As I prepare to engage in my latest challenge–a manual therapy clinic–I have spent considerable time peeling back the “what else” questions that will increase our success. My goal with the clinic is to produce very short recovery times, and the way I believe it will come is leaving no stone unturned in “clearing the road to recovery” as Willem Kramer would call it. Technology allows us a few simple, streamlined physiological measures that have relevance in measuring and improving treatment outcomes, one of which is heart rate variability testing.
Manual therapy protocols, particularly soft-tissue manipulation techniques have long been involved in the prevention and treatment of sporting injury, however, a sound understanding of the physiological basis has been a bit elusive. Soft-tissue modalities seek to affect the tissues underlying the dermis via direct manual contact. The skin is rife with mechanoreceptors, neuroendocrine structures, and immune cells that respond to mechanical stimuli including compression, traction, and shear (Tobin, 2006). In the past decade more research has been published concerning the impact of varying manual therapy treatment lengths, modalities, and pressures on the tone of the autonomic nervous system mostly via heart rate variability measures. Sporting activities and exercises can alter the tone of the ANS and subsequently modulate blood chemistry and immune function, making physical restoration of autonomic tone potentially valuable in expediting recovery and limiting illness common in athletic populations.
Heart rate variability is the measure that compares R to R wave variation between beats and is believed to have strong reliability and sensitivity in indirectly measuring tone of the autonomic nervous system. Frequency domain models are used with high frequency impulses (>.15hz) are believed to represent the tone of the vagus nerve at the sinoatrial node, which produce an increase in beat to beat variations, and low frequency impulses representative of sympathetic stimulation of the sinoatrial node (Aubert, 2003). Using power spectral density analysis, many manual therapy studies look at the impacts on the high frequency impulse and sometimes low frequency to high frequency ratio to ascertain autonomic balance.
Heart rate variability has been associated with a number of diseases and pain states and also experiences changes with improvements in fitness over the course of a sporting season in endurance athletes (Hedelin, 2000). Additionally, vagal tone is associated with alterations in immune status and circulating catecholamines that are altered by exercise intensity. Low vagal tone can be correlated with poor immune function which is facilitated further by high catecholamines, which potentially destroy natural killer cells and lead to higher incidence of respiratory infection in female field-sport athletes (Parrado, 2010; Yi, 2005).
Manual therapy techniques may effectively modulate heart rate variability and modulate neuroendocrine response, while influencing the immune system. Looking at the information available, it may be possible to deduce specific dosing characteristics of soft tissue therapies for each individual and allow insight into non-manual recovery activities.
In the coming weeks I’ll look at some studies on the matter and help you make your own decisions.