The phenomenon known as the lactate paradox has been a topic of heated debate since it gained worldwide attention following Operation Everest in the early 1980s. What began as the simple finding that blood lactate (blood [La]) for a given sub-maximal workload or VO2 following acclimatization to high altitude is reduced compared with sea-level values, morphed into a complex set of parameters that have been redefined several times in the nearly 30 years that the lactate paradox has been researched. Though several strong hypotheses have been proposed to, to date, no one hypothesis has been able fully to explain the lactate paradox. The goal of the current article was to bring together the most prominent studies done on the lactate paradox and illuminate the details brought forth by each. In doing so we hope to stimulate new hypotheses and research studies that will further our understanding of the lactate paradox.

Twenty-seven mature Standardbred mares (9–27 years, ~522 kg) were used to test the hypothesis that training and short-term cessation of training would alter total plasma total carbon dioxide (tCO2) concentrations. Plasma tCO2 concentrations were measured in blood samples (20 ml) collected at rest from the same ten unfit mares that were used in two separate studies that were conducted 1 month apart. Comparisons between the samples obtained from the two trials were made to demonstrate the consistency of plasma tCO2 concentrations in the untrained population. Another set of resting blood samples was collected from an additional 17 mares that were being utilized in a training study that was under way during the same period. All the mares were housed in groups on dry lots, and were fed approximately 12 kg of mixed alfalfa-grass hay divided into two feedings per 24 h period. During the ‘detraining’ period, the 17 horses were housed in 5 × 5 m stalls, and were fed the same hay ration. Water and trace-mineral blocks were available ad libitum. Blood samples were collected from the mares prior to the last session of their 12 weeks of training at 60% HRmax (maximum heart rate), as well as on the third day following 2 days of detraining (simulated quarantine). Plasma tCO2 concentrations were measured in duplicate using a Beckman EL-ISE analyser. For data analysis, t-tests with the a priori level of statistical significance set at P < 0.05 were used. Resting plasma tCO2 concentrations were lower (P < 0.05) in the trained horses (31.4 ± 1.9 mMol l− 1) than in the untrained horses (34.4 ± 0.9 mMol l− 1). There were no effects (P>0.05) due to cessation of training. It was concluded that training causes a decrease in plasma tCO2 concentrations that is not reversed by limited cessation of training.

Foot strike can be difficult to determine using kinematics alone, particularly when studying equine activities on more compliant surfaces, so this study was done with the aim of developing and validating a method to determine foot strike on an arena surface that can be used in conjunction with kinematics alone, and of applying the method in the context of measuring foot strike during jump landing on an arena surface. A low-cost contact mat was developed. The timing of the contact mat switching ‘on’ was compared to the timing of a force platform onset of 20 N, load and loading rate at foot strike. Two groups of 25 participants were used in two separate studies to validate the contact mat: the first measured the difference in timing with respect to two different activities (running and stepping down from a box), and the second measured the difference in timing with respect to 1- and 2-cm depths of an arena surface during running. In a third study, the mat was used to measure leading limb foot strike of six horses during jump landing, and these data were compared to kinematics from a palmar marker on the hoof wall. All data were recorded at 500 Hz. A consistent difference in delay was found between the mat and force platform onset, and as a result, no significant differences (P>0.05) in timing delay between different loading rates or depths were found. During jump landing, foot strike (determined from the mat) occurred after the vertical velocity minima and the acceleration maxima for the hoof marker, but it occurred before the point where the rate of vertical displacement began to reduce. In conclusion, further work is needed to enhance these techniques, but these preliminary results indicate that this method may be effective in determining foot strike for field-based applications.

