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00005768-201301000-0001300005768_2013_45_83_hesford_oxygenation_1miscellaneous-article< 105_0_13_6 >Medicine & Science in Sports & Exercise©2013The American College of Sports MedicineVolume 45(1)January 2013p 83–92Effect of Race Distance on Muscle Oxygenation in Short-Track Speed Skating[BASIC SCIENCES]HESFORD, CATHERINE M.1,2; LAING, STEWART4; CARDINALE, MARCO2,3; COOPER, CHRIS E.11Centre for Sport and Exercise Science, School of Biological Sciences, University of Essex, UNITED KINGDOM; 2British Olympic Medical Institute, University College London, London, UNITED KINGDOM; 3School of Medical Sciences, University of Aberdeen, Aberdeen, Scotland, UNITED KINGDOM; and 4School of Sport, Health and Exercise Sciences, Bangor University, Bangor, Wales, UNITED KINGDOMAddress for correspondence: Catherine M. Hesford, Centre for Sports and Exercise Sciences, School of Biological Sciences, University of Essex, Wivenhoe Park, Colchester, United Kingdom; E-mail: chesfo@essex.ac.uk.Submitted for publication February 2012.Accepted for publication July 2012.Supplemental digital content is available for this article. Direct URL citations appear in the printed text and are provided in the HTML and PDF versions of this article on the journal’s Web site (www.acsm-msse.org ).ABSTRACTPurpose: Previous work identified an asymmetry in tissue desaturation changes in the left and right quadriceps muscles during on-ice skating at maximal speed in males. The effect of changing race distance on the magnitude of desaturation or leg asymmetry is unknown.Methods: Six elite male skaters (age = 23 ± 1.8 yr, height = 1.8 ± 0.1 m, mass = 80.1 ± 5.7 kg, midthigh skinfold thickness = 7 ± 2 mm) and four elite female skaters (age = 21 ± 4 yr, height = 1.6 ± 0.1 m, mass = 65.2 ± 4.3 kg, midthigh skinfold thickness = 10 ± 1 mm) were studied. Subjects completed time trials over three race distances. Blood lactate concentration and O2 uptake measurements were combined with near-infrared spectroscopy measures of muscle oxygenation (TSI) and blood volume (tHb) in the right and left vastus lateralis.Results: Neither race distance nor gender had a significant effect on the magnitude of maximal muscle desaturation (ΔTSImax). Pattern of local changes in tHb during individual laps was dependent upon subtle differences in skating technique used for the different race distances. Linear regression analysis revealed asymmetry between the right and left leg desaturation in males during the final stages of each race distance, but not in females. At all race distances, local muscle desaturation reached maximal values much more quickly than global V˙O2peak.Conclusion: The use of wearable near-infrared spectroscopy devices enabled measurement of muscle oxygenation during competitive race simulation, thus providing unique insight into the effects of velocity and technique changes on local muscle oxygenation. This may have implications for training and race pacing in speed skating.Controlled laboratory and on-ice experiments of speed skating have shown that skating in the “low sitting” position (rather than upright skating) leads to reduced submaximal V˙O2 (10), increased blood lactate concentration (21), and reduced blood volume change coupled with increased muscle deoxygenation in the quadriceps muscle (22). It has also been shown that during treadmill inline skating in the “low sitting” position, a higher level of deoxygenation in the quadriceps muscle is elicited by skating at higher velocities (22). This evidence all supports the “reduced blood flow” hypothesis (26), which states that in speed skating, a combination of the “low sitting” position, long duty cycle of the gliding phase, and high intramuscular forces leads to a reduced blood flow to the working muscle. Consequently, the aerobic capacity of recruited muscle groups cannot be fully used, and this contributes to the high anaerobic demands of speed skating.There are three Olympic individual race distances in short-track speed skating: 500 m (4.5 laps), 1000 m (9 laps), and 1500 m (13.5 laps). The current male world records for these distances are 40.7 s (500 m), 83.5 s (1000 m), and 129.0 s (1500 m). For females, the records for the corresponding distances are 42.6 s, 89.1 s, and 136.7 s, respectively (31). From these records, it can be seen that the average lap times increase as the distances get longer (i.e., time for 1000 m is more than double time for 500 m). As the finishing times suggest, it is likely that local skeletal muscle and