The first rule of thumb is to remember that the breath is the driving force for the voice. Especially,exhalation.
If you take a deep breath when someone presses your costovertebral joints from your back, you can control exhalation and improve exhaling ideally,this is supposed to be good training for the voice.
Press the costovertebral joints safely and carefully, otherwise the effect is decreased by half.
You can train breathing techniques ideally, if the pressing completely matches in sync with the breathing.
For the goal of hitting high registers, the target is to press lower Cervical spine to upper Thoracic Spine. For the goal of a mixed tonal voice,the target is the thoracic vertebrae from Th3 to Th12.
If you want to improve hitting low registers,the target is from the lower Throacic spine to upper lumbar spine.
Again, remember … breathing is the driving force and strength of the voice!
Work assistance:Kenichi Sato
EDIT1:The diaphragm also helps you exercise your voice by using the
internal intercostal muscles and external intercostal muscles.
Using these tips & techniques to achieve brilliant breathing exercises will help you greatly in creating a good performance using the art of voice.