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Biomedical subjects

A L Hicks

Publications and source records attributed to A L Hicks.

25 records · Page 2Linked to original sources
PubMed1994

Effect of selective and nonselective beta-blockade on skeletal muscle excitability and fatiguability.

The effects of beta-blockade on skeletal muscle excitability and fatiguability during exercise were examined. Ten healthy males (mean age 21.9 +/- 1.1 yr) performed a 4-min fatigue protocol consisting of intermittent isometric voluntary contractions of the knee extensors in one leg. Subjects performed the exercise after treatment with placebo, 100 mg metoprolol, or an equipotent dose of propranolol (60 mg, n = 1; 80 mg, n = 8; 100 mg, n = 1) twice a day for 76 h before testing according to a randomized double-blind design. The evoked twitch torque, maximal voluntary torque, and maximal M-wave amplitude were unaffected by the beta-blockade treatments before fatigue. During the placebo trial, there were significant reductions in the evoked and voluntary torques (77 +/- 15 and 55 +/- 11%, respectively) after the fatigue protocol; however, both the voluntary electromyogram and evoked M waves were well maintained throughout fatigue. The beta-blockade treatments had no significant effect on torque or electromyogram activity over the course of the exercise. Thus, despite evidence for an impairment of dynamic exercise performance with beta 1- and beta 1,2-blockade, there appears to be no effect of these agents on muscle excitability and fatiguability during isometric muscle activity.

Adrenergic beta-1 Receptor Antagonists↗
PubMed1992

Muscle excitation in elderly adults: the effects of training.

Muscle membrane excitability is thought to decline with aging; the extent of this decline may be noninvasively assessed by measurement of the electrically evoked compound muscle action potential (M-wave). The intent of this study was two-fold: (1) to compare the M-wave in the brachioradialis (BR), tibialis anterior (TA), and thenar (TH) muscles of elderly (mean age = 66.3 +/- 3.7 years) and young (mean age = 31.2 +/- 4.9 years) adults, and (2) to determine the effects of 12 weeks of resistance training on M-wave characteristics in elderly adults. Prior to training, the elderly subjects had significantly smaller (P less than 0.05) resting M-waves than the young adults in the BR (4.8 mV vs. 8.7 mV), TA (8.8 mV vs. 11.0 mV), and TH (5.2 mV vs. 10.2 mV) muscles. During a 2-minute voluntary fatigue paradigm (3 seconds MVC per 2 seconds rest for 2 minutes), there was no evidence of excitability failure in either group. Following training, there was a significant increase (P less than 0.05) in the size of the M-wave of the TH (pretraining: 5.2 mV; posttraining: 8.96 mV) and BR (pretraining: 4.8 mV; posttraining: 6.1 mV), and a nonsignificant increase in the M-wave of the TA, but there was no change in the relative behavior of the M-wave during the 2-minute voluntary fatigue paradigm. It is suggested that the decline in muscle membrane excitation with aging may be due, at least in part, to the effects of a decreased membrane potential on the muscle fiber action potential.(ABSTRACT TRUNCATED AT 250 WORDS)

Action Potentials↗
PubMed1992

Neuromuscular fatigue during repetitive stimulation in elderly and young adults.

