The current version of ISO 10400 TR requires a length:diameter ratio of at least seven for sizes larger than 10-3/4. This bound was instituted to account for end effects in a collapse test frame. The requirement currently, however, does not justify the selection of the value of seven, nor does the TR discuss the effect of varying end conditions. This study reviews both experimental and theoretical studies aimed at quantifying the effect of length and end constraints on collapse resistance. The results are intended to (a) justify (or dispute) current ISO 10400 requirements and (b) offer guidelines for adjusting collapse test results when the sample diameter is so large that a length sufficient to satisfy the ISO requirement is impractical.