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Biomedical subjects

J R Steele

Publications and source records attributed to J R Steele.

At least 19 recordsLinked to original sources
PubMed2001

H-reflex modulation during passive lengthening and shortening of the human triceps surae.

1. The present study investigated the effects of lengthening and shortening actions on H-reflex amplitude. H-reflexes were evoked in the soleus (SOL) and medial gastrocnemius (MG) of human subjects during passive isometric, lengthening and shortening actions performed at angular velocities of 0, +/-2, +/-5 and +/-15 deg s(-1). 2. H-reflex amplitudes in both SOL and MG were significantly depressed during passive lengthening actions and facilitated during passive shortening actions, when compared with the isometric H-reflex amplitude. 3. Four experiments were performed in which the latencies from the onset of movement to delivery of the stimulus were altered. Passive H-reflex modulation during lengthening actions was found to begin at latencies of less than 60 ms suggesting that this inhibition was due to peripheral and/or spinal mechanisms. 4. It is postulated that the H-reflex modulation seen in the present study is related to the tonic discharge of muscle spindle afferents and the consequent effects of transmission within the Ia pathway. Inhibition of the H-reflex at less than 60 ms after the onset of muscle lengthening may be attributed to several mechanisms, which cannot be distinguished using the current protocol. These may include the inability to evoke volleys in Ia fibres that are refractory following muscle spindle discharge during rapid muscle lengthening, a reduced probability of transmitter release from the presynaptic terminal (homosynaptic post-activation depression) and presynaptic inhibition of Ia afferents from plantar flexor agonists. Short latency facilitation of the H-reflex may be attributed to temporal summation of excitatory postsynaptic potentials arising from muscle spindle afferents during rapid muscle lengthening. At longer latencies, presynaptic inhibition of Ia afferents cannot be excluded as a potential inhibitory mechanism.

Adult↗
PubMed2001

Is lower limb muscle synchrony during landing affected by gender? Implications for variations in ACL injury rates.

This study examined whether lower limb muscle synchrony during abrupt landings was affected by gender, thereby predisposing females to a higher incidence of non-contact anterior cruciate ligament (ACL) injuries than males. Seven males and 11 females landed in single-limb stance on a force platform after receiving a chest-height netball pass and decelerating abruptly. Ground reaction force and electromyographic data for rectus femoris, vastus lateralis, vastus medialis, semimembranosus (SM), biceps femoris, and gastrocnemius were sampled (1000 Hz) during landing. Subjects' sagittal plane motion was also filmed (200 Hz). Knee joint reaction forces and sagittal planar net moments of force were estimated using Newtonian equations of motion and inverse dynamics. Tibiofemoral shear forces (F(s)) were obtained and muscle bursts temporally analysed with respect to initial foot-ground contact (IC) and peak F(s) times. Males displayed significantly delayed SM onset relative to IC (113+/-46 ms) compared to females (173+/-54 ms; p=0.03), and significantly delayed SM peak activity relative to peak F(s) (54+/-27 ms) compared to females (77+/-15 ms; p=0.03). Delayed SM activity during landing was suggested to allow peak muscle activity to better coincide with high anterior F(s), thereby acting as an ACL synergist via increased joint compression and posterior tibial drawer. It was concluded that females displayed muscle synchrony less protective of the ACL than males, possibly increasing their susceptibility to non-contact ACL injuries.

Adult↗
PubMed2001

Does obesity influence foot structure and plantar pressure patterns in prepubescent children?

