High-intensity interval training (HIIT) is a time-efficient way of improving physical performance in healthy subjects and in patients with common chronic diseases, but less so in elite endurance athletes. The mechanisms underlying the effectiveness of HIIT are uncertain. Here, recreationally active human subjects performed highly demanding HIIT consisting of 30-s bouts of all-out cycling with 4-min rest in between bouts (≤3 min total exercise time). Skeletal muscle biopsies taken 24 h after the HIIT exercise showed an extensive fragmentation of the sarcoplasmic reticulum (SR) Ca 2+ release channel, the ryanodine receptor type 1 (RyR1). The HIIT exercise also caused a prolonged force depression and triggered major changes in the expression of genes related to endurance exercise. Subsequent experiments on elite endurance athletes performing the same HIIT exercise showed no RyR1 fragmentation or prolonged changes in the expression of endurance-related genes. Finally, mechanistic experiments performed on isolated mouse muscles exposed to HIIT-mimicking stimulation showed reactive oxygen/nitrogen species (ROS)-dependent RyR1 fragmentation, calpain activation, increased SR Ca 2+ leak at rest, and depressed force production due to impaired SR Ca 2+ release upon stimulation. In conclusion, HIIT exercise induces a ROSdependent RyR1 fragmentation in muscles of recreationally active subjects, and the resulting changes in muscle fiber Ca 2+ -handling trigger muscular adaptations. However, the same HIIT exercise does not cause RyR1 fragmentation in muscles of elite endurance athletes, which may explain why HIIT is less effective in this group.ryanodine receptor 1 | high-intensity exercise | skeletal muscle | Ca 2+ | reactive oxygen species

The general decline in physical fitness in Lithuanian schoolchildren observed between 1992 and 2002 continued between 2002 and 2012, although some aspects of fitness showed a positive trend. If this general negative trend continues, it will compromise the well-being of future adults and create a serious economic burden on the society.

Physical exercise has emerged as an alternative treatment for patients with depressive disorder. Recent animal studies show that exercise protects from depression by increased skeletal muscle kynurenine aminotransferase (KAT) expression which shifts the kynurenine metabolism away from the neurotoxic kynurenine (KYN) to the production of kynurenic acid (KYNA). In the present study, we investigated the effect of exercise on kynurenine metabolism in humans. KAT gene and protein expression was increased in the muscles of endurance-trained subjects compared with untrained subjects. Endurance exercise caused an increase in plasma KYNA within the first hour after exercise. In contrast, a bout of high-intensity eccentric exercise did not lead to increased plasma KYNA concentration. Our results show that regular endurance exercise causes adaptations in kynurenine metabolism which can have implications for exercise recommendations for patients with depressive disorder.

AimMicroRNAs (miRNAs) are stable in the circulation and are likely to function in inter-organ communication during a variety of metabolic responses that involve changes in gene expression, including exercise training. However, it is unknown whether differences in circulating-miRNA (c-miRNA) levels are characteristic of training modality.MethodsWe investigated whether levels of candidate c-miRNAs differ between elite male athletes of two different training modalities (n = 10 per group) - endurance (END) and strength (STR) - and between these groups and untrained controls (CON; n = 10). Fasted, non-exercised, morning plasma samples were analysed for 14 c-miRNAs (miR-1, miR-16-2, miR-20a-1, miR-21, miR-93, miR-103a, miR-133a, miR-146a, miR-192, miR-206, miR-221, miR-222, miR-451, miR-499). Moreover, we investigated whether c-miRNA levels were associated with quantitative performance-related phenotypes within and between groups.ResultsmiR-222 was present at different levels in the three participant groups (p = 0.028) with the highest levels being observed in END and the lowest in STR. A number of other c-miRNAs were present at higher levels in END than in STR (relative to STR, ± 1 SEM; miR-222: 1.94 fold (1.73-2.18), p = 0.011; miR-21: 1.56 fold (1.39-1.74), p = 0.013; miR-146a: 1.50 fold (1.38-1.64), p = 0.019; miR-221: 1.51 fold (1.34-1.70), p = 0.026). Regression analyses revealed several associations between candidate c-miRNA levels and strength-related performance measures before and after adjustment for muscle or fat mass, but not following adjustment for group.ConclusionCertain c-miRNAs (miR-222, miR-21, miR-146a and miR-221) differ between endurance- and resistance-trained athletes and thus have potential as useful biomarkers of exercise training and / or play a role in exercise mode-specific training adaptations. However, levels of these c-miRNAs are probably unrelated to muscle bulk or fat reserves.

