Prediction of 2000-m on-water rowing performance with measures derived from instrumented boats.

PURPOSE: Rowing instrumentation systems provide measures of stroke power, stroke rate, and boat velocity during rowing races, but how well these measures predict race performance has not been reported previously. METHODS: Data were collected per stroke from 45 2000-m races using Peach PowerLine and OptimEye S5 GPS units. The boat classes assessed were nine male singles, eight female singles, three male pairs, and six female pairs. Random effects and residuals from general linear mixed modeling of stroke velocity adjusted for stroke power, stroke rate, and mean headwind provided measures interpreted as technical efficiency, race conditions, and stroke-velocity variability. These measures, along with mean race power, mean stroke rate, and mean headwind were then included in multiple linear regressions to predict race velocity from official race times. Effects were assessed for 2 SD changes in predictors and interpreted using interval hypothesis tests. RESULTS: Effects of mean race power, mean stroke rate, and mean headwind on race velocity ranged from small to extremely large and were mostly decisively substantial. Effects of technical efficiency and race conditions ranged from trivial to extremely large but were generally unclear, while stroke-velocity variability had trivial-small and mostly unclear effects. Prediction error was small to moderate and decisively substantial. Men's pairs lacked sufficient data for analysis. CONCLUSION: On-water rowing race performance can be predicted with mean race values of power, stroke rate, and headwind. Estimates from stroke data are potentially useful predictors but require impractical numbers of boats and races to reduce their uncertainty.

Applying common filtering processes to Global Navigation Satellite System-derived acceleration during team sport locomotion.

This study aimed to observe whether there were substantial differences in acceleration during team-sport locomotion between GNSS manufacturers. Speed and acceleration were obtained from 7 professional rugby league athletes via 2 GNSS manufacturers (GPSports EVO, 10 Hz and STATSports Apex, 10 Hz) worn together during the same training sessions (n = 13). Raw GNSS data were exported from respective proprietary software and a 1 Hz, 4th-order Butterworth filter applied, with differences in speed and acceleration calculated between manufacturers. To determine the difference in acceleration and speed, a root mean square deviation (RMSD) was used. Linear mixed models were used and no substantial differences were found between manufacturers in raw and filtered speed variables. RMSD for average acceleration (m · s-2) decreased from raw (RMSD: 1.77 ± 0.37 m · s-2) to those seen at the filtered (RMSD: 0.27 ± 0.23 m · s-2) and twice filtered (0.24 ± 0.23 m · s-2) variables. Raw average acceleration (m · s-2) was substantially higher in Apex compared to EVO (Difference (Diff); CI: -0.82; -0.84 to -0.80). Following application of the common filter there was no substantial difference between GNSS models for average acceleration (Diff; CI: -0.04; -0.04 to -0.04). Acceleration variables derived from each manufacturer's proprietary software were substantially different.

Seasonal Change in Body Composition and Physique of Team Sport Athletes.

ABSTRACT: Walker, EJ, Aughey, RJ, McLaughlin, P, and McAinch, AJ. Seasonal change in body composition and physique of team sport athletes. J Strength Cond Res 36(2): 565-572, 2022-Body composition of team sport athletes was measured at 3 points across the preseason and competitive season. This repeated-measures study was conducted in 46 professional Australian football (AF) (age 23.8 ± 3.8 years), 26 soccer (age 22.7 ± 4.7 years), and 33 rugby union players (age 28.1 ± 4.2 years). A mixed-design analysis of variance was used to determine change across the season, and Pearson's correlation was used to determine the relationship between different measures. Anthropometry, dual-energy x-ray absorptiometry (DXA), and 3-dimensional (3D) scan technology were used in AF and soccer, whereas only DXA was used in rugby. Body mass remained unchanged for both AF and soccer with gains in lean mass (p < 0.01), from preseason to early in the competitive season. Skinfold measures declined in AF (p < 0.001) and soccer (p < 0.05) across the season, whereas DXA-measured fat mass only declined in soccer (p < 0.01). Rugby backs (p < 0.01) and forwards (p < 0.001) reduced body fat and gained lean mass from preseason to in-season with forwards having greater relative and absolute changes as measured by DXA. 3D technology did not show change across the season. Dual-energy x-ray absorptiometry body fat percent and the sum of skinfold correlation were large (r = 0.74 [p < 0.001, CI 0.67-0.81]). The greatest change in body composition occurs from the beginning of preseason to the start of competition, with changes returning to baseline levels toward the end of season. Dual-energy x-ray absorptiometry and skinfold measures were moderately correlated, providing a good alternative to track change in subcutaneous fat in AF and soccer athletes.

