Effect of Hyperoxia on Critical Power and V[Combining Dot Above]O2 Kinetics during Upright Cycling Introduction/Purpose Critical power (CP) is a fundamental parameter defining high-intensity exercise tolerance, however its physiological determinants are incompletely understood. The present study determined the impact of hyperoxia on CP, the time constant of phase II pulmonary oxygen uptake kinetics (τV[Combining Dot Above]O2), and muscle oxygenation (assessed by near-infrared spectroscopy) in 9 healthy men performing upright cycle ergometry. Methods CP was determined in normoxia and hyperoxia (fraction of inspired O2 = 0.5) via 4 severe-intensity constant load exercise tests to exhaustion on a cycle ergometer, repeated once in each condition. During each test, τV[Combining Dot Above]O2 and the time constant of muscle deoxyhaemoglobin kinetics (τ[HHb]), alongside absolute concentrations of muscle oxyhaemoglobin ([HbO2]), were determined. Results CP was greater (hyperoxia: 216 ± 30 vs. normoxia: 197 ± 29W; P < 0.001) whereas W’ was reduced (hyperoxia: 15.4 ± 5.2 kJ, normoxia: 17.5 ± 4.3 W; P = 0.037) in hyperoxia compared to normoxia. τV[Combining Dot Above]O2 (hyperoxia: 35 ± 12 vs normoxia: 33 ± 10 s; P = 0.33) and τ[HHb] (hyperoxia: 11 ± 5 vs. normoxia: 14 ± 5 s; P = 0.65) were unchanged between conditions, whereas [HbO2] during exercise was greater in hyperoxia compared to normoxia (hyperoxia: 73 ± 20 vs. normoxia: 66 ± 15 μM; P = 0.001). Conclusion This study provides novel insights into the physiological determinants of CP and by extension, exercise tolerance. Microvascular oxygenation and CP were improved during exercise in hyperoxia compared with normoxia. Importantly, the improved microvascular oxygenation afforded by hyperoxia did not alter τV[Combining Dot Above]O2, suggesting that microvascular O2 availability is an independent determinant of the upper limit for steady-state exercise, i.e. CP. Corresponding Author: Richie P. Goulding, Liverpool Hope University, Hope Park Campus, Liverpool, L16 9JD, +447909075938, Email: gouldingrichie@gmail.com The authors declare no external sources of funding. The authors declare no conflicts of interest. The results of the present study do not constitute endorsement by ACSM. The results of the present study are presented clearly, honestly, and without fabrication, falsification, or inappropriate data manipulation. Accepted for Publication: 22 November 2019. © 2019 American College of Sports Medicine

Greater Lower Limb Fatigability in People with Prediabetes than Controls Introduction The study purpose was to compare perceived fatigability and performance fatigability after high-velocity contractions with knee extensor muscles between people with prediabetes, type 2 diabetes (T2D), and controls without diabetes matched for age, body mass index and physical activity. Methods Twenty people with prediabetes (11 men, 9 women: 63.1±6.0 years, 26.9±4.2 kg·m2, 8,030±3,110 steps·day-1), 39 with T2D (23 men, 16 women: 61.2±8.5 years, 29.4±6.4 kg·m2, 8,440±4,220 steps·day-1), and 27 controls (13 men, 14 women: 58.1±9.4 years, 27.3±4.3 kg·m2, 8,400±3,000 steps·day-1) completed the Fatigue Impact Scale (FIS) as a measure of perceived fatigability, and a fatigue protocol including 120 maximal-effort, high-velocity concentric contractions (MVCC) (1 contraction/3s) with the knee extensors using a submaximal load (30% maximum) to quantify performance fatigability. Electrical stimulation was used to assess voluntary activation and contractile function of the knee extensor muscles before and after the fatigue protocol. Results FIS scores were not different between people with prediabetes, type 2 diabetes and controls (12.5±15.1, 18.3±22.7 and 12.6±18.6, respectively, P=0.517). However, people with prediabetes had greater reductions in MVCC power during the fatigue protocol than controls (31.8±22.6% vs. 22.1±21.1%, P<0.001), and both groups had lesser reductions than T2D (44.8±21.9%, P<0.001). Similarly, the prediabetes group had larger reductions in electrically-evoked twitch amplitude than the control group (32.5±24.9% vs. 21.3±33.0%, P<0.001), but lesser reductions than those with T2D (44.0±23.4%, P<0.001). For all three groups, a greater decline in MVCC power was associated with larger reductions of twitch amplitude (r2=0.350, P<0.001). Conclusion People with prediabetes have greater performance fatigability of the knee extensors due to contractile mechanisms compared with controls, although less than that of people