The marathon is a physiologically demanding endurance racing event (Billat et al., 2001). While 42195 m completion times of elite runners are ~130 minutes, top wheelchair athletes (i.e. "wheelers") can finish the race within 90 minutes (for those with no upper-extremity impairments, sport classes T53-54) and 115 minutes (for those with trunk and arm impairments, T51-52). Even though mechanical stress in wheelchair racing seems to be lower than in running, cardiovascular load is similar while oxygen transport demands are quite lower (Asayama et al., 1985), possibly due to less muscle mass involved in wheelers than in runners (Fletcher and Macintosh, 2017). To the best of our knowledge, only one previous study (Asayama et al., 1985) has analyzed heart rate (HR) dynamics in top-finisher marathon wheelchair athletes. The participants from this study maintained a high mean HR (171.6 [+ or -] 20.5 beats x [min.sup.-1]) continuously throughout the race. In contrast, a group of elite runners with a personal best marathon time of [less than or equal to] 2 hours and 11 minutes had a mean HR of 167 [+ or -] 5 beats x [min.sup.-1] during a 10 km test at marathon pace (Billat et al., 2001).
Classical physiological measurements of the function of the cardiovascular system, such as mean HR, are currently being complemented by new signal analyses -i.e., the heart rate variability (HRV)--that provides more precise information on the autonomic control of HR (Stanley et al., 2013). The most commonly used parasympathetic index is the natural logarithm (ln) of the root mean square differences between adjacent normal R-R intervals (Ln rMSSD) as it seems to be more reliable than other parasympathetic indices such as the high frequency (HF) component of R-R interval variability (Plews et al., 2013). Furthermore, Ln rMSSD has been used in studies of elite athletes (Plews et al. 2012). Ln rMSSD has been shown to display a coefficient of variation (CV) of 5-7% in elite endurance athletes and ~10% in recreational runners (Plews et al., 2014). Less day-to-day Ln rMSSD fluctuations (represented by CV) has been associated with more favorable adaptations to training among athletes (Flatt and Esco, 2016).
After strenuous training sessions, HR can be under sympathetic dominance, whilst recovery can be highlighted by the return of parasympathetic modulation to baseline (Brown and Weir, 2001). For example, 48 hours after strenuous exercise like a marathon, there have been reported signs of sympathetic activation in runners (Danilowicz-Szymanowicz et al., 2005). Additionally, immediately after the completion of a half marathon, elevated sympathetic cardiac drive was shown (Dalla-Vecchia et al., 2014). In a study by Hynynen et al. (2010), a decrease in vagal-related markers (rMSSD and HF) the night after completing a marathon were observed relative to values obtained following only moderate exercise.
Consequently, in elite sport, the assessment of autonomic activity using different indices of HRV have been used for different purposes such as: a) to determine the cardiac regulation during different phases of training, including tapering in disciplines such as rowing (Iellamo et al., 2002) or triathlon (Stanley et al., 2015); b) determine the timing to prescribe intense training sessions when HRV reaches a reference value, considered as the optimal freshness condition for the athlete (Kiviniemi et al., 2007; Vesterinen et al., 2016); and c) to understand the physiological disturbance caused by training load near sea-level (Ornelas et al., 2017) or under stressful environmental conditions such as at altitude (Sanz-Quinto et al., in press). Another variable which could impair autonomic control of HR is trans-meridian air travel with substantial time zone differences (Tatehishi et al., 2002), which is a common circumstance in elite sports competition.
To date, there are no studies with elite wheelchair marathon athletes that have reported the pre-post-race autonomic activity. The current case study reports the daily HRV responses to an eastward trans-meridian flight (Alicante, Spain to Oita, Japan, 8 hour time difference) and a marathon in an elite wheelchair athlete affected by the Charcot-Marie-Tooth disease (CMT).
The athlete who participated in this case study was a 35-year-old male professional wheelchair marathon athlete with CMT, class T52 by World Para Athletics. CMT is the most common hereditary peripheral neuropathy, affecting up to 30 per 100000 people worldwide (Banchs et al., 2009). CMT totally affects distal muscle function and partially affects proximal function (Banchs et al., 2009). The athlete was a highly accomplished competitor with a silver medal at the 2000 and 2004 Paralympic Games and 106 victories in road events, including Boston, Chicago, London and Oita Marathons. His main descriptive features are: height = 1.76 m; body mass = 52 kg; power output at second lactate threshold = 61 W; heart rate at second lactate threshold = 166 beatsmin-1; training 8000 km per year; former world record holder in his sport class in 800 m (116 s), 1500 m (216 s), 5000m (757 s), half marathon (3028 s) and fourth best-ever time in marathon (6125 s). This study was set up at an international road race where his finishing time (6481 s) was ranked as the world best season time in the sport class T52 at the International Paralympic Committee Athletes ranking.
The participant provided written informed consent to be a research subject in this case study. All the procedures were approved by the Ethics Research Committee of the University Miguel Hernandez (Elche, Spain).
Ten days before the race date (RD) an incremental test was performed on a specific wheelchair ergometer where steady conditions were maintained (temperature 22-24[degrees]C, humidity 73-75 %). The protocol described by Polo-Rubio (2007) included a 20 min warm-up period at constant power (20 W). The athlete started the incremental test at a brake power of 6 W, maintaining a stroke frequency between 90 and 100 strokes x [min.sup.-1], increasing the power by 3 W every 60 s until the athlete could not maintain that frequency. Power output was considered as the ergometer braking power during the last completed step of the test. The same HR monitor used in the marathon was used to register HR and a telemetry system (K4 [b.sup.2], COSMED, Rome, Italy) was used during wheelchair propulsion to measure [O.sub.2] uptake and C[O.sub.2] production. For calculating the second ventilatory threshold (Vt2), the recommendations by Chicharro et al. (1997) were followed. The Vt2 was estimated when the athlete generated 61 W, the [O.sub.2] uptake was 51 ml x [kg.sup.-1] x [min.sup.-1] and the HR reached 166 beatsmin1 In the last step, where the athlete was able to maintain the projected stroke frequency, he generated a power of 67 W, and the V[O.sub.2max] was 57 ml x kg x [min.sup.-1], reaching 176 beats x [min.sup.-1] at that intensity.
Six days before ([RD.sub.-6,-5,-4,-3,-2,-1]) the marathon day in Oita, Japan and two days after racing ([RD.sub.+1,+2]), the day-today HRV upon awakening in the supine...