Biomedical subjects

James C Martin

Publications and source records attributed to James C Martin.

6 recordsLinked to original sources

PubMed2006

Modeling sprint cycling using field-derived parameters and forward integration.

UNLABELLED: We previously reported that a mathematical model could accurately predict steady-state road-cycling power when all the model parameters were known. Application of that model to competitive cycling has been limited by the need to obtain accurate parameter values, the non-steady-state nature of many cycling events, and because the validity of the model at maximal power has not been established. PURPOSE: We determined whether modeling parameters could be accurately determined during field trials and whether the model could accurately predict cycling speed during maximal acceleration using forward integration. METHODS: First, we quantified aerodynamic drag area of six cyclists using both wind tunnel and field trials allowing for these two techniques to be compared. Next, we determined the aerodynamic drag area of three world-class sprint cyclists using the field-test protocol. Track cyclists also performed maximal standing-start time trials, during which we recorded power and speed. Finally, we used forward integration to predict cycling speed from power-time data recorded during the maximal trials allowing us to compare predicted speed with measured speed. RESULTS: Field-based values of aerodynamic drag area (0.258 +/- 0.006 m) did not differ (P = 0.53) from those measured in a wind tunnel (0.261 +/- 0.006 m2). Forward integration modeling accurately predicted cycling speed (y = x, r2 = 0.989) over the duration of the standing-start sprints. CONCLUSIONS: Field-derived values for aerodynamic drag area can be equivalent to values derived from wind tunnel testing, and these values can be used to accurately predict speed even during maximal-power acceleration by world-class sprint cyclists. This model could be useful for assessing aerodynamic issues and for predicting how subtle changes in riding position, mass, or power output will influence cycling speed.

Acceleration↗

PubMed2005

Emphysema-induced reductions in locomotory skeletal muscle contractile function.

Patients with COPD suffer from locomotory skeletal muscle contractile dysfunction. This may be due to the disease per se or as a result of some confounding factor. Therefore, the purpose of this investigation was to determine whether emphysema: (1) reduces force production; (2) increases fatigability; and (3) impairs the speed of recovery in locomotory skeletal muscle in an accepted animal model in which many confounding variables can be controlled. To explore this issue, in situ mechanical properties of gastrocnemius were measured in Syrian Golden hamsters 8 months after intratracheal instillation of either saline (control, n = 5) or elastase (emphysema, n = 7). Emphysema increased excised lung volume (80%; P < 0.01), increased fatigability (control, 25% reduction in maximal strength after 4 min of repeated contractions; emphysema, 55% reduction; P < 0.05) and decreased the recovery rate (half-times of recovery: control, 7 +/- 7 s; emphysema, 92 +/- 92 s; P < 0.05) of gastrocnemius muscle. In contrast, emphysema had no effect on maximal force, whether related to body mass or muscle mass, or force-velocity characteristics of gastrocnemius muscle. These data demonstrate that emphysema, independent of physical activity levels, pharmacological intervention, and/or nutritional status, can increase fatigability and impair the speed of recovery of locomotory skeletal muscle contractile function which may contribute to exercise intolerance of COPD patients.

Animals↗

PubMed2005

Torso stabilization reduces the metabolic cost of producing cycling power.

Many researchers have used cycling exercise to evaluate muscle metabolism. Inherent in such studies is an assumption that changes in whole-body respiration are due solely to respiration at the working muscle. Some researchers, however, have speculated that the metabolic cost of torso stabilization may contribute to the metabolic cost of cycling. Therefore, our primary purpose was to determine whether a torso stabilization device would reduce the metabolic cost of producing cycling power. Our secondary purpose was to determine the validity of the ergometer used in this study. Nine male cyclists cycled on a Velotron cycle ergometer at mechanical power outputs intended to elicit 50, 75, and 100% of their ventilatory threshold at 40, 60, and 80 rpm, with and without torso stabilization. Power was controlled by the Velotron in iso-power mode and measured with an SRM powermeter. We determined metabolic cost by indirect calorimetery and recorded power output. Torso stabilization significantly reduced metabolic cost of producing submaximal power (1%), and reduction tended to be greatest at the lower pedaling rates where pedaling force was greatest (1.6% at 40 rpm, 1.2% at 60 rpm, 0.2% at 80 rpm). Power, measured with the SRM powermeter, was strongly correlated with that specified to the Velotron ergometer control unit (R(2) > 0.99). We conclude that muscular contractions associated with torso stabilization elicit significant metabolic costs, which tend to be greatest at low pedaling rates. Researchers who intend to make precise inferences regarding metabolism in the working muscles of the legs may wish to provide torso stabilization as a means of reducing variability, particularly when comparing metabolic data across a wide range of pedaling rates.

Adult↗

PubMed2004

Lower estimates of net endogenous non-carbonic acid production are positively associated with indexes of bone health in premenopausal and perimenopausal women.