with T2D. Alison R. Harmer and Sandra K. Hunter are co-senior authors on this publication Corresponding Author: Prof. Sandra K. Hunter, Ph.D., Cramer Hall, Room 230N, PO Box 1881, Milwaukee, WI 53201. sandra.hunter@marquette.edu This work was supported by a Marquette University Way Klingler Fellowship Award to SKH and the special studies program support of the University of Sydney for ARH. Authors have no professional relationships with companies or manufacturers who will benefit from the results of the present study. Results of the present study do not constitute endorsement by ACSM. Results of the study are presented clearly, honestly and without fabrication, falsification, or inappropriate data manipulation. Accepted for Publication: 26 November 2019. © 2019 American College of Sports Medicine

Trail Runners Cannot Reach V[Combining Dot Above]O2max during a Maximal Incremental Downhill Test Purpose The purpose of this study was twofold: i) determine if well-trained athletes can achieve similar peak oxygen uptake (V[Combining Dot Above]O2peak) in downhill running (DR) versus level (LR) or uphill running (UR), and, ii) investigate if lower limb extensor muscle strength is related to the velocity at V[Combining Dot Above]O2peak (vV[Combining Dot Above]O2peak) in DR, LR and UR. Methods Eight athletes (V[Combining Dot Above]O2max=68±2 ml·min-1·kg-1) completed maximal incremental tests in LR, DR (-15% slope) and UR (+15% slope) on a treadmill (+1, +1.5 and +0.5 km·h-1 every 2 min, respectively) while cardiorespiratory responses and spatiotemporal running parameters were continuously measured. They were also tested for maximal voluntary isometric strength of hip and knee extensors and plantar flexors. Results Oxygen uptake at maximal effort was ~16-18% lower in DR vs LR and UR (~57±2, 68±2 and 70±3 ml·min-1·kg-1, respectively) despite much greater vV[Combining Dot Above]O2peak (22.7±0.6 vs 18.7±0.5 and 9.3±0.3 km·h-1, respectively). At vV[Combining Dot Above]O2peak, longer stride length and shorter contact time occurred in DR vs LR and UR (+12%, +119%, -38% and -61%, respectively). Contrary to knee extensor and plantar flexor, hip extensor isometric strength correlated to vV[Combining Dot Above]O2peak in DR, LR and UR (r=-0.86 to -0.96, p<0.05). At similar V[Combining Dot Above]O2, higher heart rate and ventilation emerged in DR vs LR and UR, associated with a more superficial ventilation pattern. Conclusions This study demonstrates that well-trained endurance athletes, accustomed to DR, achieved lower V[Combining Dot Above]O2peak despite higher vV[Combining Dot Above]O2peak during DR vs LR or UR maximal incremental tests. The specific heart rate and ventilation responses in DR might originate from altered running gait and increased lower limb musculotendinous mechanical loading, furthering our understanding of the particular physiology of DR, ultimately contributing to optimize trail race running performance. Corresponding author: Marcel Lemire, University of Strasbourg, Faculty of Sport Sciences, 14, rue René Descartes, 67084 Strasbourg, France, Tel: +33 6 51 52 50 92; Fax:+33 3 68 85 66 75; Email: marcel.lemire@unistra.fr The results of the study are presented clearly, honestly, and without fabrication, falsification, or inappropriate data manipulation. No funding was received for this study from National Institutes of Health (NIH), Welcome Trust, Howard Hughes Medical Institute (HHMI) or others. The authors report no conflict of interest. The results of the present study do not constitute endorsement by the American College of Sports Medicine. Accepted for Publication: 29 November 2019. © 2019 American College of Sports Medicine

Exercise Intensity and Recovery on Circulating Brain-derived Neurotrophic Factor Introduction BDNF is an exercise-induced neurotropin mediating neuroprotection and synaptic plasticity. Although exercise intensity is implicated as a potentially important mediator of BNDF release following exercise, the optimal exercise stimulus (interval versus continuous) and intensity (sub- versus supra-maximal) for augmenting circulating BDNF levels remains unknown. Irisin, an exercise-driven myokine, may also contribute to neuroprotection by upregulating BDNF. Purpose to examine the response and recovery of plasma BDNF and irisin following acute exercise of differing intensities. Methods Eight males (23.1±3.0 years of age; VO2max 51.2±4.4 mL·kg-1·min-1) completed four acute exercise sessions: 1) moderate-intensity continuous training (MICT, 65% VO2max); 2) vigorous-intensity continuous training (VICT, 85% VO2max); 3) sprint interval training (SIT, “all out”); and 4) no exercise (CTRL). Blood was collected pre-exercise as well as immediately, 30 min, and 90 minutes post-exercise. Plasma BDNF and irisin were assessed with commercially available ELISA kits. Results Plasma BDNF levels increased immediately following exercise in the SIT group (p<0.0001) with plasma concentrations recovering 30 and 90 min post-exercise. BDNF levels following MICT were reduced 30 min post-exercise compared to immediately post-exercise (p=0.0189), with no other changes across time points in MICT and VICT groups. Plasma BDNF AUC in SIT was significantly higher compared to CTRL, MICT, and VICT (p=0.0020). No changes in plasma irisin across exercise groups and time points were found (p>0.9999). Conclusions Plasma BDNF levels increased in an intensity-dependent manner with SIT eliciting the highest BDNF concentration immediately post-exercise. These results identify SIT as a time-efficient exercise modality to promote brain health through BDNF release. Corresponding Author: Rebecca EK MacPherson, Assistant Professor, Department of Health Sciences, Brock University, St. Catharines, Ontario, Canada, 905.688.5550 x6620. rmacpherson@brocku.ca This work was supported by a Natural Sciences and an Engineering Research Council Discovery Grant to REK MacPherson (NSERC; Grant RGPIN-2017-03904) and TJ Hazell (NSERC; Grant RGPIN-2016-06118). G. Hayward is funded by a Master’s NSERC Graduate Scholarship and L.K. Townsend was supported by an Ontario Graduate Scholarship. Conflict of Interest: No conflicts of interest to disclose. The present study do not constitute endorsement by ACSM. The results of the study are presented clearly, honestly, and without fabrication, falsification, or inappropriate data manipulation. Accepted for Publication: 2 December 2019. © 2019 American College of Sports Medicine

Pacing Behavior Development of Youth Short-Track Speed Skaters: A Longitudinal Study Purpose To analyse the development of pacing behaviour of athletes during adolescence, using a longitudinal design. Methods Lap times of male short-track speed skaters (140 skaters, 573 race performances) over two or more 1500-m races during Junior World Championships between 2010 and 2018, were analysed. Races were divided into four sections (laps 1-3, 4-7, 8-11 and 12-14). Using MLwiN (p<.05), multilevel prediction models in which repeated measures (level-1) were nested within individual athletes (level-2), were used to analyse the effect of age (15-20), race type (fast, slow) and stage of competition (final, non-final) on absolute section times (AST) and relative section times (RST; percentage of total time spent in a section). Results Between the ages of 15 and 20, total race time decreased (-6.99s) and skaters reached lower AST in laps 8-11 (-2.33s) and 12-14 (-3.28s). The RST’s of laps 1-3 (1.42%) and 4-7 (0.66%) increased and laps 8-11 (-0.53%) and 12-14 (-1.54%) decreased with age. Fast races were more evenly paced compared to slow races, with slow races having a predominantly slow first half and fast finish. Athletes in finals were faster (2.29s), specifically in laps 4-7 (0.85s) and laps 8-11 (0.84s). Conclusion Throughout adolescence, short-track speed skaters develop more conservative pacing behaviour, reserving energy during the start of the race in order to achieve a higher velocity in the final section of the race and a decrease in total race time. Coaches should take into consideration that the pacing behaviour of young athletes develops during adolescence, prepare athletes for the differences in velocity distribution between race types and inform them on how to best distribute their efforts over the different stages of competition. Corresponding author: Florentina Johanna Hettinga, Department of Sport, Exercise & Rehabilitation, Faculty of Health and Life Sciences, Northumbria University, Room 238, Northumberland Building, Newcastle Upon Tyne, NE1 8ST, United Kingdom. E-mail: florentina.hettinga@northumbria.ac.uk The authors do not have any conflict of interest. The authors declare that the results of the study are presented clearly, honestly, and without fabrication, falsification, or inappropriate data manipulation. The results of the present study do not constitute endorsement by ACSM. The authors received no specific funding for this work. Accepted for Publication: 17 November 2019. © 2019 American College of Sports Medicine

