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Michelle A. Sandrey

Clinical Question: Is there sufficient evidence to determine which low back instability tests should be incorporated into a stabilization classification exam for athletes? Clinical Bottom Line: There is moderate level 2 evidence to include, but not to use in isolation, the prone instability test along with other instability tests in a stabilization classification exam.

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Pedro L. Valenzuela, Javier S. Morales, Adrián Castillo-García and Alejandro Lucia

Purpose: To determine the acute effects of ketone supplementation on exercise performance (primary outcome) and physiological and perceptual responses to exercise (secondary outcomes). Methods: A systematic search was conducted in PubMed, Web of Science, and SPORTDiscus (since inception to July 21, 2019) to find randomized controlled trials assessing the effects of acute ketone supplementation compared with a drink containing no ketones (ie, control intervention). The standardized mean difference (Hedges g) between interventions and 95% confidence interval (CI) were computed using a random-effects model. Results: Thirteen studies met all inclusion criteria. No significant differences were observed between interventions for overall exercise performance (Hedges g = −0.05; 95% CI, −0.30 to 0.20; P = .68). Subanalyses revealed no differences between interventions when analyzing endurance time-trial performance (g = −0.04; 95% CI, −0.35 to 0.28; P = .82) or when assessing the separate effects of supplements containing ketone esters (g = −0.07; 95% CI, −0.38 to 0.24; P = .66) or salts (g = −0.02; 95% CI, −0.45 to 0.41; P = .93). All studies reported increases in plasma ketone concentration after acute ketone supplementation, but no consistent effects were reported on the metabolic (plasma lactate and glucose levels), respiratory (respiratory exchange ratio, oxygen uptake, and ventilatory rate), cardiovascular (heart rate), or perceptual responses to exercise (rating of perceived exertion). Conclusions: The present findings suggest that ketone supplementation exerts no clear influence on exercise performance (from sprints to events lasting up to ∼50 min) or metabolic, respiratory, cardiovascular, or perceptual responses to exercise. More research is needed to elucidate if this strategy could provide ergogenic effects on other exercise types (eg, ultraendurance exercise).

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Carl Foster, Jos J. de Koning, Christian Thiel, Bram Versteeg, Daniel A. Boullosa, Daniel Bok and John P. Porcari

Background: Pacing studies suggest the distribution of effort for optimizing performance. Cross-sectional studies of 1-mile world records (WRs) suggest that WR progression includes a smaller coefficient of variation of velocity. Purpose: This study evaluates whether intraindividual pacing used by elite runners to break their own WR (1 mile, 5 km, and 10 km) is related to the evolution of pacing strategy. We provide supportive data from analysis in subelite runners. Methods: Men’s WR performances (with 400-m or 1-km splits) in 1 mile, 5 km, and 10 km were retrieved from the IAAF database (from 1924 to present). Data were analyzed relative to pacing pattern when a runner improved their own WR. Similar analyses are presented for 10-km performance in subelite runners before and after intensified training. Results: WR performance was improved in 1 mile (mean [SD]: 3:59.4 [11.2] to 3:57.2 [8.6]), 5 km (13:27 [0:33] to 13:21 [0:33]), and 10 km (28:35 [1:27] to 28:21 [1:21]). The average coefficient of variation did not change in the 1 mile (3.4% [1.8%] to 3.6% [1.6%]), 5 km (2.4% [0.9%] to 2.2% [0.8%]), or 10 km (1.4% [0.1%] to 1.5% [0.6%]) with improved WR. When velocity was normalized to the percentage mean velocity for each race, the pacing pattern was almost identical. Very similar patterns were observed in subelite runners in the 10 km. When time improved from 49:20 (5:30) to 45:56 (4:58), normalized velocity was similar, terminal RPE increased (8.4 [1.6] to 9.1 [0.8]), coefficient of variation was unchanged (4.4% [1.1%] to 4.8% [2.1%]), and VO2max increased (49.8 [7.4] to 55.3 [8.8] mL·min−1·kg−1). Conclusion: The results suggest that when runners break their own best performances, they employ the same pacing pattern, which is different from when WRs are improved in cross-sectional data.

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Steven Salaga, Scott Tainsky and Michael Mondello

The authors demonstrate that betting market outcomes are a statistically significant and economically relevant driver of local market television viewership in the National Basketball Association. Ratings are higher when the local market team covers the point spread and when point spread outcome uncertainty is increased. They further illustrate that point spread market outcomes have a larger relative impact on viewership in less-popular games and when the local market team is expected to perform poorly. This suggests wagering market access serves as insurance to the league and its franchises against reduced viewership in games that are less appealing to consumers. The results assess the degree to which wagering interest has driven past revenues as well as how the legalization of sports wagering may influence future revenues.