The coactivator PGC-1α1 is activated by exercise training in skeletal muscle and promotes fatigue-resistance. In exercised muscle, PGC-1α1 enhances the expression of kynurenine aminotransferases (Kats), which convert kynurenine into kynurenic acid. This reduces kynurenine-associated neurotoxicity and generates glutamate as a byproduct. Here, we show that PGC-1α1 elevates aspartate and glutamate levels and increases the expression of glycolysis and malate-aspartate shuttle (MAS) genes. These interconnected processes improve energy utilization and transfer fuel-derived electrons to mitochondrial respiration. This PGC-1α1-dependent mechanism allows trained muscle to use kynurenine metabolism to increase the bioenergetic efficiency of glucose oxidation. Kat inhibition with carbidopa impairs aspartate biosynthesis, mitochondrial respiration, and reduces exercise performance and muscle force in mice. Our findings show that PGC-1α1 activates the MAS in skeletal muscle, supported by kynurenine catabolism, as part of the adaptations to endurance exercise. This crosstalk between kynurenine metabolism and the MAS may have important physiological and clinical implications.

Kamandulis, S, Bruzas, V, Mockus, P, Stasiulis, A, Snieckus, A, and Venckunas, T. Sport-specific repeated sprint training improves punching ability and upper-body aerobic power in experienced amateur boxers. J Strength Cond Res 32(5): 1214-1221, 2018-High-intensity interval training improves endurance and performance, but it is unclear whether sprint-type upper-body interval training is similarly effective. This study explored the effects of 4-week sport-specific sprint interval training on punch characteristics and endurance capacity in boxers. Experienced male amateur boxers (n = 18) participated in this 4-week training study and were divided into an experimental group (EG) and a control group (CG) (n = 9 per group). Both groups completed standard low-intensity training. The EG also completed 3 rounds (14 sets of 3-second all-out punching with a 10-second rest) of a simulated fight using a punching bag with a 1-minute rest between rounds 3 times per week, whereas the CG performed the same 3 rounds of a simulated fight at low intensity. Three rounds of 14 sets of 3-second all-out punching of a bag ergometer with a 10-second rest were performed to measure punching abilities. Peak oxygen consumption and peak power were measured during progressive arm cranking before and after training. In response to training peak oxygen consumption and peak power in arm-cranking test increased in EG, also punching force increased and maintenance of punching frequency and punch force improved during the simulated fight, which resulted in greater cumulative force throughout the 3 rounds. There were no changes in the CG. The study shows that 1 month of all-out punching training (3 sessions per week with ∼2 minutes of all-out punching per session) improved both upper-body aerobic power and punching abilities in experienced amateur boxers.

26Alpha-actinin-3 (ACTN3) is an integral part of the Z-line of the sarcomere. The ACTN3 R577X 27 (rs1815739) polymorphism determines the presence or absence of functional ACTN3 which may 28 influence the extent of exercise induced muscle damage. This study aimed to compare the impact of, 29 and recovery from, muscle-damaging eccentric exercise on subjects with or without functional alpha-30 actinin-3. Seventeen young men (20-33 years), homozygous for the R-(n=9) or X-(n=8) alleles, 31 performed two bouts of stretch-shortening exercise (50 drop jumps) 2 weeks apart. Muscle soreness, 32 plasma creatine kinase (CK) activity, jump height, maximal voluntary isometric torque (MVC), peak 33 concentric isokinetic torque (IT), and electrically stimulated knee extension torques at 20 Hz and at 34 100 Hz were measured at baseline and a number of timepoints up to 14 days after each bout. There 35 were no significant baseline differences between the groups. However, significant 36 timepoint*genotype interactions were observed for MVC (p=0.021) and IT (p=0.011) for the 37 immediate effect of eccentric exercise in bout 1. The RR group showed greater voluntary force 38 decrements (RR v XX, MVC: -33.3% v -24.5%, IT: -35.9% v -23.2%) and slower recovery. A 39 repeated bout effect was clearly observed but there were no differences by genotype group. ACTN3 40 genotype modulates the response of muscle function to plyometric jumping exercise, although the 41 differences are modest. ACTN3 genotype does not influence the clearly observed repeated bout 42 effect; however, XX homozygotes recover baseline voluntary torque values faster and thus may be 43 able to undertake more frequent training sesssions. 44 45

To investigate the relationships between personality traits and athletic capacity, this study compared a sample of 376 young adult men (169 athletes, 207 non-athletes; M age = 23.8 yr., SD = 3.9). 26 lab-based exercise capacity parameters were measured, as well as the Big Five major personality traits using the NEO Five-Factor Inventory. The results indicated that athletes scored higher than non-athletes for Conscientiousness but scores were not statistically different between groups for other personality traits. Team sport athletes scored higher on Extraversion than endurance athletes. All the personality traits were associated with some of the exercise capacity indices; however, these correlations were rather weak (rs < .2).