I've been taking speech therapy and working on my lung capacity and strength of my voice. These exercises have been very helpful so I want to share. I've been using a simple device called "The breather" to exercise breath support. There are settings to increase the resistance during inhalation and exhalation. Start at the first setting (1) and slowly inhale and exhale as much air as you can. Do this for a couple of minutes a few times a day until you can do it for as long as 15 minutes without feeling fatigued/winded. When you can do that, increase the resistance until you have it at the highest resistance for as long as 10-15 minutes. This is called Resistive Breathing Training (RBT). It describes strengthening the diaphragm and intercostal muscles (accessory breathing muscles surrounding the ribs). Exhalation resistance develops and strengthens the abdominal muscles.
Another exercise I've been doing is specifically for the vocal cords. I take in a deep breath, pull the armrests of my wheelchair upwards and vocalize "ah" for as long as I can. Then I open my mouth wide and inhale in as if I'm yawning and then let out a sigh. This relaxes the vocal cords after forcing them together during the "ah" phase. This exercise strengthens the ability to cough and vocalize louder.
These exercises are great for people with weak lungs/diaphragm from neurogenic disorders like Multiple Sclerosis or Spinal Cord Injury. Great for general inprovement of lung capacity, breath support and vocalization.