global metabolic demands vary significantly across the three distinct distances. However, no previous work that assesses the different physiological demands of skating over the varying short-track distances has been published.The influence of pacing strategies in long-track speed skating has previously been studied and reported (12,13,18,30), and this has permitted a greater understanding of the optimal pacing patterns for success in the long-track discipline. However, there is no previous research that focuses on the pacing differences across race distances in the short-track discipline. In short-track competitions, individual skaters often race over all three distances, and therefore, training is not specifically aimed at one particular distance. This lack of training specialization is dictated by the competition requirements, which are based on a cumulative points system. Given that skaters take part in races over all three distances, it seems wise to explore the varying pacing strategies used in the three distinct events.The difference in performance between elite male and female speed skaters has previously been assessed, and it has been calculated that slower times recorded by female athletes are likely to be due to a 20%–30% lower power output than males (24). Other work has focused on biomechanical differences between male and female skaters and has suggested that there is a difference in the skating position adopted, with females not being able to adopt the “low sitting” position to the same degree as males (23). The difference was shown to be a higher preextension knee angle in female skaters, which resulted in reduced power output and increased air resistance during skating. It should be noted that this study was conducted with long-track rather than short-track speed skaters, and it was conducted almost three decades ago. However, the recent analysis of the gender gap in this discipline (24), coupled with the differences in current world records, suggests that there are still biomechanical and/or physiological differences between male and female speed skaters.Whole-body V˙O2 and blood lactate measurements have been routinely used in an applied setting to determine metabolic demands in a given sport (1,8,17). The recent development of small and portable near-infrared spectroscopy (NIRS) devices presents the opportunity to make measurements of local muscle oxygenation and hemodynamics during on-ice skating. We recently used portable NIRS to measure changes in muscle oxygenation and blood volume during 500 m on-ice time trials (TT) in elite male short-track speed skaters (11). It was shown that the technique of cornering at high speeds in short-track speed skating creates an asymmetry between the local muscle desaturation levels in the right and left quadriceps over the course of a 500-m race simulation. The portable nature of the NIRS device was fundamental to this finding, because it is not possible to account for the effects of cornering when conducting skating experiments on a treadmill. To correctly inform training and race strategy, it is desirable to understand changes at the local muscular level, in addition to information about whole-body V˙O2 changes, in a realistic race environment. The use of portable/wearable devices presents the opportunity to perform measurements during on-ice race simulation, which in turn increases the relevance of findings for athletes and coaches.The aim of the study was to use portable NIRS devices, in conjunction with measurements of oxygen uptake and blood lactate, to develop a more profound understanding of the specific demands of a short-track speed skating race over the three Olympic distances, at both global and local muscular levels. The study also aimed to examine the differences (if any) between the muscle tissue oxygenation profiles of males and females during race simulation.Previous work has shown that NIRS-derived measurements are sufficiently sensitive to monitor changes in technique during a lap of skating (11) and to show significant differences in oxygen desaturation during different alpine skiing disciplines (28). It was therefore hypothesized that it would be possible to observe differences in NIRS-derived measurements caused by the subtle alterations in technique used when skaters race across varying distances. Previous work has also shown that greater muscle deoxygenation is elicited by skating at higher velocities (22), leading to the further hypothesis that a higher level of deoxygenation would be observed when skating