OBJECTIVE: This study examined the effects of obesity on plantar pressure distributions in prepubescent children. DESIGN: Field-based, experimental data on BMI (body mass index), foot structure and plantar pressures were collected for 13 consenting obese children and 13 non-obese controls. SUBJECTS: Thirteen obese (age 8.1+/-1.2 y; BMI 25.5+/-2.9 kg/m(2)) and 13 non-obese (age 8.4+/-0.9 y; BMI 16.9+/-1.2 kg/m(2)) prepubescent children, matched to the obese children for gender, age and height. MEASUREMENTS: Height and weight were measured to calculate BMI. Static weight-bearing footprints for the right and left foot of each subject were recorded using a pedograph to calculate the footprint angle and the Chippaux-Smirak index as representative measures of the surface area of the foot in contact with the ground. Right and left foot plantar pressures were then obtained using a mini-emed(R) pressure platform to calculate the force and pressure experienced under each child's foot during static and dynamic loaded and unloaded conditions. RESULTS: Obese subjects displayed significantly lower footprint angle (t=4.107; P=<0.001) values and higher Chippaux-Smirak index values (t=-6.176; P=<0.001) compared to their non-obese counterparts. These structural foot changes were associated with differences in plantar pressures between the two subject groups. That is, although rearfoot dynamic forces generated by the obese subjects were significantly higher than those generated by the non-obese subjects, these forces were experienced over significantly higher mean peak areas of contact with the mini-emed(R) system. Therefore, rearfoot pressures experienced by the two subject groups did not differ. However, the mean peak dynamic forefoot pressures generated by the obese subjects (39.3+/-15.7 N.cm(-2); q=3.969) were significantly higher than those generated by the non-obese subjects (32.3+/-9.2 N.cm(-2)). CONCLUSIONS: It is postulated that foot discomfort-associated structural changes and increased forefoot plantar pressures in the obese foot may hinder obese children from participating in physical activity and therefore warrants immediate further investigation.

Body Height↗
PubMed2001

The effect of upper-limb motion on lower-limb muscle synchrony. Implications for anterior cruciate ligament injury.

BACKGROUND: A high prevalence of rupture of the anterior cruciate ligament is associated with activities that incorporate both abrupt deceleration and catching a ball. In the present study, we examined whether the upper-limb motion involved in catching a ball affected the synchrony of the lower-limb muscles during tasks known to stress the anterior cruciate ligament-namely, abrupt decelerative landings. METHODS: Seven male and eleven female subjects decelerated abruptly to land in single-limb stance after catching a chest-height pass and after no catching. Ground-reaction force and electromyographic data for six lower-limb muscles were sampled while the subjects' landing technique was filmed. The joint-reaction forces and the sagittal planar net moments for the knee then were calculated to derive the tibiofemoral shear forces. The muscle onsets and peak muscle activities were temporally analyzed with respect to the time of initial foot-ground contact, the peak resultant ground-reaction force, and the peak tibiofemoral shear force. RESULTS: When catching a pass, the subjects demonstrated significantly (p < 0.05) earlier rectus femoris onset relative to the timing of the initial foot-ground contact and of the peak tibiofemoral shear force, and they showed delayed biceps femoris onset relative to the timing of the peak tibiofemoral shear force compared with the findings in the trials without catching. CONCLUSIONS: We concluded that catching a ball during an abrupt landing could increase the potential for an anterior cruciate ligament injury by limiting the time available for the hamstring muscles to generate posterior tibial-drawer force before the onset of the quadriceps-induced anterior tibial translation. CLINICAL RELEVANCE: The integrity of the anterior cruciate ligament during landing relies on the proper coordination of the lower-limb muscles, particularly the quadriceps and the hamstrings. The present study demonstrated that motion of the upper-limbs may interfere with recruitment of these muscles, thereby predisposing the anterior cruciate ligament to injury.

Adult↗
PubMed2000

Tension regulation during lengthening and shortening actions of the human soleus muscle.

