canaries in the coal mine

Noun

 * 1) * 2011, "Barefoot" Ken Bob Saxton & Roy M. Wallack, Barefoot Running Step by Step, Fair Winds Press (2011), ISBN 9781592334650, page 101:
 * Runners who are less sensitive than I, or more macho, or simply better able to tolerate pain, might have laughed at my tiny blisters, but the fact is that these little problems are indicators of bigger problems with our technique. They are canaries in the coal mine — signs of impending back pain, knee pain, foot pain, and other big issues destined to come back to haunt you in the long run.
 * 1) * 2011, "Barefoot" Ken Bob Saxton & Roy M. Wallack, Barefoot Running Step by Step, Fair Winds Press (2011), ISBN 9781592334650, page 101:
 * Runners who are less sensitive than I, or more macho, or simply better able to tolerate pain, might have laughed at my tiny blisters, but the fact is that these little problems are indicators of bigger problems with our technique. They are canaries in the coal mine — signs of impending back pain, knee pain, foot pain, and other big issues destined to come back to haunt you in the long run.
 * Runners who are less sensitive than I, or more macho, or simply better able to tolerate pain, might have laughed at my tiny blisters, but the fact is that these little problems are indicators of bigger problems with our technique. They are canaries in the coal mine — signs of impending back pain, knee pain, foot pain, and other big issues destined to come back to haunt you in the long run.