Short-Term Creatine Supplementation and Repeated Sprint Ability-A Systematic Review and Meta-Analysis.

The aim of this study was to conduct a systematic review and meta-analysis of the effects of short-term creatine supplementation on repeated sprint ability. Fourteen studies met the inclusion criteria of adopting double-blind randomized placebo-controlled designs in which participants (age: 18-60 years) completed a repeated sprint test (number of sprints: 4 < n ≤ 20; sprint duration: ≤10 s; recovery duration: ≤90 s) before and after supplementing with creatine or placebo for 3-7 days in a dose of ∼20 g/day. No exclusion restrictions were placed on the mode of exercise. Meta-analyses were completed using random-effects models, with effects on measures of peak power output, mean power output, and fatigue (performance decline) during each repeated sprint test presented as standardized mean difference (δ), and with effects on body mass and posttest blood lactate concentration presented as raw mean difference (D). Relative to placebo, creatine resulted in a significant increase in body mass (D = 0.79 kg; p < .00001) and mean power output (δ = 0.61; p = .002). However, there was no effect of creatine on measures of peak power (δ = 0.41; p = .10), fatigue (δ = 0.08; p = .61), or posttest blood lactate concentration (D = 0.22 L/min; p = .60). In conclusion, creatine supplementation may increase mean power output during repeated sprint tests, although the absence of corresponding effects on peak power and fatigue means that more research, with measurements of intramuscular creatine content, is necessary to confirm.

Does personalised nutrition advice based on apolipoprotein E and methylenetetrahydrofolate reductase genotype affect dietary behaviour?

Background: Dietary intake is linked to numerous modifiable risk factors of cardiovascular disease. Current dietary recommendations in the UK to reduce the risk of cardiovascular disease are not being met. A genotype-based personalised approach to dietary recommendations may motivate individuals to make positive changes in their dietary behaviour. Aim: To determine the effect of a personalised nutrition intervention, based on apolipoprotein E (ApoE, rs7412; rs429358) and methylenetetrahydrofolate reductase (MTHFR, rs1801133) genotype, on reported dietary intake of saturated fat and folate in participants informed of a risk genotype compared to those informed of non-risk genotype. Methods: Baseline data (n = 99) were collected to determine genotype (non-risk vs risk), dietary intake and cardiovascular risk (Q-Risk®2 cardiovascular risk calculator). Participants were provided with personalised nutrition advice via email based on their ApoE and MTHFR genotype and reported intake of folate and saturated fat. After 10 days, dietary intake data were reported for a second time. Results: Personalised nutrition advice led to favourable dietary changes, irrespective of genotype, in participants who were not meeting dietary recommendations at baseline for saturated fat (p < 0.001) and folate (p = 0.002). Only participants who were informed of a risk ApoE genotype met saturated fat recommendations following personalised nutrition advice. Conclusion: Incorporation of genotype-based personalised nutrition advice in a diet behaviour intervention may elicit favourable changes in dietary behaviour in participants informed of a risk genotype. Participants informed of a non-risk genotype also respond to personalised nutrition advice favourably but to a lesser extent.

Methodological Approaches and Related Challenges Associated With the Determination of Critical Power and Curvature Constant.

Muniz-Pumares, D, Karsten, B, Triska, C, and Glaister, M. Methodological approaches and related challenges associated with the determination of critical power and W'. J Strength Cond Res 33(2): 584-596, 2019-The relationship between exercise intensity and time to task failure (P-T relationship) is hyperbolic, and characterized by its asymptote (critical power [CP]) and curvature constant (W'). The determination of these parameters is of interest for researchers and practitioners, but the testing protocol for CP and W' determination has not yet been standardized. Conventionally, a series of constant work rate (CWR) tests to task failure have been used to construct the P-T relationship. However, the duration, number, and recovery between predictive CWR and the mathematical model (hyperbolic or derived linear models) are known to affect CP and W'. Moreover, repeating CWR may be deemed as a cumbersome and impractical protocol. Recently, CP and W' have been determined in field and laboratory settings using time trials, but the validity of these methods has raised concerns. Alternatively, a 3-minute all-out test (3MT) has been suggested, as it provides a simpler method for the determination of CP and W', whereby power output at the end of the test represents CP, and the amount of work performed above this end-test power equates to W'. However, the 3MT still requires an initial incremental test and may overestimate CP. The aim of this review is, therefore, to appraise current methods to estimate CP and W', providing guidelines and suggestions for future research where appropriate.