at the shortest race distances, which correspond to the highest average speed.METHODSSix male and four female elite short-track speed skaters, all of Olympic standard, took part in this study. Male subject group characteristics were as follows: mean ± SD age = 23 ± 1.8 yr, height = 1.8 ± 0.1 m, mass = 80.1 ± 5.7 kg, and midthigh skinfold thickness = 7 ± 2 mm. Female subject group characteristics were as follows: mean ± SD age = 21 ± 4 yr, height = 1.6 ± 0.1 m, mass = 65.2 ± 4.3 kg, midthigh skinfold thickness = 10 ± 1 mm. All subjects gave their informed consent before participation. The study was approved by the ethics committee of the University College London.Testing took place at Nottingham National Ice Centre, on a regulation short-track speed skating oval (111.12 m). Over the course of a 10-d period, subjects performed, in a randomized order and on three distinct occasions (separated by at least 24 h), TT over the three Olympic racing distances: 500 m (4.5 laps), 1000 m (9 laps), and 1500 m (13.5 laps). As in competition, the skating direction was always anticlockwise around the track. Before each TT, subjects were informed to undertake their own warm-up, as they would when preparing for a competitive race. TT was completed individually, and subjects were informed that they should try to attain the fastest time possible.Local measurementsDuring each TT, muscle oxygenation in both left and right vastus lateralis (VL) was continuously monitored using recently developed wireless spatially resolved dual-wavelength spectrometers (Portamon; Artinis Medical Systems, BV, The Netherlands). This model has previously been used to investigate muscle oxygenation and hemodynamics during laboratory (20,25) and field-based (3,4,11) studies. The unit is self-contained and compact, measuring 83 × 52 × 20 mm and weighing 84 g, including battery. It houses three pairs of light-emitting diodes, which emit light of wavelengths 760 and 850 nm. These wavelengths allow for the detection of concentration changes in the chromophores hemoglobin (Hb) and myoglobin. However, it is generally considered that the myoglobin contribution is the more minor component, so in line with the previous workers, we will ignore it for the sake of clarity (5,6). Using this method, changes are reported from an arbitrary baseline value taken before the start of exercise.Changes in the sum of the two signals (Δ[HbO2 ] + Δ[Hb]) reflect changes in the concentration of the chromophores. Changes in this parameter reflect changes in the concentration of total Hb (tHb) and hence report on the volume of blood in the muscle interrogated by the NIR light. If there are no opposing changes in red cell velocity, NIR-measured changes in blood volume will reflect change in volume blood flow and hence in oxygen delivery to the muscle tissue (29). We report the data here as has been done previously (6) in units of micromolar-centimeters (μM·cm).The inability to measure absolute chromophore concentrations can be addressed by a technique called spatially resolved spectroscopy. In the Portamon device, the three light sources are in a spatially resolved configuration, distanced 30, 35, and 40 mm from the one light receiver. The gradient of the light attenuation enables a deeper more muscle-biased measurement, with less interference from surface skin and fat layers. It is also insensitive to light scattering, allowing the diffusion equation for light transport to be used to yield an absolute measure of tissue oxygen saturation (TSI%) (27).The devices were positioned on the belly of the VL, midway between the greater trochanter of the femur and the lateral epicondyle. To ensure the optodes and detector did not move relative to the subject’s skin, the device was fixed into position using surgical tape and then secured with a bandage. Care was taken to ensure that this affixation was sufficient to prevent any movement of the device during the testing, without limiting the subject’s movement in any way. All subjects reported that the device was comfortable to wear and did not restrict their movements in any way. It has previously been shown that quadriceps muscle oxygenation is nonuniform during exercise (14–16,19), so precise and consistent optode placement was crucial.Global measurementsIn addition to the NIRS measurements obtained during each race simulation, respiratory gases were measured using a K4b2 pulmonary gas analyzer (COSMED, Italy). To determine blood lactate, ear lobe blood samples were taken using Lactate Pro blood lactate meters (Arkray, Japan), immediately before and after the completion of each TT, and also 3, 6, and 9 min post-TT.Video analysisEach TT was filmed using a Sony HDV 1080i miniDV camera (Tokyo, Japan). Frame-by-frame tracking was subsequently carried out by coding every stage of each lap using Dartfish® Video Analysis Software (Fribourg, Switzerland) and synchronizing the video and physiological data for the purposes of visual analysis. This allowed analysis of instantaneous fluctuations in TSI% and tHb in relation to the position of the skater on the lap. Video analysis was also used to analyze skating stride pattern during the first lap of each TT and to calculate the amount of time spent in the “hang” phase during the 500 m TT.Data analysisThe NIRS data were collected wirelessly at 10 Hz and displayed in real time in one leg (right) and stored in the device for the other. There were no data dropouts for either method. All TSI and chromophore concentration changes were presented relative to a baseline value taken immediately before the start of the race simulation. For the purposes of further analysis, a 10-point moving average was applied. The data of all subjects were subsequently averaged over the duration of the race for the first step of the analysis to identify significant differences over time. Linear regression of whole TT ΔTSI% (after initial desaturation) was carried out to examine the effects of leg, gender, and stage of TT on ΔTSI% slope values. Slopes and y-intercept values were considered significantly different if their 95% confidence intervals (CI) did not overlap. Paired t-tests were used to compare changes in tHb values (ΔtHb) during lap 3 of all TT. Two-way ANOVA with repeated measures was used to analyze the effect of race distance and/or gender on a variety of measurement variables: pre- and post-TT blood lactate concentration, ΔTSImax, number of steps taken on the first lap, mean time (s) spent in cornering phase during 500 m, and V˙O2peak and ΔTSI% for each lap. Where significance was observed, Bonferroni multiple comparison tests were carried out. All statistical analysis was carried out using GraphPad Prism 5 (GraphPad Software, San Diego, CA). Alpha was set at P < 0.05 level.RESULTSIn male skaters, race simulations were completed in 44.8 ± 0.4 s (500 m), 94.9 ± 2.01 s (1000 m), and 151.0 ± 4.0 s (1500 m). Female skaters completed the corresponding TT in 48.3 ± 1.5 s, 105.3 ± 4.6 s, and 166.8 ± 7.9 s, respectively. Resulting mean velocity for males was 11.2 ± 0.1 m·s−1 (500 m), 10.5 ± 0.2 m·s−1 (1000 m), and 9.9 ± 0.3 m·s−1 (1500 m), and for females, 10.4 ± 0.1 m·s−1 (500 m), 9.5 ± 0.2 m·s−1 (1000 m), and 9.0 ± 0.4 m·s−1 (1500 m). Figure 1 displays the velocity profiles and time taken to complete each lap (±SD) for males and females during TT over each distance. In the 500 m, respective lap times for males and females remained fairly constant throughout, implying an evenly paced race. In the 1000 m, both male and females recorded progressively higher lap times as the TT progressed, with the final lap taking around 2 s longer than the second lap. In the 1500 m, a different pacing pattern was seen: in males, lap times were higher at the start of the TT, and then reduced by around 1 s per lap at lap six. A slight decrease in mean velocity was also seen in the females at this stage of the TT, but the magnitude of change was small when compared with the change observed in the male skaters.FIGURE 1. Mean (±SD) lap times for males and females during TT over three race distances: 500, 1000, and 1500 m. Lap time are shown for full laps only, times for the final half lap in the 500 m, and 1500 m are not displayed.As previously described (7), the start of the race requires a “running” action to build up speed and momentum before the “gliding” action of skating begins. It can be seen in Figure 1 that for all TT, lap 1 was the slowest. With regard to the time taken to complete lap 1, there was a significant interaction between race distance and gender: lap 1 time became significantly higher as race distance increased in both males (11.6 ± 0.4 in 500 m, 12.5 ± 0.3 in 1000 m, and 14.5 ± 0.3 in 1500 m, P < 0.0001) and in females (12.9 ± 0.3 in 500 m, 13.5 ± 0.3 in 1000 m, and 14.2 ± 0.2 in 1500 m, P < 0.0001). Time taken to complete lap 1 was significantly less in males than females for 500 m (P < 0.0001) and 1000 m (P < 0.001), but there was no difference in the 1500-m event. Analysis of the number of steps taken during the opening lap of each race revealed that in both males and females, a higher