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Biomedical subjects

G K Lofthus

Publications and source records attributed to G K Lofthus.

5 recordsLinked to original sources
PubMed1981

Sensorimotor performance and limb preference.

The purpose of the study was to examine simple and choice fractionated reaction time components with respect to limb preference. Subjects (10 males, 10 females) participated in two experiments. The first experiment involved sensorimotor performance of the hands under four conditions of preferred only, nonpreferred only, bilateral simultaneous, and choice handgrip reaction time. The second experiment involved preferred and nonpreferred knee extension under the same conditions. Simple RT results indicated that performance task measures differed only for the preferred bilateral hand RT and corresponding premotor time. Under choice situations, the most rapid scores occurred with preferred unilateral reaction times due to briefer premotor times. The influence of the central, premotor component relative to simple and choice performance is discussed. Results are also presented with respect to male and female differences.

Adult↗
PubMed1981

Fractionated reaction times and performance times as a function of practice.

The purpose of this study was to assess the effects of practice and its influence upon the onset of EMG firing for agonist and antagonist muscles associated with a 75 degree ballistic right forearm flexion task. In addition, the performance measures of reaction time and movement time were measured. Twelve females performed 2 bouts of 15 trials each on 3 practice days. Analysis of the data indicated that subjects improved their response performance as a function of reduced reaction time (in particular, biceps motor time values). Practice had no effect upon the onset of biceps, brachialis, or triceps EMG firing. The greatest intraindividual variability was found with the EMG latency associated with the antagonist muscle. Between individual variability was greatest with triceps latency and actual limb displacement (movement time). These results are discussed in terms of stored neuromotor memory programs and coordinated movement.

Adult↗
PubMed1980

Respiratory and heart rate responses to tethered controlled frequency breathing swimming.

The purpose of this study was to investigate the respiratory and heart rate (fH) responses to tethered controlled frequency breathing (CFB) swimming. Controlled frequency breathing swimming is an aquatic training technique in which ventilatory rate is voluntarily reduced in order to induce systemic hypoxia during training. Nine elite college swimmers experienced with CFB were studied. The tethered swimming tests were discontinuous, with 4 min work bouts interspersed with equal duration rest periods. The resisting forces during tethered swimming were 5.63, 6.82, and 7.95 kg. Each subject was tested breathing every two (control), three, four, and five arm strokes. Subjects performed all four breathing frequencies at a constant arm stroke rate of 30/min during freestyle swimming. As ventilatory volume decreased due to CFB, O2 extraction and estimated tidal volume significantly increased (P less than .05) to maintain a constant O2 consumption for a given workload. Carbon dioxide production, respiratory exchange ratio, and fH did not change significantly in response to CFB. Estimated alveolar partial pressure of O2 (PAO2) decreased and PACO2 increased significantly during CFB. However, estimated saturation of arterial blood with O2 (SAO2) was essentially undiminished during CFB. These responses do not indicate hypoxia, but rather hypercapnia during CFB.

Adolescent↗
PubMed1979

Temporal firing sequences of antagonistic muscles.

The purpose of this study was to assess the relationship between paired agonist/antagonist muscle firing times and accompanying time to peak EMG amplitudes with a 75 degree ballistic right forearm flexion task during experimental conditions of A) no external limb resistance, B) 3.1 Kg., and C) 9.8 Kg. of premovement limb resistance. In addition, total reaction time and movement time values were compared relative to the experimental conditions. Twelve male subjects practiced the flexion task for three days until criterion measures stabilized. Following five control measures on each of the next two days, 10 trials each of conditions A, B, C appearing in random order were administered. Results indicated that as external limb resistance increased (from A to B to C), movement time decreased by 30 msec., total reaction time increased by 52 msec., while biceps latency remained unchanged. There were significant (p less than0.05) increases in triceps latency, biceps and triceps time to peak EMG amplitude only with respect to the greatest external resistance (condition C). It is speculated that coordination may be defined in terms of the temporal firing sequences within an agonist/antagonist muscle group.

Adult↗