The average singer who goes from practicing or exercising many
times per week down to once a week or less will see a marked
decrease in their range. Humans have a natural vocal range, or
tessitura. The average is about an octave, though many can sing
a span of an octave and a half or even a two-octave span (three-
octave range) even "cold". Outside that range is largely a "use
it or lose it" area, and the further from that range, the more
effort (in the practice and technique sense, not outright
"pushing") is required to maintain access to those notes.
However, this should not be permanent. If you quit singing
technically for a year, then start again, you will start at your
natural tessitura, which you retain simply by speaking regularly
and singing along with the radio. But, as you continue to
practice, your range will increase. One last point: tessituras
can shift, both naturally through aging and artificially through
singing to one side or the other of your tessitura. This is not
range-building; the muscles