PubMed Health⌕ Search

Biomedical subjects

D A MacLeod

Publications and source records attributed to D A MacLeod.

At least 19 recordsLinked to original sources
PubMed2001

The effect of knee-flexion angle on wheelchair turning.

The increasingly popular hyperflexed knee-flexion angle was evaluated to determine its effects on wheelchair turning. Twenty able-bodied subjects were tested comparing the effect of full knee extension and full knee flexion on a number of parameters. We empirically measured the angular velocity of subjects spinning 720 degrees in place, subjects' perceived ease of wheelchair turning, the overall length of the wheelchair, the anteroposterior position of the center of mass (COM), rolling resistance, turning resistance and rear-wheel traction. The combined moment of inertia of the wheelchair and system was modeled. We found that, in comparison with full extension, fully flexing the knees increased angular velocity by 40% and was perceived to be 66% easier by subjects. Overall length decreased by 39%, COM moved rearward 38%, rolling and turning resistance decreased by 21% and 17% respectively, rear-wheel traction increased by 12% and moment of inertia decreased by 42%. All empirically tested parameters were statistically significant (p<0.007). We conclude that the knee-flexion angle has a significant effect on wheelchair turning. The implications of these findings for wheelchair design and prescription will need to be validated on actual wheelchair users and for smaller increments in knee-flexion range.

Adolescent↗
PubMed2001

Locomotor-respiratory coupling during axillary crutch ambulation.

OBJECTIVE: To test the hypotheses that locomotor-respiratory coupling occurs in humans using axillary crutches in a swing-through ambulation pattern and that expiration occurs during crutch-stance phase during locomotor-respiratory coupling. DESIGN: Eighteen able-bodied persons were trained in one-footed swing-through gait with axillary crutches. Then, as subjects walked at "somewhat hard" speeds (Borg) on a motorized treadmill for 5 min, we recorded signals from a crutch pressure switch and a mouthpiece-mounted thermocouple. Coupling was defined as being present when the onset of inspiration varied by < or = 5% with respect to the onset of the crutch gait cycle for a minimum of 10 consecutive gait cycles and when there was no drift on a raster plot of the respiratory phases relative to the onset of the gait cycle. RESULTS: Ten (56%) of the 18 subjects exhibited locomotor-respiratory coupling on 1-4 occasions each, with episodes lasting 11.3-148 sec. In 17 (89%) of the 19 episodes of 1:1 locomotor-respiratory coupling, expiration occurred during the crutch-stance phase of the gait cycle and inspiration occurred during crutch swing. CONCLUSIONS: Transient 1:1 locomotor-respiratory coupling occurs in many able-bodied subjects ambulating with axillary crutches and a swing-through gait. Expiration is most often associated with the crutch-stance phase of the gait cycle. This study may have implications for training axillary crutch users.

Adult↗
PubMed2000

The contribution of vision to wheelie balance.

OBJECTIVE: To test the hypothesis that vision plays an important role in the maintenance of balance during a stationary wheelchair maneuver in which the wheelchair user lifts and maintains the chair's front wheels off the floor (wheelie). DESIGN: Within-subject comparisons of the ability of subjects to perform wheelies with their eyes open (EO) and their eyes closed (EC). SETTING: Kinesiologic laboratory. PARTICIPANTS: Ten able-bodied adults, a sample of convenience. MAIN OUTCOME MEASURES: Postural sway, as reflected by the standard deviation of sagittal-plane movements of the center of pressure of the chair's right rear wheel on a force platform during a 10-second stationary wheelie balance, and the number of mistrials. RESULTS: The postural sway for all trials (3 EO and EC data collections at the end of each of 3 one-hour training sessions) was 88% greater with the EC than with the EO condition (p < .001) and the number of mistrials was 324% greater (p = .001). By the end of the final training session, the postural sway with the EC (4.0cm) was still 100% greater than with the EO (2.0cm) (p < .001) although there was no longer a difference in the number of mistrials. CONCLUSION: Vision plays an important role in the maintenance of a stationary wheelie, but wheelies can be maintained with the eyes closed. These findings are relevant to the training of wheelchair users and also provide broader insights into the nature of wheelchair function and dynamic balance.

Adult↗
PubMed1999

Walker inlet-closure strap for unsteady patients with lower-extremity amputations.

Some patients with lower-extremity amputations who use a walker fall backwards after advancing too far forward into the walker's base of support. In a pilot study of 14 patients with unilateral lower-extremity amputations who stepped into the forward two thirds of the walker base, this problem was corrected by using a knee-high elastic strap to close the open posterior "inlet" of the walker. Without the strap, the stance-phase position of the leading ankle was in the forward third of the walker base for 8 subjects and in the middle third for 6. With the walker strap, the ankle position was in the middle third for one subject, in the posterior third for 6, and at or behind the walker inlet for 7 (p < .0002). This simple intervention appears to correct the potentially dangerous behavior of stepping too far into the walker base.

