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Joshua T. Slysz and Jamie F. Burr

Context: The combined effect of neuromuscular electrical stimulation (NMES) and blood flow restriction (BFR) on muscle mass and strength has not been thoroughly investigated. Objective: To examine the effects of combined and independent BFR and a low-intensity NMES on skeletal muscle adaptation. Design: Exploratory study. Setting: Laboratory. Participants: Twenty recreationally active subjects. Main Outcome Measures: Subjects had each leg randomly allocated to 1 of 4 possible intervention groups: (1) cyclic BFR alone, (2) NMES alone, (3) BFR + NMES, or (4) control. Each leg was stimulated in its respective intervention group for 32 minutes, 4 days per week for 6 weeks. Mean differences in size (in grams) and isometric strength (in kilograms), between week 0 and week 6, were calculated for each group. Results: Leg strength increased 32 (19) kg in the BFR + NMES group, which differed from the 3 (11) kg change in the control group (P = .03). The isolated NMES and BFR groups revealed increases of 16 (28) kg and 18 (17) kg, respectively, but these did not statistically differ from the control, or one another. No alterations were statistically significant for leg size. Conclusion: Compared with a control that received no treatment, the novel combination of BFR and NMES led to increasing muscular strength of the knee extensors, but not muscle mass which had a large interindividual variability in response.

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Megan A. Kuikman, Margo Mountjoy, Trent Stellingwerff, and Jamie F. Burr

Relative energy deficiency in sport (RED-S) can result in negative health and performance outcomes in both male and female athletes. The underlying etiology of RED-S is low energy availability (LEA), which occurs when there is insufficient dietary energy intake to meet exercise energy expenditure, corrected for fat-free mass, leaving inadequate energy available to ensure homeostasis and adequate energy turnover (optimize normal bodily functions to positively impact health), but also optimizing recovery, training adaptations, and performance. As such, treatment of RED-S involves increasing energy intake and/or decreasing exercise energy expenditure to address the underlying LEA. Clinically, however, the time burden and methodological errors associated with the quantification of energy intake, exercise energy expenditure, and fat-free mass to assess energy availability in free-living conditions make it difficult for the practitioner to implement in everyday practice. Furthermore, interpretation is complicated by the lack of validated energy availability thresholds, which can result in compromised health and performance outcomes in male and female athletes across various stages of maturation, ethnic races, and different types of sports. This narrative review focuses on pragmatic nonpharmacological strategies in the treatment of RED-S, featuring factors such as low carbohydrate availability, within-day prolonged periods of LEA, insufficient intake of bone-building nutrients, lack of mechanical bone stress, and/or psychogenic stress. This includes the implementation of strategies that address exacerbating factors of LEA, as well as novel treatment methods and underlying mechanisms of action, while highlighting areas of further research.

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Christian P. Cheung, Joshua T. Slysz, and Jamie F. Burr

Purpose: Ischemic preconditioning (IPC) through purposeful circulatory occlusion may enhance exercise performance. The value of IPC for improving performance is controversial owing to challenges with employing effective placebo controls. This study examines the efficacy of IPC versus a deceptive sham protocol for improving performance to determine whether benefits of IPC are attributable to true physiological effects. It was hypothesized that IPC would favorably alter performance more than a sham treatment and that physiological responses to exercise would be affected only after IPC treatment. Methods: In a randomized order, 16 participants performed incremental exercise to exhaustion on a cycle ergometer in control conditions and after sham and IPC treatments. Participants rated their belief as to the efficacy of each treatment compared with control. Results: Time to exhaustion was greatest after IPC (control = 1331 [270] s, IPC = 1429 [300] s, sham = 1343 [255] s, P = .02), despite negative performance expectations after IPC and positive expectation after sham. Maximal aerobic power remained unchanged after both SHAM and IPC (control = 42.0 [5.2], IPC = 41.7 [5.5], sham = 41.6 [5.5] mL·kg−1·min−1, P = .7), as did submaximal lactate concentration (control = 8.9 [2.6], sham = 8.0 [1.9], IPC = 7.7 [2.1] mmol, P = .1) and oxygen uptake (control = 37.8 [4.8], sham = 37.5 [5.3], IPC = 37.5 [5.5] mL·kg−1·min−1, P = .6). Conclusions: IPC before cycling exercise provides an ergogenic benefit that is not attributable to a placebo effect from positive expectation and that was not explained by traditionally suggested mechanisms.

