Researchers in India who compared the heart rate variability of men who practised yoga regularly and men who did not, concluded that practising yoga was associated with a healthier heart because the heart rate variability of the yoga practitioners showed evidence of stronger control by the parasympathetic (vagal) nervous system.

The study was the work of Ramesh Kumar Sunkaria, Vinod Kumar, and Suresh Chandra Saxena of the Electrical Engineering Department, at the Indian Institute of Technology in Roorkee, in Uttrakhand, and is to be published in a forthcoming 2010 issue of the International Journal of Medical Engineering and Informatics.

Heart rate variability is a measure of the beat-to-beat changes in heart rate. In healthy people it is high, whereas people with cardiac abnormalities generally have low HRV.

The autonomic nervous system regulates heart rate via two routes: the sympathetic and parasympathetic nervous systems.

The sympathetic nervous system causes HRV to go up, while the parasympathetic depresses it. When working well together, the two ensure that the heart rate is steady but ready to respond to changes caused by eating, the fight or flight response, or arousal, the researchers told the press.

Earlier research suggests that HRV is also a marker of dynamic and cumulative load. As a measure of dynamic load, it responds to stress, such as when we are under pressure to make a complex decision quickly, our HRV drops.

As a marker of cumulative load, it declines with age, in contrast to heart rate which rarely changes signficantly with age. Research suggests that regular physical activity (which also slows down the aging process), raises HRV, presumably by improving parasympathetic control which raises "vagal tone".

Many yoga practitioners believe yoga improves health through regular practice that focuses on breathing, stretching, postures, relaxation and meditation.

For the study, the researchers analyzed the HRV spectra of the electrocardiograms (ECGs) of 42 healthy male yoga practitioners and 42 healthy male non-practitioners aged from 18 to 48 years. All participants were volunteers.

The researchers said that HRV spectral analysis is an important way of exploring heart health and how the heart is regulated. By looking at different frequency bands of HRV in short term episodes, it is possible to see for example how well the heart responds to changes in the body controlled by the sympathetic and the parasympathetic nervous systems.

For example, very low frequency (VLF) variations are linked to temperature control changes. while low frequency peaks are linked to sympathetic control and high frequency peaks with parasympathetic control, explained the researchers.