The International Triathlon Union (ITU) serves as the governing body for all internationally sanctioned multisport events. These multisport competitions place a unique demand on athletes due to their need to perform a variety of sport modalities in a single event. Similarly, the coaches of these athletes have to manage acute and chronic training loads from a variety of modalities that further complicates the training model. Whether utilizing a traditional periodization model or an alternative periodization model (Issurin, 2010), key physiological measures such as maximal oxygen uptake ([VO.sub.2max]), ventilatory threshold (VT), heart rate (HR), and blood lactate (BL) are often used to monitor, prescribe, and measure training related performance gains for endurance athletes (Bunc et al., 1995). While each of these periodization models have limitations (Issurin, 2010) they all aim to build fitness and ultimately increase athletic performance.
Scientific research, and the presentation of this research to the public, plays an important role in progressing sport and the periodization methods in sport. Investigating the compounding effects of multisport events on athletic performance requires complex experimental designs with transitions from one modality to another. The compounding effects of the first two exercise bouts on the final run performance have become an increasingly popular topic of research as the winner of a multisport event is often decided during the last leg of the competition (Landers et al., 2000; Vleck et al., 2006). De Vito et al. (1995) previously reported a decline in maximal oxygen uptake ([VO.sub.2max]) and [VO.sub.2] (ml x [kg.sup.-1] x [min.sup.-1]) at VT during the final running leg of an ITU Triathlon simulation. De Vito et al. (1995) concluded that these declines could potentially influence performance during the last leg of a triathlon race and recommended that coaches and athletes consider this information when developing racing strategies. While triathlon and duathlon events have some similar characteristics, the physiological consequences associated with the transition phases may invoke different physiological responses. Few studies have investigated the effects of cycling on a subsequent running bout (Bernard et al., 2003; Gottschall and Palmer, 2000; Hue et al., 2000; Suriano et al., 2007) or running on subsequent cycling performance (Chapman et al., 2008; Gottschall and Palmer, 2000; Suriano et al., 2007; Vercruyssen et al., 2002). The compounding effects of a duathlon event on running performance have been minimally investigated (Moncada-Jimenez et al., 2009; Sparks et al., 2005; 2013; Vallier et al., 2003). Both Moncada-Jimenez et al. (2009) and Sparks et al. (2013) investigated the effects of dietary modifications on duathlon performance. While both of these studies reported significant differences in carbohydrate and fat metabolism between dietary modifications, neither found significant differences in overall time. Conversely, Sparks et al. (2005) reported that carbohydrate and fat oxidation did not differ significantly between duathlon simulations performed at 10[degrees]C and 30[degrees]C. However, they did report that overall performance was faster in the 10[degrees]C environment compared to 30[degrees]C. Vallier et al. (2003) investigated the energy cost of running during an outdoor duathlon simulation, reporting that the energy cost of running was not significantly different between the initial, and final, running bouts. Each of these studies provides unique and insightful information on duathlon performance. The external validity of Vallier et al. (2003) provides highly meaningful information about multisport performance to coaches and athletes alike, however, insight into the compounding effect of the first two legs of the duathlon event on performance during the final running bout may have been limited by pacing strategy. While the physiological consequences of either a triathlon or duathlon event may be different due to the different transitional demands of each event, the alterations in final running performance observed during triathlon (De Vito et al., 1995) and duathlon (Vallier et al., 2003) simulations warrant further investigation.
Thus, the purpose of this study was to further expand on previous findings of duathlon performance by having athletes complete a duathlon simulation at the highest attainable intensity within a controlled laboratory setting. Specifically, our objective was to compare performance between a single-bout treadmill run and the final run of a duathlon simulation. Measures of maximal oxygen uptake ([VO.sub.2max]), ventilatory threshold (VT), and running economy (RE) were used to assess differences between trials. We hypothesized that 1) [VO.sub.2peak] would remain the same between Trial-1 and Trial-3 2) that VT would decrease, and 3) that RE would decrease during the final running bout of the duathlon simulation.
Seven highly-trained multisport male athletes (age: 34 [+ or -] 9 years; height: 1.78 [+ or -] 0.04 m; weight: 73.9 [+ or -] 2.7 kg) were recruited to participate in this study. Participants included professional and elite age-group athletes who had been training a minimum of fifteen hours per week for a minimum of six months prior to beginning the study. Prior to participating in the study, each subject was fully informed of the methodological procedures. This study was approved by the Biomedical Institutional Review Board of the University of North Carolina at Chapel Hill. Participants provided written consent before completing a physical examination, medical history questionnaire, and a Par-Q (physical activity readiness questionnaire). Once participants were deemed healthy and low-risk (American College of Sports Medicine, 2010), they were scheduled for their first session.
Each athlete completed three testing sessions separated by a minimum of 72 hours and completed within a span of three weeks (Figure 1). Participants were asked to abstain from intense training 24 hours prior to each testing session. Trial-1 consisted of a single incremental treadmill test to determine [VO.sub.2max]. Trial-2 consisted of a 10 km run at VT proceeded by an incremental test on the cycle ergometer to determine [VO.sub.2max]. During Trial-3, participants performed a 10 km run and 30 km cycling bout at threshold before transitioning back to the treadmill to perform an incremental treadmill test to volitional exhaustion.
Incremental tests, as well as running and cycling bouts, were performed using the T2100 GE treadmill system (General Electric Company, USA) and Lode Corival electromagnetic breaking cycle ergometer (Lode B.V., Groningen, Netherlands). Athletes provided their saddle height (center of the bottom...