Tramadol Does Not Improve Performance or Impair Motor Function in Trained Cyclists PURPOSE To investigate the hypothesis that a therapeutic oral dose of Tramadol improves cycling time trial performance and compromises motor-cognitive performance in highly trained cyclists. METHODS Following two familiarization trials, 16 highly trained cyclists completed a preloaded time trial (1 hour at 60 % of peak power followed by a 15 km time trial) after ingestion of 100 mg Tramadol or placebo in a double-blind placebo-controlled counterbalanced cross-over design separated by at least 4 days wash-out. Visuo-motor tracking and math tasks were completed during the preload (n=10) to evaluate effects on cognition and fine motor performance. RESULTS Time trial mean power output (298±42 W vs. 294±44 W) and performance (1474±77 s vs. 1483±85 s) were similar with Tramadol and placebo treatment, respectively. In addition, there were no differences in perceived exertion, reported pain, blood pH, lactate or HCO3- concentrations across trials. Heart rate was higher (P<0.001) during the Tramadol time trial (171±8 bpm) compared to placebo (167±9 bpm). None of the combined motor-cognitive tasks were impaired by Tramadol ingestion, in fact fine motor performance was slightly improved (P<0.05) in the Tramadol trial compared to placebo. CONCLUSION In highly trained cyclists, ingestion of 100 mg Tramadol does not improve performance in a 15 km cycling time trial that was completed after a one hour preload at 60 % peak power. Additionally, a therapeutic dose of Tramadol does not compromise complex motor-cognitive or simple fine motor performances. Correspondence: Nikolai Baastrup Nordsborg, Department of Nutrition, Exercise and Sports (NEXS), Faculty of Science, University of Copenhagen, nbn@nexs.ku.dk, Tel.: +45 35321612, Fax: +45 35320870 The study was funded by Anti-Doping Denmark. During preparation of this paper JB was funded by Partnership for Clean Competition and ABA, TCB by World Anti-Doping Agency. The results of the present study do not constitute endorsement by the American College of Sports Medicine. The results of the study are presented clearly, honestly, and without fabrication, falsification, or inappropriate data manipulation. Competing interests: None declared. Accepted for Publication: 6 November 2019. © 2019 American College of Sports Medicine

Energy Deficit Required for Exercise-induced Improvements in Glycemia the Next Day Purpose This study determined the impact of an exercise-induced energy deficit on postprandial and 24h glycemic control the day after a session of exercise. Methods Fifteen healthy participants (m/f=5/10, 27±6 yrs, BMI=24±3 kg·m-2, VO2peak=36±9 mL·kg-1·min-1) completed two separate 5-day experimental trials performed under “free-living” conditions. On day 1 of each trial, participants were fitted with a continuous glucose monitor (CGM) and abstained from exercise. Day 2 served as a non-exercise control (NoEx). On day 3, participants exercised at ~1500h (65% VO2peak) until they expended 350 kcals (~45min). The diet during both experimental trials were identical with the exception of meals after this exercise session. During one trial, the dinner after exercise did not replenish the 350 kcals expended during exercise, thereby establishing an exercise energy deficit (ExDEF). During the other experimental trial, the dinner after exercise contained an additional 350 kcals to compensate for the energy expended during exercise, and thereby maintained energy balance after exercise (ExBAL). Free-living glycemia was measured the day before exercise (NoEx) and the day after exercise under ExDEF and ExBAL conditions. Results The day after exercise, 3h postprandial area under curve (AUC) was lower after breakfast in ExDEF compared with ExBAL (16.0±1.8 vs. 17.0±1.6 mmol·L-1·h-1·3h, P=0.01), but did not differ between groups after lunch (P=0.24), dinner (P=0.39), or evening snack (P=0.45). Despite differences in the glycemic response to breakfast, 24h glycemia did not differ between ExDEF and ExBAL (AUC= 128±10 vs. 131±10 mmol·L-1·h-1·24h, respectively; P=0.54). Conclusion: An exercise-induced energy deficit lowered the glycemic response to breakfast the next day – but this energy deficit did not impact total 24h glycemia the day after exercise in metabolically healthy adults. Address for correspondence: Jeffrey F. Horowitz, Ph.D., School of Kinesiology, University of Michigan, 401 Washtenaw Ave., Ann Arbor, MI 48109-2214, Phone: (734) 647-1076, Fax: (734) 936-1925. Email: jeffhoro@umich.edu This study was supported by The National Institutes of Health R01DK077966, T32DK101357, P30DK089503; American Diabetes Association 1-16-ICTS-048; Canadian Institutes of Health Research (338735). The results of the study are presented clearly, honestly, and without fabrication, falsification, or inappropriate data manipulation. The results of the present study do not constitute endorsement by ACSM. Accepted for Publication: 24 October 2019. © 2019 American College of Sports Medicine

