Sympathetic activation by the cold pressor test does not increase the muscle force generation capacity

Area of Science:

• Exercise Physiology
• Neuroscience
• Skeletal Muscle Physiology

Background:

• Sympathetic nervous system activation is theorized to enhance skeletal muscle function (inotropic effect).
• Previous animal and in vitro studies suggest catecholamines and adrenergic agonists may have ergogenic properties.
• Evidence for sympathetic nervous system-induced ergogenic effects in humans remains unclear.

Purpose of the Study:

• To investigate inotropic effects of physiological sympathetic activation on human skeletal muscle.
• To determine if the cold pressor test (CPT) influences muscle force capacity.
• To examine potential differences in response between tibialis anterior and soleus muscles.

Main Methods:

• Healthy subjects (n=9 for each muscle) underwent electrical stimulation of tibialis anterior and soleus muscles.
• Stimulation included single pulses, double pulses (variable intervals), and short pulse trains (5-14 Hz).
• Muscle force was measured before, during, and after sympathetic activation induced by the CPT.

Main Results:

• CPT significantly decreased muscle force by approximately 10% for single and double pulse stimulation in the tibialis anterior.
• Smaller force decreases were observed with train stimulation in the tibialis anterior; no significant changes occurred in the soleus.
• No increase in muscle force capacity was observed following CPT in either muscle.

Conclusions:

• Physiological sympathetic activation via CPT does not enhance human skeletal muscle force.
• The observed decrease in force suggests a prevailing weakening sympathetic action on type I muscle fibers.
• Findings contradict the putative potentiating action of sympathetic activation on human skeletal muscle.