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Biomedical subjects

L N Burkett

Publications and source records attributed to L N Burkett.

At least 19 recordsLinked to original sources
PubMed1998

Augmented upper body contribution to oxygen uptake during upper body exercise with concurrent leg functional electrical stimulation in persons with spinal cord injury.

The purpose of this pilot study was to compare the contribution of upper body musculature to VO2 with and without concurrent leg FES (LFES). Eight subjects with spinal cord injury, lesion levels range C6-T12, performed upper body exercise (UBE) during no LFES (NOS), LFES at 40 mA (LOS), and 80 mA (HIS), at rest, 60% and 80% of VO2peak. Resting VO2 values were obtained during NOS, LOS and HIS conditions and were then subtracted from their respective whole body VO2 values to give an estimate of upper body VO2. Small and non significant increases were found in the HIS vs NOS condition at 60% VO2peak. Larger differences of 7.8% were found in the HIS vs NOS condition at 80% VO2peak (11.35+/-3.8 ml kg(-1) min(-1) to 12.24+/-4.0 ml kg(-1) min(-1)), although this too was not significant, perhaps due to the small number of subjects in this study and the consequently low statistical power to detect a significant difference. We discuss the implications for these preliminary results in the context of the existing literature on this topic.

Adult↗
PubMed1997

Non-exercise VO2max estimation for physically active college students.

This study sought to develop a maximal oxygen consumption (VO2max) regression model derived strictly from self-reported non-exercise (N-EX) predictor variables. The VO2max (mean +/- SD; 44.05 +/- 6.6 ml.kg-1.min-1) of 100 physically active college students (50 females, 50 males), aged 18 to 29 yr, was measured using a treadmill protocol and open circuit calorimetry. Questionnaire-based predictor variables used in the N-EX regression model included (a) the subject's perceived functional ability (PFA) to walk, jog, or run given distances, (b) habitual physical activity (PA-R) data, (c) body mass index (BMI), and (d) gender. BMI (kg.m-2) was computed from self-reported body weight in pounds and self-reported body height in feet and inches. The questionnaire-based N-EX regression model (R = 0.85, SEE = 3.44 ml.kg-1.min-1) developed in this study exceeded the accuracy of previously developed N-EX regression models and is comparable to many exercise-based regression models in the literature. Cross-validation using PRESS (predicted residual sum of squares) statistics demonstrated minimal shrinkage (R = 0.84, SEE = 3.60 ml.kg-1.min-1) of the present regression model. The PFA data were useful in explaining observed VO2max variance (squared partial r2 = 0.155, P < 0.0001) and enhanced the ability of the N-EX regression model to accurately predict criterion VO2max. These results suggest that a questionnaire-based N-EX regression model provides a valid and convenient method for predicting VO2max in physically active college students.

Adolescent↗
PubMed1996

Cardiorespiratory capacity of individuals with mental retardation including Down syndrome.

This study evaluated the cardiorespiratory capacity of persons with MR with and without Down syndrome. Analyses of individual data records of maximal exercise tests with metabolic analyses were conducted on tests of 111 subjects (31 men and 16 women with DS; 35 men and 29 women without DS) from six participating centers. All centers used a walking treadmill protocol previously shown to produce valid and reliable maximal tests with this population. Peak oxygen uptake and peak minute ventilation were higher in men than in women (P < 0.006), and in subjects without DS (P < 0.006). Peak heart rate was also higher in subjects without DS (P < 0.006). Peak respiratory exchange ratio (RER) was higher in subjects without DS (P < 0.006). Using peak RER as a covariate did not change the results. An analysis of peak minute ventilation, heart rate and VO2 of subjects with a peak RER above 1.1 revealed the same results. These data show that individuals with mental retardation have low levels of peak VO2, consistent with low levels of cardiovascular fitness. Individuals with Down syndrome have even lower levels of peak VO2 than their peers without Down syndrome, a finding that is possibly mitigated by the lower peak heart rates of the individuals with Down syndrome.

Adult↗
PubMed1995

Relative changes in blood flow with functional electrical stimulation during exercise of the paralyzed lower limbs.

Eight spinal cord injured (SCI) patients performed three sets of exercise with two conditions, 60% and 80% of VO2peak, with an arm crank ergometer. Functional neuromuscular stimulation was used to induce static leg contractions in two of the above sets of exercise. The three exercise sets were performed with no functional neuromuscular stimulation (NOS); with functional neuromuscular stimulation at 40 milliamperes; and with functional neuromuscular stimulation at 80 milliamperes (HIS). The lower limb blood flow was estimated by a photoelectric plethysmograph. Results showed that the lower limb blood flow was consistently reduced across both functional neuromuscular stimulation levels (17.4% from NOS to LOS; 13.8% from LOS to HIS; and 28.8% from NOS to HIS), and work loads (15.3% from rest to 60% VO2peak; 38.0% from 60% VO2peak to 80% VO2peak; and 47.5% from rest to 80% VO2peak). Rate-pressure product was decreased by 8.3% between NOS and HIS at 60% VO2peak (15.7 +/- 3.4 to 14.4 +/- 3.8), by 6.8% between NOS and HIS at 80% VO2peak (18.9 +/- 53 to 17.6 +/- 4.8), and by 12.4% between LOS and HIS at 80% VO2peak (20.1 +/- 6.7 to 17.6 +/- 4.8). These data indicate that in SCI (a) functional neuromuscular stimulation-induced contractions of the lower limb muscles can increase blood flow and thus reduce venous blood pooling in the paralyzed muscles, and (b) such improvements are associated with a reduced rate pressure product.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1995

Arm crank exercise with static leg FNS in persons with spinal cord injury.