The effect of weightlifting shoes on the kinetics and kinematics of the back squat.

Weightlifting shoes (WS) are often used by athletes to facilitate their squat technique; however, the nature of these benefits is not well understood. In this study, the effects of footwear and load on the mechanics of squatting were assessed for 32 participants (age: 25.4 ± 4.4 years; mass 72.87 ± 11.35 kg) grouped by sex and experience. Participants completed loaded and unloaded back squats wearing both WS and athletic shoes (AS). Data were collected utilising a 3D motion capture system synchronised with a force platform and used to calculate kinematic and kinetic descriptors of squatting. For both load conditions, WS gave significantly (P < 0.05) reduced ankle flexion and increased knee flexion than AS, as well as a more upright trunk and greater knee moment for the unloaded condition. In addition, the experienced group experienced a significantly greater increase in knee and hip flexion with WS than the novices when unloaded. These results are consistent with the idea that WS permit a more knee flexed, upright posture during squatting, and provide preliminary evidence that experienced squatters are more able to exploit this effect. Decisions about footwear should recognise the effect of footwear on movement and reflect an athlete's movement capabilities and training objectives.

A comparison of methods to estimate anaerobic capacity: Accumulated oxygen deficit and W' during constant and all-out work-rate profiles.

This study investigated (i) whether the accumulated oxygen deficit (AOD) and curvature constant of the power-duration relationship (W') are different during constant work-rate to exhaustion (CWR) and 3-min all-out (3MT) tests and (ii) the relationship between AOD and W' during CWR and 3MT. Twenty-one male cyclists (age: 40 ± 6 years; maximal oxygen uptake [V̇O2max]: 58 ± 7 ml · kg-1 · min-1) completed preliminary tests to determine the V̇O2-power output relationship and V̇O2max. Subsequently, AOD and W' were determined as the difference between oxygen demand and oxygen uptake and work completed above critical power, respectively, in CWR and 3MT. There were no differences between tests for duration, work, or average power output (P ≥ 0.05). AOD was greater in the CWR test (4.18 ± 0.95 vs. 3.68 ± 0.98 L; P = 0.004), whereas W' was greater in 3MT (9.55 ± 4.00 vs. 11.37 ± 3.84 kJ; P = 0.010). AOD and W' were significantly correlated in both CWR (P < 0.001, r = 0.654) and 3MT (P < 0.001, r = 0.654). In conclusion, despite positive correlations between AOD and W' in CWR and 3MT, between-test differences in the magnitude of AOD and W', suggest that both measures have different underpinning mechanisms.

The validity and reliability of an iPhone app for measuring vertical jump performance.

The purpose of this investigation was to analyse the concurrent validity and reliability of an iPhone app (called: My Jump) for measuring vertical jump performance. Twenty recreationally active healthy men (age: 22.1 ± 3.6 years) completed five maximal countermovement jumps, which were evaluated using a force platform (time in the air method) and a specially designed iPhone app. My jump was developed to calculate the jump height from flight time using the high-speed video recording facility on the iPhone 5 s. Jump heights of the 100 jumps measured, for both devices, were compared using the intraclass correlation coefficient, Pearson product moment correlation coefficient (r), Cronbach's alpha (α), coefficient of variation and Bland-Altman plots. There was almost perfect agreement between the force platform and My Jump for the countermovement jump height (intraclass correlation coefficient = 0.997, P < 0.001; Bland-Altman bias = 1.1 ± 0.5 cm, P < 0.001). In comparison with the force platform, My Jump showed good validity for the CMJ height (r = 0.995, P < 0.001). The results of the present study showed that CMJ height can be easily, accurately and reliably evaluated using a specially developed iPhone 5 s app.

Effects of dietary nitrate, caffeine, and their combination on 20-km cycling time trial performance.

