Abstract

The purposes of the present investigation were: (1) to evaluate a possible use of changes in the mean spectral frequency (MSF) of the EMG power spectra as a measure of reflex cardiovascular responses originating from the muscles during static exercise; and (2) to study the relation between muscle fibre composition, EMG, and the cardiovascular response. Heart rate (HR), arterial blood pressure (B), myoelectric signal (EMG), and intramuscular temperature (Tm) were measured during prolonged static contractions in five healthy male subjects (25-44 yrs). Two studies were performed. In study I constant EMG contraction muscle force in the first 5 s of the knee-extensor contraction was set to 20 MVC (maximal voluntary contraction), and in the rest of the 5 min contraction the myoelectric signal was kept constant by visual feedback from an oscilloscope. In study II (constant force contraction), two 1 h 7 MVC isometric contractions of the elbow-flexors and extensors were performed on two separate days. The results from the constant EMG contractions indicate the existence of a common trigger for both the increase in BP and the decrease in EMG MSF; and the extracellular (K) is put forward as a candidate. In study II, the demonstrated link between muscle fibre composition and cardiovascular responses during light, static work is explained from differences in metabolic characteristics and in the maintenance of homeostasis in slow and fast twitch muscles, respectively. Finally, the relative importance of central and peripheral control mechanisms in regulation of the circulation during static work is discussed on the basis of the demonstrated changes in EMG MSF and amplitude. Verf.-Referat