The road goes ever on and on-a socio-physiological analysis of travel-related issues in Super Rugby.

Air travel is a key factor in Super Rugby and can have a negative influence on players' performance and well-being. The aim of this study was to identify the current practice to reduce the effects of air travel and to understand the rationale behind these interventions. "Travel managers" from eight Super Rugby teams were interviewed and answered a questionnaire. A qualitative description was performed to identify common themes and differences between participants' answers. To protect the privacy and identity of the participants, all data have been de-identified and represented as two fictionalised amalgams (Bob and Peter). The rationale behind each intervention appeared to be based on a mix of anecdotal, practice and, occasionally, literature, confirming that scientific findings are not always easily translatable to applied settings. Two different approaches, clinical (Bob) and holistic (Peter), were identified. Even if both characters acknowledge that travel variables are too many to control, it appears that team culture and practices are perceived as important as biological interventions in controlling the negative effects of travel on players' performance and well-being.

The longest journeys in Super Rugby: 11 years of travel and performance indicators.

Regular air travel is common in sport. The aim of this study was to understand the extent to which travel has affected Super Rugby teams' performance from 2006, the first season with available Key Performance Indicators (KPIs), to 2016. Data were analysed with mixed linear models for the effects of number of time-zones crossed (east or west), travel duration, the away-match disadvantage, difference in ranking, a set of amendments to the laws of Rugby Union in 2008, a change in competition format (introduction of a conference system) in 2011, and a secular trend. In 2006, the predicted combined effects of travelling 24 h across 12 time-zones and playing away were trivial or small and negative but generally unclear for most of the KPIs in both directions of travel. In 2016 more effects were clear, small and negative for westward travel, while most effects for eastward travel were clear, small to moderate and negative. Most KPIs showed small to moderate increases over the 11 years, while difference in ranking, the introduction of new rules and game format led to mostly small changes. Changes in the physical demands of the game, and inadequate recovery time for long-haul travel can explain these effects.

Out of your zone? 21 years of travel and performance in Super Rugby.

The extent to which travel has affected Super Rugby teams' performances was analysed using outcomes of all matches played from the beginning of the competition in 1996 to the end of the 2016 season. Points difference and matches won or lost were predicted with general and generalized mixed linear models. The predictors were the linear effects of number of time zones crossed and travel duration based on the teams' locations for each match and their locations in the previous week. The away-match disadvantage was also estimated, along with trends in all these effects. In 1996 the predicted combined effect of eastward travel across 12 time zones was a reduction of 5.8 points scored per match, resulting in 4.1 more matches lost every 10 matches. Corresponding effects for westward travel were 6.4 points and 3.1 matches. In 2016 effects travelling eastward were 3.7 points and 2.3 matches, whereas travelling westward the effects were 3.7 points and 1.5 matches. These travel effects were due mainly to the away-match disadvantage: 5.7 points and 3.2 matches in 1996; 5.2 points and 2.3 matches in 2016. Teams in Super Rugby are dealing successfully with long-haul travel and should now focus on reducing the away-match disadvantage.

Discovering frequently recurring movement sequences in team-sport athlete spatiotemporal data.

