Grounding improves vagal tone and increases HRV. Check out these studies conducted at Penn State College of Medicine on grounding and preterm infants https://pennstatehealthnews.org/2017/08/grounding-technique-may-improve-health-outcomes-of-babies-in-the-nicu/

Download the SweetBeat HRV app at www.beathealthy.com. You can use a Bluetooth low energy heart rate monitor chest strap or the Zoom fitness band. Go to www.zoomhrv.com and use promo code ZOOMSB10 for $10 off the Zoom. Outside the United States go to Amazon and use the same promo code.