Live High Train High (LHTH) refers to athletes living and training at natural altitude for a period of time (usually 2-4 weeks) to prepare for competitions at altitude, or to improve sea-level performance (Saunders et al., 2009). The potential benefit of LHTH over other forms of altitude training such as Live High Train Low (LHTL) is the provision of an additional hypoxic training stress which may increase the relative intensity of training (Pugliese et al., 2014), in addition to the acclimatization benefits of altitude residence, including accelerated erythropoiesis (Friedmann-Bette, 2008).
The general consensus from coaches and athletes is that LHTH improves physiological capacities and performance in competition during endurance events, a notion evidenced by its frequent and continued use by elite athletes (Pugliese et al., 2014; Solli et al., 2017) and supported by several studies in the literature (Daniels and Oldridge, 1970; Gore et al., 1998; Bonne et al., 2014). Accordingly, a meta-analysis reported a 1.6 [+ or -] 2.7% improvement in performance for elite athletes following LHTH (Bonetti and Hopkins, 2009). However, the large variability in these results (exemplified by a standard deviation approaching twice the mean effect) is confirmed by studies reporting no change or a decrement in performance following LHTH (Adams et al., 1975; Jensen et al., 1993; Levine and Stray-Gundersen, 1997; Bailey et al., 1998; Gough et al., 2012). Factors which might explain these equivocal findings include the altitude at which athletes lived and trained (Bailey et al., 1998), relative intensity of training sessions (Lundby et al., 2012), athlete iron status or supplementation protocol (Stray-Gundersen et al., 1992), and a reduction in training quality mediated by lower oxygen availability (Chapman et al., 1998).
To analyze and establish causal relationships between the training performed and the resultant physiological and performance adaptations, it is imperative to precisely and reliably quantify training load (TL) (Mujika, 2013). A limitation of many LHTH studies is that only basic metrics such as overall training volume or duration have been reported (Adams et al., 1975; Gore et al., 1997; Bailey et al., 1998). Without appropriate quantification, it is no surprise that both the literature and anecdotal evidence from coaches is conflicting regarding the best training strategies to employ during altitude camps, and the optimal time to compete thereafter (Chapman et al., 2014). Longitudinal TL data from LHTH training sojourns, combined with related athlete performance data may assist coaches and scientists to identify training periodization strategies that may be employed by elite athletes during LHTH to improve sea-level performance.
As such, in a cohort of elite runners, we sought to firstly; quantify the training load (TL) periodization during LHTH, and secondly; describe the physiological and performance changes following LHTH at 2100 m.
Eight athletes (6 males, 2 females; age, 25 [+ or -] 6 years; VOpeak, 70 [+ or -] 4 mLkg-1min-1; Season's Best as % of World Lead, 90% [+ or -] 5%;) participated in 3-4 weeks of LHTH in Flagstaff, USA (elevation 2100 m) after 4 weeks of quantified near sea-level training (three weeks LHTH, n = 3; four weeks LHTH, n = 5). Of these athletes, 5 represented Australia internationally at the 2016 Olympic/Paralympic Games and/or 2015 IAAF World Championships. Three athletes (participants 4, 7 and 8) had previously trained in Flagstaff and four of the remaining athletes (participants 1, 2, 3 and 6) had experienced LHTH at 1600 to 1800 m in Australia. All of these athletes had participated in at least 1 LHTH camp in Australia within the 4 months preceding the investigation. Additionally, 4 of these athletes (participants 2, 4, 7 and 8) had an extensive history of altitude training utilizing both natural LHTH and simulated LHTL over the preceding 3 to 5 years (2-3 camps annually). One athlete (participant 5) had never engaged in altitude training previously. All procedures and risks were explained to participants before they provided written informed consent to participate. Ethical approval for the investigation was granted by the institutional ethics committees (University of Canberra HREC ref. no. 15-45 and Australian Institute of Sport approval no. 20150613) and all procedures complied with the Declaration of Helsinki.
The investigation was an observational cohort case study examining the training of elite middle-distance runners during an in-season training intervention. Participants' training sessions were individually tailored and designed by their coaches, and were not manipulated or directly influenced by researchers involved in the study.
