In athletics, there’s a term called Heart Rate Drift. It indicates our body’s response to work over time. In everyday life we might call this running out of steam. In either case, the effect may not be initially obvious.
In the graph you can see how my heart rate increased over the course of 5 high-intensity intervals (no.’s 2, 4, 6, 8, & 10). Notice that my run pace increased during the first three intervals as I ramped up the effort. (I held back a bit on the first couple because I didn’t want to flash burn and have nothing left for the bulk of the planned work, and I wanted to warm up the body to the workload.) I then attempted to maintain the output, but you can see by the drop in pace on #10 that I succumbed to fatigue. (Note: Numbers 11-13 were low-intensity recovery. Also, the graph does not depict the duration of each of the 13 intervals.)
Despite the stabilising and even declining output, my average and maximum heart rate in each of the five-minute efforts continued to climb. This is Heart Rate Drift—pulse increases, or drifts upwards even when the workload is maintained or lowered. It happens at low-intensity efforts as well, if the duration is long enough, due to energy and substrate depletion, heating, over-cooling, dehydration, hunger, and more.
Fatigue is also revealed when the workload (usually measured by pace or power) must be lowered in order to maintain a stable pulse.
The main take away is that in order to train our physiology for a given workload we have to stay below the point where deterioration takes hold. In my interval example above, I had trained at the desired level for the correct number of bouts, and doing a sixth high-intensity interval would not have benefited me physiologically. As a side note about interval work, it has to be built upon a solid engine, one that can motor along at a sustainable level. The primary focus in fitness is always to build, maintain, and improve that (aerobic) engine, thereby enabling us to motor longer, or more efficiently for a given duration.
Life is in some ways analogous to sport. Maintaining a healthy foundation sets us up for success, but the more we work, the longer we’re busy or stressed, the less rest we take, etc. the more we tire. It doesn’t matter how much we enjoy our task(s), we can’t carry on indefinitely but instead eventually decline into a state of fatigue, even exhaustion.
As in bioenergetics, there are subtler tendencies influencing either decline or development. In our high-paced world with constant stimulation, the body and mind become overwhelmed by sights, sounds, activities, and other sensory input. In essence, it leads to an upward drift in stress and a depreciation in our capacity to handle the same workload. We turn to various types of depressants and stimulants in order to cope.
Interestingly, I’ve noticed that every time I have an extended hiatus from our high-paced society, whether it be while living at the cabin in nature or in a longer meditation retreat, my system quietens. It doesn’t require, or shall I admittedly say ‘crave’, the same degree of stimulation or sedation. My impulses don’t disappear: I’m still a human with many engrained patterns. But there’s an internal shift towards a more peaceful and sustainable format.
Recently, when sitting down for meditation, my body and mind suddenly dropped into what I can only describe as a low-processing mode. All but the basic functions switched off. There was just a simple human being sitting while the birds chirped, the fire crackled, and a slight drizzle fell on the roof. When this systemwide de-stimulation process occurs there’s a concurrent improvement in my fitness metrics: my pace and power output increase for particular heart rates and my heart rate decreases relative to a given output. This happens because stress hormones and mental habit patterns that habitually rev the internal hamster wheels are lower, thereby providing an opportunity to unravel and restore, which moves me away from the point of deterioration.
Whether you’re looking for improved athletic performance or life/work enhancement, let your physiology inform your awareness and your decision-making process so that you alleviate negative drift and decline that indicates wear and tear.