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Biomedical subjects

A R Lind

Publications and source records attributed to A R Lind.

61 records · Page 4Linked to original sources
PubMed1967

Local and central circulatory responses to sustained contractions and the effect of free or restricted arterial inflow on post-exercise hyperaemia.

1. The cardiovascular responses to sustained contractions at tensions from 5 to 30% maximal voluntary contraction (MVC) have been examined. At 5 and 10% MVC blood pressure, heart rate and forearm blood flow all reached a steady state during the contraction; post-exercise hyperaemia did not show peak flows higher than those found during exercise. At tensions of 20 and 30% MVC, none of the measurements showed a steady state during the contractions, but increased steadily throughout the contraction; post-exercise hyperaemia characteristically showed peak flows in excess of any flow measured during contractions. The results obtained at a tension of 15% MVC did not show a steady-state during the contraction but the following hyperaemia showed a similar pattern to that seen at the lower tensions.2. Digital compression of the brachial artery after sustained handgrip contractions for periods of 3 or 6 min after the contraction ended resulted in only a small reduction, on average by 5-15%, of the post-exercise hyperaemia.3. Consideration of the evidence leads to the view that in physiological circumstances the post-exercise hyperaemia following sustained contractions bears a close relationship to the metabolism of the active muscles.

Adult↗
PubMed1967

Circulatory responses to sustained hand-grip contractions performed during other exercise, both rhythmic and static.

1. The cardiovascular responses to sustained hand-grip contractions at 20, 30 and 50% maximal voluntary contraction (MVC) were measured in subjects who were engaged in treadmill walking at three different rates with oxygen intakes of 1.1, 1.7 and 2.8l./min. The increments in heart rate and blood pressure at tensions of 20 and 30% MVC were similar at all rates of walking, but the response to a contraction at 50% MVC was lower at the hardest work rate than at the two easier rates.2. When two or more muscle groups contracted at the same relative tension, the increments in heart rate and blood pressure were the same, whether they contracted separately or together.3. When two or more muscle groups contracted simultaneously at different relative tensions, the increments in heart rate and blood pressure were the same as when the muscle group, at the higher relative tension, contracted separately at that tension.4. The blood flow to a muscle engaged in sustained contraction was increased when a second muscle group contracted at a higher relative tension.

Adult↗
PubMedDate not supplied

Isometric tension from rotary stimulation of fast and slow cat muscles.

In cats anesthetized with alpha-chloralose, different populations of motor units in soleus, plantaris, and medial gastrocnemius muscles were stimulated in rotation through surgically divided groups of ventral roots. As a result, smooth muscular contractions were obtained at low frequencies of rotary stimulation, and maximal tetanic tensions were induced at frequencies within the upper range of voluntary contractions. The frequencies necessary to induce maximal tetanic contractions were lower for slow-twitch muscles than for fast-twitch muscles. It is speculated that the primary benefit resulting from asynchronous stimulation of the muscles is in the engagement of the tendon, which permits motor units to exert their tension without having to overcome a major portion of the elastic damping.

Animals↗
PubMedDate not supplied

Amplitude of the surface electromyogram during fatiguing isometric contractions.

Five voluntee subjects held isometric handgrip contractions at specific submaximal tensions until the required tension could no longer be maintained. At the start of those contractions, the amplitude of the surface electromyogram (EMG) was linearly related to the tension exerted; the amplitude of the EMG increased linearly throughout these substained contractions by a constant amount--about 30% of the maximum. During sustained contractions, brief, intermittent maximal efforts showed that strength declined linearly at all tensions. At 25% maximal voluntary contraction (MVC), there was a linear fall in the EMG amplitude associated with the brief maximal efforts, but the fall in strength was more rapid than the fall in EMG amplitude. At 70% MVC, there was no fall in the EMG amplitude in response to the brief maximal efforts, while the muscle strength fell linearly.

Adult↗