number of steps are taken at the start of the shorter distances (30 ± 1, 29 ± 1, and 25 ± 4 steps for males in the 500, 1000, and 1500 m, respectively). Corresponding values for females are 35 ± 1, 32 ± 3, and 25 ± 1. The number of steps taken to complete the first lap was significantly lower in males than in females for the 500-m distance (P < 0.05).For males, the increase from prerace to postrace blood lactate concentration was significant across all race distances (P = 0.004) and was twofold in 500 m (pre vs post = 3.3 ± 0.5 vs 6.8 ±0.6) and almost fourfold in both 1000 m (2.5 ± 0.5 vs 9.8 ± 0.5) and 1500 m (2.6 ± 0.3 vs 8.5 ± 0.8). Post–1000-m blood lactate was significantly higher than post–500-m blood lactate (9.8 ± 0.5 vs 6.8 ± 0.1 mmol·L−1, P = 0.005). No significant differences were observed at 3, 6, and 9 min postrace between distances. In females, there was also a significant difference between pre- and post-TT blood lactate concentration across all distances (P = 0.04): pre versus post = 3.8 ± 0.6 versus 7.2 ± 1.6 in 500 m, 3.4 ± 0.8 versus 8.7 ± 1.2 in 1000 m, and 2.8 ± 0.3 versus 9.7 ± 2.0 in 1500 m. In females, race distance did not significantly affect the magnitude of the increase in blood lactate concentration.Figure 2 displays TSI data for both the right and left VL during all three TT distances. The general trend is for a rapid O2 desaturation in the first 10 to 15 s of the TT (caused by an imbalance between O2 supply and demand immediately after the onset of high-intensity exercise) followed by a relatively stable TSI for the remainder of the event. In males, there is no significant effect of either race distance or leg on maximum desaturation (ΔTSImax): 500 m = −26.7 ± 7.6 (right), −19.7 ± 4.5 (left); 1000 m = −26.8 ± 13.8 (right), −23.9 ± 6.0; 1500 m = −24.2 ± 9.1 (right), −20.9 ± 5.4 (left). Although there is no significant effect of race distance for females, there is a difference between the two legs, with ΔTSImax significantly greater in the left (P = 0.01): 500 m = −21.8 ± 5.3 (right), −25.2 ± 7.2 (left); 1000 m = −18.9 ± 8.0 (right), −24.0 ± 5.9 (left); 1500 m = −21.2 ± 4.4 (right), −26.0 ± 4.2 (left). The small sample size and relatively high SD in the female data set precluded a meaningful comparison of a gender effect on the ΔTSImax.FIGURE 2. Time course of mean TSI% changes during 500-, 1000-, and 1500-m TT in the right and left VL. Top panel = males, bottom panel = females.Linear regression analysis was applied to all ΔTSI% values after the initial desaturation (Table 1). For TT over the longer distances, linear regression is divided into sections to specifically analyze the trends at different stages of the event. The first time point for the regression was designated as the point at which the rapid initial desaturation had ended in both legs. This was after 10 s for the 500- and 1000-m events and after 15 s for the 1500 m. In the 500-m TT, leg asymmetry, signaled by significantly different slope values between the left and right legs, is observed in both males and females. This is also the case in the comparable stage (up to 50 s) of the 1000- and 1500-m distances. However, during the final stage of these distances, there is a significant difference between the right and left leg in the males, but not in the females.TABLE 1 Results of linear regression analysis of changes in VL TSI%.Figure 3 shows that peak V˙O2 in males was significantly higher during lap 1 of 500 m than lap 1 of 1500 m (49.04 ± 5.35 vs 31.56 ± 5.24 mL·kg−1·min−1, P < 0.05); however, there were no other significant differences in V˙O2peak on other laps during the race simulations. In females, 500-m V˙O2 peak is significantly higher than for 1000 m in lap 1, but again, there were no other differences through the remainder of the TT.FIGURE 3. Mean (±SD) peak values per lap for whole-body V˙O2 during TT over all three distances in males (top panel) and females (bottom panel).Comparison of mean ΔTSI% over the course of each lap (Fig. 4) shows that the greatest reduction in oxygen saturation in the muscle, ΔTSImax, occurs by lap 2 at the latest in all TT distances for both males and females. The pooled NIRS data, which offers a single TSI value per lap, also support the evidence from the linear regression analysis (Table 1) relating to an interaction between leg asymmetry and gender. The difference in the lap-by-lap trend between the right and left leg in the males is far more apparent than that in the female group: values for male’s right TSI% are seen to remain fairly constant throughout the