Smoking and Biochemical, Performance, and Muscle Adaptation to Military Training Purpose To determine whether physical performance adaptation is impaired in smokers during early stages of military training, and to examine some of the putative mechanistic candidates that could explain any impairment. Methods We examined measures of oxidative stress (malondialdehyde (MDA), lipid hydroperoxides), inflammation (C-reactive protein (CRP), interleukin-6), antioxidants (Vitamins A, E and carotenes) and hormones (cortisol, testosterone, insulin-like growth factor-1) in 65 male British Army Infantry recruits (mean ± SD age: 21 ± 3 yr; mass: 75.5 ± 8.4 kg; height: 1.78 ± 0.07 m) at week 1, week 5 and week 10 of basic training. Physical performance (static lift, grip strength, jump height, 2.4 km run time and two-minute press up and sit up scores) was examined and lower-leg muscle and adipose cross-sectional area (CSA) and density measured by peripheral Quantitative Computed Tomography. Results Basic Military training, irrespective of smoking status, elicited improvement in all physical performance parameters (main time effect; P < 0.05) except grip strength and jump height, and resulted in increased muscle area and decreased fat area in the lower leg (P < 0.05). MDA was higher in smokers at baseline, and both MDA and CRP were greater in smokers during training (main group effect; P < 0.05), than non-smokers. Absolute performance measures, muscle characteristics of the lower leg and other oxidative stress, antioxidant, endocrine and inflammatory markers were similar in the two groups. Conclusions Oxidative stress and inflammation were elevated in habitual smokers during basic military training, but there was no clear evidence that this was detrimental to physical adaptation in this population over the timescale studied. CORRESPONDING AUTHOR: Prof. Keith Stokes, Department for Health, University of Bath, Bath, United Kingdom, BA2 7AY. Email: k.stokes@bath.ac.uk This research was funded by the Army Recruiting and Training Division (UK Ministry of Defence: Army). All authors declare that they have no conflict of interest. The results of the present study do not constitute endorsement by ACSM. The results of this study are presented clearly, honestly and without fabrication, falsification or inappropriate data manipulation. Accepted for Publication: 14 November 2019. © 2019 American College of Sports Medicine

Bilateral Gait Six and Twelve Months Post-ACL Reconstruction Compared to Controls Purpose To compare gait biomechanics throughout stance phase 6 and 12 months following unilateral anterior cruciate ligament reconstruction (ACLR) between ACLR and contralateral limbs and compared to controls. Methods Vertical ground reaction force (vGRF), knee flexion angle (KFA), and internal knee extension moment (KEM) were collected bilaterally 6 and 12 months post-ACLR in 30 individuals (50% female, 22±3 years, body mass index [BMI]=23.8±2.2kg/m2) and at a single time point in 30 matched uninjured controls (50% female, 22±4 years, BMI=23.6±2.1kg/m2). Functional analyses of variance were used to evaluate the effects of limb (ACLR, contralateral, and control) and time (6 and 12 months) on biomechanical outcomes throughout stance. Results Compared to the uninjured controls, the ACLR group demonstrated bilaterally lesser vGRF (ACLR=9%BW, contralateral=4%BW) during early stance and greater vGRF during mid-stance (ACLR=5%BW, contralateral=4%BW) 6 months post-ACLR. Compared to the uninjured controls, the ACLR group demonstrated bilaterally lesser vGRF (ACLR=10%BW, contralateral=8%BW) during early stance and greater vGRF during mid-stance (ACLR=5%BW, contralateral=5%BW) 12 months post-ACLR. Compared to controls, the ACLR limb demonstrated lesser KFA during early stance at 6 (2.3°) and 12 months post-ACLR (2.0°), and the contralateral limb demonstrated lesser KFA during early stance at 12 months post-ACLR (2.8°). Compared to controls, the ACLR limb