Cardiovascular and respiratory responses to changes in central command during isometric exercise at constant muscle tension

Abstract

SUMMARY1. Experiments were designed to show whether elements of the command descending from higher centres to exercising muscles provide an input for cardiovascular and respiratory control. Vibration, known to be a powerful stimulus to the primary afferents from muscle spindles, was applied to the biceps tendon of human subjects performing sustained isometric contractions with the biceps or the triceps muscle. When the biceps was contracting this activation of muscle spindle primary afferents in it provided an element of reflex excitation, so that less central command was required to achieve a given tension. When triceps was contracting, the activation of muscle spindle primary afferents in its antagonist, biceps, contributed an element of reflex inhibition, so that more central command than normally was required to achieve a given tension. The cardiovascular and respiratory responses to an isometric effort could thus be investigated at any tension when the central command was normal, decreased, or increased.2. Blood pressure, heart rate, and pulmonary ventilation all increase in an isometric effort. The increase in each is less when the central command is reduced. The increase in each is greater when the central command is increased.3. It is concluded that there is irradiation of cardiovascular and respiratory control centres by the descending central command during voluntary muscular contractions in man.

Relationship between motor corticospinal excitability and ventilatory response during intense exercise

“…In the present study, we observed a significant decrease in MEP from IE 1st to IE 2nd . Therefore, the findings in the present study not only support the above concept (Amman et al 2013) but also suggest that effort-mediated ventilatory response during fatiguing IE cannot be explained by the conventional framework of central command that drives breathing via neural mechanisms consisting of parallel activation of motor and respiratory centers (Goodwin et al 1972;Heigenhauser et al 1983;Krogh and Lindhard 1913;Marcora et al 2008). Recent studies (Decety et al 1991;Thornton et al 2001;Williamson et al 2002Williamson et al , 2006Yunoki et al 2009) using a cognitive approach to dissociate peripheral neural signals from central command have suggested that central command-mediated response does not necessarily require parallel activation of central motor command.…”

“…Effort-mediated ventilatory response during exercise is generally explained by a feedforward mechanism involving activation of the cardiorespiratory center, which is induced, in parallel, by activation of the motor cortex (central motor command) (Goodwin et al 1972;Heigenhauser et al 1983;Krogh and Lindhard 1913;Marcora et al 2008). However, it has been confirmed that during IE performed after muscle glycogen reduction, integrated electromyogram (iEMG) activity recorded in exercising muscle, which reflects central motor command (Amann et al 2006;Amann and Dempsey 2008), does not increase while ventilation is elevated (Osborne and Schneider 2006;Perrey et al 2003;Yamanaka et al 2012).…”

Epidural anaesthesia and cardiovascular responses to static exercise in man.

“…However, in experimental models in which one of the components is increased or decreased, the other may produce a near appropriate cardiovascular response. For example, some studies have emphasized the importance of the central neural component (Freyschuss, 1970;Goodwin, McCloskey & Mitchell, 1972;Schibye, Mitchell, Payne & Saltin, 1981;Secher, 1985;Leonard et al 1985) and others have emphasized the importance of the reflex neural component (Alam & Smirk, 1937;Hultgren & Sj6holm, 1982). Also animal studies have shown that cardiovascular responses similar to those occurring during exercise can be produced by either central or reflex neural mechanisms.…”

Exercise pressor reflex in health and diseases: Animal studies

“…Central command emanates from the rostral brain and radiates to neural circuits in the brainstem, thereby causing parallel activation of motor and sympathetic neurons 1) . The muscle based reflex, termed 'exercise pressor reflex' (EPR) 2) , is evoked as thin fiber muscle afferents (groups III and IV) are stimulated by mechanical deformation of the afferents' receptive fields, as well as by metabolic byproducts during exercise (muscle mechano-and metaboreflexes, respectively).…”