by Rick Crawford

Heart rate (HR) still rules as the master indicator of your body’s status. It’s like the rest of the gauges on the dashboard. Your car has a temperature gauge, a fuel gauge, an oil pressure gauge, a tachometer, and a speedometer … all of which tell what’s going on in the running engine. Those gauges tell if you’re running low on fuel, running the engine too hard, if you’re overheating, and how fast you’re going. The heart tells a lot about our bodies. It tells us what’s going on when our engine is running. It tells us when it’s fatigued or overheated. It tells us when we’re unmotivated or depressed. It tells us when the parking brake is on. It has been advertised lately that the heart is a finicky indicator of output, but that is not true, it just has more than one job to do other than indicate output.

HR tells the whole story

Since the heart obeys the Central Nervous System (CNS), it tells the story of what the CNS and the rest of the body has been through. Power, being the absolute end-all that it is, tells what’s going on right now on the bike. But what led to that wattage at that moment? Form is the culmination of past work and adaptations that manifest in the temporary current state. It’s important to note that Lactate Threshold (LT) is not a static HR or wattage, but rather a fleeting chemical status that is hugely variable and happens in a fairly large range of HR and power output. If HR is low at LT, there’s a reason for it and ideally, we need to know why that is. HR tells the whole story. Fatigue of some sort is the usually the reason, but what kind of fatigue and why? Low HR usually indicates some degree of central fatigue, that is, fatigue of the CNS that manifests as a low HR. This is a natural occurrence and necessary for growth, but should be watched carefully and completely understood.

Along with wattage, HR completes the athlete’s dashboard. Together these two parameters , along with perception, are the bomb. They behave in relation to each other in a predictable fashion. A rested and untrained athlete will have relatively high HR and relatively low power as it has not been developed. As a training cycle advances, HR will tend to trend downwards, and power will trend upwards as form develops. HR trends downward as a function of central fatigue, and power trends upwards as a function of physiological adaptation. The point comes when fatigue suppresses power output. It should be clear that central fatigue cannot be allowed to continuously trend downward as catastrophic collapse is eminent, therefore training cycles must include recovery that allows continuous progression. It is a predictable cycle. When you’re as fresh as a daisy and HR is high, you are probably a little below the peak on the form curve, and when you’re centrally fatigued and HR is low, you’re likely past the peak. HR and power do this dance through every training cycle.

Sensation also important

Perception is a key element also. LT always feels the same whether power is great or poor. So the only way an athlete knows where LT is on any given training ride is by being keen to what the sensations are. These sensations, correlated against HR and power are the key components of the athlete’s dashboard.

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