In the present study we investigated tension regulation in the human soleus (SOL) muscle during controlled lengthening and shortening actions. Eleven subjects performed plantar flexor efforts on an ankle torque motor through 30 degrees of ankle displacement (75 degrees -105 degrees internal ankle angle) at lengthening and shortening velocities of 5, 15 and 30 degrees. S(-1). To isolate the SOL from the remainder of the triceps surae, the subject's knee was flexed to 60 degrees during all trials. Voluntary plantar flexor efforts were performed under two test conditions: (1) maximal voluntary activation (MVA) of the SOL, and (2) constant submaximal voluntary activation (SVA) of the SOL. SVA trials were performed with direct visual feedback of the SOL electromyogram (EMG) at a level resulting in a torque output of 30% of isometric maximum. Angle-specific (90 degrees ankle angle) torque and EMG of the SOL, medial gastrocnemius (MG) and tibialis anterior (TA) were recorded. In seven subjects from the initial group, the test protocol was repeated under submaximal percutaneous electrical activation (SEA) of SOL (to 30% isometric maximal effort). Lengthening torques were significantly greater than shortening torques in all test conditions. Lengthening torques in MVA and SVA were independent of velocity and remained at the isometric level, whereas SEA torques were greater than isometric torques and increased at higher lengthening velocities. Shortening torques were lower than the isometric level for all conditions. However, whereas SVA and SEA torques decreased at higher velocities of shortening, MVA torques were independent of velocity. These results indicate velocity- and activation-type-specific tension regulation in the human SOL muscle.

Adult↗
PubMed2000

Does using an ejector chair affect muscle activation patterns in rheumatoid arthritic patients? A preliminary investigation.

The present study examined knee and arm extensor muscle activation patterns displayed by 12 elderly female rheumatoid arthritic patients (mean age = 65.5 +/- 8.6 yr) rising from an instrumented Eser ejector chair under four conditions: high seat (540 mm), low seat (450 mm), with and without ejector assistance. Electromyographic (EMG) signals were sampled (1000 Hz) for vastus lateralis (VL), vastus medialis (VM), rectus femoris (RF) and triceps brachii (TB) using a Noraxon Telemyo System (bandwidth 0-340 Hz). Muscle onset, offset and peak activity relative to loss of seat contact (SS), and integrated EMG, were calculated for each muscle burst before SS. A high seat significantly (p < or = 005) decreased VL and TB intensity but did not change muscle activation patterns compared with rising from a low seat. Ejector assistance significantly increased VM and RF burst duration and RF intensity but had no effect on vastii muscle intensity. It was concluded that concerns pertaining to muscle disuse when rising with ejector assistance were unfounded in the present study. However, further research is required to investigate the effects of habitual use of a mechanical ejector device on muscle activation patterns.

Aged↗
PubMed2000

A preliminary investigation of injury prevention strategies in Netball: are players heeding the advice?

All netball players who sought treatment for injury during the three-day 1995 New South Wales State Netball Championships were surveyed. Of 940 participants, 131 incurred injuries (139.4 injuries per 1,000 players; 23.8 injuries per 1,000 playing hours). Ankle and knee injuries were most frequent, with ligament sprains, bruising/contusions, and muscle strains presenting as the most common injury types. The most frequent causes of injury were incorrect landings, collisions with players, being struck by the ball, or repetitive movements. Although most players heeded advice pertaining to warm-up, occurrence of injuries during warm-up and cool-down suggested that activities performed during these periods may be inappropriate. To reduce risk of ankle ligament sprain in netball, high-cut netball shoes have been advocated. However, only 5.1% of players surveyed wore high-cut shoes. Furthermore, although players have been advised to seek immediate treatment when injured, 54.7% of players finished the game before seeking treatment. Relative to previous netball injury investigations, the frequency and nature of injuries, and the injury prevention behaviours of players have not changed. Therefore, wider promotion of injury prevention resources, combined with research into the effectiveness of these resources and how players can be encouraged to adopt appropriate injury prevention strategies in netball, is recommended.

Adolescent↗
PubMed2000

Does obesity influence foot structure in prepubescent children?