TT (after initial desaturation), whereas left leg values increase at varying rates from lap 1 or 2 onward. In contrast, the difference between left and right leg average lap values is less pronounced in females.FIGURE 4. Mean values for ΔTSI% (change from baseline) during each lap over all three race distances. Top right panel = male’s right VL; top left panel = male’s left VL; bottom right panel = female’s right VL; bottom left panel = female’s left VL.To explore the possible reasons for presence of leg asymmetry in the TSI data for the shorter race distances, it is necessary to examine changes in tHb (local blood volume changes) over the course of one lap. Hence, Figure 5 displays the time course of ΔtHb changes (±SEM) during lap 3 of each race distance. Lap 3 was chosen for this analysis because by this point, the initial desaturation at race start has occurred, and the specific skating techniques used for different sections of the lap are apparent (11). It is therefore possible to examine the fluctuations in tHb, which are due to differences in technique on different sections of the lap. Because each TT was video recorded and synchronized with NIRS-derived data, it is possible to present group mean changes from the start of lap 3, even though each skater started this lap at a slightly different point in the time course of the overall TT, depending upon their velocity. It can be seen that there are clear differences in tHb changes between left and right leg in males for the 500- and 1000-m distances. The increase in left leg tHb and concurrent decrease in right leg tHb corresponds to the skater traveling around the bend, which occurs twice per lap. The technique used to do this at the highest speeds is called the “hang,” during which the skater travels around the apex of the corner solely on the right skate, as has previously been described (11). The mean hang time for males during the 500 m was 1.14 ± 0.11 s, which was significantly longer than the mean hang time for females over the same distance: 0.86 ± 0.17 s (P < 0.0001). The minimum tHb values (ΔtHbmin) reached on lap 3 were significantly different between the right and left leg for males in the 500 m and 1000 m (P < 0.01). The asymmetry between the left and right leg data is not seen for the female subjects over any race distance or for the male skaters during lap 3 of the 1500 m when they are traveling at a slower velocity compared with lap 3 of the shorter distances. Analysis of synchronized NIRS and video data shows that tHb changes over the course of lap 3 in the 1500 m represent the local changes in blood flow caused by each individual skating step/glide. See video, SDC 1, http://links.lww.com/MSS/A187 which shows tHb changes in the right and left VL during one lap of the 1500 m TT in a representative subject.FIGURE 5. Mean changes (±SEM) in tHb during the course of one lap (lap 3) of TT over all race distances.DISCUSSIONThis study used wearable wireless NIRS technology to monitor the right and left VL muscle oxygenation during maximal on-ice skating over three distances in elite short-track speed skaters. The information presented provides an analysis of the physiological differences between three short-track race distances in males and females from both a local muscle and global physiological perspective. In contrast to the hypothesis, increasing race distance (decreasing mean skating velocity) did not affect the maximal value of muscle oxygen desaturation. However, the consequences of altering race distance, hence slightly altering skating technique, were reflected in differences in NIRS-detected patterns of asymmetry between the two legs. The relatively high frequency of NIRS data collection permitted analysis of the effects of differing velocity and technique on the changes in the right and left VL during 1 lap. In addition to this, the combination of local muscle oxygenation data and blood lactate values also provides information pertaining to the different pacing strategies used by males and females across the three race distances.Whole-body physiological measurements showed similar trends across all three race distances, with the exception of the significantly higher V˙O2peak during the first lap of the 500-m TT for males and females. The highest V˙O2peak values are seen to occur toward the end of each TT. In contrast, Figure 4 shows that local muscle TSI values reach minimum levels in the first two laps of each TT. This shows that local muscle desaturation at the beginning of the event occurs very rapidly, whereas