What is cardiac drift?
Cardiac drift is a stress response of the cardiovascular system, it can be measured and presents itself as a progressive increase in cardiac output (acting on heart rate) while the training load remains constant. This principle helps demonstrate how duration affects the stress response for endurance exercise. The longer we exercise, the higher the stress response and up regulation of cardiac output occur.
Cardiac Output (Q) = Heart Rate (bpm) x Stroke Volume (in ml per ‘beat’)
At sub maximal intensities, we rarely experience heavy accumulation of fatigue (biochemical, musculoskeletal, cognititive). We could assume that heart rate (HR) would remain constant (red dotted line). However, given enough stimulus (duration) and maintaining a set intensity (pace/km) heart rate will indeed be higher at the end of the bout and will continually but slightly sum-mate by the end of the duration.
Stress hormones play a key role in regulating heart rate, adrenaline, cortisol and many other hormones are up regulated by biological signals present in longer duration bouts of exercise. In addition, several external factors may be present. Hot humid conditions present a demand for our systems ability to regulate heat. This explains why heart rates will often be elevated in these conditions.
As a training principle, summation explains why the benefit of repeated bouts of exercise can have a cumulative effect leading to similar adaptations as larger few single bouts. This applies to bouts within and/or between training sessions.
More time spent at desired training speed (vVO2peak, v5K, v10K, vLT etc). shorter reps (< 2 min) can be at or faster than longer reps (> 3 min). Rest between intervals play a key role in this paradigm. For shorter reps, 1:1 or less than 1 minute is appropriate to limit the ability to rest. You are challenging the specimen to recovery under a manageable stress. In longer reps, you can emphasize pace while giving relatively more recovery to hit times. Both protocols can promote the same response.
You can get the same cumulative effect when doing say, many 400m repeats separated by short rest, as you do by doing longer but fewer bouts separated by relatively longer rest periods. How does this fit into programming? Typically a high rep high volume workout would be put early in training then as you progress through your program you can funnel into more specific work bouts in a bottom-up model.
A simple progression:
16 x 400m @ 3K-5K; 1 min rest.
8 x 800m @ 5K; 2 min rest.
7 x 1000m @ +/- 5K; 2 min rest.
6 x 1200m @ + 5K; 3 min rest.
4 x 1600m @ 5K-10K; 3-4 min rest.
The Kin+ Advantage
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As an athlete it is important to focus on the task at hand, while having a strong belief in your long term development. Leave the thinking to the pros. At Kin+ we establish a healthy coach-athlete relationship with our clients that maximizes compliance and results. Through true individualized and responsive coaching, we help our clients realize their potential. Ask yourself, or of programs you have used in the past: do you know why you are doing a certain session? If you can't explain why you should be doing it, contact us for a training block or programming.