Persons with spinal cord injury experience considerable difficulty, during aerobic exercise, in achieving even moderate levels of oxygen uptake. Therefore, the effect of static functional neuromuscular stimulation (FNS) on this parameter during arm crank exercise (ACE) was investigated. Eight subjects with spinal cord injury, lesion levels range C6-T12, performed ACE at 60% and 80% of VO2peak, both with and without concurrent FNS of the lower limbs. ACE was performed with no FNS, with FNS at 40 milliamperes (mA), and with FNS at 80 mA. Significant differences in oxygen uptake were found between ACE without FNS and ACE with FNS-80 mA at 60% VO2peak (10% increase, 12.5 ml.kg-1.min-1 to 13.7 ml.kg-1.min-1, P < 0.05), and between ACE without FNS and ACE with FNS-80 mA at 80% VO2peak (16%, increase, 14.8 ml.kg-1.min-1 to 17.2 ml.kg-1.min-1, P < 0.01). A 10% difference between ACE without FNS and ACE with FNS-40 mA, did not reach significance. These data indicate that, in this population of subjects with spinal cord injury, (a) FNS can increase submaximal ACE oxygen uptake, and (b) that such increases are enhanced both at higher levels of FNS and of work load. Implications for wellness are discussed.

Adult↗
PubMed1993

Effects of aerobic training in adolescents with Down syndrome.

The purpose of this study was to evaluate the effects that aerobic training has on adolescents and young adults with Down syndrome. Fourteen individuals with Down syndrome (mean age = 17.7 yr) participated in a 10-wk walking/jogging exercise training study. A pre- and post-training walking treadmill test was performed to determine the following parameters: peak oxygen uptake (VO2, absolute and relative), minute ventilation (VE, l.min-1), heart rate HR, b.min-1), RER (VCO2/VO2), and time and grade to exhaustion. Following the pre-training evaluations, subjects were assigned to a control group (N = 4) or an exercise group (N = 10). The exercise group underwent a 10-wk walk/jog training program at a frequency of 3 times per week, for a duration of 30 min, and at an intensity of approximately 65-75% peak HR. Following training, both control and experimental groups showed no changes in peak VO2 (absolute and relative), VE, HR, and RER. The exercise group, however, did demonstrate a significant improvement in peak exercise time (and grade). Although the training program did not produce improvements in aerobic capacity, it did produce gains in walking capacity. It was concluded that the adolescents and young adults may not be able to improve their aerobic capacity when performing a walk/jog training program.

Adolescent↗
PubMed1990

Exercise capacity of untrained spinal cord injured individuals and the relationship of peak oxygen uptake to level of injury.

Twenty spinal cord injured individuals were tested for maximal oxygen uptake (VO2 peak using a hysteresis brake wheelchair ergometer. The subjects were divided into 4 groups as follows: (a) quadriplegics (4 subjects); (b) untrained female paraplegics (5 subjects); (c) untrained male paraplegics (7 subjects); and (d) trained male paraplegics (4 subjects). The VO2 peak were analysed by a one way ANOVA and Fisher's LSD multiple comparisons. The F-ratio (50.93) was significant (p = less than 0.0001). Fisher's LSD post hoc multiple comparisons found the following differences: (a) quadriplegics were significantly lower than the untrained paraplegic females, untrained paraplegic males and trained paraplegic males; (b) untrained females were significantly lower than the untrained male paraplegics, and trained paraplegic males; (c) untrained paraplegic males were significantly lower than the trained male paraplegics. A Spearman Rho correlation was calculated using injury level and VO2 max for all the untrained SCI individuals. The correlation was 0.68 and had a significance level of 0.0019. The present study combined with the known research literature gives strong evidence that VO2 peak in the untrained SCI is highly related to level of injury.

Exercise Test↗
PubMed1990

Maximal exercise testing of mentally retarded adolescents and adults: reliability study.