Accidental Falls↗
PubMed1996

Adding loads to occupied wheelchairs: effect on static rear and forward stability.

OBJECTIVE: To determine the extent to which loads added in different positions affect the static rear and forward stability of an occupied wheelchair. DESIGN: Controlled, cross-over study. INTERVENTION: Loads from 0 to 10kg (in 1-kg increments) were added to five positions: high rear (HR), low rear (LR, beneath the seat and behind the crossbrace), on the lap (LAP), low anterior (LA, beneath the seat and anterior to the crossbrace), and on the footrests (FR). We also used a computer model to evaluate the relationship between stability and load, with a range of loads (0 to 100kg, in 10-kg increments) beyond the loads that were practical to test empirically. OUTCOME MEASURE: On a tilting platform, we measured the static stability (in degrees) of a wheelchair occupied by an anthropomorphic test dummy (ATD). RESULTS: The greatest increase in rear stability was with FR loads, changes of 64% and 227% for 10-kg and 100-kg loads, respectively. Only HR loads reduced rear stability, by 32% and 64%. The greatest increase in forward stability was with LR loads, by 13% and 92%. The greatest reduction in forward stability was with FR loads, by 10% and 149%. To minimize the effect of added loads on stability, the LAP and LA positions would be preferred. CONCLUSION: Added loads affect wheelchair stability as a function of the load magnitude. The extent and direction of the effect is profoundly influenced by load position.

Accidents↗
PubMed1995

Wheelchair stability: effect of body position.

When a wheelchair user reaches and leans, the static stability decreases in the direction of the lean and increases in the opposite direction. The purpose of this study was to determine the extent of this effect. We studied 21 nondisabled subjects in a representative wheelchair, measuring the static forward, rear, and lateral stability on a tilting platform. Reaching and leaning away from the tip added stability, with mean increases ranging from 9.1% to 124.3% of the neutral-position values, whereas reaching and leaning toward the tip reduced stability, with mean decreases ranging from 25.2% to 52.3% (p < 0.0001). The stability range ("away" minus "toward") varied from 52.4% to 149.5%. Reaching forward had a greater effect on stability than did reaching back or to the side. Wheelchair users with the ability to control their body positions can profoundly affect the stability of their wheelchairs, a factor that should be considered in wheelchair selection and training.

Adult↗
PubMed1993

Effect of cardiac-locomotor coupling on the metabolic efficiency of pedalling.

Coupling between cardiac and locomotor rhythms (CLC) has been reported while subjects exercise at cadences that are natural to them. The hypothesis that oxygen consumption (VO2) would be lower when subjects pedalled at the rate producing 1:1 coupling of heart and pedalling rates than when they pedalled at noncoupled rates was tested with 12 men on a cycle ergometer. At a moderate power output based on their VO2max, subjects pedalled at six different pedalling rates while VO2 and heart rate were measured. The pedalling rates were the preferred frequency, frequencies 15 and 30% above and below the preferred frequency, and the 1:1 coupled frequency. In 8 of the 12 subjects it was possible to fit their data with significant regression equations relating VO2 to pedalling rate, but in no subject was the 1:1 coupled state energetically beneficial, suggesting that any functional significance of CLC is unrelated to metabolic efficiency.

Adult↗
PubMed1993

Standard and four-footed canes: their effect on the standing balance of patients with hemiparesis.

We studied 14 patients to test the hypotheses that, when patients with hemiparesis use a cane to assist standing balance, their postural sway decreases and the average position of their center of pressure (COP) shifts forward and towards the cane side, and that there is no difference in either of these parameters between standard and four-footed canes. Each subject stood on a Kistler force platform for three ten-second intervals: one without a cane, one with a standard cane, and one with a four-footed cane. Matched-pairs t tests revealed a significant decrease in both the mediolateral (ML) and anteroposterior (AP) travel (postural sway) when the subjects used the standard cane. There was also a significant shift of the average ML position of the COP toward the cane side when they used a standard cane, but no significant difference in the average AP position. When they used the four-footed cane, neither the differences in travel nor the differences in COP position were significant, although they were similar in magnitude to those measured when they used the standard cane, compared with which there was no significant difference. Two conclusions appear warranted. First, a standard cane has a significant effect on force-platform measures of the standing balance of persons with hemiparesis of mild-to-moderate severity--specifically a reduction in the extent of ML and AP postural sway and a shift in the mean position of the COP toward the cane side. Second, as regards such measures of standing balance, a four-footed cane appears to offer no advantage over a standard one.

Adult↗
PubMed1992

Failure of accentuated vertical body movements to induce cardiac-locomotor coupling.