BACKGROUND: The link between acid-base homeostasis and skeletal integrity has gained increasing prominence in the literature. Estimation of the net rate of endogenous non-carbonic acid production (NEAP) from dietary protein and potassium content enables exploration of the effects of dietary acidity or alkalinity on bone. OBJECTIVE: The study aimed to ascertain whether lower dietary acidity (lower dietary protein intake but higher potassium intake-ie, low estimate of NEAP) was associated with greater axial and peripheral bone mass and less bone turnover, independent of key confounding factors. DESIGN: Baseline (cross-sectional) results of a population-based study were examined further. The database includes spine and hip bone mineral density (BMD) in 1056 premenopausal or perimenopausal women aged 45-54 y and forearm bone mass and the urinary markers of bone resorption in 62 women. A validated food-frequency questionnaire was used to measure dietary intakes. RESULTS: Lower estimates of energy-adjusted NEAP were correlated with greater spine and hip BMD and greater forearm bone mass (P < 0.02 to P < 0.05). Hip and forearm bone mass decreased significantly across increasing quartiles of energy-adjusted NEAP (P < 0.02 to P < 0.03), and trends at the spine were similar (P < 0.09). Differences remained significant after adjustment for age, weight, height, and menstrual status. Lower estimates of energy-adjusted NEAP were also correlated with lower excretion of deoxypyridinoline and were significant predictors of spine and forearm bone mass. CONCLUSIONS: These novel findings provide evidence of a positive link between a ratio of lower protein to higher potassium dietary intake (ie, less dietary acid) and skeletal integrity.

Bone Density↗

PubMed2002

Pedal trajectory alters maximal single-leg cycling power.

PURPOSE: Muscular power produced during in vitro cyclic contraction has been reported to vary with muscle-length trajectory. The purpose of this study was to determine whether maximal human single-leg cycling power could be similarly altered by manipulating pedal trajectory. METHOD: Seven trained cyclists performed maximal single-leg cycle ergometry. Pedal trajectory was manipulated by repositioning the ergometer drive sprocket off-center with respect to the crank axle, such that the leg-extension phase occupied 42, 50, or 58% of the cycle time (LEP42, LEP50, and LEP58, respectively). RESULTS: Maximum instantaneous power was 12% greater for LEP58 (1984 +/- 143 W) than LEP50 (1838 +/- 126 W), which was 8% greater than that for LEP42 (1645 +/- 112 W). Maximum power, averaged over a complete revolution of the crank, was 4% greater for LEP58 (636 +/- 59 W) than for LEP50 (613 +/- 53 W), which was 18% greater than that for LEP42 (520 +/- 43 W). CONCLUSIONS: These findings, paralleling those for an in vitro model, confirmed our hypothesis that maximal single-leg cycling power could be altered by manipulating pedal trajectory. Alterations in power were likely due to concomitant effects of muscle-shortening velocity, muscle excitation, and biomechanical constraints. Additional research is needed to determine whether greater leg-extension phase ratios can elicit further increases in power and whether similar results can be obtained during bilateral cycling.

Adult↗

PubMedDate not supplied

The Future of Family Medicine: a collaborative project of the family medicine community.

BACKGROUND: Recognizing fundamental flaws in the fragmented US health care systems and the potential of an integrative, generalist approach, the leadership of 7 national family medicine organizations initiated the Future of Family Medicine (FFM) project in 2002. The goal of the project was to develop a strategy to transform and renew the discipline of family medicine to meet the needs of patients in a changing health care environment. METHODS: A national research study was conducted by independent research firms. Interviews and focus groups identified key issues for diverse constituencies, including patients, payers, residents, students, family physicians, and other clinicians. Subsequently, interviews were conducted with nationally representative samples of 9 key constituencies. Based in part on these data, 5 task forces addressed key issues to meet the project goal. A Project Leadership Committee synthesized the task force reports into the report presented here. RESULTS: The project identified core values, a New Model of practice, and a process for development, research, education, partnership, and change with great potential to transform the ability of family medicine to improve the health and health care of the nation. The proposed New Model of practice has the following characteristics: a patient-centered team approach; elimination of barriers to access; advanced information systems, including an electronic health record; redesigned, more functional offices; a focus on quality and outcomes; and enhanced practice finance. A unified communications strategy will be developed to promote the New Model of family medicine to multiple audiences. The study concluded that the discipline needs to oversee the training of family physicians who are committed to excellence, steeped in the core values of the discipline, competent to provide family medicine's basket of services within the New Model, and capable of adapting to varying patient needs and changing care technologies. Family medicine education must continue to include training in maternity care, the care of hospitalized patients, community and population health, and culturally effective and proficient care. A comprehensive lifelong learning program for each family physician will support continuous personal, professional, and clinical practice assessment and improvement. Ultimately, systemwide changes will be needed to ensure high-quality health care for all Americans. Such changes include taking steps to ensure that every American has a personal medical home, promoting the use and reporting of quality measures to improve performance and service, advocating that every American have health care coverage for basic services and protection against extraordinary health care costs, advancing research that supports the clinical decision making of family physicians and other primary care clinicians, and developing reimbursement models to sustain family medicine and primary care practices. CONCLUSIONS: The leadership of US family medicine organizations is committed to a transformative process. In partnership with others, this process has the potential to integrate health care to improve the health of all Americans.

Ambulatory Care Information Systems↗