Athlete external load is typically analysed from predetermined movement thresholds. The combination of movement sequences and differences in these movements between playing positions is also currently unknown. This study developed a method to discover the frequently recurring movement sequences across playing position during matches. The external load of 12 international female netball athletes was collected by a local positioning system during four national-level matches. Velocity, acceleration and angular velocity were calculated from positional (X, Y) data, clustered via one-dimensional k-means and assigned a unique alphabetic label. Combinations of velocity, acceleration and angular velocity movement were compared using the Levenshtein distance and similarities computed by the longest common substring problem. The contribution of each movement sequence, according to playing position and relative to the wider data set, was then calculated via the Minkowski distance. A total of 10 frequently recurring combinations of movement were discovered, regardless of playing position. Only the wing attack, goal attack and goal defence playing positions are closely related. We developed a technique to discover the movement sequences, according to playing position, performed by elite netballers. This methodology can be extended to discover the frequently recurring movements within other team sports and across levels of competition.

Relative Match Intensities at High Altitude in Highly-Trained Young Soccer Players (ISA3600).

To compare relative match intensities of sea-level versus high-altitude native soccer players during a 2-week camp at 3600 m, data from 7 sea-level (Australian U17 National team, AUS) and 6 high-altitude (a Bolivian U18 team, BOL) native soccer players were analysed. Two matches were played at sea-level and three at 3600 m on Days 1, 6 and 13. The Yo-Yo Intermittent recovery test (vYo-YoIR1) was performed at sea-level, and on Days 3 and 10. Match activity profiles were measured via 10-Hz GPS. Distance covered >14.4 km.h(-1) (D>14.4 km·h(-1)) and >80% of vYo-YoIR1 (D>80%vYo-YoIR1) were examined. Upon arrival at altitude, there was a greater decrement in vYo-YoIR1 (Cohen's d +1.0, 90%CL ± 0.8) and D>14.4 km·h(-1) (+0.5 ± 0.8) in AUS. D>14.4 km.h(-1) was similarly reduced relative to vYo-YoIR1 in both groups, so that D>80%vYo-YoIR1 remained similarly unchanged (-0.1 ± 0.8). Throughout the altitude sojourn, vYo-YoIR1 and D>14.4 km·h(-1) increased in parallel in AUS, so that D>80%vYo-YoIR1 remained stable in AUS (+6.0%/match, 90%CL ± 6.7); conversely D>80%vYo-YoIR1 decreased largely in BOL (-12.2%/match ± 6.2). In sea-level natives competing at high-altitude, changes in match running performance likely follow those in high-intensity running performance. Bolivian data confirm that increases in 'fitness' do not necessarily translate into greater match running performance, but rather in reduced relative exercise intensity. Key pointsWhen playing at high-altitude, players may alter their activities during matches in relation to their transient maximal physical capacities, possibly to maintain a 'tolerable' relative exercise intensity.While there is no doubt that running performance per se in not the main determinant of match outcomes (Carling, 2013), fitness levels influence relative match intensity (Buchheit et al., 2012, Mendez-Villanueva et al., 2013), which in-turn may impact on decision making and skill performance (Rampinini et al., 2008).In the context of high-altitude competitions, it is therefore recommended to arrive early enough (i.e., ~2 weeks) to allow (at least partial) acclimatisation, and in turn, allow sea-level native players to regulate their running activities in relation to both actual game demands and relative match intensity.

Activity profiles of professional soccer, rugby league and Australian football match play.

Abstract We compared the match activity profiles of elite footballers from Australian football (AF), rugby league (RL) and soccer (SOC), using identical movement definitions. Ninety-four elite footballers from AF, RL or SOC clubs in Australia participated in this study. Movement data were collected using a 5-Hz global positioning system from matches during the 2008-2011 competitive seasons, including measures of velocity, distance, acceleration and bouts of repeat sprints (RS). Australian footballers covered the greatest relative running distances (129 ± 17 m.min-1) compared to RL (97 ± 16 m.min-1) and SOC (104 ± 10 m.min-1) (effect size [ES]; 1.0-2.8). The relative distance covered (4.92 ± 2.10 m.min-1 vs. 5.42 ± 2.49 m.min-1; 0.74 ± 0.78 m.min-1 vs. 0.97 ± 0.80 m.min-1) and the number of high-velocity running (0.4 ± 0.2 no.min-1 vs. 0.4 ± 0.2 no.min-1) and sprint (0.06 ± 0.06 no.min-1 vs. 0.08 ± 0.07 no.min-1) efforts between RL and SOC players were similar (ES; 0.1-0.3). Rugby league players undertook the highest relative number of accelerations (1.10 ± 0.56 no.min-1). RS bouts were uncommon for all codes. RL and SOC players perform less running than AF players, possibly due to limited open space as a consequence of field size and code specific rules. While training in football should be code specific, there may be some transference of conditioning drills across codes.