OBJECTIVE: This study examines the relationship between obesity and foot structure in prepubescent children. DESIGN: Field-based, experimental data on BMI (body mass index) and foot structure were collected for 431 consenting children from 18 randomly selected primary schools. SUBJECTS: Of the 431 participants, 62 obese (BMI>95th percentile) and 62 non-obese (10th percentile 90th percentile) children (age = 8.5+/-0.5 y) were selected. MEASUREMENTS: Height and weight were measured to calculate BMI. Static weight-bearing footprints for the right and left foot of each subject were then taken using a pedograph to calculate the Footprint Angle and the Chippaux-Smirak Index as representative measures of the surface area of the foot in contact with the ground. RESULTS: A significant difference was found between the Footprint Angle of the obese and non-obese subjects for both the left (t = 3.663; P<0.001) and right (t = 3.742; P<0.001) feet whereby obese subjects displayed a reduced angle. Chippaux-Smirak Index scores were also significantly different for both the left (t = -6.362; P<0.001) and right (t=-5.675; P<0.001) feet between the two subject groups where a greater score for the obese subjects was evident. A decreased footprint angle and an increased Chippaux-Smirak Index are characteristic of structural foot changes that have been associated with compromised foot function. CONCLUSIONS: Excess body mass appears to have a significant effect on the foot structure of prepubescent children whereby young obese children display structural foot characteristics which may develop into problematic symptoms if excessive weight gain continues. Further investigation into possible consequences, particularly any effects on foot function, is warranted.

Body Mass Index↗
PubMed2000

Does fatigue induced by repeated dynamic efforts affect hamstring muscle function?

PURPOSE: The purpose of this study was to determine the effects of hamstring fatigue induced by repeated maximal efforts on hamstring muscle function during maximal sprint running. METHODS: Twelve subjects performed three maximal 40-m sprints during which time high-speed film of the subjects' sprint action and EMG of five lower extremity muscles were recorded (nonfatigued condition, NFC). Subjects then performed specific and general hamstring fatigue tasks followed by three final 40-m sprints (fatigued condition, FC) during which time high-speed film and EMG of the same muscles were again recorded. RESULTS: Statistical analysis of the kinematic data indicated the following significant (P < 0.05) changes in the subjects' running action from the NFC to the FC: decreased hip and knee flexion at maximum knee extension in the swing phase of the sprint cycle, decreased leg angular velocity immediately before foot-ground contact (FGC), and decreased angular displacement of the trunk, thigh, and leg segments during the late swing phase. Statistical analysis of the EMG data indicated a significant increase in the duration of hamstring activity and earlier cessation of rectus femoris activity during the swing phase of the sprint stride. CONCLUSIONS: It was concluded that these changes in the kinematic and EMG parameters of sprint running primarily served as protective mechanisms to reduce stress placed on the hamstring muscles at critical phases of the stride cycle.

Adult↗
PubMed1999

Warm-up effect on active and passive arthrometric assessment of knee laxity.

OBJECTIVE: To determine the influence of a warm-up protocol suitable for use in clinical settings on tibial displacement and muscle activity during arthrometric knee laxity assessment. DESIGN: Intervention study in which the subjects served as their own controls. SETTING: The Biomechanics Research Laboratory, University of Wollongong, Wollongong, New South Wales, Australia. SUBJECTS: Ten volunteers who reported no history of knee trauma or disease. INTERVENTION: A warm-up consisting of 10 minutes of ergometer cycling (60rpm) followed by two sets of three hamstring muscle stretches. MAIN OUTCOME MEASURES: Outcome measures were: (1) anterior tibial translation and knee extension force assessed using a Dynamic Cruciate Tester for each subject's right knee during active and passive testing, and (2) intensity of quadriceps and hamstring muscle activity during knee laxity testing. RESULTS: There was significantly less quadriceps activity after warm-up (t = 2.419, p = .039). However, there was no significant difference between anterior tibial translation, knee extension force, or hamstring muscle activity results before and after warm-up in either active or passive tests. CONCLUSION: A warm-up suitable for use in a clinical setting is not required before arthrometric assessment of knee laxity.

