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

Abstract

A positive inotropic action by the sympathetic nervous system on skeletal muscles has been observed and investigated in animal and in vitro studies. This action provided a theoretical basis for the putative ergogenic action of catecholamines and adrenergic agonists, although there is no clear evidence of this effect in humans. The aim of this study was to investigate the occurrence of inotropic effects associated to physiological sympathetic activation in healthy subjects. The muscle force capacity was investigated in the tibialis anterior (n = 9 subjects) and in the soleus (n = 9) muscles electrically stimulated with single pulses and double pulses with variable interspike interval (4-1,000 ms) and short pulse trains (frequency: 5-14 Hz) before, during, and after sympathetic activation by the cold pressor test (CPT). CPT significantly decreased by 10.4 ± 7.2 and 10.6 ± 4.4% the force produced by single and double pulse stimulation, respectively, and produced smaller decreases in the force obtained by train stimulation in the tibialis anterior, while no significant changes were observed in either type of contraction in the soleus muscle. CPT failed to induce any increase in the force capacity of the investigated muscles. The prevalent decrease in force evidenced in this study supports the concept that the weakening sympathetic action on type I fiber, already shown to occur in humans, prevails over the putative potentiating action.

Robust estimation of average twitch contraction forces of populations of motor units in humans

“…(4) includes three variables to characterize the average twitch profile and one to provide a better estimation in case of underdetermined systems. The twitch response was modeled using a modified version of the impulse response described by Fuglevand et al (Fuglevand et al, 1993) that has been proposed by Roatta and Farina (Roatta and Farina, 2011) in a previous study:…”

Dietary milk fat globule membrane supplementation combined with regular exercise improves skeletal muscle strength in healthy adults: a randomized double-blind, placebo-controlled, crossover trial

“…Motor unit activity during the exertion of muscle force was evaluated using surface electromyography (EMG) [ 14 , 15 ]. The surface EMG signals of the intermediate portion of the right vastus medialis were detected during leg extension strength measurement with the Ambu® Blue Sensor M (Ambu Ltd., Ballerup, Denmark).…”

Stress‐induced increase in muscle force: truth or myth?

“…Very recently, the adrenergic effects on skeletal muscles have been investigated during a physiological stress response in humans (Roatta et al 2008; Roatta & Farina, 2011). Interestingly, these studies showed weakening of selectively activated low‐threshold (thus presumably slow‐twitch) motor units during activation of the sympathetic nervous system by the cold pressor test (painful stimulus induced by immersion of one hand in icy water; Roatta et al 2008), in accordance with the positive lusitropic effect.…”

“…Interestingly, these studies showed weakening of selectively activated low‐threshold (thus presumably slow‐twitch) motor units during activation of the sympathetic nervous system by the cold pressor test (painful stimulus induced by immersion of one hand in icy water; Roatta et al 2008), in accordance with the positive lusitropic effect. Further, it was not possible, using the same physiological stressor, to identify a positive inotropic effect when assessing all muscle fibres in the soleus and in the tibialis anterior muscles (Roatta & Farina, 2011). Of course, we cannot exclude that a stronger or different type of stress is necessary to produce a detectable enhancement of force.…”