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Biomedical subjects

J Hamill

Publications and source records attributed to J Hamill.

At least 37 records · Page 2Linked to original sources
PubMed1997

Caval thrombectomy for severe staphylococcal osteomyelitis.

Two children are presented in whom thrombosis of the inferior vena cava developed in association with an acute staphylococcal osteomyelitis. One case involved the left femur and the other the left ileum. Both children had diffuse bilateral staphylococcal pneumonia from presumed septic embolization. There were close similarities between their illness and management, except that the child who survived underwent a caval thrombectomy in the acute phase of her illness. It is hypothesized that the thrombectomy played an important role in her recovery.

Acute Disease↗
PubMed1997

Impact shock and attenuation during in-line skating.

Although impact and shock attenuation associated with foot contact during running has been studied extensively, much less is known about these phenomena during in-line skating (ILS). The purpose of this study was to describe these impact characteristics for ILS and to test the hypothesis that there is lower impact shock during ILS than in running at preferred velocities. Subjects ran and skated on a treadmill at preferred velocity, with low-mass accelerometers attached to both the distal tibia and head. Tibia and head acceleration data during stance were used to calculate peak acceleration (PA), peak frequency (PF), and median frequency (MedF). Impact attenuation (IA) between the tibia and head was quantified by comparison of PA values and by calculating a transfer function between the head and tibia frequency spectra. PA, PF, and MedF values were significantly lower in ILS than in running for both tibial and head data, whereas ILS was similar between the two movements. The ILS condition exhibited almost no power in the frequency range between 10 and 20 Hz, which has been associated with the foot impacting the ground. It is concluded that in-line skating results in less impact shock to the body with each foot contact, and may be a useful exercise modality for those wishing to reduce impact shock during aerobic training.

Adult↗
PubMed1996

The prediction of power and efficiency during near-maximal rowing.

The relationship between power and gross efficiency during near-maximal rowing, and physiological measures of strength, power, aerobic and anaerobic capacities and United State Rowing Association (USRA) performance tests (independent variables) was investigated among collegiate male rowers. Criterion measures of rowing power and gross efficiency were measured in a moving-water rowing tank, using an oar instrumented with strain gauges to assess force and a potentiometer to assess oar position. Bivariate correlation analysis (n = 28) indicated no relationship between the independent variables and rowing gross efficiency (P > 0.05). Rowing power [mean (SD) 483.4 (34.75) W] was significantly related to inboard leg extension strength (IL strength, r = 0.63), outboard leg extension strength (r = 0.45), combined leg extension strength (r = 0.45), and time to complete the USRA 2000-m simulated rowing race (r = -0.52; P <0.05). Stepwise regression using resampling cross-validation of 15 random samples (21 subjects per sample selected from a total group of 28 intercollegiate oarsmen) indicated that predictors of rowing power were IL strength and blood lactate following a peak oxygen uptake rowing test with significant multiple correlations of R 0.61 to 0.86 (P <0.05). The standard error of estimate (SEM) ranged from 18.1 to 29.9 W, or 5.3 (0.77) percent of the criterion value. Cross-validation with a hold-out group (seven subjects per sample) was performed for each equation and correlations ranged from R = 0.14 to 0.97 (SEM = 8.0 to 38.9 W). In conclusion, data from the present study suggest that to increase rowing power, training should emphasize leg strength and anaerobic training to decrease the level of lactate accumulated during rowing.

Adult↗
PubMed1995

Energetic Cost and Stability During Human Walking at the Preferred Stride Velocity.

The possibility that preferred modes of locomotion emerge from dynamical and optimality constraints and the energetic and dynamical constraints on preferred and predicted walking frequency are explored in this article. Participants were required to walk on a treadmill at their preferred frequency, at a frequency predicted as the resonance of a hybrid pendulum-spring model of the legs, and at frequencies +/-15%, +/-25%, +/-35% of the predicted frequency. Walking at the preferred and predicted frequencies resulted in minimal metabolic costs and maximal stability of the head and joint actions. Mechanical energy conservation was constant across conditions. The head was more stable than the joints. The joints appeared to be in service of the head in maintaining a stable trajectory. The major findings of this study suggest a complementary relationship between energetic (physiological) and stability constraints in the adoption of a preferred frequency of walking. Multiple subsystems may be involved in constraining observed macroscopic behavior in intact biological systems. The approach and results of the study imply that a useful tack in understanding how dynamical control structures arise is to study the potential criteria that serve to act as constraints on skilled movement patterns in unimpaired and impaired populations.