Adult↗
PubMed1999

Effects of chronic anterior cruciate ligament deficiency on muscle activation patterns during an abrupt deceleration task.

OBJECTIVE: This study examined the influence of chronic anterior cruciate ligament deficiency on muscle activation patterns displayed during abrupt deceleration, relative to timing of tibiofemoral shear forces (Fs) generated during the task. DESIGN: Experimental data were collected for both limbs of 11 chronic functional anterior cruciate ligament deficient subjects and 11 matched controls. METHODS: Electromyographic, high speed film and ground reaction force data were sampled as subjects landed in single-limb stance on a force platform after receiving a chest level pass and decelerating abruptly. Temporal characteristics of each muscle burst relative to initial foot-ground contact were derived and Fs were calculated from net joint reaction forces and the patellar tendon force occasioned by the net moments and inertial forces predicted about the knee. RESULTS: Compared to controls, anterior cruciate ligament deficient subjects displayed a delay in hamstring activation so that peak hamstring activity was more synchronous with initial contact and with the high Fs which occurred after initial contact. CONCLUSIONS: It was concluded the delayed hamstring activation was an adaptation developed to enable peak muscle activity to better coincide with the high anterior Fs, thereby stabilizing the injured limb against a giving-way episode via increased joint compression and posterior tibial drawer.

Adult↗
PubMed1999

Transrectal versus transvaginal abscess drainage: survey of patient tolerance and effect on activities of daily living.

PURPOSE: To evaluate patient perception of pain related to transrectal and transvaginal drainage and the catheter's effect on activities of daily living. MATERIALS AND METHODS: From July 1993 to August 1997, 22 male and 40 female patients (mean age, 41 years; age range, 4-80 years) underwent transrectal or transvaginal aspiration or drainage. Fifty-seven drainages were performed. In a follow-up survey, patients were asked to score pain experienced during the procedure and afterward on a scale of 1-10 and to rate the effect of the catheter on their activities of daily living. RESULTS: Twenty-two patients participated in the telephone survey. For those able to recall the insertion procedure, the mean pain score was 3.2 for transrectal and 5.9 for transvaginal drainage. Mean indwelling catheter pain was 1.6 for transrectal and 4.8 for transvaginal drainage. Pain after removal was 1.4 for transrectal and 2.3 for transvaginal drainage. Only one patient with a transrectal catheter reported severe limitation (bowel movement), with no reports of any serious effect on urinating, bathing, sitting, or walking. Transvaginally placed catheters caused marked limitation in all categories and were more painful than transrectal catheters (P < .05). CONCLUSION: Of the transrectal and transvaginal approaches, transrectal is better tolerated.

Abdominal Abscess↗
PubMed1999

Breast motion and sports brassiere design. Implications for future research.

Exercise usually results in a large displacement of the breasts, often leading to breast pain. Although breast pain is a common concern of exercising females, little research has been conducted in the area of breast pain. It has been suggested that a cause of breast pain is excessive breast motion. As the female breast does not contain strong intrinsic structural support, this breast motion is difficult to reduce. It is suggested that the primary anatomical support for the breast is the Cooper's ligaments; however, their true functional properties are unknown. Because of the lack of internal breast support it has been suggested that the skin covering the breast may also act as a support structure for the breast, but this has not been quantified. In an attempt to reduce breast motion, external breast supports (brassieres) have been developed. This article discusses components of current sports brassieres with implications for future research required to improve brassiere design and performance.

Biomechanical Phenomena↗
PubMed1999

Household-shoe wearing and purchasing habits. A survey of people aged 65 years and older.

