HIIT consists of repeated bouts of short to moderate duration exercise completed at

intensities greater than the anaerobic threshold, interspersed with brief periods of low-intensity or passive rest. HIIT is designed to repeatedly stress the body, physiologically, resulting in chronic adaptations and improving metabolic and energy efficiency [9, 10]. Helgerud et al. [11] found that HIIT significantly augmented maximal oxygen consumption (VO2PEAK) and time to exhaustion (TTE) greater than a traditional training program with moderately-trained males. The velocity at which ventilatory threshold (VT) occurred increased as well, which may signify a higher training capacity and, therefore, should also represent an improvement in endurance performance. It was determined during this study that different protocols of HIIT, matched for frequency and total work done, provided similar results [11]. In support, Burke et al. [12] examined the effects FG-4592 solubility dmso of two different interval training protocols on VO2PEAK, VT, and lactate threshold Selleck Elafibranor in a group of untrained women, demonstrating that both interval-training protocols significantly

improved all performance variables. Similarly, an increase in Selleckchem PF-04929113 VO2PEAK and VT was found in three groups of well-trained cyclists following three different HIIT protocols of varying intensities and work-to-rest ratios [9]. Phosphocreatine (PCr), a high-energy storage molecule within skeletal muscle, provides immediate replenishment

of ATP during intense exercise [13]. Multiple HIIT bouts are designed Forskolin in vitro to deplete PCr stores in the working skeletal muscle, reducing power output. It has been reported that it takes more than six minutes to fully recover depleted PCr stores after exercise-induced PCr depletion [14]. Therefore, if recovery intervals during HIIT bouts are less than six minutes, PCr may not be fully replenished, resulting in a reduced ability to meet the demands of cellular ATP resynthesis and a reduced performance [13]. Supplementing with creatine (Cr) has been demonstrated to effectively augment muscle phosphocreatine (PCr) stores [15]. Specifically, one study showed a 20% increase in muscle creatine with ingestion of 20 g of Cr per day for just 5 days [16]. It has been suggested that increases in skeletal muscle PCr concentration may improve muscle buffering capacity and moderate glycolysis [17, 18]. In addition, Cr supplementation may increase the rate of PCr resynthesis between HIIT exercise bouts and enhance mitochondrial shuttling of ATP into the cytoplasm, providing significant physiological adaptations [15, 16]. Current research suggests that Cr supplementation, when combined with training, has been shown to significantly augment performance [19]. Moreover, the combination of Cr supplementation and HIIT may lead to greater improvements in VO2PEAK, VT, and TTE than previously reported with HIIT or Cr supplementation alone.