Incremental exercise consists of three domains of exercise intensity demarcated by two thresholds. The first of these thresholds, derived from gas exchange measurements, is defined as the metabolic threshold (V̇O₂θ¸) above which lactate accumulates. Correctly and reliably identified, V̇O₂θ¸ is a non-invasive, sub-maximal marker of aerobic function with practical value. This investigation compared variability in selection of V̇O₂θ¸ among interpreters with different levels of experience as well as from auto-detection algorithms employed by a commercially available metabolic cart (MC). Ten healthy young men performed three replicates of incremental cycle exercise during which gas exchange measurements were collected breath-by-breath. Two experienced interpreters (E) and four novice interpreters (N) determined V̇O₂θ¸ from plots of specific response variables. Interpreters noted methods used and confidence in their selections. V̇O₂θ¸ was automatically determined by the MC. Interclass correlations indicated that E agreed with each other (mean difference, 21 mL·min^-1) and with the MC (23 mL·min^-1), but not with N (-664 to 364 mL·min^-1); N did not agree among themselves. Despite good overall agreement between E and MC, differences >500 mL·min^-1 were seen in 50% of individual cases. N expressed unduly higher confidence and used different V̇O₂θ¸ selection strategies compared with E. Experience and use of a systematic approach is essential for correctly identifying V̇O₂θ¸. Current guidelines for exercise testing and interpretation do not include recommendations for such an approach. Data from this study suggests that this may be a serious shortcoming. Until an alternative schema for V̇O₂θ¸ detection is developed prospectively, strategies based on the present study will give practitioners a systematic and consistent approach to threshold detection.

• Experience and use of a systematic approach is essential for correctly identifying the metabolic threshold (V̇O₂θ).

• Current guidelines for exercise testing and interpretation do not include recommendations for such an approach.

• Until an alternative schema for V̇O₂θ detection is developed prospectively, strategies based on the present study will give practitioners a systematic and consistent approach to threshold detection.