title: Relaxing on a bed of nails: an exploratory study of the effects on the autonomic, cardiovascular, and respiratory systems, and saliva cortisol.
abstract: OBJECTIVE
  This study investigated subjective and physiologic responses of lying on a bed of nails (BN) called the Shakti-mat and of listening to relaxing instructions and music. The BN has 6210 sharp-edge 5-mm plastic nails about 5 mm apart.
  
  
  METHODS
  Thirty-two (32) healthy participants went through four conditions in randomized orders combining BN and relaxing instructions.
  
  
  RESULTS
  The subjective pain ratings on the BN increased immediately and reached a peak within 30 seconds. The pain then subsided gradually, indicating a habituation effect. Self-rated relaxation increased over time in all conditions. Systolic and diastolic blood pressures were higher, heart rate was slower, and there was more high-frequency power heart rate variability (HRV), and signs of increasing circulation in the back on the BN. The relaxation instruction especially affected breathing and the HRV-indices standard deviations of normal interbeat intervals and low-frequency power, both known to be responsive to slow breathing. There were no differences in saliva cortisol.
  
  
  CONCLUSIONS
  Healthy participants habituated to the induced pain on the BN and were able to subjectively relax. When on a BN, signs of both sympathetic and parasympathetic nervous system activity were observed. The pain may hypothetically have triggered a parasympathetic response.
authors.affiliation: Institute of Psychophysiological Behavioural Medicine, Bergvik, Sweden. erik.olsson@pubcare.uu.se
authors.forename: Erik M G
authors.initials: EM
authors.lastname: Olsson
authors.forename: Bo
authors.initials: B
authors.lastname: von Schéele
mesh_terms: D000328:Adult; D000339:Affect / Q000502:physiology*; D001341:Autonomic Nervous System / Q000502:physiology*; D001415:Back / Q000098:blood supply; D001794:Blood Pressure / Q000502:physiology; D005260:Female; D006185:Habituation, Psychophysiologic / Q000502:physiology*; D006339:Heart Rate / Q000502:physiology; D006801:Humans; D006854:Hydrocortisone / Q000378:metabolism; D008297:Male; D008875:Middle Aged; D009147:Music Therapy; D010146:Pain / Q000503:physiopathology / Q000517:prevention & control / Q000523:psychology; D058748:Pain Perception / Q000502:physiology*; D012063:Relaxation / Q000502:physiology / Q000523:psychology; D012119:Respiration; D012463:Saliva / Q000737:chemistry; D012879:Skin Physiological Phenomena
chemical_list: D006854:Hydrocortisone