride length adjustments, on the magnitude and consistency of ground reaction force and segment angle profiles of the stance phase of human running. Seven male subjects (height, 1.77 m ± 0.081; mass, 72.4 kg ± 7.52; age range, 23 to 32 years) were asked to run at a mean velocity of 3.2 m · s–1 under three conditions (normal, short, and long strides). Four trials were completed for each condition. For each trial, the ground reaction forces were measured and the orientations of the foot, shank, and thigh computed. There were no statistically significant differences (p > .05) between the coefficients of variation of ground reaction force and segment angle profiles under the three conditions, so these profiles were produced consistently. Peak active vertical ground reaction forces, their timings, and segment angles at foot off were not significantly different across conditions. In contrast, significant differences between conditions were found for peak vertical impact forces and their timings, and for the three lower limb segment angles at the start of force plate contact. These results have implications for human gait studies, which require subjects to target the force plate. Targeting may be acceptable depending on the variables to be analyzed.

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Antti Mero and Paavo V. Komi

The effects of running at supramaximal velocity on biomechanical variables were studied in 13 male and 9 female sprinters. Cinematographical analysis was employed to investigate the biomechanics of the running technique. In supramaximal running the velocity increased by 8.5%, stride rate by 1.7%, and stride length by 6.8% over that of the normal maximal running. The elite male sprinters increased their stride rate significantly but did not increase their stride length. The major biomechanical differences between supramaximal and maximal running occurred during the contact phase. In supramaximal running the inclination of the ground shank at the beginning of eccentric phase was more "braking" and the angle of the ground knee was greater. During the ground contact phase, the maximal horizontal velocity of the swinging thigh was faster. The duration of the contact phase was shorter and the flight phase was longer in the supramaximal run as compared to the maximal run. It was concluded that in supramaximal effort it is possible to run at a higher stride rate than in maximal running. Data suggest that supramaximal sprinting can be beneficial in preparing for competition and as an additional stimulus for the neuromuscular system during training. This may result in adaptation of the neuromuscular system to a higher performance level.