Blood-based biomarkers can provide an objective individualized measure of training load, recovery, and health status in order to reduce injury risk and maximize performance. Despite enormous potentials, especially owing to currently evolving technology, such as point-of-care testing, and advantages, in terms of objectivity and non-interference with the training process, there are several pitfalls in the use and interpretation of biomarkers. Confounding variables such as preanalytical conditions, inter-individual differences, or an individual chronic workload can lead to variance in resting levels. In addition, statistical considerations such as the detection of meaningful minimal changes are often neglected. The lack of generally applicable and individual reference levels further complicates the interpretation of level changes and thus load management via biomarkers. Here, the potentials and pitfalls of blood-based biomarkers are described, followed by an overview of established biomarkers currently used to support workload management. Creatine kinase is discussed in terms of its evidence for workload management to illustrate the limited applicability of established markers for workload management to date. We conclude with recommendations for best practices in the use and interpretation of biomarkers in a sport-specific context.

Endothelial microparticles (EMP) are complex vesicular structures shed from activated or apoptotic endothelial cells. As endurance exercise affects the endothelium, the objective of the study was to examine levels of EMP and angiogenic growth factors following different endurance exercise protocols. 12 subjects performed 3 different endurance exercise protocols: 1. High volume training (HVT; 130 min at 55% peak power output (PPO); 2. 4×4 min at 95% PPO; 3. 4×30 sec all-out. EMPs were quantified using flow cytometry after staining platelet-poor-plasma. Events positive for Annexin-V and CD31, and negative for CD42b, were classified as EMPs. Vascular endothelial growth factor (VEGF), migratory inhibiting factor (MIF) and hepatocyte growth factor (HGF) were determined by ELISA technique. For all these measurements venous blood samples were taken pre, 0′, 30′, 60′ and 180′ after each intervention. Furthermore, in vitro experiments were performed to explore the effect of collected sera on target endothelial functions and MP uptake capacities. VEGF and HGF significantly increased after HIT interventions. All three interventions caused a significant decrease in EMP levels post exercise compared to pre values. The sera taken after exercise increased the uptake of EMP in target endothelial cells compared to sera taken under resting conditions, which was shown to be phosphatidylserin-dependent. Increased EMP uptake was associated with an improved protection of target cells against apoptosis. Sera taken prior and after exercise promoted target endothelial cell migration, which was abrogated after inhibition of VEGF. Physical exercise leads to decreased EMP levels and promotes a phosphatidylserin-dependent uptake of EMP into target endothelial cells, which is associated with a protection of target cells against apoptosis.

Aim: mircoRNAs (miRNAs), small non-coding RNAs regulating gene expression, are stably secreted into the blood and circulating miRNAs (c-miRNAs) may play an important role in cell–cell communication. Furthermore, c-miRNAs might serve as novel biomarkers of the current vascular cell status. Here, we examined how the levels of three vascular c-miRNAs (c-miR-16, c-miR-21, c-miR-126) are acutely affected by different exercise intensities and volumes. Methods: 12 subjects performed 3 different endurance exercise protocols: 1. High-Volume Training (HVT; 130 min at 55% peak power output (PPO); 2. High-Intensity Training (HIT; 4 × 4 min at 95% PPO); 3. Sprint-Interval Training (SIT; 4 × 30 s all-out). c-miRNAs were quantified using quantitative real-time PCR with TaqMan probes at time points pre, 0′, 30′, 60′, and 180′ after each intervention. The expression of miR-126 and miR-21 was analyzed in vitro, in human coronary artery endothelial cells, human THP-1 monocytes, human platelets, human endothelial microparticles (EMPs) and human vascular smooth muscle cells (VSMCs). To investigate the transfer of miRNAs via EMPs, VSMCs were incubated with EMPs. Results: HVT and SIT revealed large increases on c-miR-21 [1.9-fold by HVT (cohen's d = 0.85); 1.5-fold by SIT (cohen's d = 0.85)] and c-miR-126 [2.2-fold by SIT (cohen's d = 1.06); 1.9-fold by HVT (cohen's d = 0.85)] post-exercise compared to pre-values, while HIT revealed only small to moderate changes on c-miRs-21 (cohen's d = −0.28) and c-miR-126 (cohen's d = 0.53). c-miR-16 was only slightly affected by SIT (1.4-fold; cohen's d = 0.57), HVT (1.3-fold; cohen's d = 0.61) or HIT (1.1-fold; cohen's d = 0.2). Further in vitro experiments revealed that miR-126 and miR-21 are mainly of endothelial origin. Importantly, under conditions of endothelial apoptosis, miR-126 and miR-21 are packed from endothelial cells into endothelial microparticles, which were shown to transfer miR-126 into target vascular smooth muscle cells. Conclusion: Taken together, we found that HVT and SIT are associated with the release of endothelial miRNAs into the circulation, which can function as intercellular communication devices regulating vascular biology.

In the last years, mainly 2 high-intensity-training (HIT) protocols became common: First, a Wingate-based “all-out” protocol and second, a 4×4 min protocol. However, no direct comparison between these protocols exists, and also a comparison with high-volume-training (HVT) is missing. Therefore, the aim of the present study was to compare these 3 endurance training protocols on metabolic, hormonal, and psychological responses. Twelve subjects performed: 1) HVT [130 min at 55% peak power output (PPO)]; 2) 4×4 min at 95% PPO; 3) 4×30 s all-out. Human growth hormone (hGH), testosterone, and cortisol were determined before (pre) and 0′, 30′, 60′, 180′ after each intervention. Metabolic stimuli and perturbations were characterized by lactate, blood gas (pH, BE, HCO₃ ⁻, pO₂, PCO₂), and spirometric analysis. Furthermore, changes of the person’s perceived physical state were determined. The 4×30 s training caused the highest increases in cortisol and hGH, followed by 4 × 4 min and HVT. Testosterone levels were significantly increased by all 3 exercise protocols. Metabolic stress was highest during and after 4×30 s, followed by 4×4 min and HVT. The 4×30 s training was also the most demanding intervention from an athlete’s point of view. In conclusion, the results suggest that 4×30 s and 4×4 min promote anabolic processes more than HVT, due to higher increases of hGH, testosterone, and the T/C ratio. It can be speculated that the acute hormonal increase and the metabolic perturbations might play a positive role in optimizing training adaptation and in eliciting health benefits as it has been shown by previous long term training studies using similar exercise protocols.