Understanding HRV

By Alan Sherry CSP Gym

Stress: When people think of stress, they think of its mental properties, the worries and anxieties of everyday life. Stress however can and should be defined as anything that disrupts our allostasis/homeostasis. Taking this into account, we can conclude that pretty much anything we do in our daily lives can place our body under stress.

Stress is non-specific, in other words your body will not differentiate between stressors, whether physical or emotional. The body does not know whether you just hit multiple 1RM attempts, performed an intense anaerobic conditioning session, stayed up all night worrying about which bills need to be paid or had an argument with your significant other. Albeit to differing degrees, it still only recognises stress.

The stress response then is the body’s concerted effort to maintain allostasis in the event of this stress, or group of stressors, and is absolutely vital to life. It does this by rapidly increasing various hormones and/or mobilising energy to where it’s needed based off of these perceived stressors.

Almost everyone has heard of the Central Nervous System, the brain and spinal cord, but it is the Autonomic Nervous System (ANS) that does the work behind the scenes trying to keep us alive by keeping our bodies in a constant state of balance.

The Autonomic Nervous System does this job through its two main branches:

1) Sympathetic
2) Parasympathetic.

Although both branches have opposing effects, they work in harmony in a synergistic/push-pull fashion to regulate many different bodily functions such as blood sugar, heart rate, oxygen uptake, blood PH as well as a cascade of various hormones.

The heart is the most important muscle in the human body. It is responsible for constantly delivering blood, oxygen and nutrients throughout the body failing which we would die. Contrary to popular belief the heart does not beat like a metronome, with precise beats. The rhythm of the heart has a natural fluctuation due to the different inputs of the previously mentioned Autonomic Nervous System. By looking at the variance between heart beats we can see the balance, or lack of, between sympathetic and parasympathetic branches.

The Sympathetic System: The sympathetic system’s job is to speed up various processes within the body. It is also responsible for the fight or flight stress response and can be seen as being catabolic in nature. This response will increase heart rate and blood pressure, inhibits digestion, reduces appetite, and diverts blood to the working musculature and releases sugars / fats into the bloodstream for energy usage.

The Parasympathetic System: The parasympathetic system does the opposite. It is responsible for decreasing heart rate and blood pressure, stimulating digestion, increasing appetite, dilating blood vessels and promoting energy storage. It can be seen as being anabolic in nature. Using training as the example stressor, there is a large sympathetic shift that occurs with all its ensuing process' ( i.e. heart rate goes up, blood pressure increases, energy stores are mobilised etc…) Once the stressor, in this case training, has passed there is then a parasympathetic shift which pull’s those process’ back down allowing our body to settle back into homeostasis.

Generally speaking the harder the stress, the longer it takes the body to achieve this this re-balancing act. If sympathetic function is high and parasympathetic low, this is a sign that the body is under acute stress (training for example) and the body’s energy supplies and process’ are being used to meet that physical demand. This is generally seen through a reduction in HRV score and parasympathetic protocols are advised here to induce restoration.

On the other hand, if sympathetic function is low and parasympathetic function is high, this is a sign that the body is in a stage of restoration and adaption. Acutely, this can also be a sign of 'detraining' for example when an athlete that undergoes high amounts of aerobic volume stops a sharp increase in parasympathetic dominance can happen as a sign that there isn't enough of a stimulus for adaption to keep occurring.

Recovery: It is also important to understand which recovery strategies should be employed based off nervous system functioning. If the client is sympathetic then parasympathetic recovery strategies are needed for restoration. Far too often the same stressor is applied as a recovery modality which can end up pushing the client and athlete further away from balance into an overtrained state - the complete opposite of what recovery protocols should be doing.

Example recovery strategies for sympathetic dominance would be:
- Reduced Intensity (90% work, alactic/lactic pieces etc)
- Light Massage
- Yoga/Meditation
- Sleep
- Active Aerobic Recovery

Example recovery strategies for parasympathetic dominance:
- Reduce Volume (or Intensity)
- Deep Tissue Massage
- Sauna
- Cold Water Immersion

In essence with HRV we can take a look 'under the hood' and view the athletes unique physiological stress response allowing for optimal training and recovery strategies to be implemented and potentially doing away with outdated protocols such as de-loads and optimising peaking phases for competition.

We can also use HRV and RHR as simple tests for cardiovascular function and use the continuing data to truly crack the clients quest for health and longevity through fitness.