the global response of increasing V˙O2 occurs more slowly, and highlights a dissociation between local and global O2 supply/demand in this event, regardless of race distance. The difference between pre- and postrace blood lactate values across all distances was large and statistically significant, with a twofold increase seen in the 500 m, and an almost fourfold increase in the 1000- and 1500-m TT. These changes are higher than previously reported values for increase in blood lactate concentration during treadmill skating (21,22), and this is likely due to the high skating velocity achieved during the TT, in combination with the use of the “hang” phase. The combination of the extremely high intramuscular forces required to achieve and maintain velocity and the static component of the “hang” phase lead to an inability to deliver sufficient oxygen to meet the bioenergetic requirements of the quadriceps muscles. This leads to an increased reliance on anaerobic metabolism as demonstrated by the high concentration of blood lactate observed in this work.Contrary to our hypothesis, race distance did not significantly affect maximum value of VL desaturation. This may be because the difference in mean velocity during each race distance was fairly small: 11.2 ± 0.1 m·s−1 (500 m), 10.5 ± 0.2 m·s−1 (1000 m), and 9.9 ± 0.3 m·s−1 (1500 m) for the males. In previous work, which did find a significant effect of velocity on muscle deoxygenation level (22), the differences in velocity were similar. However, the actual velocities were markedly lower than in our study (2.68 and 3.13 m·s−1), suggesting the differences are only observed in submaximal skating. Thus, the testing protocol used in previous studies differed from the on-ice race simulation in two important ways: the treadmill testing was not carried out at speeds that were relevant to short-track speed skating competition, and treadmill skating cannot replicate the effects of cornering. It is possible that the combination of high velocity (across all TT distances), the low sitting position, and the high intramuscular forces, particularly during cornering in on-ice short-track speed skating, leads to a maximal desaturation, which is not altered by small changes in mean velocity. Previous treadmill tests have also been limited by the maximal speed of the treadmill of 8.5 m·s−1 (10) and also differed from on-ice skating by conducting treadmill testing at an incline of 4% (22). The use of the portable NIRS for this investigation, and the fact that this allows on-ice testing, is crucial: it permits the skater to dictate the speed in a realistic way and therefore increases the relevance and accuracy of the data gathered.The significantly greater ΔTSImax across all distances in the left VL of females may be attributable to the high step rate they use. Because females skaters take more steps on their first lap (where the majority of oxygen desaturation occurs), it is possible that the result is a slightly higher oxygen cost on the left leg (which is the inside leg). A detailed biomechanical analysis of hip and knee joint angles in the two legs during the opening lap would be necessary to prove this speculation, and this may be a useful future study to undertake.There were clear differences between males and females during the main body of the race (post–lap 1). In males, there was asymmetry between the right and left leg data (as defined by significantly different linear regression slope values) during the final sector of each race distance; this was not the case for females in the 1000 or 1500 m. Because leg asymmetry has been associated with the technique used to skate at maximum speeds (11), this suggests NIRS-derived measurements can detect changes in pacing/skating velocity in this discipline. In the 1500 m, the males started the race at the same velocity as the females (approximately 14 s for lap 1) but attained a quicker overall time (151 s for males, 166 s for females). Thus, their pacing strategy was to increase their speed throughout the course of the TT, and this is mirrored by the leg asymmetry observed in the final sector of the race, but not the middle sector. This corroborates previous work that showed that during simulated competition, athletes will preserve the capacity for anaerobic energy expenditure for the duration of the event rather than going “all-out” straight away (9). In contrast, females do not speed up to the same extent toward the end of the 1500-m TT, and thus, no asymmetry in VL data in the final sector is observed. This suggests