Biomedical subjects

Timothy E Kirby

Publications and source records attributed to Timothy E Kirby.

5 recordsLinked to original sources

PubMed2006

A comparison of military circumference equations to skinfold-based equations to estimate body composition.

UNLABELLED: Circumference-based military equations (CBEs) were compared with a skinfold-based equation (SBE) to estimate body fat. OBJECTIVE: We determined the correlation between CBEs and SBE, evaluated the efficacy of CBE methods, and examined the difference in methods to identify noncompliant personnel. Circumference and skinfold measurements were taken in sequential order for 1,191 male civil service employees (37.9 +/- 7.9 years). RESULTS: Percent body fat was estimated for SBE (18.4 +/- 6.1) and three different CBEs: Marine Corps (19.6 +/- 5.8), Navy/Air Force (20.4 +/- 5.8), and Army (20.6 +/- 5.2). A moderate correlation coefficient existed between SBE and CBEs (r = 0.76-0.79). A greater body fat percentage was estimated in noncompliant personnel with circumference methods. CONCLUSIONS: Data moderately correlate CBEs and SBE. However, CBEs predict higher estimates, resulting in a greater number of personnel classified as noncompliant.

Adolescent↗

PubMed2005

Nonthermal ultrasound and exercise in skeletal muscle regeneration.

OBJECTIVE: To determine whether continuous nonthermal therapeutic ultrasound (US) and low-intensity exercise (Ex) influence skeletal muscle regeneration after a standardized contusion injury in an animal model. DESIGN: Randomized controlled trial with blinded comparisons in a 2 x 2 factorial (US by Ex) design. SETTING: Animal care facility and exercise physiology biochemistry laboratory. ANIMALS: Twenty male Wistar rats (age, 8 mo) received a reproducible bilateral contusion injury to the gastrocnemius muscles. Ten gastrocnemius muscles from 5 noninjured, nontreated rats provided baseline control data. INTERVENTIONS: US (continuous duty cycle, 3 MHz; intensity, 0.1 W/cm2 ; transducer, 1cm2 ; duration, 5 min/d; duty cycle, 100%) and exercise (20 min/d of low-intensity treadmill walking at 14 m/min). Gastrocnemius muscles from injured rats received exercise treatment alone (Ex + NoUS), exercise and US treatment (Ex + US), US treatment alone (NoEx + US), and no treatment (NoEx + NoUS). MAIN OUTCOME MEASURES: Ninety-six-hour postinjury muscle mass, contractile protein concentration, fiber cross-sectional area, number of nuclei per fiber, and myonuclear density. RESULTS: Myonuclei per fiber were statistically greater in injured than in noninjured gastrocnemius muscle (P < .05). There were no statistical differences (P > .01) among the 4 injured treatment groups for any of the outcome measures chosen as biomarkers of skeletal muscle regeneration. CONCLUSIONS: There is no evidence that the specific continuous US and Ex protocols investigated enhanced skeletal muscle regeneration after contusion injury.

Animals↗

PubMed2003

Maximal lactate steady state declines during the aging process.

Increased participation of aged individuals in athletics warrants basic research focused on delineating age-related changes in performance variables. On the basis of potential age-related declines in aerobic enzyme activities and a shift in the expression of myosin heavy chain (MHC) isoforms, we hypothesized that maximal lactate steady-state (MLSS) exercise intensity would be altered as a function of age. Three age groups [young athletes (YA), 25.9 +/- 1.0 yr, middle-age athletes (MA), 43.2 +/- 1.0 yr, and older athletes (OA), 64.6 +/- 2.7 yr] of male, competitive cyclists and triathletes matched for training intensity and duration were studied. Subjects performed a maximal O2 consumption (V(o2 max)) test followed by a series of 30-min exercise trials to determine MLSS. A muscle biopsy of the vastus lateralis was procured on a separate visit. There were differences (P < 0.05) in V(o2 max) among all age groups (YA = 67.7 +/- 1.2 ml x kg-1x min-1, MA = 56.0 +/- 2.6 ml x kg-1x min-1, OA = 47.0 +/- 2.6 ml x kg-1 x min-1). When expressed as a percentage of V(o2 max), there was also an age-related decrease (P < 0.05) in the relative MLSS exercise intensity (YA = 80.8 +/- 0.9%, MA = 76.1 +/- 1.4%, OA = 69.9 +/- 1.5%). There were no significant age-related changes in citrate synthase activity or MHC isoform profile. The hypothesis is supported as there is an age-related decline in MLSS exercise intensity in athletes matched for training intensity and duration. Although type I MHC isoform, combined with age, is helpful in predicting (r = 0.76, P < 0.05) relative MLSS intensity, it does not explain the age-related decline in MLSS.

Adult↗

PubMed2002

Changes in concentrations of neuroendocrine hormones and catecholamines in dogs with myocardial failure induced by rapid ventricular pacing.

OBJECTIVE: To describe neuroendocrine responses that develop in dogs subjected to prolonged periods of ventricular pacing. ANIMALS: 14 adult male hound-type dogs. PROCEDURE: Samples were obtained and neuroendocrine responses measured before (baseline) and after 3 periods of ventricular pacing. A pacemaker was used to induce heart rates of 180, 200, and 220 beats/min (BPM). Each heart rate was maintained for 3 weeks before increasing to the next rate. Atrial natriuretic peptide, antidiuretic hormone, aldosterone, norepinephrine, epinephrine, and dopamine concentrations and plasma renin activity were measured. Severity of left ventricular compromise was estimated. RESULTS: Shortening fraction decreased significantly with increasing heart rates (mean +/- SE, 35.5 +/- 1.4, 25.0 +/- 1.4, 19.5 +/- 1.9, and 12.2 +/- 2.3 for baseline, 180 BPM, 200 BPM, and 220 BPM, respectively). Atrial natriuretic peptide concentrations increased significantly at 180 BPM (44.1 +/- 3.0 pg/mL) and 200 BPM (54.8 +/- 5.5 pg/mL), compared with baseline concentration (36.8 +/- 2.6 pg/mL). Dopamine concentration increased significantly at 200 BPM (70.4 +/- 10.4 pg/mL), compared with baseline concentration (44.2 73 pg/mL). Norepinephrine concentrations increased significantly from baseline concentration (451 +/- 46.2 pg/mL) to 678 +/- 69.8, 856 +/- 99.6, and 1,003 +/- 2676 pg/mL at 180, 200, and 220 BPM, respectively. CONCLUSIONS AND CLINICAL RELEVANCE: Dogs subjected to ventricular pacing for 9 weeks developed neuroendocrine responses similar to those that develop in humans with more chronic heart failure and, except for epinephrine concentrations, similar to those for dogs subjected to ventricular pacing for < 6 weeks.

Aldosterone↗

PubMed2002

Evaluation of a step-counter during treadmill walking in 7-12 year old African-American children.

The primary purpose of this study was to evaluate the accuracy of the Digiwalker step-counter in recording the number of steps by African-American children during level treadmill walking and the accuracy of the Digiwalker when placed inside a pouch at midline rather than when placed at midline of the thigh. A secondary purpose of this study was to examine the relationship between the number of steps and physiological response to walking. Study subjects were a sub-set of thirty-one children recruited from a larger study evaluating the effects of an after school program on cardiovascular risk factors in this population. The Digiwalker was consistent in the steps recorded when time and speed were held constant and the Digiwalker was able to detect increases in steps with small increases in walking speed. In addition, the use of a soft-cased pouch appears to be an appropriate alternate placement site for the Digiwalker.

Age Factors↗