A couple of recently published scientific papers took my interest, one of which was on bicarb-loading.
There has been a lot of papers written on milkshaking in Thoroughbreds including its effect on cardiorespiratory limits and exercise, the proper amount, and the exact mechanisms behind its success and there is also some conflicting research on its efficacy. However, one of the more interesting papers surmised that the better horses had naturally higher pre-race TCO2 levels, that is, they had a better natural lactate buffering capacity (lasix administration also had an effect). A paper just released by Higgens et al, studied the effects of elevated levels of sodium bicarbonate (NaHCO3) on the acute power output and time to fatigue of maximally stimulated mouse soleus and EDL muscles. This study examined the effects of elevated buffer capacity through administration of sodium bicarbonate (NaHCO3) on maximally stimulated isolated mouse soleus (SOL) and extensor digitorum longus (EDL) muscles. The elevated buffering capacity was of an equivalent level to that achieved in humans with acute oral supplementation. Although significant differences were not observed in whole group data, the fatigability of muscle performance was variable, suggesting that there might be inter-individual differences in response toNaHCO3 supplementation. These findings are pretty much in agreement with what may in the veterinary community will tell you in regards the the efficacy of "milkshaking" in Thoroughbreds. While in general the Thoroughbred responds to bicarbonate loading, or milkshaking, some are high responders and get a lot out of it while for others it is not nearly as effective. Certainly for those trainers that walk the line of manipulating TCO2 levels, the very fact that there are multiple reasons for changes in TCO2 levels, including some less understood genetic ones, manipulating TCO2 levels is a dangerous game to play.
Using RNA-seq Kim et al, did a fantastic study on the evolutionary process of the mechanisms behind response to exercise stress in the Horse (Equus Caballus) and found an evolutionary layer of responsiveness to exercise-stress in the skeletal muscle of the racing horse. By estimating genome-wide ratios using six mammalian genomes and data derived from 20 horses, they were able to peel back the evolutionary layers of adaptations to exercise-stress in the horse. They found that the oldest and thickest layer consisted of system-wide tissue and organ adaptations and that during the period of horse domestication, the older layer is mainly responsible for adaptations to inflammation and energy metabolism.
Lustgarten, et al undertook an identification of serum analytes and metabolites associated with aerobic capacity in humans. Using a standard chemistry screen and untargeted mass spectrometry (MS)-based metabolomic profiling, they identified significant associations between baseline levels of serum analytes or metabolites with VO2max (77 subjects, age range 18-35 years). Use of multivariable linear regression identified three analytes (standard chemistry screen) and twenty-three metabolites (MS-based metabolomics) containing significant, sex-adjusted associations with VO2max. In addition, fourteen metabolites were found to contain sex-specific associations with aerobic capacity. However, the results of the stepwise model were found to be sensitive to outliers; therefore, random forest (RF) regression was performed. Use of RF regression identified a combination of seven covariates that explained 57.6 % of the variability inherent in VO2max. Furthermore, inclusion of significant analytes, metabolites and sex-specific metabolites into a stepwise regression model identified the combination of five metabolites in males and seven metabolites in females as being able to explain 80 and 58 % of the variability inherent in VO2max, respectively.