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Megan A. Kuikman, Margo Mountjoy, Trent Stellingwerff, and Jamie F. Burr

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Kyle M.A. Thompson, Alanna K. Whinton, Shane Ferth, Lawrence L. Spriet, and Jamie F. Burr

Ischemic preconditioning (IPC) was initially developed to protect the myocardium from ischemia through altered cardiocyte metabolism. Because of the observed effects on metabolism and oxygen kinetics, IPC gained interest as a potential ergogenic aid in sports. Limited research evaluating the effects of IPC on maximal short-duration activities has been performed, and of the existing literature, mixed outcomes resulting from intrasubject variation may have clouded the efficacy of this technique for enhancing sprint performance. Therefore, the current study employed a randomized repeated-measures crossover design with IPC, placebo (SHAM), and control conditions while using sprint-trained athletes (N = 18) to determine the effect of IPC (3 × 5-min occlusions, with 5-min reperfusion), concluding 15 min prior to maximal 10-s and 20-m sprinting. A visual analog scale was used in conjunction with the sprint trials to evaluate any possible placebo effect on performance. Despite a “significantly beneficial” perception of the IPC treatment compared with the SHAM trials (P < .001), no changes in sprint performance were observed after either the IPC or SHAM condition over 10 m (IPC Δ  < 0.01 [0.02] s, SHAM Δ  < 0.01 [0.02] s) or 20 m (IPC Δ = −0.01 [0.03] s, SHAM Δ < 0.01 [0.03] s) compared with control. Thus, an IPC protocol does not improve 10- or 20-m sprint performance in sprint-trained athletes.

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Brittany T. MacEwen, Travis J. Saunders, Dany J. MacDonald, and Jamie F. Burr


Sit-stand desks reduce workplace sitting time among healthy office workers; however, their metabolic and behavioral impact in higher risk populations remains unknown.


25 office workers with abdominal obesity were randomized to an intervention (sit-stand workstation) or control group (seated desk) for 12 weeks. Physical activity, sedentary behavior, and cardiometabolic risk factors were assessed before and after the intervention period in both groups.


In comparison with the control group, which did not change, the intervention group experienced significant reductions in workday (344 ± 107 to 186 ± 101 min/day) and total (645 ± 140 to 528 ± 91 min/day) sitting time, as well as increases in workday standing time (154 ± 108 to 301 ± 101 min/day, P < .05). There were no changes in sitting or standing time outside of work hours, steps taken each day, or any marker of cardiometabolic risk in either group (all P > .05).


Sit-stand desks were effective in reducing workplace sedentary behavior in an at-risk population, with no change in sedentary behavior or physical activity outside of work hours. However, these changes were not sufficient to improve markers of cardiometabolic risk in this population.

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Alexandra M. Coates, Jordan A. Berard, Trevor J. King, and Jamie F. Burr

Context: The physiological determinants of ultramarathon success have rarely been assessed and likely differ in their contributions to performance as race distance increases. Purpose : To examine predictors of performance in athletes who completed either a 50-, 80-, or 160-km trail race over a 20-km loop course on the same day. Methods: Measures of running history, aerobic fitness, running economy, body mass loss, hematocrit alterations, age, and cardiovascular health were examined in relation to race-day performance. Performance was defined as the percentage difference from the winning time at a given race distance, with 0% representing the fastest possible time. Results: In the 50-km race, training volumes, cardiovascular health, aerobic fitness, and a greater loss of body mass during the race were all related to better performance (all P < .05). Using multiple linear regression, peak velocity achieved in the maximal oxygen uptake test (β = −11.7, P = .002) and baseline blood pressure (β = 3.1, P = .007) were the best performance predictors for the men’s 50-km race (r = .98, r 2 = .96, P < .001), while peak velocity achieved in the maximal oxygen uptake test (β = −13.6, P = .001) and loss of body mass (β = 12.8, P = .03) were the best predictors for women (r = .94, r 2 = .87, P = .001). In the 80-km race, only peak velocity achieved in the maximal oxygen uptake test predicted performance (β = −20.3, r = .88, r 2 = .78, P < .001). In the 160-km race, there were no significant performance determinants. Conclusions: While classic determinants of running performance, including cardiovascular health and running fitness, predict 50-km trail-running success, performance in longer-distance races appears to be less influenced by such physiological parameters.

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Jeremy N. Cohen, Kyle M.A. Thompson, Veronica K. Jamnik, Norman Gledhill, and Jamie F. Burr