Journal Article↗
PubMed1995

Ovarian Sertoli-Leydig cell tumor with retiform pattern.

Sertoli-Leydig cell tumors (SLCT) are sex cord-stromal tumors which exhibit testicular differentiation.1 They account for less than 0.2% of ovarian neoplasms in total but comprise 4% of ovarian tumors in females under 20 yrs of age.2 The morphological appearance of these tumors varies more widely than that of any other ovarian tumor except for the teratomas. Histologically they are now classified into 5 categories: well-differentiated, intermediately differentiated, poorly differentiated, heterologous and retiform.1 We describe the case of an ovarian Sertoli-Leydig cell tumor with retiform pattern in a 7 yr old girl.

Child↗
PubMed1994

Lower extremity mechanics and energy cost of walking in high-heeled shoes.

In today's society, many women wear high-heeled shoes. However, the effect that shoes of different heel heights have on the biomechanics and energy cost of gait has not been fully investigated. In the present study, the energy cost and the lower extremity mechanics in shoes of different heel heights (1.25 cm, 3.81 cm, 5.08 cm, and 7.62 cm) were examined in 15 female subjects, seven of whom could be considered experienced high-heel wearers. Kinematic data from high-speed video and kinetic data from a force platform were collected to describe lower extremity mechanics while subjects walked overground at a speed of 4.2 km/hour. Heart rate and oxygen consumption were monitored while subjects walked on a treadmill, also at 4.2 km/hour. There were no significant differences in any of the parameters as a function of experience in wearing high heels; therefore, the data were pooled for further analysis. Analysis of the biomechanical data revealed that ankle plantar flexion, knee flexion, vertical ground reaction force, and the maximum anteroposterior braking force increased as a function of heel height. In addition, the timing of the subtalar and knee joint action was asynchronous with the increase in heel height. Metabolically, heart rate and oxygen consumption also increased with heel height. There were many significant differences between the 5.08-cm and the 7.62-cm heel conditions. Therefore, to maintain comfort and decrease the risk of injury, women may be advised not to wear shoes with a heel height greater than 5.08 cm.

Adolescent↗
PubMed1993

Multicentre evaluation of azithromycin and penicillin V in the treatment of acute streptococcal pharyngitis and tonsillitis in children.

Of 96 children (aged 2-12 years) with either acute pharyngitis or acute tonsillitis, 49 received a single daily dose of azithromycin 10 mg/kg (maximum 500 mg) for three days, and 47 received penicillin V at a dose of 125 mg or 250 mg qid (depending on body weight) for ten days. Clinical assessments and laboratory safety tests were performed during and after therapy. Before enrollment, all patients were screened for group A beta-haemolytic streptococci (GABHS) with a rapid test, and a throat swab was taken for confirmatory culture. The presence of GABHS at baseline was confirmed in 41 azithromycin- and 44 penicillin V-treated patients. Cure or improvement was seen in 98% and 100% of azithromycin- and penicillin V-treated patients, respectively. At day 11, bacterial eradication was achieved in 39/41 (95%) azithromycin-treated patients, 38 (93%) of whom were considered clinically cured, while one patient (2%) relapsed. In the penicillin V group, 42/44 (95%) had GABHS eradicated, with 41 (93%) clinically cured and three patients (7%) improved. The remaining two patients in each group were clinically cured despite persistence of Streptococcus pyogenes. At follow-up evaluation (day 30), re-occurrence was observed in 5/37 (14%) and 3/40 (8%) of azithromycin- and penicillin V-treated patients, respectively; all patients were asymptomatic. Both drugs were well-tolerated with only two patients in the azithromycin group complaining of side effects. Treatment related laboratory test abnormalities were observed in 6/47 (13%) and 4/45 (9%) azithromycin- and penicillin V-treated patients, respectively, but none was judged to be clinically significant.(ABSTRACT TRUNCATED AT 250 WORDS)

Acute Disease↗
PubMed1992

Timing of lower extremity joint actions during treadmill running.