Update in the understanding of altitude-induced limitations to performance in team-sport athletes.

The internationalism of field-based team sports (TS) such as football and rugby requires teams to compete in tournaments held at low to moderate altitude (∼1200-2500 m). In TS, acceleration, speed and aerobic endurance are physical characteristics associated with ball possession and, ultimately, scoring. While these qualities are affected by the development of neuromuscular fatigue at sea level, arterial hypoxaemia induced by exposure to altitude may further hinder the capacity to perform consecutive accelerations (CAC) or sprint endurance and thereby change the outcome of a match. The higher the altitude, the more severe the hypoxaemia, and thus, the larger the expected decline in aerobic endurance, CAC and match running performance. Therefore, it is critical for athletes and coaches to understand how arterial hypoxaemia affects aerobic endurance and CAC and the magnitude of decline they may face at altitude for optimal preparation and increased chances of success. This mini review summarises the effects of acute altitude/hypoxia exposure on aerobic endurance, CAC and activity profiles of TS athletes performing in the laboratory and during matches at natural altitude, and analyses the latest findings about the consequences of arterial hypoxaemia on the relationship between peripheral perturbations, neural adjustments and performance during repeated sprints or CAC. Finally, we briefly discuss how altitude training can potentially help athletes prepare for competition at altitude.

Yin and yang, or peas in a pod? Individual-sport versus team-sport athletes and altitude training.

The question of whether altitude training can enhance subsequent sea-level performance has been well investigated over many decades. However, research on this topic has focused on athletes from individual or endurance sports, with scant number of studies on team-sport athletes. Questions that need to be answered include whether this type of training may enhance team-sport athlete performance, when success in team-sport is often more based on technical and tactical ability rather than physical capacity per se. This review will contrast and compare athletes from two sports representative of endurance (cycling) and team-sports (soccer). Specifically, we draw on the respective competition schedules, physiological capacities, activity profiles and energetics of each sport to compare the similarities between athletes from these sports and discuss the relative merits of altitude training for these athletes. The application of conventional live-high, train-high; live-high, train-low; and intermittent hypoxic training for team-sport athletes in the context of the above will be presented. When the above points are considered, we will conclude that dependent on resources and training objectives, altitude training can be seen as an attractive proposition to enhance the physical performance of team-sport athletes without the need for an obvious increase in training load.

Predicting sickness during a 2-week soccer camp at 3600 m (ISA3600).

OBJECTIVES: To examine the time course of changes in wellness and health status markers before and after episodes of sickness in young soccer players during a high-altitude training camp (La Paz, 3600 m). METHODS: Wellness and fatigue were assessed daily on awakening using specifically-designed questionnaires and resting measures of heart rate and heart rate variability. The rating of perceived exertion and heart rate responses to a submaximal run (9 km/h) were also collected during each training session. Players who missed the morning screening for at least two consecutive days were considered as sick. RESULTS: Four players met the inclusion criteria. With the exception of submaximal exercise heart rate, which showed an almost certain and large increase before the day of sickness (4%; 90% confidence interval 3 to 6), there was no clear change in any of the other psychometric or physiological variables. There was a very likely moderate increase (79%, 22 to 64) in self-reported training load the day before the heart rate increase in sick players (4 of the 4 players, 100%). In contrast, training load was likely and slightly decreased (-24%, -78 to -11) in players who also showed an increased heart rate but remained healthy. CONCLUSIONS: A >4% increased heart rate during submaximal exercise in response to a moderate increase in perceived training load the previous day may be an indicator of sickness the next day. All other variables, that is, resting heart rate, heart rate variability and psychometric questionnaires may be less powerful at predicting sickness.

Changes in blood gas transport of altitude native soccer players near sea-level and sea-level native soccer players at altitude (ISA3600).