The aim of this study was to examine the acute supplementation effects of dietary nitrate, caffeine, and their combination on 20-km cycling time trial performance. Using a randomized, counterbalanced, double-blind Latin-square design, 14 competitive female cyclists (age: 31 ± 7 years; height: 1.69 ± 0.07 m; body mass: 61.6 ± 6.0 kg) completed four 20-km time trials on a racing bicycle fitted to a turbo trainer. Approximately 2.5 hours before each trial, subjects consumed a 70-ml dose of concentrated beetroot juice containing either 0.45 g of dietary nitrate or with the nitrate content removed (placebo). One hour before each trial, subjects consumed a capsule containing either 5 mg·kg of caffeine or maltodextrin (placebo). There was a significant effect of supplementation on power output (p = 0.001), with post hoc tests revealing higher power outputs in caffeine (205 ± 21 W) vs. nitrate (194 ± 22 W) and placebo (194 ± 25 W) trials only. Caffeine-induced improvements in power output corresponded with significantly higher measures of heart rate (caffeine: 166 ± 12 b·min vs. placebo: 159 ± 15 b·min; p = 0.02), blood lactate (caffeine: 6.54 ± 2.40 mmol·L vs. placebo: 4.50 ± 2.11 mmol·L; p < 0.001), and respiratory exchange ratio (caffeine: 0.95 ± 0.04 vs. placebo: 0.91 ± 0.05; p = 0.03). There were no effects (p ≥ 0.05) of supplementation on cycling cadence, rating of perceived exertion, (Equation is included in full-text article.), or integrated electromyographic activity. The results of this study support the well-established beneficial effects of caffeine supplementation on endurance performance. In contrast, acute supplementation with dietary nitrate seems to have no effect on endurance performance and adds nothing to the benefits afforded by caffeine supplementation.

The interactive effects of recovery mode and duration on subsequent repeated sprint performance.

The aim of this study was to examine the interactive effects of recovery mode and duration on subsequent repeated short sprint (RSS) performance. Ten male recreational athletes (age, 27.9 ± 5.0 years; height, 1.80 ± 0.07 m; mass, 81.6 ± 13.5 kg) performed 4 randomized trials consisting of a 30-second cycle sprint, followed by a specified recovery period (45 or 180 seconds), and a subsequent set of RSS (7 × 5 seconds, 20-second passive rest periods). Recovery mode was either active (AR; 70% of the power output at lactate threshold) or passive (PR). Mean heart rate and V[Combining Dot Above]O2 were significantly higher (p ≤ 0.05) in AR than in PR over both recovery durations. Although the difference in V[Combining Dot Above]O2 reached significance after 10-15 seconds, a significant (p ≤ 0.05) difference in heart rate was observed only after 26 seconds (45-second trials) - 75 seconds (180-second trials). Blood lactate was significantly (p ≤ 0.05) lower in AR than in PR only after 135 seconds (mean difference, 2.16 mmol·L; 95% likely range, 0.77-3.55 mmol·L). Mean peak power output in the RSS test was significantly (p ≤ 0.05) higher following PR45 than AR45 (12.0 ± 1.4 vs. 11.4 ± 1.4 W·kg) and following AR180 than PR180 (12.7 ± 1.2 vs. 12.0 ± 1.2 W·kg). In conclusion, when rest periods are short, a PR strategy appears to optimize subsequent RSS performance. However, as the recovery duration increases subsequent RSS performance appears to benefit from an AR strategy.

The Reliability of a Single-Trial Measurement of Maximal Accumulated Oxygen Deficit Determined via Perceptually-Regulated Exercise.

Purpose: The aim of this study was to evaluate the reliability of a single-trial determination of maximal accumulated oxygen deficit (MAOD) achieved via the aid of perceptually-regulated incremental exercise. Methods: 14 trained male cyclists (age: 45 ± 8 yrs; height: 1.82 ± 0.06 m; mass: 79.7 ± 6.7 kg; V˙O2max: 4.09 ± 0.57 L·min-1) performed three trials of a submaximal incremental cycling test followed by a test to exhaustion at 116% of predicted V˙O2max. The intensity for each stage of the incremental test was regulated by participants to elicit perceived exertion levels of 9-15 on the Borg (6-20) scale. Linear regression was used to estimate V˙O2max at a perceived exertion level of 19. MAOD was calculated from the difference between predicted and actual oxygen demand in the test to exhaustion, reported in oxygen equivalents (O2 eq). A separate incremental test was used to measure V˙O2max directly. Results: Correlation coefficients between perceived exertion and V˙O2 across trials were strong (r ≥0.99), and there were no between-trial differences in predicted V˙O2max (4.03 ± 1.04, 3.76 ± 0.53, and 3.69 ± 0.64 L·min-1, respectively; p = .142) or MAOD (2.75 ± 2.28, 2.50 ± 1.53, and 2.93 ± 1.40 L O2 eq, respectively; p = .633). Nevertheless, the coefficients of variation for predicted V˙O2max (14.2%) and MAOD (142.8%) were poor. Conclusions: The prediction of V˙O2max from perceptually-regulated exercise displays a level of test-retest reliability which prevents its use as a means of evaluating MAOD reliably in a single-trial.