demonstrated lesser KEM during early stance at both 6 (0.011BW*height) and 12 months (0.007BW*height) post-ACLR, and the contralateral limb demonstrated lesser KEM during early stance only at 12 months (0.006BW*height). Conclusion Walking biomechanics are altered bilaterally following ACLR. During the first 12 months post-ACLR, both the ACLR and contralateral limbs demonstrate biomechanical differences compared to control limbs. Differences between the contralateral and control limbs increase from 6 to 12 months post-ACLR. Key Terms: Vertical ground reaction force, knee flexion angle, knee extension moment, walking biomechanics, anterior cruciate ligament. Corresponding Author: Hope C. Davis-Wilson, MA, University of North Carolina at Chapel Hill, CB#8700, 209 Fetzer Hall, Chapel Hill, NC 27599 Email: davishc@live.unc.edu The current study was funded by grants from: 1) National Athletic Trainers Association Research and Education Foundation (New Investigator Research Grant Award [#14NewInv001]); 2) North Carolina Translational and Clinical Sciences (TraCS) Institute Planning Grant, National Institutes of Health National Institute of Arthritis & Musculoskeletal and Skin Diseases (1R03AR066840-01A1). Conflict of Interest: The results of the present study do not constitute endorsement by ACSM. The results of this study are presented clearly, honestly, and without fabrication, falsification, or inappropriate data manipulation. There are no professional relationships with companies or manufacturers who will benefit from the results of the present study to disclose. Accepted for Publication: 16 October 2019. © 2019 American College of Sports Medicine

Distinct Coordination Strategies Associated with the Drop Vertical Jump Task Introduction Coordination of multiple degrees of freedom in the performance of dynamic and complex motor tasks presents a challenging neuromuscular control problem. Experiments have inferred that humans exhibit self-organized, preferred coordination patterns, which emerge due to actor and task constraints on performance. The purpose of this study was to determine if the set of effective coordination strategies that exist for a task centers on a small number of robust, invariant patterns of behavior. Methods Kinetic movement patterns computed from a cohort of 780 primarily female adolescent athletes performing a drop vertical jump task (DVJ) were analyzed in order to discover distinct groups into which individuals could be classified based on the similarity of movement coordination solutions. Results Clustering of reduced-dimension joint moment of force time series revealed three very distinct, precisely delineated movement profiles that persisted across trials, and which exhibited different functional performance outcomes, despite no other apparent group differences. The same analysis was also performed on a different task—a single-leg drop landing (SLD)—which also produced distinct movement profiles; however, the three DVJ profiles did not translate to this task as group assignment was inconsistent between these two tasks. Conclusion The task demands of the DVJ and SLD—successful landing, reversal of downward momentum, and, in the case of the DVJ, vertical propulsion toward a maximally positioned target—constrain movement performance such that only a few successful outcomes emerge. Discovery of the observed strategies in the context of associated task constraints may help our understanding of how injury risk movement patterns emerge during specific tasks, as well as how the natural dynamics of the system may be exploited to improve these patterns. Correspondence: Christopher A. DiCesare, M.S., Division of Sports Medicine, Cincinnati Children’s Hospital Medical Center, 3333 Burnet Ave. MLC-10001. Cincinnati, OH 45229. E-mail: christopher.dicesare@cchmc.org The authors would like to acknowledge funding support from the National Institutes of Health/NIAMS Grants R21AR065068-01A1, U01AR067997, R01-AR056259, R01-AR049735, R01-AR055563 and R03AR057551. The study sponsors held no role in the design, data collection, analysis or interpretation in the present study. The authors have no conflicts of interest to report. The data presented in this manuscript have not been falsified or manipulated in any way, and the authors have agreed on its presentation. The results of the presented study do not constitute endorsement by the American College of Sports Medicine. Accepted for Publication: 22 November 2019. © 2019 American College of Sports Medicine