The adaptation of blood flow and pressure following physical activity
Abstract
Physical activity causes great adaptations in the entire organism. These adaptations can be more or less permanent. In detail, as far as haematic flow and blood pressure are concerned, some changes can be exploited to prevent hypertension and in the treatment of mild hypertension without using pharmaceuticals. On the other hand, other sport activities can cause hypertension or make it worse.
The adaptation of blood flow and pressure following physical activity
Following physical activity, and more generally exercise, the need for oxygen and energetic substrata is significantly increased, above all in those areas of the body primarily involved.
In order to face these changing needs, the cardiac muscle increases its work frequency to support a greater haematic flow, which can be 13 times greater than in normal conditions(1).
By analysing more closely what happens to the working muscle it is possible to encounter not only greater blood flow, but also a greater flow during muscle contraction(2).
This result is determined by the marked pressure caused by the muscle on the vascular structures, which provokes compression and the consequent sudden and considerable blood flow.
This process can explain two phenomena:
- the potential increase in blood pressure following exercise done to increase muscle volume and/or maximal strength;
- a working muscle becomes tired and strained.
The increase in blood pressure and the potential worsening of hypertension are particularly frequent when muscular work is stimulated by overloading.
Compression on blood vessels, due to the aforementioned reasons, causes greater resistance to blood flow(3). In order to oppose this resistance, blood pressure is also increased, which will be proportional to the volume of muscular mass involved(4).
It must be stressed that the greater the stress on the heart, itself a muscle, the greater contribution of oxygen is required. This situation is not always easily managed by subjects with coronary problems, which could give rise to a high-risk situation.
Vascular compression, however, also determines a greater difficulty in O2 transit, energetic substrata and the sudden removal of catabolites.
All of this affects the rise of fatigue and, in the case of anaerobic activity, it also causes the rapid accumulation of lactic acid in the muscles.
The consequence of an acid environment is the alteration of the O2-haemoglobin affinity (variable in virtue of the pH, temperature and concentration of 2.3-diphosphoglycerate(5)) involved in the release of oxygen by the haemoglobin(6).
Therefore, the result will not only be less oxygen flow, but also greater difficulty in its transfer to tissues and the inhibition of phosphofructokinase, imputed in the glycolitic process(7).
The increase in pressure, induced by exercise aimed at increasing muscular mass and maximal strength, is obviously reversible. Furthermore, it appears less prominent in individuals who are already fit(8). In any case, it is not advisable to subject hypertensive individuals to this type of training(9).
In the same way and for similar reasons, it is not advisable to give isometric exercises, even if they are not the maximal kind, because the pressure values could become particularly serious.
Second Part ->
Dr. Pierluigi De Pascalis
Founder and training manager of nonsolofitness.it
_________________________
(1)Guyton A. C.; Hall J. E., Textbook of Medical Physiology, Tenth Edition, 2000
(2)Barcroft H.; Dornhorst A.C.: The blood flow through the human calf during rhythmic exercise. Journal of Physiology 109:402, 1949
(3)MacDougall, J.D., et al.: Arterial blood pressure response to resistance exercise. J. Appl. Physiol., 58:785, 1985
(4)Mitchell, J.H., and Raven, P.B.: Cardiovascular adaptation to physical activity. In Physical Activity, Fitness, and Health. 1994
(5)De Pascalis P., A scuola di fitness, Ed. Calzetti Mariucci, Perugia 2006
(6)Farber M, et al. Effect of decreased O2 affinity of haemoglobin ok work performance during exercise in healthy humans. J Lab Clin Med 1984; 104:166-175
(7) Danforth WH. Activation of the glycolytic pathway in muscle. In: Chanche B, Estabrook RW, ed. Control of Energy Metabolism. New York Academic Press, 1965:287-298.
(8)Fleck S. J., Dean L. S., Resistance training experience and the pressure response during resistance exercise, Journal of Applied Physiology, 63, 116-120, 1987
(9)American College of Sports Medicine. Position Stand. Physical activity, physical fitness, and hypertension. Med. Sci Sports Exercise, 1993
|