Few data are available regarding maximal exercise testing of mentally retarded individuals. No data are available on the reliability of maximal exercise testing of mentally retarded individuals. The purpose of this study was to determine the reliability of graded exercise testing of mentally retarded adolescents and adults. The testing was conducted at two geographically different centers. At Center A, 14 mentally retarded adolescents (11 boys, three girls) with Down syndrome, who were educable or trainable, were recruited from a nonresidential school. The subjects completed two Balke-Ware treadmill protocols until exhaustion. The treadmill time and heart rate (HR) were recorded. The time between tests was approximately one week. At Center B, 21 mentally retarded adults (14 women, seven men means IQ = 56) were recruited from local workshops and group homes. These subjects completed a treadmill walking protocol, with metabolic measurements, until exhaustion. The time between tests varied from one to four months. At Center A, the subjects achieved a mean treadmill time of 8.72min on test one and 8.84min on test two (means HR = 174 and 175bpm, respectively). The reliability coefficient between the two tests was .94. At Center B, the subjects achieved a mean V0(2)max of 27.2mL.kg-1.min-1 on test one and 26.9mL.kg-1.min-1 on test two. The reliability coefficient was .93. These data show that maximal exercise testing is reliable for these populations of mentally retarded individuals, exhibiting similar values to their nonretarded peers.

Adolescent↗
PubMed1986

The effect of training on exercise-induced R-wave amplitude changes in young females.

The effects of an exercise training program on R-wave amplitude (Ramp) changes during graded exercise were investigated in 14 adolescent females. The experimental group (EG) (N = 6) underwent a 20-wk aerobic exercise program. Eight subjects served as controls (CG). Oxygen uptake (VO2), heart rate (HR), and Ramp were determined during incremental exercise to exhaustion, pre- and post-program. The Ramp was calculated by using the average of 10 electrocardiographic complexes to provide a stable criterion. Pre-training, EG and CG were not significantly different for VO2max and HRmax; Ramp decreased significantly between rest and 5 min prior to exhaustion for both groups (P less than 0.05). Ramp changes were significant between the first min of exercise and 2 min prior to exhaustion for EG (P less than 0.05) and between the first min of exercise and 1 min prior to exhaustion for CG (P less than 0.05). These changes occurred at 87% of VO2max and 95% of HRmax for EG and at 93% of VO2max and 97% of HRmax for CG. CG showed no change in these variables post-program except for Ramp exhibiting a significant change between rest and the first min of exercise (P less than 0.05). EG showed a significant increase in VO2max (P less than 0.05), and Ramp changes during exercise were delayed. The first significant change occurred between rest and 3 min prior to exhaustion (P less than 0.05), and the second change occurred between the first min of exercise and exhaustion (P less than 0.05). Thus the latter Ramp change was delayed to 100% of VO2max and HRmax post-training.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1985

Effects of shoes and foot orthotics on VO2 and selected frontal plane knee kinematics.

The objective of this study was to investigate the effects of shoes and foot orthotics on running economy and selected frontal plane knee kinematics during the support phase of running. Twenty-one male runners who had been fitted with orthotics served as subjects. Subjects participated in three submaximal runs on a treadmill under the following conditions: barefoot, shoes, and shoes plus orthotics. A run consisted of 1 min at 161 m . min-1, 2 min at 180 m . min-1, and 4 min at 201 m . min-1. VO2 was calculated for the last 3 min of each test. Frontal plane motion was filmed during the sixth min of each submaximal run, and linear and angular displacement of the knee were then calculated from film data. Results from the mechanical aspect of this study indicate that there were no significant differences among the means for linear displacement of the knee. Angular displacement of the knee during barefoot running was significantly (P less than 0.05) less than shoe and shoe-plus-orthotic conditions. There was no difference, however, between shoes and shoes plus orthotics. The economy results revealed that the aerobic cost of running increased as the amount of mass added to the foot increased. In absolute terms (1 . min-1), running in shoes plus orthotics was significantly (P less than 0.05) more costly than running barefoot. It appears that if orthotics do, in fact, improve running economy by improving running mechanics, the amount of improvement is negated by the additional cost of running associated with the mass of the orthotics.

Energy Metabolism↗
PubMed1978

Field testing of cardiorespiratory fitness in primary school children.

The purpose of the investigation was to explore the validity of using timed distance runs as predictors of cardiorespiratory fitness in first, second and third grade children. Maximal oxygen uptake (Vo2 max), determined via the open-circut method during treadmill running, and performance on runs of 800, 1200 and 1600 meters were compared for 83 children. Males were found to exceed females on Vo2 max and possessed significantly faster times on all the distances run. The 1600-meter run proved to be the best predictor of Vo2 max (ml/kg) in both sexes. Test-retest reliability of the 1600-meter run was checked with 120 students and found to range from +.824 for first grade females to + .918 for third grade males. Normative values for first, second, and third grade students were calculated from data collected on 1440 elementary students. All subjects studied had previously received instruction and practice on the phenomenon of paced distance running.

Child↗
PubMed1977

Field estimation of VO2 max in children eight years of age.

The purpose of the investigation was to explore the validity of using timed distance runs as predictorr of cardiorespiratory fitness in young untrained children. Maximal oxygen consumption and performance in runs of 549, 1207, and 1609 meters (600 yards, 3/4 mile, and 1 mile) were compared in 38 children eight years of age. Males were found to exceed females on Vo2max and possessed significantly faster times in the 1207 and 1609 meter runs. The females exhibited greater six-site skinfold totals. The 1609 meter run proved to be the best predictor of Vo2max (ml/kg) in males. However, none of the three distances was acceptable for females.

Adolescent↗