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David Morawetz, Tobias Dünnwald, Martin Faulhaber, Hannes Gatterer, Lukas Höllrigl, Christian Raschner and Wolfgang Schobersberger

Background: The altering effects of hypoxia on aerobic/anaerobic performance are well documented and form the basis of this study. Application of hyperoxic gases (inspiratory fraction of oxygen [FiO2] > 0.2095) prior to competition or training (hyperoxic preconditioning) can compensate for the negative influence of acute hypoxia. Purpose: To investigate whether oxygen supplementation immediately prior to exercise (FiO2 = 1.0) improves all-out exercise performance in normobaric hypoxia (3500 m) in highly skilled skiers. Methods: In this single-blind, randomized, crossover study, 17 subjects performed a 60-second constant-load, all-out test in a normobaric hypoxic chamber. After a short period of adaptation to hypoxia (60 min), they received either pure oxygen or chamber air for 5 minutes prior to the all-out test (hyperoxic preconditioning vs nonhyperoxic preconditioning). Capillary blood was collected 3 times, and muscle oxygenation was assessed with near-infrared spectroscopy. Results: Absolute and relative peak power (P = .073 vs P = .103) as well as mean power (P = .330 vs P = .569) did not significantly differ after the hyperoxic preconditioning phase. PaO2 increased from 51.3 (3) to 451.9 (89.0) mm Hg, and SaO2 increased from 88.2% (1.7%) to 100% (0.2%) and dropped to 83.8% (4.2%) after the all-out test. Deoxygenation (P = .700) and reoxygenation rates (P = .185) did not significantly differ for both preconditioned settings. Conclusions: Therefore, the authors conclude that hyperoxic preconditioning did not enhance 60-second all-out exercise performance in acute hypoxia (3500 m).

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Erik Sesbreno, Gary Slater, Margo Mountjoy and Stuart D.R. Galloway

The monitoring of body composition is common in sports given the association with performance. Surface anthropometry is often preferred when monitoring changes for its convenience, practicality, and portability. However, anthropometry does not provide valid estimates of absolute lean tissue in elite athletes. The aim of this investigation was to develop anthropometric models for estimating fat-free mass (FFM) and skeletal muscle mass (SMM) using an accepted reference physique assessment technique. Sixty-four athletes across 18 sports underwent surface anthropometry and dual-energy X-ray absorptiometry (DXA) assessment. Anthropometric models for estimating FFM and SMM were developed using forward selection multiple linear regression analysis and contrasted against previously developed equations. Most anthropometric models under review performed poorly compared with DXA. However, models derived from athletic populations such as the Withers equation demonstrated a stronger correlation with DXA estimates of FFM (r = .98). Equations that incorporated skinfolds with limb girths were more effective at explaining the variance in DXA estimates of lean tissue (Sesbreno FFM [R2 = .94] and Lee SMM [R2 = .94] models). The Sesbreno equation could be useful for estimating absolute indices of lean tissue across a range of physiques if an accepted option like DXA is inaccessible. Future work should explore the validity of the Sesbreno model across a broader range of physiques common to athletic populations.

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Jessica Ross and Peter D. MacIntyre

Flow is a desirable state of consciousness and absorption in an optimally challenging activity. Prior research has investigated individual differences in flow. The present study investigates flow by contrasting physical versus mental activities, using a mixed-methods, sequential explanatory design. The sample from the quantitative phase included 205 undergraduate university students assessed on measures of personality, difficulties in emotion regulation, and flow. The big-five traits intellect and conscientiousness, as well as the emotion regulation subscale “lack of emotional clarity” predicted flow during mental activities, but unexpectedly no variables significantly predicted physical flow activities. The second phase used semi-structured interviews with 10 participants. Analyses of the interviews helped further explain the statistical findings, revealing four main themes: role of stress, source of guilt, presence of others, and satisfaction and fulfillment. We conclude that flow is especially relevant in physical activities which have advantages over mental activities in opportunities to experience flow.

