Exercise-related changes in the anabolic index (testosterone to cortisol ratio) and serum amyloid A concentration in endurance and racehorses at different fitness levels

Abstract

Increased training loads in both human and equine athletes are generally implemented to improve their physical performance. These loads are tolerated only within appropriate training periodization with regard to recovery time. Otherwise, training overload causes failure in the systemic adaptation, which at first leads to overreaching, and progressively to overtraining syndrome (OTS). Exercise endocrinology, and anabolic/catabolic balance as an indicator of athlete performance status and OTS has continued to attract attention. In human medicine, changes in testosterone and cortisol levels, as well as the testosterone to cortisol ratio (T/C; anabolic index), are suggested to be sensitive stress markers. However, there is a lack of research investigating these parameters for use in equine sports medicine. The aim of the study was to investigate the differences in testosterone, cortisol, and T/C in response to a single training session in two types of equine sports: endurance and race, together with serum amyloid A (SAA), the main acute phase response indicator of physical effort, and the overall health status in horses. Two groups of horses were enrolled in the study: endurance (n = 12) and racehorses (n = 32) of different fitness level. Blood samples were obtained before and after the exercise. On average, T increased 2.5 times after the race training in experienced racehorses and dropped in endurance horses regardless the fitness level (p < 0.05). In endurance horses, a decrease in T/C occurred after training in inexperienced horses (p < 0.05). In racehorses, a T/C decrease occurred in the inexperienced group (p < 0.05) and an increase in the experienced (p < 0.01). In conclusion, T/C ratio was found to be a potentially reliable indicator of fitness status especially in racing horses. These findings provide insight into the physiological response of the horses to different types of exercise and the potential use of hormone levels as markers of performance and adaptation.

Immunology of Physical Exercise: Is Equus caballus an Appropriate Animal Model for Human Athletes?

“…Additionally, in a study performed on 47 elite endurance horses, there was no SAA increase after a 160 km ride. Similar findings with no increase in SAA after exercise were obtained in racehorses [37,41,42]; however, in a more recent study, in an inexperienced group, a slight elevation in SAA occurred after exercise [40], as well as one and two days after the race [43].…”

“…A minimum of a 10-fold increase in SAA blood concentration was documented in horses completing endurance rides over the longest distances (120 and 160 km), but not shorter (up to 60 km) [37,38], with unchanged concentrations of CRP and haptoglobin [39]. In a more recent study, SAA increase occurred only in inexperienced endurance horses after a 100 km ride [40]. Additionally, in a study performed on 47 elite endurance horses, there was no SAA increase after a 160 km ride.…”

Effect of Regular Training on Platelet Function in Untrained Thoroughbreds

“…Depending on the intensity, duration, and type of physical exercise, the equine metabolism also has to adapt to endocrine system requirements. For example, different fitness levels influence cortisol release in endurance and racehorses [13], and in humans, a negative relationship between the plasma concentration of cortisol and platelet reactivity to arachidonic acid and ADP has recently been shown [14]. Moreover, it was also recently shown that proteins involved in the regulation of platelet function, such as matrix metalloproteinase 2 (MMP-2) [15], were shown to change in racehorses at different levels of training [16].…”

Identification of Differentially Expressed Genes after Endurance Runs in Karbadian Horses to Determine Candidates for Stress Indicators and Performance Capability

“…While, previously, the lactate concentration [72,73] was primarily used as a parameter for the degree of exhaustion, today, hormones such as testosterone and cortisol are also used for evaluation in addition to cytokines. An anabolic index determined from the ratio of these hormones is a possible parameter but is more suitable for racing horses than for endurance horses [74]. Differences in expression of these genes could therefore possibly indicate individually varying adaptability and could thus be markers for the monitoring to avoid training overload as well as for identifying horses with higher stress resistance [68].…”