Agreement Between Lactate Threshold And Critical Speed In Trained And World Class Distance Runners

The anaerobic threshold has traditionally been identified by lactate threshold laboratory-based testing (LT2) and a more recent field-based test, critical speed (CS). While anaerobic threshold paces derived from these tests have been used interchangeably, it is unclear whether there is agreement between LT2 and CS, especially in World Class runners. PURPOSE: To confirm if there is agreement between the speeds at which LT2 and CS occur. METHODS: Trained and World Class runners (McKay Tiers 2/3 vs. 4/5; n = 20 [53% female]; VO2maxspeed = 4.6 ± 0.56 m/s) actively competing in the 1500 m to marathon completed LT2 and CS tests separated by ~4 days. The graded treadmill LT2 protocol consisted of 6-9 stages that started ~2 min slower than 10 k race pace and increased 0.4 mph every 4 min until blood lactate rose over 4 mmol. Blood lactate was taken as an average of duplicate measures and LT2 (m/s) was determined using the Modified D-Max method. The treadmill gradient then increased 1% every minute until volitional exhaustion for determination of VO2max. The CS workout included 3 maximal effort (RPE >17) intervals of 3200 m, 2000 m and 1000 m on an outdoor track separated by 30 min recovery. CS (m/s) was calculated from a linear distance-time regression. In a follow-up questionnaire, participants were asked to report whether LT2 or CS corresponded more closely with their longer tempo or shorter interval paces. Comparison of the anaerobic threshold speed between LT2 and CS was assessed using a dependent t-test. In addition, Pearson’s r and bias (CS-LT2) ± 95% limits of agreement were determined. RESULTS: CS occurred at a significantly faster speed than LT2 (4.24 ± 0.57 vs. 4.12 ± 0.52 m/s; p = 0.003). There was a strong relationship between LT2 and CS (r = 0.97). Bias ±95% limits of agreement were 0.12 ± 0.14 m/s. The majority (75%) of participants reported LT2 more closely corresponded with longer tempo run paces while 75% reported CS more closely corresponded with shorter interval paces. CONCLUSION: Our findings support CS may occur at speeds higher than LT2 in trained to World Class runners and thus it is recommended that anaerobic threshold speeds derived from these tests should not be used interchangeably. However, CS and LT2 derived anaerobic threshold paces may correspond with different workout intensities and training purposes.