Interaction mechanisms of muscular and cardiovascular systems of elite cyclists in different physiological states during a muscular activity

Objective. The objective of the work is to study the activity and relationships of muscular (MS) and cardiovascular (CVS) systems of cyclists in various physiological states during muscular activity. Material and methods. The study involved 15 highly skilled athletes. Methods for recording heart rate (HR) and electrical activity of the lower extremity muscles were used. HR was recorded by AsCARD Gray v.07.205 electrocardiograph, whereas a Noraxon MR 3.10, TeleMyo 2400 DTS electromyograph was used for recording electrical activity of muscles. Experimental material was processed by different statistical methods, including sliding smoothing, correlation and regression analysis.
Results. It was found that increase and synchronization of MS and CVS activity during physical exercise performance on a 300 W bicycle ergometer before a forced failure is characterized by a change in the form of their interaction: from linear at rest and under fatigue, to exponential during working in and in steady state. The exponential character of HR dependence on the activity of the lower extremity muscles indicates an increase in integration degree of CVS and MS, enhancement in the reactivity of CVS to MS activity by the end of the working in and steady state periods. The strongest impact on HR changes is exerted by interconnected activity of quadriceps muscle of thigh (QMT), gastrocnemius muscle (GM) and long peroneal muscle (LPM), that of QMT, GM and biceps femoris (BF), that of GM, LPM and BF, and that of QMT, BF and GM at rest, during working in, in steady state and under fatigue, respectively.
Conclusions. The ratio of interacting muscles of the lower extremities has a greater impact on CVS activity than the partial influence of individual muscles, or the sum of their individual effects. Fatigue is characterized by redistribution of the lower extremity muscle activity, inclusion of additional mechanisms for cardiac activity stimulation, reduction of electrical activity and discoordination in the relationships between the leading muscles.