OBJECTIVES: The optimal strategy for soccer teams playing at altitude is not known, that is, 'fly-in, fly-out' versus short-term acclimatisation. Here, we document changes in blood gas and vascular volumes of sea-level (Australian, n=20) and altitude (Bolivian, n=19) native soccer players at 3600 m. METHODS: Haemoglobin-oxygen saturation (Hb-sO2), arterial oxygen content (CaO2), haemoglobin mass (Hbmass), blood volume (BV) and blood gas concentrations were measured before descent (Bolivians only), together with aerobic fitness (via Yo-YoIR1), near sea-level, after ascent and during 13 days at 3600 m. RESULTS: At baseline, haemoglobin concentration [Hb] and Hbmass were higher in Bolivians (mean ± SD; 18.2 ± 1.0 g/dL, 12.8 ± 0.8 g/kg) than Australians (15.0 ± 0.9 g/dL, 11.6 ± 0.7 g/kg; both p ≤ 0.001). Near sea-level, [Hb] of Bolivians decreased to 16.6 ± 0.9 g/dL, but normalised upon return to 3600 m; Hbmass was constant regardless of altitude. In Australians, [Hb] increased after 12 days at 3600 m to 17.3 ± 1.0 g/dL; Hbmass increased by 3.0 ± 2.7% (p ≤ 0.01). BV decreased in both teams at altitude by ∼400 mL. Arterial partial pressure for oxygen (PaO2), Hb-sO2 and CaO2 of both teams decreased within 2 h of arrival at 3600 m (p ≤ 0.001) but increased over the following days, with CaO2 overcompensated in Australians (+1.7 ± 1.2 mL/100 mL; p ≤ 0.001). Yo-YoIR1 was lower on the 3rd versus 10th day at altitude and was significantly related to CaO2. CONCLUSIONS: The marked drop in PaO2 and CaO2 observed after ascent does not support the 'fly-in, fly-out' approach for soccer teams to play immediately after arrival at altitude. Although short-term acclimatisation was sufficient for Australians to stabilise their CaO2 (mostly due to loss of plasma volume), 12 days appears insufficient to reach chronic levels of adaption.

Wellness, fatigue and physical performance acclimatisation to a 2-week soccer camp at 3600 m (ISA3600).

OBJECTIVES: To examine the time course of wellness, fatigue and performance during an altitude training camp (La Paz, 3600 m) in two groups of either sea-level (Australian) or altitude (Bolivian) native young soccer players. METHODS: Wellness and fatigue were assessed using questionnaires and resting heart rate (HR) and HR variability. Physical performance was assessed using HR responses to a submaximal run, a Yo-Yo Intermittent recovery test level 1 (Yo-YoIR1) and a 20 m sprint. Most measures were performed daily, with the exception of Yo-YoIR1 and 20 m sprints, which were performed near sea level and on days 3 and 10 at altitude. RESULTS: Compared with near sea level, Australians had moderate-to-large impairments in wellness and Yo-YoIR1 relative to the Bolivians on arrival at altitude. The acclimatisation of most measures to altitude was substantially slower in Australians than Bolivians, with only Bolivians reaching near sea-level baseline high-intensity running by the end of the camp. Both teams had moderately impaired 20 m sprinting at the end of the camp. Exercise HR had large associations (r>0.5-0.7) with changes in Yo-YoIR1 in both groups. CONCLUSIONS: Despite partial physiological and perceptual acclimatisation, 2 weeks is insufficient for restoration of physical performance in young sea-level native soccer players. Because of the possible decrement in 20 m sprint time, a greater emphasis on speed training may be required during and after altitude training. The specific time course of restoration for each variable suggests that they measure different aspects of acclimatisation to 3600 m; they should therefore be used in combination to assess adaptation to altitude.

Soccer activity profile of altitude versus sea-level natives during acclimatisation to 3600 m (ISA3600).

