The following is taken from the Financial Times – http://on.ft.com/1VB1avV
Thanks to advances in technology, knowing when your body has not quite recovered from strenuous exercise has become a lot easier. A measurement called heart rate variability, or HRV, can estimate your body’s stress levels.
While you may have noticed a measurement of your heart rate at the doctor’s office or on a sports watch, this number is really just an average. Your heart actually beats slightly faster when you breathe in and slower when you exhale. The difference is the variability.
A simplified explanation in this limited space is that the body is constantly sending feedback to the brain. The so-called lizard brain — the autonomic nervous system — which keeps the body functioning unconsciously, is divided into two branches: the parasympathetic and the sympathetic.
The parasympathetic, known as the rest-and-digest system, is under the control of the vagus nerve and controls such things as heart rate. The sympathetic system has been linked to the fight-or-flight response that helps you set a personal record in your run.
Picture a see-saw, with the parasympathetic system stronger and sympathetic system weaker in recovery and vice versa during training.
According to an academic study carried out in Finland, daily use of heart rate variability to determine workout schedules “efficiently improved” cardio fitness in a group of untrained athletes. The study concluded that on days when the HRV reading declined, taking a break from exercise had a positive effect on their overall endurance.
Ronda Collier, chief executive of Sweetwater Health, a Californian start-up that is commercialising the HRV measurement process, says that training times can be optimised by observing your HRV over time.
“Because the HRV number is associated with the tone of the vagus nerve, we know from research that those numbers are decreased from hard workouts and are also affected by emotional stress,” she says.
For the past couple of months, I have been measuring my HRV using two iPhone apps: SweetBeat HRV ($9.99) and ithlete ($8.99).
With these apps, you put on a cardiac chest strap shortly after you wake in the morning and then breathe slowly for a number of minutes while the app measures your HRV, displaying a number from 1 to 100, which is actually a composite of many measures.
When your HRV number declines substantially compared with previous days, it is a sign that you need to take a break. The number rebounds after a rest period and you are ready to resume exercise.
According to Ms Collier, these measurements can do far more than shape your workouts. Because they are an accurate measure of emotional as well as physical stress, they can guide you on when to tackle challenges such as a difficult talk with a colleague or a partner.
Even better, interventions such as meditation can help the recovery process along and benefit your HRV.