What it is and How it can be used to monitor
Readiness to Train and Recovery Status
The Autonomic Nervous System
The Autonomic Nervous System consists of two sub-systems. They are the sympathetic and parasympathetic systems. As most will know both these systems are central in managing all our involuntary actions and reactions that take place throughout the various organs of the body. When we are relaxed and rested our parasympathetic system is balanced with our sympathetic system, but when for example, you get a fright or have to react within a stressful situation (the classic ‘flight or fight response’) the sympathetic system takes over. Various hormones such as adrenaline are pumped through to certain organs we get ready to move or fight. Our pupils dilate and our heart rate speeds up and blood is shunted to the muscles so as to flee or to fight.
When danger is over our parasympathetic system stars to become prominent again and the Vagus Nerve starts to exert its calming influence on our organs and body reactions.
So during a given day both systems work together to manage the stress responses and the recovery responses to these stresses. HRV is a reflection of the balance between these two most important Autonomic or Involuntary systems. Thus, as we have seen in our last blog, when we measure the interval between RR waves we get a snapshot of how well our ANS system is balanced. HRV also tells us if the parasympathetic system is dominating as in when we feel rested, calm and in control. When the sympathetic system is more dominant as in when we have to get ready to talk to a group or to meet our athletes or to start training and competing, then the sympathetic system starts to kick in and it exerts its important influence in releasing hormones and speeding up heart rate as well as many other important actions within our body.
When we start to calm down and relax the parasympathetic system becomes dominant and in this environment recovery starts to happen.
HRV an ideal system to monitor Training, Competition and Other Stressors
Training load is an important factor to monitor in sport as it is related to the stress and fatigue and ultimately the adaptation and gains that are made in performance. Other lifestyle stressors such as sleep or the lack of it, work and study related stressors, relationships and environment are all equally if not more important in affecting the balance within the ANS. For example, a recent study examining the contribution of lifestyle stressors and training loads in youth sportplayers showed that non-training stressors were more relevant in accounting for any overtraining that occurred.
HRV when assessed using a short time period (say a 5 minute period in the morning) gives us a snapshot of the balance within the ANS. When assessed over a longer duration as during a 24 hour period the balance within the ANS is well described and we can determine the quality of sleep and recovery that has taken place at nighttime.
In our next blog we will look at some key studies that investigated the role of HRV in tracking fatigue and recovery in endurance, sprint and weightlifting individuals. These studies point to HRV as a very useful tool in monitoring athletes and players.
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