It has been suggested that a disruption in timing between the subtalar and knee joints may be a possible mechanism for knee injury. It has also been documented that shoe construction can alter rearfoot motion. The purpose of the study was to describe the relationship between the subtalar and knee joint actions during the support phase of treadmill running while wearing different shoes. Twelve healthy subjects ran in each of three running shoes with unique midsole durometers (C1, 70; C2, 55; C3, 45). High-speed video (200 Hz) of the rear and sagittal views of each subject/condition were taken during the last minute of a 5-min run. Retro-reflective markers were processed to determine the rearfoot angle and the sagittal view knee angle. The shoes were also subjected to a midsole material impact test. The impact test results indicated a linear trend in peak g and time to peak g across midsoles with the firmer midsole having a greater peak g and a shorter time to peak g. The results of the kinematic analysis indicated that there were no significant differences among the shoe conditions for the knee flexion parameters. However, there were significant differences in both the magnitude and the time to maximum pronation between the two firmer midsole conditions (C1 and C2) and the softer midsole condition (C3), indicating a nonlinear trend for these parameters. The softer midsole exhibited greater pronation values and a shorter time to maximum pronation.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1992

Effect of internal work on the calculation of optimal pedaling rates.

The purpose of this study was to calculate optimal pedaling rates based upon external work (EW) rate and mechanical work (MW) rate criteria that respectively exclude and include the internal work (IW) rate of the lower limbs. Metabolic and kinematic data were collected as 12 males pedaled an ergometer at rates of 40, 60, 80, and 98 rpm while producing external power outputs of 49, 98, and 146 W. Energy expenditure (EE) was calculated from steady rate oxygen uptake and respiratory exchange ratio values. The IW rate was determined from digitized kinematic data by modeling the thigh, shank, and foot as a three-segment linked system and calculating their changes in potential, translational kinetic, and rotational kinetic energy. The EW rate was calculated from the observed pedaling rate and the ergometer resistance. The MW rate was defined as the sum of the EW rate and IW rate. At each level of external power output, the MW rate increased linearly with pedaling rate increments while the EE displayed a curvilinear relationship. Both gross efficiency (GE = EW rate/EE) and mechanical efficiency (ME = MW rate/EE) responded quadratically to pedaling rate treatments but a repeated measures ANOVA revealed significant differences in their beta 0, beta 1, and beta 2 regression coefficients. Optimal pedaling rates calculated from ME were consistently higher (82 to 101 rpm) than those determined from GE (35 to 57 rpm). The pedaling rates that optimized ME, but not GE, are similar to the rates reported to be biomechanically optimal and preferred by trained cyclists. This study demonstrates that the choice of a work rate criterion can alter the meaning and interpretation of metabolic data.

Adult↗
PubMed1991

Effects of asymmetric load carrying on the biomechanics of walking.

The purpose of the study was to investigate the effects of an asymmetric sidepack carrying system on frontal plane joint moments of force in both lower extremities and in the L5/S1 joint during level walking. Ground reaction force data and frontal plane film records were obtained from five males performing three walking conditions: 0, 10 and 20% bodyweight loads in a sidepack supported by the left shoulder. Inverse dynamics were used to calculate the lower extremity moments during stance and a static model of the pelvis was used to calculate the L5/S1 moments during single support for each limb. Normal walking was characterized by symmetric kinetics between left and right limbs and around the L5/S1 joint. The asymmetric loads produced unbalanced lateral trunk muscle dominance between left and right limb stance phases, increased right hip and knee moments and decreased left hip and knee moments. During normal walking, the L5/S1 moment was dominant on the contralateral trunk side for both limbs. The asymmetric loads applied to the left side caused a shift in L5/S1 moment dominance to the right side during left and right single support phases.

Adult↗
PubMed1991

Predicting the minimal energy costs of human walking.