OBJECTIVES: We investigated the effect of high altitude on the match activity profile of elite youth high altitude and sea level residents. METHODS: Twenty Sea Level (Australian) and 19 Altitude-resident (Bolivian) soccer players played five games, two near sea level (430 m) and three in La Paz (3600 m). Match activity profile was quantified via global positioning system with the peak 5 min period for distance ((D5(peak)) and high velocity running (>4.17 m/s, HIVR5(peak)); as well as the 5 min period immediately subsequent to the peak for both distance (D5(sub)) and high-velocity running (HIVR5(sub)) identified using a rolling 5 min epoch. The games at 3600 m were compared with the average of the two near sea-level games. RESULTS: The total distance per minute was reduced by a small magnitude in the first match at altitude in both teams, without any change in low-velocity running. There were variable changes in HiVR, D5(peak) and HiVR5(peak) from match to match for each team. There were within-team reductions in D5(peak) in each game at altitude compared with those at near sea level, and this reduction was greater by a small magnitude in Australians than Bolivians in game 4. The effect of altitude on HiVR5(peak) was moderately lower in Australians compared with Bolivians in game 3. There was no clear difference in the effect of altitude on maximal accelerations between teams. CONCLUSIONS: High altitude reduces the distance covered by elite youth soccer players during matches. Neither 13 days of acclimatisation nor lifelong residence at high altitude protects against detrimental effects of altitude on match activity profile.

The sleep of elite athletes at sea level and high altitude: a comparison of sea-level natives and high-altitude natives (ISA3600).

BACKGROUND: Altitude exposure causes acute sleep disruption in non-athletes, but little is known about its effects in elite athletes. The aim of this study was to examine the effects of altitude on two groups of elite athletes, that is, sea-level natives and high-altitude natives. METHODS: Sea-level natives were members of the Australian under-17 soccer team (n=14). High-altitude natives were members of a Bolivian under-20 club team (n=12). Teams participated in an 18-day (19 nights) training camp in Bolivia, with 6 nights at near sea level in Santa Cruz (430 m) and 13 nights at high altitude in La Paz (3600 m). Sleep was assessed on every day/night using activity monitors. RESULTS: The Australians' sleep was shorter, and of poorer quality, on the first night at altitude compared with sea level. Sleep quality returned to normal by the end of the first week at altitude, but sleep quantity had still not stabilised at its normal level after 2 weeks. The quantity and quality of sleep obtained by the Bolivians was similar, or greater, on all nights at altitude compared with sea level. The Australians tended to obtain more sleep than the Bolivians at sea level and altitude, but the quality of the Bolivians' sleep tended to be better than that of the Australians at altitude. CONCLUSIONS: Exposure to high altitude causes acute and chronic disruption to the sleep of elite athletes who are sea-level natives, but it does not affect the sleep of elite athletes who are high-altitude natives.

Methods of the international study on soccer at altitude 3600 m (ISA3600).

BACKGROUND: We describe here the 3-year process underpinning a multinational collaboration to investigate soccer played at high altitude--La Paz, Bolivia (3600 m). There were two main aims: first, to quantify the extent to which running performance would be altered at 3600 m compared with near sea level; and second, to characterise the time course of acclimatisation of running performance and underlying physiology to training and playing at 3600 m. In addition, this project was able to measure the physiological changes and the effect on running performance of altitude-adapted soccer players from 3600 m playing at low altitude. METHODS: A U20 Bolivian team ('The Strongest' from La Paz, n=19) played a series of five games against a U17 team from sea level in Australia (The Joeys, n=20). 2 games were played near sea level (Santa Cruz 430 m) over 5 days and then three games were played in La Paz over the next 12 days. Measures were (1) game and training running performance--including global positioning system (GPS) data on distance travelled and velocity of movement; (2) blood--including haemoglobin mass, blood volume, blood gases and acid-base status; (3) acclimatisation--including resting heart rate variability, perceived altitude sickness, as well as heart rate and perceived exertion responses to a submaximal running test; and (4) sleep patterns. CONCLUSIONS: Pivotal to the success of the project were the strong professional networks of the collaborators, with most exceeding 10 years, the links of several of the researchers to soccer federations, as well as the interest and support of the two head coaches.

The impact of altitude on the sleep of young elite soccer players (ISA3600).

