Heat acclimation improves exercise performance in hot conditions and increases heat shock protein 70 and 90 of skeletal muscles in Thoroughbred horses.

This study aimed to determine whether heat acclimation could induce adaptations in exercise performance, thermoregulation, and the expression of proteins associated with heat stress in the skeletal muscles of Thoroughbreds. Thirteen trained Thoroughbreds performed 3 weeks of training protocols, consisting of cantering at 90% maximal oxygen consumption (VO2max) for 2 min 2 days/week and cantering at 7 m/s for 3 min 1 day/week, followed by a 20-min walk in either a control group (CON; Wet Bulb Globe Temperature [WBGT] 12-13°C; n = 6) or a heat acclimation group (HA; WBGT 29-30°C; n = 7). Before and after heat acclimation, standardized exercise tests (SET) were conducted, cantering at 7 m/s for 90 s and at 115% VO2max until fatigue in hot conditions. Increases in run time (p = 0.0301), peak cardiac output (p = 0.0248), and peak stroke volume (p = 0.0113) were greater in HA than in CON. Pulmonary artery temperature at 7 m/s was lower in HA than in CON (p = 0.0332). The expression of heat shock protein 70 (p = 0.0201) and 90 (p = 0.0167) increased in HA, but not in CON. These results suggest that heat acclimation elicits improvements in exercise performance and thermoregulation under hot conditions, with a protective adaptation to heat stress in equine skeletal muscles.

Risk Factors for Epistaxis in Thoroughbred Flat Races in Japan (2001-2020).

We investigated the risk factors for epistaxis in Japanese flat races over a 20-year period. The veterinary records of horses identified as having epistaxis by endoscopy on the race day, and the official racing records of all flat races from April to September between 2001 and 2020, were reviewed. The racecourses (n = 10), surface type, surface condition, race class, race distance, race year, sex, age, two training centers, ambient temperature, and body weight on race days were assessed using multivariable logistic regression (p < 0.05). Of 475,709 race starts, 616 (1.30 cases per 1000 starts; 95% confidence interval [CI], 1.20-1.40) included an epistaxis event. Nine variables were significantly associated with epistaxis. Seven of the variables have been reported in previous studies: lower ambient temperature, soft surface conditions, shorter racing distances (≤1400 m), increasing age, females and geldings compared to males, training center, and race year. However, two novel variables were identified as significantly associated with epistaxis, increasing body weight per 20 kg (p < 0.001, odds ratio [OR], 1.33; 95% CI, 1.25-1.41) and the racecourses that the horses were running at (p < 0.001, especially Sapporo [OR; 4.74, 95% CI, 3.07-7.31], Hakodate [OR, 4.66; 95% CI, 3.05-7.11], and Kokura [OR, 4.14; 95% CI, 2.65-6.48] compared to the reference racecourse [Kyoto]). These results can facilitate developing interventions to reduce epistaxis in flat racing.

Acute exercise in a hot environment increases heat shock protein 70 and peroxisome proliferator-activated receptor γ coactivator 1α mRNA in Thoroughbred horse skeletal muscle.

Heat acclimatization or acclimation training in horses is practiced to reduce physiological strain and improve exercise performance in the heat, which can involve metabolic improvement in skeletal muscle. However, there is limited information concerning the acute signaling responses of equine skeletal muscle after exercise in a hot environment. The purpose of this study was to investigate the hypothesis that exercise in hot conditions induces greater changes in heat shock proteins and mitochondrial-related signaling in equine skeletal muscle compared with exercise in cool conditions. Fifteen trained Thoroughbred horses [4.6 ± 0.4 (mean ± SE) years old; 503 ± 14 kg] were assigned to perform a treadmill exercise test in cool conditions [COOL; Wet Bulb Globe Temperature (WBGT), 12.5°C; n = 8] or hot conditions (HOT; WBGT, 29.5°C; n = 7) consisting of walking at 1.7 m/s for 1 min, trotting at 4 m/s for 5 min, and cantering at 7 m/s for 2 min and at 90% of VO2max for 2 min, followed by walking at 1.7 m/s for 20 min. Heart rate during exercise and plasma lactate concentration immediately after exercise were measured. Biopsy samples were obtained from the middle gluteal muscle before and at 4 h after exercise, and relative quantitative analysis of mRNA expression using real-time RT-PCR was performed. Data were analyzed with using mixed models. There were no significant differences between the two groups in peak heart rate (COOL, 213 ± 3 bpm; HOT, 214 ± 4 bpm; p = 0.782) and plasma lactate concentration (COOL, 13.1 ± 1.4 mmoL/L; HOT, 17.5 ± 1.7 mmoL/L; p = 0.060), while HSP-70 (COOL, 1.9-fold, p = 0.207; HOT, 2.4-fold, p = 0.045), PGC-1α (COOL, 3.8-fold, p = 0.424; HOT, 8.4-fold, p = 0.010), HIF-1α (COOL, 1.6-fold, p = 0.315; HOT, 2.2-fold, p = 0.018) and PDK4 (COOL, 7.6-fold, p = 0.412; HOT, 14.1-fold, p = 0.047) mRNA increased significantly only in HOT at 4 h after exercise. These data indicate that acute exercise in a hot environment facilitates protective response to heat stress (HSP-70), mitochondrial biogenesis (PGC-1α and HIF-1α) and fatty acid oxidation (PDK4).

Effects of different winter climates in Japan on body composition of young Thoroughbreds in training.

