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Effects of blood pressure on force production in cat and human muscle
1School of Physiology and Pharmacology, University of New South Wales, Kensington, Australia.
Insights
Reduced blood pressure significantly impairs muscle force production, particularly in aerobic fibers. This highlights the critical role of blood flow and perfusion pressure in maintaining muscular strength and motor control during exercise.
Area of Science:
- Physiology
- Exercise Physiology
- Motor Control
Background:
- Muscle force production is essential for motor control and exercise.
- The influence of local blood pressure on muscle performance requires further investigation.
Purpose of the Study:
- To investigate the impact of reduced arterial pressure on muscle blood flow and force production in cats.
- To examine the relationship between muscle perfusion pressure and force output in human ankle extensor muscles during rhythmic contractions.
Main Methods:
- Anesthetized cats: reduction of local arterial pressure and measurement of blood flow and force in specific muscles (soleus, medial gastrocnemius, caudofemoralis).
- Human subjects: legs-up tilt to alter muscle perfusion pressure during rhythmic ankle extensor contractions, with electromyogram (EMG) recording.
Main Results:
- In cats, decreased arterial pressure significantly reduced blood flow and force in slow-twitch soleus and medial gastrocnemius muscles, but not in fast-twitch caudofemoralis.
- In humans, increased EMG activity was observed during legs-up tilt, indicating augmented muscle activation to maintain force as perfusion pressure decreased.
- These findings suggest that force production in human muscles, particularly those with aerobic fibers, is sensitive to changes in perfusion pressure.
Conclusions:
- Muscle force production is critically dependent on adequate blood pressure and flow, especially for aerobic muscle fibers.
- Reduced perfusion pressure necessitates increased muscle activation to sustain contractions, impacting motor control.
- These findings have implications for understanding cardiovascular control during exercise and conditions affecting blood pressure.
Abstract:
In anesthetized cats reducing local arterial pressure from 125 to 75 Torr decreased blood flow (53 +/- 5%) and force production (57 +/- 7%) in soleus and medial gastrocnemius. Force was produced in these muscles by aerobic, slowly fatiguing fibers. Similar reductions in arterial pressure did not affect force production in caudofemoralis, which contains mainly fast-fatiguing fibers. In human subjects the electromyogram produced by the ankle extensors during rhythmic constant-force contractions increased as the contracting muscles were raised above the heart during legs-up tilt. This suggests that force production of active muscle fibers at a given level of activation fell with muscle perfusion pressure, thus requiring augmentation of muscle activity to sustain the standard contractions. Because aerobic fibers contributed to these contractions, it appears that force production of human muscle fibers is sensitive to small changes in perfusion pressure and, presumably, blood flow. The critical dependence of developed muscular force on blood pressure is of importance to motor control and may also play a significant role in cardiovascular control during exercise.