BACKGROUND: Altitude training is used by elite athletes to improve sports performance, but it may also disrupt sleep. The aim of this study was to examine the effects of 2 weeks at high altitude on the sleep of young elite athletes. METHODS: Participants (n=10) were members of the Australian under-17 soccer team on an 18-day (19-night) training camp in Bolivia, with six nights at near sea level in Santa Cruz (430 m) and 13 nights at high altitude in La Paz (3600 m). Sleep was monitored using polysomnography during a baseline night at 430 m and three nights at 3600 m (immediately after ascent, 1 week after ascent and 2 weeks after ascent). Data were analysed using effect size statistics. RESULTS: All results are reported as comparisons with baseline. Rapid eye movement (REM) sleep was likely lower immediately upon ascent to altitude, possibly lower after 1 week and similar after 2 weeks. On all three nights at altitude, hypopneas and desaturations were almost certainly higher; oxygen saturation was almost certainly lower; and central apnoeas, respiratory arousals and periodic breathing were very likely higher. The effects on REM sleep were common to all but one participant, but the effects on breathing were specific to only half the participants. CONCLUSIONS: The immediate effects of terrestrial altitude of 3600 m are to reduce the amount of REM sleep obtained by young elite athletes, and to cause 50% of them to have impaired breathing during sleep. REM sleep returns to normal after 2 weeks at altitude, but impaired breathing does not improve.

Profiling Professional Rugby Union Activity After Peak Match Periods.

The aim of this investigation was to quantify professional rugby union player activity profiles after the most intense (peak) passages of matches. Movement data were collected from 30 elite and 30 subelite professional rugby union athletes across respective competitive seasons. Accelerometer-derived PlayerLoad and global navigation satellite system-derived measures of mean speed and metabolic power were analyzed using a rolling-average method to identify the most intense 5- to 600-second passages (ie, worst-case scenarios) within matches. Player activity profiles immediately post their peak 5- to 600-second match intensity were identified using 5 epoch duration-matched intervals. Mean speed, metabolic power, and PlayerLoad declined sharply (∼29%-86%) after the most intense 5 to 600 seconds of matches. Following the most intense periods of rugby matches, exercise intensity declined below the average match-half intensity 81% of the time and seldom returned to or exceeded it, likely due to a host of individual physical and physiological characteristics, transient and/or accumulative fatigue, contextual factors, and pacing strategies. Typically, player exercise intensities after the most intense passages of matches were similar between match halves, positional groups, and levels of rugby competition. Accurate identification of the peak exercise intensities of matches and movement thereafter using novel methodologies has improved the limited understanding of professional rugby union player activity profiles following the worst-case scenarios of matches. Findings of the present study may inform match-representative training prescription, monitoring, and tactical match decisions (eg, substitutions and positional changes).

Validity and reliability of GPS for measuring instantaneous velocity during acceleration, deceleration, and constant motion.

In this study, we assessed the validity and reliability of 5 and 10 Hz global positioning systems (GPS) for measuring instantaneous velocity during acceleration, deceleration, and constant velocity while straight-line running. Three participants performed 80 running trials while wearing two GPS units each (5 Hz, V2.0 and 10 Hz, V4.0; MinimaxX, Catapult Innovations, Scoresby, VIC, Australia). The criterion measure used to assess GPS validity was instantaneous velocity recorded using a tripod-mounted laser. Validity was established using the standard error of the estimate (± 90% confidence limits). Reliability was determined using typical error (± 90% confidence limits, expressed as coefficient of variation) and Pearson's correlation. The 10 Hz GPS devices were two to three times more accurate than the 5 Hz devices when compared with a criterion value for instantaneous velocity during tasks completed at a range of velocities (coefficient of variation 3.1-11.3%). Similarly, the 10 Hz GPS units were up to six-fold more reliable for measuring instantaneous velocity than the 5 Hz units (coefficient of variation 1.9-6.0%). Newer GPS may provide an acceptable tool for the measurement of constant velocity, acceleration, and deceleration during straight-line running and have sufficient sensitivity for detecting changes in performance in team sport. However, researchers must account for the inherent match-to-match variation reported when using these devices.