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Liam Sayer, Nidia Rodriguez-Sanchez, Paola Rodriguez-Giustiniani, Christopher Irwin, Danielle McCartney, Gregory R. Cox, Stuart D.R. Galloway and Ben Desbrow

This study investigated the effect of drinking rate on fluid retention of milk and water following exercise-induced dehydration. In Part A, 12 male participants lost 1.9% ± 0.3% body mass through cycle exercise on four occasions. Following exercise, plain water or low-fat milk equal to the volume of sweat lost during exercise was provided. Beverages were ingested over 30 or 90 min, resulting in four beverage treatments: water 30 min, water 90 min, milk 30 min, and milk 90 min. In Part B, 12 participants (nine males and three females) lost 2.0% ± 0.3% body mass through cycle exercise on four occasions. Following exercise, plain water equal to the volume of sweat lost during exercise was provided. Water was ingested over 15 min (DR15), 45 min (DR45), or 90 min (DR90), with either DR15 or DR45 repeated. In both trials, nude body mass, urine volume, urine specific gravity and osmolality, plasma osmolality, and subjective ratings of gastrointestinal symptoms were obtained preexercise and every hour for 3 hr after the onset of drinking. In Part A, no effect of drinking rate was observed on the proportion of fluid retained, but milk retention was greater (p < .01) than water (water 30 min: 57% ± 16%, water 90 min: 60% ± 20%, milk 30 min: 83% ± 6%, and milk 90 min: 85% ± 7%). In Part B, fluid retention was greater in DR90 (57% ± 13%) than DR15 (50% ± 11%, p < .05), but this was within test–retest variation determined from the repeated trials (coefficient of variation: 17%). Within the range of drinking rates investigated the nutrient composition of a beverage has a more pronounced impact on fluid retention than the ingestion rate.

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Peter J. Whalley, Chey G. Dearing and Carl D. Paton

Purpose: Caffeine is frequently used by athletes as an ergogenic aid. Various alternate forms of caffeine administration are available, which may produce different effects. This investigation compares the effects of different forms of caffeine supplementation on 5-km running performance, and the relationship between athlete ability and degree of enhancement attained. Methods: Fourteen amateur runners completed a series of self-paced outdoor time trials following unknown ingestion of a placebo (P) or one of 3 alternate forms of caffeine supplement. Trials were randomized in a crossover design with caffeine (approximately 3–4.5 mg·kg−1) administered 15 minutes before each trial via chewing gum (CG), dissolvable mouth strips (CS), or tablet (CT). Results: Compared with P, all caffeine supplements led to worthwhile enhancements in running performance with a mean (±95% confidence limit) overall effect across all supplements of 1.4% ± 0.9%. Individual caffeine treatment effects (CG = 0.9% ± 1.4%, CS = 1.2% ± 1.0%, and CT = 2.0% ± 1.1%) were not significantly different (P > .05) from each other; however, CT trials produced the largest gain and was significantly different (P = .02) compared with P. There was no significant difference in heart rate or rate of perceived exertion across the performance trials. The magnitude of caffeine enhancement was also strongly correlated (r = .87) with no-treatment performance time. Conclusions: The findings showed that irrespective of delivery form, moderate dose of caffeine supplementation produces worthwhile gains in 5-km running performance compared with a P. Furthermore, the magnitude of caffeine enhancement is highly individualized, but it appears related to athlete performance ability.

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Manuel Terraza-Rebollo and Ernest Baiget

Purpose: To examine the postactivation potentiation effect on serve velocity and accuracy in young competition tennis players using complex training, and comparing different upper and lower body heavy-load resistance exercises (HLRE). Methods: Fifteen competition tennis players (9 boys and 6 girls; age 15.6 [1.5] y) performed 1 control session and 3 experimental sessions using HLRE in a crossover randomized design: (1) bench press, (2) half squat, (3) bench press plus half squat, and (4) control trial. HLRE were performed by accomplishing 3 sets of 3 repetitions when bench press or half squat conditions were performed and 2 sets of 3 repetitions of each exercise when bench press plus half squat condition was performed at 80% 1-repetition maximum, lifting the load at maximum speed. To assess the serve velocity and accuracy, all participants performed 32 flat serves after the HLRE, divided into 4 sets of 8 serves (0, 5, 10, and 15 min postexercise), resting 20 seconds between serves, and 2 minutes and 40 seconds between sets. Results: There were no significant (P > .05) differences in ball velocity and accuracy following each recovery time and exercise, compared with the basal situation. Conclusions: These results suggest that complex training using HLRE is not a useful method for eliciting the postactivation potentiation effect in tennis serve and does not have any effect in serve accuracy in young competition tennis players.