QS Study

Mechanism of increase Heart Rate in Moderate Exercise

Heart rate is the speed of the heartbeat measured by the number of contractions of the heart per minute. Cardiovascular reflex responses to visceral afferent stimulation are either excitatory or inhibitory. The beat-to-beat activity of the heart within the entire organism ought to be adjustable to the changing requirements of that organism.

Both nervous and chemical factors are playing role in increasing heart rate. Increased heart rate in moderate exercise due to —

(i) Reflexes originating in the receptors of moving joints.

(ii) Contraction of skeletal muscle

→↑ Blood in circulation →↑ VR

→↑ CO →↑ HR

(iii) Stimulation of chemoreceptor in muscles by acid metabolites.

(iv) Sympathetico – adrenal activation causing secretion much larger amounts of epinephrine in the blood.

(v) A rise in body temperature

(vi) Stimulation of stretch receptor in the atrium by rapid venous return in heart thus causing brain-bridge reflex.

Fig: Heart Rate in Moderate Exercise

Blood flow in the skeletal muscle during exercise: During rest, blood flow through skeletal muscle averages 3 – 4 ml/min 100 g of muscle. During extreme exercise in the well-conditioned athlete, this rate can increase 15 – 25 fold rising to 50 to 80 ml/ min/100 g of muscle.

Two incidents are to be noticed –

  • There is intermittent flow during muscle contractions
  • An opening of muscle capillaries during exercise.

During exercise, you need to train at a pace and intensity where your heart rate increases, but not exceeds, 70% – 75% of your theoretical maximum heart rate (TMHR). How do you calculate your MHR?

Your MHR = 70 % x (225 minus your age).

A 35-year-old’s MHR will be:

70/100 x (225 – 35) = 70/100 x 190  = 133 – 142 (75 % will be 142)/li