Instantaneous heart rate increase with dynamic exercise: central command and muscle-heart reflex contributions

Abstract

R-R interval (RRI) changes were recorded from 15 healthy volunteers in response to volitional unloaded cycling and passively induced cycling (PC). PC was also combined with electrical stimulation (n = 5) to increase muscle mechanoreceptor activation. The electrocardiogram and leg electromyographic activity were continuously sampled by computer at 1,000 Hz, and an electronic trigger was used to designate the instant of pedal movement within an RRI. Changes in RRI were expressed as the difference of the interval in which the trigger was activated (onset RRI) and the average of resting intervals (4-8 intervals). Volitional unloaded cycling produced the greatest decrease in the onset RRI [907 +/- 11 (SE) to 855 +/- 10 ms; -5.4 +/- 0.4%; P < 0.01] when movement was initiated within the first one-third of the interval. A shortening of the onset RRI was also detected when trigger activation occurred in the last one-third of the interval (906 +/- 12 to 875 +/- 11 ms; -3.1 +/- 0.4%; P < 0.01). There were no significant effects of PC alone on the onset RRI. However, PC+electrical stimulation shortened the onset RRI (906 +/- 12 to 883 +/- 11 ms; -2.5 +/- 0.2%; P < 0.05) but only when the movement was initiated within the first one-third of the interval.(ABSTRACT TRUNCATED AT 250 WORDS)

Autonomic Adjustments to Exercise in Humans

“…These initial observations, intuitively, albeit indirectly, suggested a fast feed-forward neural mechanism, and were supported by subsequent studies demonstrating an increase in HR within the first beat during static arm contraction (143) and large muscle dynamic exercise (153,231,382). A more definitive role for central command in the initial HR response to exercise has been provided from studies using passive cycling exercise (382) and partial motor paralysis (153,301) to alter the level of central command influence. According to the latter approach, partial neuromuscular blockade decreases the contractile ability of the paralyzed muscles and thus, a greater neurally generated signal is required to maintain the same level of absolute force (i.e., exaggerated central command input).…”

Resposta da frequência cardíaca durante o exercício isométrico de pacientes submetidos à reabilitação cardíaca fase III

“…Neural impulses related to the mechanical activity are transmitted initially by muscle receptors through afferent fibers from groups III and IV and reach areas of cardiovascular control almost simultaneously to the neural impulses from central command 4,19,20 . The neural impulses related to muscle metabolic activity are transmitted primarily by afferent muscle fibers from group IV and reach the area of vascular control with a delay of some seconds 17,21,22 . The afferent muscle receptors from groups III and IV are divided in ergoreceptors (group III), which are activated by muscle contraction, and nociceptors (group IV), activated by stimuli responsible for muscle pain sensation 20,23 .…”

Contribution of tonic vagal modulation of heart rate, central respiratory drive, respiratory depth, and respiratory frequency to respiratory sinus arrhythmia during mental stress and physical exercise

“…This is most likely explained by a fundamental difference in the neural regulation of heart rate in these two conditions. During physical exercise, tonic vagal modulation of heart rate is reduced and tonic sympathetic modulation of heart rate is enhanced by a combination of a feedforward "central command" and a feedback signal from the chemo-and mechanoreceptors in the working muscles~Potts & Mitchell, 1998;Rowell & O'Leary, 1990;Williamson, Nobrega, Winchester, Zim, & Mitchell, 1995!. During stress, only the central command will be active with a relatively negligible increase in feedback from muscle activity. Because the muscle-heart reflexes largely operate through resetting of the baro-reflex~Potts & Mitchell, 1998; Potts, Shi, & Raven, 1993!, their effect will be mainly parasympathetic in origin, specifically in the first minutes of exercise.…”