Purpose: Along with past performance, professional teams consider physical fitness and physiological potential in determining the value of prospective draft picks. The National Hockey League (NHL) Combine fitness results have been examined for their ability to predict draft order, but not bona fide hockey performance. Therefore, we sought to identify the relationships of combine fitness test results to short- and long-term NHL performance. Methods: During NHL Combine fitness testing (1994–2007), a standardized battery of tests was conducted. Player performance (1995–2020) was quantified using career cumulative points, time on ice, transitional period to playing in the NHL, and NHL career length. Forward and defensive positions were considered separately. Goalies were not considered. Stepwise linear regression analysis was used to identify fitness variables that predict NHL success. Results: Overall models ranged in their predictive ability from 2% to 16%. The transitional period was predicted by peak leg power and aerobic capacity ( V ˙ O 2 max ; forwards, R 2 = .03, and defense, R 2 = .06, both P < .01). Points and time on ice within seasons 1 to 3 were predicted by peak leg power and V ˙ O 2 max for forwards and defense (R 2 = .02–.09, P < .01). Among players accumulating 10 NHL seasons, cumulative points were inversely related to upper-body push-strength-related variables in forwards (R 2 = .11) and defense (R 2 = .16; both P < .01). Conclusions: The NHL Combine fitness testing offers meaningful data that can inform the likelihood of future success. Peak leg power and V ˙ O 2 max predict league entry and early career success. Counterintuitively, upper-body strength is inversely related to long-term performance, which may offer insight into recruitment strategies, player development, or differential team roles.

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Jennifer Sygo, Alexandra M. Coates, Erik Sesbreno, Margo L. Mountjoy, and Jamie F. Burr

Low energy availability (LEA), and subsequent relative energy deficiency in sport, has been observed in endurance, aesthetic, and team sport athletes, with limited data on prevalence in athletes in short-burst activities such as sprinting. We examined prevalence of signs and symptoms of LEA in elite female sprinters at the start of the training season (PRE), and at the end of a 5-month indoor training period (POST). Four of 13 female sprinters (31%) presented at PRE testing with at least one primary (amenorrhea, low bone mineral density, low follicle-stimulating hormone, luteinizing hormone, or estradiol, resting metabolic rate ≤29 kcal/kg fat-free mass, Low Energy Availability in Females Questionnaire score ≥8) and one secondary indicator of LEA (fasting blood glucose <4 mmol/L, free triiodothyronine <3.5 pmol/L, ferritin <25 μg/L, low-density lipoprotein cholesterol >3.0 mmol/L, fasting insulin <20 pmol/L, low insulin-like growth factor-1, systolic blood pressure <90 mmHg, and/or diastolic blood pressure <60 mmHg). At POST, seven out of 13 athletes (54%) presented with at least one primary and one secondary indicator of LEA, three of whom had also presented with indicators of LEA at PRE. Five out of 13 (39%) athletes had previous stress fracture history, though this was not associated with current indicators of LEA (PRE: r = .52, p = .07; POST: r = −.07, p = .82). In conclusion, elite female sprinters may present with signs and symptoms of LEA, even after off-season rest. Medical and coaching staff should be aware of the signs and symptoms of LEA and relative energy deficiency in sport and should include appropriate screening and intervention strategies when working with sprinters.

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Devin G. McCarthy, Kate A. Wickham, Tyler F. Vermeulen, Danielle L. Nyman, Shane Ferth, Jamie M. Pereira, Dennis J. Larson, Jamie F. Burr, and Lawrence L. Spriet

During play, ice hockey goaltenders routinely dehydrate through sweating and lose ≥2% body mass, which may impair thermoregulation and performance. Purpose: This randomized, crossover study examined the effects of mild dehydration on goaltender on-ice thermoregulation, heart rate, fatigue, and performance. Methods: Eleven goaltenders played a 70-minute scrimmage followed by a shootout and drills to analyze reaction time and movements. On ice, they either consumed no fluid (NF) and lost 2.4% (0.3%) body mass or maintained body mass with water (WAT) or a carbohydrate–electrolyte solution (CES). Save percentage, rating of perceived exertion, heart rate, and core temperature were recorded throughout, and a postskate questionnaire assessed perceived fatigue. Results: Relative to NF, intake of both fluids decreased heart rate (interaction: P = .03), core temperature (peak NF = 39.0°C [0.1°C], WAT = 38.6°C [0.1°C], and CES = 38.5°C [0.1°C]; P = .005), and rating of perceived exertion in the scrimmage (post hoc: P < .04), as well as increasing save percentage in the final 10 minutes of scrimmage (NF = 75.8% [1.9%], WAT = 81.7% [2.3%], and CES = 81.3% [2.3%], post hoc: P < .04). In drills, movement speed (post hoc: P < .05) and reaction time (post hoc: P < .04) were slower in the NF versus both fluid conditions. Intake of either fluid similarly reduced postskate questionnaire scores (condition: P < .0001). Only CES significantly reduced rating of perceived exertion in drills (post hoc: P < .05) and increased peak movement power versus NF (post hoc: P = .02). Shootout save percentage was similar between conditions (P = .37). Conclusions: Mild dehydration increased physiological strain and fatigue and decreased ice hockey goaltender performance versus maintaining hydration. Also, maintaining hydration with a CES versus WAT may further reduce perceived fatigue and positively affect movements.