The investigation took place immediately following the Australian domestic track season, and before the American/European summer season, in April-June. The training of each athlete was monitored for 7-8 weeks in total, and was divided into 2 phases. The first phase involved athletes completing 4 weeks of their own, coach-prescribed training at or close to sea-level (i.e. Lead-in phase). Six athletes completed the first 2-3 weeks of this phase in their home environment in Australia, then travelled overseas, in most cases for competition (n = 2 in Nassau, Bahamas, n = 2 in San Francisco, USA). During the final week of this lead-in phase, these 6 athletes convened in San Francisco, where they resided for the remaining 4-7 days of this period, thus acclimating to the same time-zone as Flagstaff and minimizing any effects of jet-lag (Fowler et al., 2017) occurring simultaneously to altitude adjustment. The remaining 2 athletes completed this entire phase in Australia. Immediately following, participants travelled to Flagstaff (2100 m elevation) to complete 3-4 weeks (hypoxic dose = 1109-1512 km. [h.sup.-1]; Garvican-Lewis et al., 2016) of LHTH (i.e. Altitude phase). All participants were supplemented with oral iron (Ferro-Grad C, Abbott Laboratories, Australia, 105 g elemental iron) daily for at least 1 week prior to and for the duration of LHTH to ensure erythropoietic adaptations were not compromised by insufficient iron availability (Stray-Gundersen et al., 1992). Athletes competed in competitive races within a week of completing LHTH. Laboratory testing of running economy and haemoglobin mass occurred at the commencement and conclusion of the altitude phase (within 24-48 hours of arrival and departure to/from Flagstaff).
The structure of a typical training week for all athletes is shown in Table 1. Whilst generally adhering to this similar structure, training was individualized for each athlete based on previous altitude training experience (Table 2), preferred event (Table 3), physiological characteristics, and anecdotal results regarding the best training strategy for the current altitudes; therefore, not all athletes were on identical training programs. For example, race pace and some [??][O.sub.2max] intensity sessions were modified to include additional recoveries between intervals in order to maintain running speed, whereas threshold and low-intensity training were not modified (i.e. same interval/recovery length), but performed at a reduced speed and/or higher perceived effort compared to sea-level (Sharma et al., 2017). All athletes completed a taper during the final week of the camp in preparation for upcoming races occurring immediately following LHTH, following either 2 or 3 weeks of full training depending on their total camp duration. Training was completed between 2100 to 2700 m with the exception of one race pace session (~ 90 min) completed at 1400 m (Sedona, USA) towards the end of the training camp.
Each athlete recorded all their running training on a GPS watch (Forerunner, Garmin International, Kansas, USA), including total distance (kilometers) and duration (min). Duration was also recorded for cross training or strength training sessions. A session rating of perceived exertion (sRPE) score on a modified Borg scale was provided for all training sessions (Foster, 1998). Training volume (TV) was calculated as total running distance completed each week in kilometers. Daily TL was calculated as the duration of each training session multiplied by sRPE, then summated to give weekly TL. To assess the relationship between weekly TL and TV at sea-level and altitude, weekly TL was divided by weekly TV to give a load/volume ratio.
The research project was arranged around domestic and international track and field competitions, and the race times of athletes were collated as a record of performance. Running performance was recorded before and after LHTH. The season's best time achieved during the track season preceding the investigation was used as the pre-altitude measure. For 7 of 8 athletes, post-altitude races were completed within 8 days of descending from altitude. These races took place in the USA (Boston, n = 3; Nashville, n = 2; San Diego, n = 1) and Europe (Oslo, n = 1). One participant began competing after 4 weeks at sea-level (Participant 8, who in consultation with his coach, elected to race following a period of sea-level training due to timing of season objectives and personal preference). All races were completed at or near to sea-level (19 to 182 m) on standard 400 m athletics tracks. Of the athletes, 1 competed in the half-marathon, 5 in the 1500 m, 1 in the mile (1609 m), and 1 in the 800 m. Athletes were free to employ their own preparations and use of legal ergogenic aids such as caffeine, but were asked to keep this consistent between races.
An incremental running test was completed at sea-level prior to departure to altitude on a custom built motorized treadmill (Australian Institute of Sport, Australia) to determine [??][O.sub.2peak]. The test consisted of a self-selected warm-up followed by an...