Cardiac-locomotor coupling (CLC) has been reported during a variety of rhythmic human activities. One reason postulated for such coupling is that axial movements of the viscera during some activities (the "visceral piston") may enhance expulsion of blood from the heart; if so, accentuated vertical movements of the body should provide a powerful stimulus to coupling. To test this hypothesis, we studied 20 subjects hopping and 20 others skipping rope for greater than or equal to 10 min while electrocardiographic and force-platform signals were recorded, from which we derived the subjects' exercise and heart rates. The incidence and intensity of apparent coupling in the test subjects were compared with those of cross-over controls, where the heart rate of each subject was related to the hopping or skipping rate of a matched subject. Ratios consistent with coupling were seen in 10 (50%) hopping subjects under test conditions and in 13 (65%) under control conditions; among skipping subjects, the incidences were 11 (55%) and 10 (50%). In neither group of subjects was the difference in the incidences or the intensities of apparent CLC statistically significant. Our failure to detect CLC while our subjects were hopping or skipping suggests that the visceral piston is unimportant to the CLC phenomenon.

Adult↗
PubMed1992

Locomotor-respiratory coupling during wheelchair propulsion.

Visceral movement due to impact loading is believed to play a role in the locomotor-respiratory coupling (LRC) that has been detected in a number of mammalian species. In the bird and bat species in which LRC has been described, the effect of the wing muscles on the timing of respiration appears to be a dominant influence. To test the hypothesis that LRC occurs in humans propelling wheelchairs (where there is no impact loading and the arms are used for locomotion), we studied 10 wheelchair athletes on a motorized treadmill at three speeds. Each subject's data were analyzed by spectral analysis (based on the fast Fourier transform), which detected apparent LRC (rates within 1% of a single-digit integer ratio) in 12 (40%) of the 30 test settings. However, a control analysis, in which each subject's arm-thrust rates were compared with another subject's breathing rates, revealed apparent (but false) coupling in 8 (27%), not significantly less often (using the chi 2 test). These findings appear to refute the hypothesis that LRC occurs during wheelchair propulsion. These data are consistent with the theory that the visceral piston is important to LRC and suggest that rhythmic arm movements are insufficient to induce the phenomenon in this setting.

Adult↗
PubMed1991

Rugby injuries.

Explore the source record for details and available documents.

Football↗
PubMed1991

Cardiac-locomotor coupling while finger tapping: Part II. A cross-over control study.

Cardiac-locomotor coupling (CLC) has been reported by us while people finger tap at cadences natural to them. Since then, we have developed a simple cross-over control strategy in which the heart rate of one subject is related to the finger-tapping rate of another. Of the 20 normal subjects previously studied while tapping a telegraph key at a comfortable rate for 10 min., reevaluation of their data showed that 9 (45%) and 4 (20%) of them, under test and control conditions, respectively, appeared to couple at a single-digit integer ratio. Neither the incidence nor the intensity of apparent CLC under the two conditions was significantly different. Raster plots of the most tightly related rates gave no evidence of phase locking. These results have two implications. First, previously published reports on CLC (and other entrainment phenomena) should be interpreted with caution, and cross-over controls should be considered in future research. Second, the absence of CLC during finger tapping suggests that CLC may only be functionally significant during exercise of large muscle groups (e.g., by minimization of cardiac afterload) or when impact-loading occurs (e.g., by enhancing cardiac ventricular emptying.

Arousal↗
PubMed1990

The effects of simulated knee-flexion contractures on standing balance.

The effects of simulated unilateral and bilateral knee-flexion contractures on standing balance were studied by testing 15 normal subjects on a Kistler force platform. Postural sway (mediolateral and anteroposterior travel) and the mean position of the center of pressure (as a percentage of the distance between the midlines of the feet and from heels to toes) were determined from 20 s of data. Unilateral and bilateral knee-flexion contractures of 15 degrees and 30 degrees were simulated for each subject by means of an adjustable line from the subject's waist to the sole of each foot. Paired t tests were used to compare balance parameters while standing with the simulated contractures with those during relaxed standing. Mediolateral travel increased by a mean difference of 3.6 cm with a 30 degree unilateral contracture (P less than 0.01) and by 5.0 cm with 30 degrees bilateral contractures (P less than 0.01). Anteroposterior travel increased by 4.7 cm (P less than 0.05) and 8.8 cm (P = 0.08) with 15 degrees and 30 degrees bilateral contractures, respectively. With a unilateral contracture of 30 degrees, the center of pressure shifted 15.6% (P less than 0.0005) toward the unflexed side, changes that were not eliminated by correction of the induced leg-length discrepancy. The center of pressure moved anteriorly by 8.3% with 30 degrees bilateral contractures (P less than 0.001). The results provide insight into how knee-flexion contractures alter standing balance, and underline the importance of preventing and treating this common disorder.

Adult↗