Changes in the body composition of 50 Thoroughbreds colts and fillies, born between 2004 and 2010, were compared between those reared at the Hidaka Training and Research Center (Hidaka), Hokkaido, which is extremely cold in winter, and those reared at the Miyazaki Yearling Training Farm (Miyazaki), Kyushu, which is mildly cold in winter. The horses were divided into two sex groups and reared and trained in Hidaka or Miyazaki for 7 months from October of one year of age to April of two years of age. Body weight (BW), rump fat thickness (RFT), fat-free mass (FFM), and percentage of fat (%F) were used as parameters of body composition. This study revealed that BW and FFM were higher, and %F was lower in colts than in fillies at both training sites. Among colts, Miyazaki colts tended to have higher FFM values than Hidaka colts, and %F was significantly lower in Miyazaki colts than in Hidaka colts. Furthermore, from October to April, Miyazaki horses had a higher rate of increase in BW than Hidaka horses in both sexes and a higher rate of increase in FFM in colts. The higher rate of increase in FFM in Miyazaki colts suggests that training young Thoroughbreds in winter under mildly cold climate is more effective, than severely cold climate, particularly in colts.

Dynamics of cardiorespiratory response during and after the six-minute walk test in patients with heart failure.

Purpose: The six-minute walk test (6MWT) is a useful measure to evaluate exercise capacity with a simple method. The kinetics of oxygen uptake ([Formula: see text]O2) throughout constant-load exercise on cardiopulmonary exercise testing (CPX) are composed of three phases and the [Formula: see text]O2 kinetics are delayed in patients with heart failure (HF). This study aimed to investigate the kinetics of the cardiorespiratory response during and after the 6MWT according to exercise capacity. Methods: Forty-nine patients with HF performed CPX and the 6MWT. They were divided into two groups by 6MWT distance: 34 patients walked ≥300 m (HF-M), and 15 patients walked <300 m (HF-L). [Formula: see text]O2, minute ventilation ([Formula: see text]E), breathing frequency, tidal volume, and heart rate, both during and after the 6MWT, were recorded. The time courses of each parameter were compared between the two groups. CPX was used to assess functional capacity and physiological responses. Results: In the HF-M group, [Formula: see text]O2 and [Formula: see text]E stabilized from 3 min during the 6MWT and recovered for 3 min, respectively, after the 6MWT ended. In the HF-L group, [Formula: see text]O2 and VE stabilized from 4 min, respectively, during the 6MWT and did not recover within 3 min after the 6MWT ended. On CPX in the HF-M group, [Formula: see text]O2 peak, and anaerobic threshold were significantly higher, while the relationship between minute ventilation and carbon dioxide production was lower compared with the HF-L group. Conclusion: In lower exercise capacity patients with HF had slower [Formula: see text]O2 and [Formula: see text]E kinetics during and after the 6MWT.

Dyspnea During In-Hospital Rehabilitation as a Predictor of Rehospitalization and Mortality in Patients With Acute Heart Failure.

PURPOSE: Consensus articles that explore rehabilitation exercise for heart failure (HF) mainly focus on stable patients with chronic HF. Results from investigations that focus on the relationship between clinical outcomes and exercise during rehabilitation of patients with acute heart failure (AHF) have produced insufficient data. The aim of this study was to evaluate the correlation between clinical outcomes and dyspnea during in-hospital early rehabilitation in patients with AHF. METHODS: Dyspnea was measured using a 5-point Likert scale (5PLS) during rest and at the initiation of upright sitting and standing. Dyspnea was defined as 5PLS ≥2. The primary endpoint was combined all-cause death or rehospitalization for HF. RESULTS: A total of 221 patients were included in this study; 81 patients (37%) died or were hospitalized during the follow-up period. In patients with dyspnea during upright sitting and standing, the event-free ratio was significantly lower compared with patients without dyspnea (P = .008 and P < .001, respectively). Body mass index (hazard ratio [HR] = 0.91, P = .011), noninvasive positive pressure ventilation usage (HR = 1.96, P = .042), and 5PLS ≥2 at the initiation of standing (HR = 2.63, P = .008) were detected as predictors of primary endpoint. New York Heart Association class IV at admission (OR = 3.17, P = .0114) and pre-admission Katz ADL index <6 (OR = 3.76, P = .0007) were isolated as risk factors for dyspnea when standing. CONCLUSIONS: Dyspnea during standing was associated with unfavorable events in patients with AHF as a comprehensive indicator.

Influence of Complications of Diabetes Mellitus on Exercise Tolerance of Patients with Heart Failure: Focusing on autonomic nervous activity and heart rate response during cardiopulmonary exercise tests.

PURPOSE: The purpose of this study was to clarify the influence of complications of diabetes on the exercise tolerance of patients with heart failure. METHODS: The subjects of this study were 69 patients (44 men; mean age: 62.2 ± 13.4 years) who were hospitalized and diagnosed with heart failure between November 2016 and November 2017. The subjects all took part in a cardiopulmonary exercise test. The patients' medical background, indexes obtained from lower-limb muscle strength and the cardiopulmonary exercise test, heart rate response indexes [Δ heart rate (ΔHR)], and autonomic nervous activities were measured, and these individual indexes were compared between the diabetic group and the non-diabetic group. RESULTS: Compared with the non-diabetic group, the peak oxygen uptake (peak V̇O2) and ΔHR in the diabetic group were significantly lower (13.0 ± 2.2 vs. 14.9 ± 4.4 ml/kg/min and 27.2 ± 11.7 vs. 36.7 ± 14.7 bpm, respectively) (p<0.05). Regarding the autonomic nervous activity during the cardiopulmonary exercise test in the diabetic group, there was a significant decrease of parasympathetic nerve activity and a significant lack of increase in sympathetic nerve activity (p<0.05). CONCLUSIONS: Patients with heart failure and diabetes had lower levels of exercise tolerance, as compared with patients without complications. It was suggested that the decrease in heart rate response was due to the decrease of autonomic nervous activity and that this may play a role in reduced exercise tolerance.