If you feel like you are losing energy, take in 3-4 short but deep in and out breaths. Follow these with a long cosmic breath. This works well with stimulating acupressure points or with a cross-crawl or hemisphere switching exercise. Warning - if you feel yourself getting dizzy STOP and rest and breath slowly. This type of breathing needs to be done while you are walking or standing.
Lung capacity is increased by arm movements.
Walk about brandishing your arms or one or more objects of equal weight - a cane, wooden spoon, baton, paper towel tubes, pencils, etc. Create expressive arm movements like you are attacking an imaginary foe or dueling with Basil Rathbone. Or if you wish to be more sedate, simply stand and do a horizontal figure eights in the air, first with one hand, then the other, and then with both together. Raise your metabolism breathing - Inhale deeply through your nose pulling your diaphragm up and sucking in your abdomen at the same time. Hold it and count slowly to 3-5.