title: Lactate threshold predicting time-trial performance: impact of heat and acclimation.
abstract: The relationship between exercise performance and lactate and ventilatory thresholds under two distinct environmental conditions is unknown. We examined the relationships between six lactate threshold methods (blood- and ventilation-based) and exercise performance in cyclists in hot and cool environments. Twelve cyclists performed a lactate threshold test, a maximal O(2) uptake (Vo(2max)) test, and a 1-h time trial in hot (38°C) and cool (13°C) conditions, before and after heat acclimation. Eight control subjects completed the same tests before and after 10 days of identical exercise in a cool environment. The highest correlations were observed with the blood-based lactate indexes; however, even the indirect ventilation-based indexes were well correlated with mean power during the time trial. Averaged bias was 15.4 ± 3.6 W higher for the ventilation- than the blood-based measures (P < 0.05). The bias of blood-based measures in the hot condition was increased: the time trial was overestimated by 37.7 ± 3.6 W compared with only 24.1 ± 3.2 W in the cool condition (P < 0.05). Acclimation had no effect on the bias of the blood-based indexes (P = 0.51) but exacerbated the overestimation by some ventilation-based indexes by an additional 34.5 ± 14.1 W (P < 0.05). Blood-based methods to determine lactate threshold show less bias and smaller variance than ventilation-based methods when predicting time-trial performance in cool environments. Of the blood-based methods, the inflection point between steady-state lactate and rising lactate (INFL) was the best method to predict time-trial performance. Lastly, in the hot condition, ventilation-based predictions are less accurate after heat acclimation, while blood-based predictions remain valid in both environments after heat acclimation.
authors.affiliation: Department of Human Physiology, University of Oregon, Eugene, OR 97403-1240, USA.
authors.forename: Santiago
authors.initials: S
authors.lastname: Lorenzo
authors.forename: Christopher T
authors.initials: CT
authors.lastname: Minson
authors.forename: Tony G
authors.initials: TG
authors.lastname: Babb
authors.forename: John R
authors.initials: JR
authors.lastname: Halliwill
mesh_terms: D000064:Acclimatization; D000222:Adaptation, Physiological; D000293:Adolescent; D000328:Adult; D015308:Anaerobic Threshold; D001642:Bicycling; D003080:Cold Temperature; D005080:Exercise Test; D005260:Female; D018882:Heat Stress Disorders / Q000097:blood / Q000503:physiopathology / Q000517:prevention & control*; D006358:Hot Temperature; D006801:Humans; D019344:Lactic Acid / Q000097:blood*; D008297:Male; D009119:Muscle Contraction; D018482:Muscle, Skeletal / Q000378:metabolism* / Q000503:physiopathology; D009922:Oregon; D010101:Oxygen Consumption; D010807:Physical Endurance; D012123:Pulmonary Ventilation; D013997:Time Factors; D055815:Young Adult
chemical_list: D019344:Lactic Acid