Preferred stride frequency (PSF) of human walking has been shown to be predictable as the resonant frequency of a force-drive harmonic oscillator (FDHO). The purpose of this study was to determine whether walking at the PSF and FDHO leads to minimal metabolic and mechanical costs. Subjects walked on a level treadmill at the PSF, FDHO, and frequencies above and below. Effects of stride length (SL) and speed (S) were assessed by two conditions, one in which SL was constant and the other in which S was constant. The predictability of PSF from resonance was replicated. Walking at the PSF and FDHO frequencies resulted in metabolic costs which were not significantly different (P greater than 0.05). A U-shaped oxygen consumption curve was observed with the minimum at the PSF and FDHO conditions when S was constant. A two-component curve in which a breakpoint was observed was found in the SL constant condition. A significant increase in metabolic cost was observed above the PSF/FDHO (P less than 0.01). Internal work (power) values were not significantly different between walking frequencies for the S constant condition. In the SL constant condition, internal work values showed linear increases as frequency increased. It was concluded that PSF of walking arises from the interface of the resonance properties of the limbs as oscillators and the tendency of biological systems to self-optimize.

Adult↗
PubMed1990

Physiological and biomechanical differences between wheelchair-dependent and able-bodied subjects during wheelchair ergometry.

The purpose of this study was to compare the physiological and biomechanical responses of wheelchair-dependent persons (WCD) to able-bodied persons (AB) during manual wheelchair ergometry. Five WCD and five AB performed a discontinuous wheelchair ergometer test starting at 12.8 W at 30 rev.min-1 (57 m.min-1) with increments of 7.0 W at 6-min intervals. Biomechanical data were collected 3.5 min into each stage followed by the collection of physiological data. After the fifth stage, peak oxygen consumption was determined by having the subject work against a resistance of 14.7-19.6 N at 30 rev.min-1. The WCD had significantly higher net mechanical efficiency at 26.7, 33.6 and 40.6 W in comparison to the AB. The WCD had significantly greater shoulder extension at the point of initial wheel contact as measured by the shoulder angle, while the AB had significantly greater shoulder range of motion at all work rates in comparison to the WCD. The results demonstrate that a significant physiological difference exists in the manner by which WCD and AB accomplish wheelchair ergometry. The biomechanical differences between AB and WCD were found to be a prominent factor contributing to the higher mechanical efficiency of WCD over AB. It was concluded that basic physiological and biomechanical differences exist between WCD and AB in manual wheelchair locomotion and that these differences are important considerations to the interpretation of data in wheelchair ergometry studies.

Adult↗
PubMed1988

Effects of shoe type on cardiorespiratory responses and rearfoot motion during treadmill running.

Running kinematics and physiological responses to high intensity submaximal treadmill running in training shoes and racing flats were evaluated. Eight women (mean age = 21.9 yr) completed a peak VO2 test on the treadmill (mean peak VO2 = 49.2 ml.kg-1.min-1). In two subsequent testing sessions, subjects completed 15-min runs at a speed corresponding to 90% of peak VO2 (range = 9.9-13.4 km.hr-1) while wearing training shoes and racing flats (balanced order assignment). No significant time effect or time by shoe condition interaction was observed for the rearfoot motion variables. Maximum rearfoot angle and total rearfoot motion averaged 42% and 13.9% higher, respectively, for the racing flat (P less than 0.05). There were significant increases over time for VO2, VE, HR, and RPE, indicating an increase in cardiorespiratory response and the perception of effort over the course of the 15-min run. Thus, metabolic and perceptual indications of fatigue at the end of the run emerged but were not accompanied by rearfoot motion changes in either running shoe. These results indicate that rearfoot motion is a function of shoe design and did not change during 15 min of high intensity running.

Adult↗
PubMed1987

A biomechanical analysis of two functional knee braces.

The influence of knee bracing was evaluated during the activity of running by examining ground reaction forces and knee joint movement parameters assessed electrogoniometrically. Twenty-one subjects were assigned to 1 of 3 groups based on medical records provided by a physician: normal or non-injury group; anterior cruciate ligament lesion/laxity group; and anterior cruciate ligament repair group. Four test conditions were investigated: healthy or control limb; injured or experimental limb; Generation II knee brace; and Marquette Knee Stabilizer knee brace. Ten running trials were performed for each condition at a photoelectrically controlled running pace (3.33 +/- 0.11 m X s-1). There were no significant differences as a result of group membership for both electrogoniometer and force platform analyses (P less than 0.05). There was a significant difference across the four test conditions. Both knee brace applications were shown to significantly reduce knee flexion during swing and support, total rotation, and total varus/valgus movement parameters of the experimental knee joint. Both brace applications were also shown to alter the experimental limb by increasing the relative time to the achievement of the initial collision force, creating a greater collision force and thereby creating larger impulses in both the vertical and foreaft directions during the initial contact phase.