that the females in our study followed a different pacing strategy, or that they were not able to produce sufficient power output to significantly increase skating velocity at this time as the males were able to do.The differences between the left and right leg tHb data over the course of one lap (Fig. 5) also showed the differences in asymmetry between males and females, with a clear asymmetry between the right and left leg local blood volume changes (ΔtHb) being shown for the males in the 500- and 1000-m events. The asymmetry seen in the male’s but not the female’s data for the 500 m appears to be related to the amount of time spent in the “hang” phase, given that this was significantly higher for males than females over this race distance. Because the technique of “hanging” around the corner is not used by females to the same extent, it is suggested that this explains the differing local TSI and tHb changes concerning the right and left leg data. This further supports the suggestion that NIRS-derived measurements can be used to monitor differences in technique and/or pacing in this event and supports work that has shown this for other events (28). Analysis of lap 3 of the 1500-m event showed a similar profile in males and females. Because the males started this race at a much slower pace than for the shorter distances, the “hang” phase was not used, and the male’s technique for cornering was similar to that of the females. This is reflected in the NIRS-derived data, which show very similar patterns of tHb changes for both males and females. During this lap, the combination of the high temporal resolution of the NIRS measurements (10 Hz) and the portable nature of the device enabled the measurement of the local blood volume changes in each leg resulting from each skating glide; this is the first time that such data have been shown for any skating discipline. Given the close relationship of tHb changes with blood flow and the theoretical ability to calculate muscle oxygen consumption from cyclical tHb changes (2), this study opens up the possibility of future real-time quantitative measures of muscle hemodynamics and oxygen consumption in the field.Post-TT blood lactate values in males were significantly higher for 1000 than 500 m, but there was no significant difference between 500- and 1500-m postrace values, perhaps suggesting a delayed onset of blood lactate accumulation in the 1500 m, as a result of the slower start in that event. One thousand five hundred meters was the only event during which male’s lap 1 time was comparable with that of the females. Thus, it might be proposed that if they had started at a slightly higher velocity, the males may have been able to complete the TT in a faster time (at a higher anaerobic cost due to the larger power outputs produced). However, previous work exploring the effects of this “fast start” pacing profile in elite long-track speed skaters over the 1500-m distance did not find such a strategy improved performance when compared with self-regulated pacing (12).The use of portable NIRS in this study has highlighted the differences in the right and left leg muscle saturation during the three race distances. The use of the portable tool to acquire local muscle measurements in vivo, in combination with the global measures, which were taken, builds a more comprehensive understanding of the metabolic demands of short-track speed skating. It has been shown that although there is little or no effect of race distance on global physiological variables, the effect of both race distance and technique on local NIRS-derived measurements is more apparent. It would perhaps be unwise to view this work as a comparison between male and female short-track speed skaters per se, given the relatively small size of the subject groups. Instead, the results presented offer insight into the local metabolic consequences of skating at maximal velocity, and the effects of the alterations in technique when skating velocity is reduced, even by a small amount. Therefore, the information garnered from this work may have implications for athletes and coaches in terms of specificity of training, concerning both leg asymmetry and race distance.The authors wish to thank the Performance Director, Head Coach, and athletes of the short-track speed skating squad for their cooperation and enthusiasm in this project. 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in Short-Track Speed SkatingHESFORD, CATHERINE M.; LAING, STEWART; CARDINALE, MARCO; COOPER, CHRIS E.Basic Sciences145