There is a known relationship between the way athletes interpret the feelings of pre-competitive arousal and their subsequent performance. In equestrian sports, riders' interpretation of their horses' temperament may be an additional unique factor that influences the levels of riders' arousal and performance. The aims of this study were to investigate the effect of intensity and direction of arousal and self-confidence on dressage and showjumping performance, and to investigate how perception of equine temperament traits affects arousal and performance components. Twenty-two student riders (6 males and 16 females) competing on unfamiliar horses were asked to participate in the study. Prior to the competition, riders completed the Revised Competitive Sport Anxiety Inventory-2 with direction scales, and rated their horses' temperament traits using an adapted Five Factor Personality Questionnaire. Dressage performance scores were found to be positively correlated with cognitive arousal intensity (r = − 0.5, P < 0.05) and self-confidence intensity (r = 0.59, P < 0.05). Showjumping faults were negatively correlated with somatic arousal direction scores (r = − 0.5, P < 0.05). The ‘active’ equine temperament was positively correlated with somatic arousal intensity in showjumping (r = 0.5, P < 0.05) and negatively correlated with cognitive arousal direction in dressage (r = − 0.71, P < 0.005). These findings suggest that riders' self-confidence and perception of their horses' temperament are important factors in the relationship between arousal and performance.

To examine the management and training practices of 2-year-old racehorses, cross-sectional survey data were collected from 55 racehorse trainers in the Central Districts (n = 15) and the Northern Districts (n = 40) of New Zealand during summer 2007–08. Trainers in the Northern Districts had a higher proportion of 2-year-olds in work at one time (0.31 vs. 0.22, P = 0.001) than trainers in the Central Districts. Group S (trainers with 10–19 horses in work) had a higher proportion of 2-year-olds in work than both groups M (20–30 horses in work) and L ( ≥ 40 horses in work) (0.38 vs. 0.24 vs. 0.29, respectively, P = 0.001). Most horses were broken prior to the start of the official 2-year-old racing year. Most trainers had a standard pattern of training, and they cited early education as the primary reason for training 2-year-olds; the primary training milestones used to evaluate the horses' training were the first training gallop and the entry in a race trial. Training programmes were geared towards 2-year-olds being ready for trialling and racing earlier in the Northern Districts than in the Central Districts. Training practices were affected more by the trainer's location than by the number of horses trained.

Ten mature Standardbred mares (9–13 years, ~522 kg) were used to test the hypothesis that pelleted dietary supplementation would alter total plasma bicarbonate (tCO2) concentrations. All the mares used in this study were unconditioned, but were familiarized to the laboratory setting and running on a treadmill. Each of the ten mares was semi-randomly assigned one of four dietary treatments. The four treatments (oats as control and three pelleted feed supplements: Drive, Omolene and Strategy) were administered in a crossover fashion throughout a 4-week testing period. These products were chosen based on the frequency of their use by Standardbred/Thoroughbred owners and trainers in New Jersey. The horses underwent a simulated race test (SRT) on a treadmill (6% grade) at the end of each administration period. During the SRT, horses ran for 2 min at 4 m s− 1, 2 min at the speed previously shown to correspond to VO2max and 2 min at 4 m s− 1. Blood was collected before supplement treatment ( − 4 h), 10 min prior to exercise and at 0, 60 and 90 min post-exercise. Plasma concentrations of bicarbonate, sodium, potassium and chloride were measured using a Beckman ELISE analyser. The major finding of this study indicates that the plasma [tCO2], chloride and sodium concentrations were not altered by the dietary supplements studied (P>0.05). There were differences (P < 0.05) in plasma [tCO2] across sampling intervals ( − 4 h, − 10 min, +0 min, +60 min and +90 min) that were attributable to acute exercise (mean ± SE: 34.4 ± 0.9, 33.2 ± 1.1, 20.2 ± 0.8, 31.5 ± 0.8, 30.3 ± 1.6 mmol l− 1). There was a slight effect of treatment (P < − 0.05) on potassium levels. However, exercise was the main factor that caused substantial changes (P < 0.05) in the plasma tCO2, potassium, haematocrit and total protein concentrations. It was concluded that the pelleted diet supplements examined do not alter plasma [tCO2] in horses.