Adult↗
PubMed1986

Co-activation of sprinter and distance runner muscles in isokinetic exercise.

The purpose of this study was to investigate the extent of co-activation of quadriceps and hamstring musculature in sprinters and distance runners. Nine female intercollegiate track athletes performed maximal knee extensions and flexions on a modified orthotron isokinetic dynamometer at two speeds (100 degrees and 400 degrees X s-1). Simultaneous recordings of torque, joint position, and agonist/antagonist electromyographic activity from the quadriceps and hamstrings were computer-processed. The results revealed the hamstrings to be considerably more active during knee extension than the quadriceps during flexion. The integrated electromyographic activity of co-contracting hamstrings and quadriceps, throughout the joint range, averaged 33 and 6%, respectively, of the same muscle group during its agonist phase. Hamstring co-activation increased sharply during the last 25% of knee extension, generating 58% of the integrated electromyographic agonist activity. Co-activation of the sprinters' hamstrings was four times that of distance runners (57/14%), however, the faster speed of movement (400 degrees X s-1) increased hamstring coactivation of distance runners more acutely than sprinters in the final phase of extension. The data suggest that the hamstrings are used to a much greater extent than quadriceps for limb deceleration and that the distraction of antagonist muscle tension should be considered when analyzing agonist isokinetic torques. Furthermore, the relatively high co-activation of the hamstrings, particularly during the last 25% of extension, may induce hamstring soreness or strain in vulnerable subjects.

Adult↗
PubMed1985

A comparison between free-weight and isokinetic bench pressing.

The purpose of the study was to evaluate selected parameters describing performance characteristics of a free-weight and isokinetic bench press. A secondary purpose was an attempt to clarify the technique requirements essential for a successful lift. Parameters describing the free-weight condition were generated from cinematographic data (150 fps) for five trials each at 90 and 75% of the subject's maximal performance (1RM). Isokinetic data were obtained from an instrumented Cybex Power Bench Press at two speeds corresponding to the average speeds for the free-weight conditions. Despite differences, accommodation appeared to occur for both methods when the lifts were performed maximally. A "sticking region" was defined as the portion of the free-weight activity when the subjects' force application was less than the weight of the bar. No significant difference (P less than 0.05) was observed between the 90% 1RM (26.02%) and 75% 1RM (26.94%) mean relative time values for these regions. For the Cybex device, the percentage of the activity which was isokinetic was longer for the slower speeds of rotation (0.47 rad X s-1 = 70%) and steadily decreased until the movement was only 50% isokinetic at 1.74 rad X s-1. The observed relationships between applied force-time data along with anatomical considerations suggest an ideal technique for the lift.

Biomechanical Phenomena↗
PubMed1984

Electromyographic patterns accompanying isokinetic exercise under varying speed and sequencing conditions.

The purposes of this study were: a) to investigate electromyographic patterns accompanying isokinetic exercise under varying speed and sequencing conditions, and b) to investigate the role of antagonist coactivation under these same conditions. Five adult males performed maximal knee extensions and flexions on a modified Orthotron isokinetic dynamometer. Tests were done at four speeds (100-400 degrees/sec) and under two counterbalanced conditions: extension followed by flexion (E/F) and flexion followed by extension (F/E). Simultaneous recordings of torque, knee joint position and agonist/antagonist EMG changes from the quadriceps and hamstring musculature were collected and analyzed. No consistent EMG patterns emerged that inferred intermittent surges of muscular activity as the primary mechanism yielding double peaked torques that characteristically occur in isokinetic exercise. Further analyses revealed relatively small co-contractions of antagonists during the various phases of movement. The findings suggest that gravity and inertia of the limb/lever system were the major factors responsible for limb deceleration and substantive antagonist co-contraction was not required for braking. If isokinetic knee flexion and extension exercises are used for conditioning or developmental purposes of healthy subjects, any distraction of the co-contracting antagonist from the recorded force of the agonist appears to be small once the activity is learned.

Adolescent↗