The purpose of this investigation was to examine the integrity of neuromuscular transmission and impulse propagation during fatigue by examining the muscle compound action potential (M wave) in elderly and young adults. The tibialis anterior muscle of nine elderly [mean = 67.7 (SE 1.7) years] and nine young [mean = 26.7 (SE 1.2) years] adults was maximally stimulated repetitively at frequencies of 20, 30 or 40 Hz for 60 s on separate occasions. There was a significantly smaller resting M wave amplitude [7.9 (SE 0.4) mV versus 9.9 (SE 0.6) mV] and M wave area [0.038 (SE 0.005) mV s versus 0.06 (SE 0.004) mV.s] in the elderly versus the young adults respectively. Measurement of the evoked muscle contractile properties revealed significantly (P < 0.05) longer twitch durations and a significantly (P < 0.05) greater peak twitch torque [4.6 (SE 0.4) Nm versus 3.2 (SE 0.5) Nm] in the elderly versus the young adults, respectively. The elderly adults had a significantly greater torque decline during the 20-Hz trial; however, the decline in torque during the 30-Hz and 40-Hz trials was similar in the elderly and the young adults (30 Hz: 40%; 40 Hz: 56%). Throughout each of the stimulation trials, the decline in torque was accompanied by a significant reduction in M wave amplitude (20 Hz: 14%; 30 Hz: 53%; 40 Hz: 67%); M wave area also declined significantly during the 30-Hz (31%) and 40-Hz (53%) trials. There was no significant difference between the elderly and the young adults in the reduction in the M wave amplitude or area during each trial.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1991

Twitch potentiation during fatiguing exercise in the elderly: the effects of training.

Twitch potentiation was studied during a fatigue paradigm involving intermittent maximum voluntary contractions (MVCs) of the tibialis anterior muscle in the elderly and in young adults. Resting twitch torques were similar between groups, but twitch potentiation was significantly greater (241% vs 166%) in the young; the recovery of the twitch after fatigue was similar between groups. Contraction time, time to peak torque and half-relaxation time were all significantly slower in the elderly. Following 12 weeks of resistance training in the elderly, there was no significant change in the twitch contractile properties at rest, but there was a significant main effect of training on the degree of twitch potentiation during the same fatigue protocol (peak potentiation 192% post-training vs 165% pretraining). These data suggest that the mechanism(s) responsible for twitch potentiation following MVCs may be influenced by both aging and training.

Aged↗
PubMed1989

Prolongation of twitch potentiating mechanism throughout muscle fatigue and recovery.

Measurements have been made of twitch amplitudes in human ankle dorsiflexor muscles during and following fatiguing electrical stimulation. In six subjects, studied with the arterial circulation occluded, the twitch was observed to undergo an early potentiation (mean, 99 +/- 50%) followed by complete disappearance. A second, smaller phase of potentiation (mean, 25 +/- 30%) occurred during recovery and gave way to prolonged depression of the twitch. A comparison of these results with those obtained with an intact circulation suggested that the four phases in the behavior of the twitch were the net result of two processes, potentiation and fatigue, with different time courses. Provided they are timed appropriately, observations of twitch amplitude can provide useful information concerning the development of, and recovery from, muscle fatigue.

Adult↗
PubMed1987

Acute changes in high-density lipoprotein cholesterol with exercise of different intensities.

The purpose of this study was to investigate the acute effects of exercise on plasma high-density lipoprotein cholesterol (HDL-C) and to determine whether the magnitude of this response would be affected by the intensity of the exercise. Twelve men (19-41 yr) ran an equivalent distance (9-12 km) on a treadmill on two separate occasions. On one occasion the exercise was performed at a speed that elicited 60% of the subject's maximal O2 uptake (VO2max), and on the other occasion exercise was performed at a speed that elicited 90% of VO2max. Changes in total cholesterol, triglycerides (TG), HDL-C, HDL apoprotein A (HDL-A), HDL saturation, lactate (LA), and free fatty acids (FFA) were measured during the course of each run, and all values were corrected for changes in plasma volume as indicated by hematocrit. There were significant increases (P less than 0.01) in HDL-C, HDL-A, and HDL saturation with exercise at both intensities, but greater increases in HDL-C (25 vs. 14%) and HDL-A (18 vs. 8%) were observed with the higher intensity exercise. Plasma FFA and TG did not differ between conditions, but LA concentrations rose significantly during the high-intensity exercise. These results indicate that increases in HDL components can occur with a relatively moderate exercise session and that the magnitude of these increases are directly related to the exercise intensity.

Adult↗