Thereare days when we go out for a run and although we don’t feel like we are going fast or doing anything much we feel more tired than usual. It can happen as a result of particularly busy days, or from sleeping poorly, or for the most varied array of reasons.
In the past few weeks, in which I have been experiencing quite intense work and private moments, I have had several such situations. It doesn’t necessarily mean that something is happening to my body or that I’m pushing it too far as far as I can go, but it’s still a way for it to ask me to pay more attention.
By using practically around the clock a Garmin (currently the Forerunner 255, to be precise) I am able to record a lot of the data related to my body, and this helps me, for example, to monitor hours and type of sleep, stress levels, and even heart rate trends. This last point is of paramount importance in the fatigue I described earlier. In particular, as far as the training part is concerned, the ability to visualize graphically how beats evolve as we perform our activity allows us to highlight an important aspect, that of the
cardiac drift
.
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Not really a drift in the strict sense, but what is meant to be expressed basically is just that and can be summarized in the concept that our heart, even if physical exertion is kept theoretically constant, will tend to increase beats gradually over time, leading us toward the threshold value. This incremental change has several triggers, but the main one is the development of heat and what this brings about.
The temperature
Our heart works best when it is not under thermal stress. While running, no matter how quiet our running may be, we tend to produce heat. Some of it we dissipate with sweat, which is a defense mechanism of our body useful to bring the temperature back toward more bearable values, and some we turn into energy (or rather, some of the heat produced stimulates and accelerates cellular activity).
However, the body’s attempt to decrease the temperature through sweating causes a loss of fluids, also leading to the thickening of blood in the vessels. Because exerting effort-running, for example-muscles require much more oxygen than normal to function, the heart finds itself in a position where it has to increase cardiac output (that is, how much blood to put into the circulation) or increase beats. In most cases it does both, because after a certain period of time-more or less short depending on the training conditions-it can no longer send a certain amount of blood into the bloodstream in a certain amount of time, and therefore must increase the number of beats. Even if the apparent effort, speed or pace remains constant.
In cases where fluid loss is gradual and still allows the athlete to run and maintain a steady pace, the increase in beats will occur gradually as the exertion we make goes on over time.
WHAT DOES IT ALL MEAN?
Cardiac drift-in any training plan in which we rely on threshold values and heart rates-plays a major role, mainly because we run the risk of incorrectly assessing the individual workout (perhaps the one on which we then go on to calculate the pace for our race performance), leading us toward an error easily circumvented by knowing how our heart has behaved over time.
In this regard, development and technological support applied to a sporting activity such as running are coming our way, and going to look at our running history to see when we had the biggest issues could and should become part of the things we do quite frequently to monitor our health. In one of the latest studies on the subject, it is pointed out-again, I would be inclined to write-how the way to minimize cardiac drift is also to run longer in the summer or otherwise in the heat: to drink a lot, even and especially during activity and even if we don’t have the thirst stimulus.
A brief but necessary clarification for women runners. During the lutein phase, that is, the phase from ovulation to about halfway through the menstrual cycle, until the eventual onset of menstruation and the subsequent follicular phase (if pregnancy does not set in), it is possible for cardiac drift to occur with greater intensity even without major thermal stresses. At this stage, therefore, it is good to pay special attention and listen-even more-to the signals that our bodies send us.
(Main image credits: Maridav on DepositPhotos.com)
Bibliografia parziale Menstrual cycle effects on cardiovascular drift and maximal oxygen uptake during exercise heat stress, di Stone et al., 2021; Cardiovascular Drift During Heat Stress, di Wingo et al., 2012.