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G W Orr

Publications and source records attributed to G W Orr.

5 recordsLinked to original sources
PubMed1983

Anaerobic threshold, blood lactate, and muscle metabolites in progressive exercise.

The purpose of this study was to investigate the interrelationship between the ventilatory anaerobic threshold (VAT), the blood lactate anaerobic threshold (LAT), and the alteration in muscle metabolism. Ten subjects (5 men and 5 women) performed progressive exercise to exhaustion on two occasions for determination of the VAT and the LAT. For both AT criteria, the initial breakpoints (P less than 0.05) in the relationship between ventilation (VE) and O2 uptake (VO2VAT) and lactate (La) and power output (POLAT) were determined by multisegmental linear regression. During three subsequent tests the subjects performed progressive exercise to various percentages of the VO2VAT. Biopsies were obtained from the musculus vastus lateralis for determination of selected glycolytic intermediates at the cessation of exercise. It was found that the VO2VAT, expressed in terms of power output (POVAT), occurred at a higher value (P less than 0.05) than the POLAT (1,004 vs. 621 kg X min-1). Blood La values at these power outputs were 2.09 and 1.25 mM, respectively. Determination of the muscle La concentration at 79, 94, and 110% of VO2VAT indicated significant increases (P less than 0.05) from rest values of 1.59 to 4.49, 6.37, and 11.3 mmol X kg wet wt-1, respectively. It is concluded that the gas exchange AT as determined by the relationship between VE and VO2VAT and the AT as determined by blood La accumulation (LAT) are not coincidental. In addition the elevation in muscle anaerobic glycolysis precedes both the VAT and the blood LAT in this progressive exercise test.

Adolescent↗
PubMed1982

A computer linear regression model to determine ventilatory anaerobic threshold.

The anaerobic threshold has generally been determined by simple visual inspection of ventilation or other gas-exchange data obtained during incremental exercise. To establish objective criteria for the determination of anaerobic threshold, a computer algorithm has been developed that models the ventilatory response to exercise using multisegment linear regression. The best-fit regression model is chosen by minimizing the pooled residual sum of squares . The anaerobic threshold is reported as the first break point in that model. The computer-determined anaerobic threshold values for 37 subjects were compared with subjectively determined values as chosen by four independent observers. The observers' estimates, when pooled to yield a single a single value for each subject, gave a mean value for the gas-exchange anaerobic threshold of 2.26 +/- 0.69 l/min. The estimates by the computer method averaged 2.21 +/- 0.65 l/min. The correlation coefficient for these two methods was 0.94.

Adult↗
PubMed1981

Errors in the use of isokinetic dynamometers.

The use of constant velocity dynamometers in functional testing and in exercise and therapy programs has been increasing in the past few years. For movements in the horizontal plane there are no gravitational errors. However, in vertical movements the limbs are not only working against the dynamometer but also are either aided or opposed by gravity. Far too often these gravitational forces have not been taken into account, and the error involved can be quite large. 1. A study on four subjects using knee extension (against gravity) and flexion (with gravity) showed the error in mechanical work to vary from 26-43% in extension and from 55-510% in flexion. 2. A relatively simple solution is offered to overcome the problem by compensating for the gravitational errors over the full range of movement. The time course of the error is such as to cause erroneous magnitudes of recorded moments which are a maximum at low level contractions and minimum at high level contractions. 3. The effect of gravitational and other acceleration errors are such as to cause false early peaks in the muscle moment curves resulting in erroneous conclusions about muscle function.

Biomechanical Phenomena↗