A mail survey was conducted to assess the types of household footwear currently being worn by a random sample of independently living men and women aged 65 years and older as well as their needs related to the purchase and wearing of household footwear. Questionnaires were completed by 128 people. The greatest number of respondents wore slippers all day around the home, purchasing these shoes because of their convenience and comfort. Respondents were not willing to purchase expensive shoes for household wear and infrequently replaced them, despite the fact that such footwear was worn for extended periods each day. It was concluded that further research is required to design a household shoe that fits well and accommodates a variety of foot pathologies typical of the elderly foot; the shoe should be comfortable, relatively inexpensive, and safe for typical household surfaces.

Aged↗
PubMed1998

A kinematic and kinetic analysis of the sit-to-stand transfer using an ejector chair: implications for elderly rheumatoid arthritic patients.

Twelve elderly female rheumatoid arthritis patients (mean age = 65.5 +/- 8.6 yr) were assessed rising from an instrumented Eser Ejector chair under four conditions: high seat (540 mm), low seat (450 mm), with and without the ejector mechanism operating. Sagittal plane motion, ground reaction forces, and vertical chair arm rest forces were recorded during each trial with the signals synchronised at initial subject head movement. When rising from a high seat, subjects displayed significantly (p < 0.05) greater time to seat off; greater trunk, knee and ankle angles at seat off; increased ankle angular displacement; decreased knee angular displacement; and decreased total net and normalised arm rest forces compared to rising from a low seat. When rising using the ejector mechanism, time to seat off and trunk and knee angle at seat off significantly increased, whereas trunk and knee angular displacement, and total net and normalised arm rest forces significantly decreased compared to rising unassisted. Regardless of seat height or ejector mechanism use, there were no significant differences in the peak, or time to peak horizontal velocity of the subjects' total body centre of mass, or net knee and ankle moments. It was concluded that increased seat height and use of the ejector mechanism facilitated sit-to-stand transfers performed by elderly female rheumatoid arthritic patients. However, using the ejector chair may be preferred by these patients compared to merely raising seat height because it does not necessitate the use of a footstool, a possible obstacle contributing to falls.

Activities of Daily Living↗
PubMed1998

Reproducibility of knee laxity assessment results using the dynamic cruciate tester.

The purpose of the study was to examine reproducibility of knee laxity measurements obtained using the Dynamic Cruciate Tester (DCT) from day-to-day, set-to-set, and trial-to-trial. In Part I, peak anterior tibial translation (ATT) was assessed for 1 anterior cruciate ligament (ACL) deficient and 16 control subjects during two sets of three active trials (maximal isometric quadriceps contractions) and three passive trials (240 N load) conducted over four consecutive days. In Part II, peak ATT was recorded for 12 chronic ACL deficient subjects during one set of five active and five passive trials within one day. Results were analysed using mixed repeated measures ANOVA designs with intraclass reliability coefficients (ICC) calculated from the ANOVA results. There were no significant differences in the mean peak ATT results among the four tests days or between the two test sets conducted within a day, with ICC ranging from R1 = 0.939 to 0.980. It was concluded peak ATT measurements obtained using the DCT were reproducible from day-to-day and set-to-set. A significant main effect of trial was found on both active (F(2,32) = 13.93; p < 0.001) and passive (F(2,32) = 57.21; p < 0.001) peak ATT results. It was therefore recommended a full pretrial should be conducted before knee laxity assessment using the DCT to ensure reproducible results.

Adult↗
PubMed1998

Foot-care awareness. A survey of persons aged 65 years and older.

The authors conducted a mail survey that examined foot problems, rates of utilization of foot-health services, and the perception of foot problems as medical conditions in a sample of people aged 65 years and older who lived independently. Although 71% of the 128 respondents reported suffering from foot problems, only 39% had consulted medical personnel about their feet, and only 26% identified their foot pathologies as medical conditions. More female than male respondents experienced foot problems and had visited medical personnel about their feet. Increased education of older individuals about their foot-care requirements, as well as increased access to podiatric medical services, is recommended.

Aged↗