The influence of intensified and reduced training on nocturnal growth hormone (GH) secretion and elimination dynamics was studied in young (1.5 yr) Standardbred geldings to detect potential markers indicative for early overtraining. Ten horses trained on a treadmill for 32 wk in age-, breed-, and gender-matched fixed pairs. Training was divided into four phases (4, 18, 6, and 4 wk, respectively): 1) habituation to high-speed treadmill trotting, 2) normal training, in which speed and duration of training sessions were gradually increased, 3) in this phase, the horses were divided into 2 groups: control (C) and intensified trained (IT) group. In IT, training intensity, duration, and frequency were further increased, whereas in control these remained unaltered, and 4) reduced training (RT). At the end of phases 2, 3, and 4, blood was sampled overnight every 5 min for 8 h for assessment of GH secretory dynamics using pulse detection, deconvolution analysis, and approximate entropy (ApEn). Intensified training induced overtraining (performance decreased by 19% compared with C), which was associated with an increase in concentration peaks number (3.6 vs. 2.0, respectively), a smaller peak secretion pattern with a prolonged half-life (15.2 vs. 7.3 min, respectively), and an increased ApEn (0.89 vs. 0.49, respectively). RT did not lead to full recovery for the overtrained horses. The increased irregularity of nocturnal GH pulsatility pattern is indicative of a loss of coordinated control of GH regulation. Longer phases of somatostatin withdrawal are hypothesized to be the underlying mechanism for the observed changes in GH pulsatility pattern.
Autoimmune thyroiditis (AIT) is one of the most common autoimmune diseases; genetic as well as environmental factors contribute to its pathogenesis. The thyroid is the organ with the highest selenium content per unit weight. Selenium status appears to have an impact on the development of thyroid pathologies. We investigated a possible difference of selenium serum levels as a marker of nutritional selenium supply between patients with AIT in central Lower Austria and a matched group of healthy persons living in the same region. Selenium serum levels in the patients with AIT were 98.0 ± 15.6 μg/l. A significant difference to the matched group of normal persons, whose selenium serum levels were 103.2 ± 12.4 μg/l, could not be detected by the t-test (p>0.05). We considered the serum selenium levels to be indicators of selenium supply (by alimentation). A serum level of 120-160 μg/l of selenium represents the normal range. According to this, most patients and control persons showed mild to moderate selenium deficiency (80-120 μg/l selenium). Although our data present slightly higher selenium levels in normal persons than in patients with AIT, this weak and statistically insignificant trend is not sufficient to support the conclusion of a link between inadequate selenium supply and autoimmune thyroid disease.
To study whether quantitative needle electromyography (QEMG) is more sensitive to detect training (mal)adaptation than muscle enzyme activities, 12 standardbred geldings trained for 32 wk in age-, breed-, and sex-matched fixed pairs. After a habituation and normal training (NT) phase (phases 1 and 2, 4 and 18 wk, respectively), with increasing intensity and duration and frequency of training sessions, an intensified training (IT) group (phase 3, 6 wk) and a control group (which continued training as in the last week of phase 2) were formed. Thereafter, all horses entered a reduced training phase (phase 4, 4 wk). One hour before a standardized exercise test (SET; treadmill), QEMG analysis and biochemical enzyme activity were performed in muscle or in biopsies from vastus lateralis and pectoralis descendens muscle in order to identify causes of changes in exercise performance and eventual (mal)adaptation in skeletal muscle. NT resulted in a significant adaptation of QEMG parameters, whereas in muscle biopsies hexokinase activity was significantly decreased. Compared with NT controls, IT induced a stronger adaptation (e.g., higher amplitude, shorter duration, and fewer turns) in QEMG variables resembling potentially synchronization of individual motor unit fiber action potentials. Despite a 19% decrease in performance of the SET after IT, enzyme activities of 3-hydroxyacyl dehydrogenase and citrate synthase displayed similar increases in control and IT animals. We conclude that 1) QEMG analysis is a more sensitive tool to monitor training adaptation than muscle enzyme activities but does not discriminate between overreaching and normal training adaptations at this training level and 2) the decreased performance as noted in this study after IT originates most likely from a central (brain) rather than peripheral level. equine; motor unit action potential analysis; training adaptation; muscle metabolism; enzymology; overreaching THE AIM OF PHYSICAL TRAINING is to increase performance capacity by gradually increasing both duration and intensity of the exercise bouts. Each exercise session induces, dependent on the total training load, disturbances in cellular homeostasis. If the training load is balanced with the individual's exercise tolerance, regenerative processes will restore or increase athletic performance within a couple of days (35,36,39,40). In this situation adaptive processes result in, among others, increments in aerobic key enzymes in skeletal muscle (32) or excitability after endurance, strength, or sprint training (7,23,25,28,29) . However, sustained vigorous training, often coupled with other stressors, may result in incomplete recovery, and decrement rather than improvement or maintenance of performance will occur. This process is termed overreaching, which might lead to the more severe chronic situation called overtraining (33,40).Since overtraining and, to a lesser extent, overreaching are severe conditions leading to decreases in performance capacity for several weeks to several months, this obviou...
The p38 pathway and JNK are activated in the vastus lateralis muscle after a single 20-minute bout of submaximal exercise in trained horses. Phosphorylation of HSP27 as detected in the study reported here is most likely induced through the p38 signaling pathway.
In equine skeletal muscle, GLUT4 and FAT/CD36 are expressed in a fiber type selective manner.
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