The efficacy of genotype-based dietary or physical activity advice in changing behavior to reduce the risk of cardiovascular disease, type II diabetes mellitus or obesity: a systematic review and meta-analysis.

CONTEXT: Despite clear evidence that adherence to dietary and physical activity advice can reduce the risk of cardiometabolic disease, a significant proportion of the population do not follow recommendations. Personalized advice based on genetic variation has been proposed for motivating behavior change, although research on its benefits to date has been contradictory. OBJECTIVE: To evaluate the efficacy of genotype-based dietary or physical activity advice in changing behavior in the general population and in individuals who are at risk of cardiovascular disease (CVD) or type II diabetes mellitus (T2DM). DATA SOURCES: MEDLINE, EMBASE, PsycInfo, and the Cochrane Central Register of Controlled Trials (CENTRAL) were searched up to January 7, 2022. Randomized controlled trials of a genotype-based dietary and/or physical activity advice intervention that aimed to change dietary and/or physical activity behavior were included. DATA EXTRACTION: Abstracts of 7899 records were screened, and 14 reports from 11 studies met the inclusion criteria. DATA ANALYSIS: Genotype-based dietary or physical activity advice was found to have no effect on dietary behavior in any of the studies (standardized mean difference [SMD] .00 [-.11 to .11], P = .98), even when analyzed by subgroup: "at risk" (SMD .00 [-.16 to .16, P = .99]; general population (SMD .01 [-.14 to .16], P = .87). The physical activity behavior findings were similar for all studies (SMD -.01 [-.10 to .08], P = .88), even when analyzed by subgroup: "at risk" (SMD .07 [-.18 to .31], P = .59); general population (SMD -.02 [-.13 to .10], P = .77). The quality of the evidence for the dietary behavior outcome was low; for the physical activity behavior outcome it was moderate. CONCLUSIONS: Genotype-based advice does not affect dietary or physical activity behavior more than general advice or advice based on lifestyle or phenotypic measures. This was consistent in studies that recruited participants from the general population as well as in studies that had recruited participants from populations at risk of CVD or T2DM. SYSTEMATIC REVIEW REGISTRATION: PROSPERO registration no. CRD42021231147.

A cross-sectional retrospective survey of injury situation and prevalence in female recreational netball players with a focus on knee injuries.

OBJECTIVES: To examine situations of injury and injury prevalence in female adult recreational netball players with a focus on knee injuries. DESIGN: Cross sectional retrospective online survey. PARTICIPANTS: 193 female adult recreational netball players. MAIN OUTCOME MEASURES: Any injury sustained in the previous 12 months, situation of injury, any knee injuries sustained in the previous five years, the length of time unable to play netball, and knee injury management. RESULTS: In the previous 12 months, 61% of respondents sustained injury to the lower limb, and 27% to the upper limb. Lower limb injury situations were mostly landings (46%). Upper limb injury situations were mostly collisions with an opponent (27%). 46% reported sustaining a knee injury in the previous five years. Following knee injury, players were unable to play netball for 6.8 ± 7.0 months (training); and 8.2 ± 7.4 months (matches) respectively. CONCLUSIONS: Lower limb injury is more common than upper limb injury in recreational adult female adult netball players. Landing was the most common situation of injury for the lower limb including knee injuries. In the previous five years, nearly half of the players had sustained a knee injury resulting in more than six months out of the game.

Sleep duration and quality in elite athletes measured using wristwatch actigraphy.

Sleep is known to be an important component of recovery from training, yet little is known about the quality and quantity of sleep achieved by elite athletes. The aim of the present study was to quantify sleep in elite athletes using wristwatch actigraphy. Individual nights of sleep from a cohort of Olympic athletes (n = 47) from various sports were analysed and compared to non-athletic controls (n = 20). There were significant differences between athletes and controls in all measures apart from 'time asleep' (p = 0.27), suggesting poorer characteristics of sleep in the athlete group. There was a significant effect of gender on 'time awake' (mean difference: 12 minutes higher in males; 95% likely range: 3 to 21 minutes) and 'sleep efficiency' (mean difference: 2.4 lower in males; 95% likely range: 0.1 to 4.8). Athletes showed poorer markers of sleep quality than an age and sex matched non-athletic control group (Sleep efficiency: 80.6 ± 6.4% and 88.7 ± 3.6%, respectively. Fragmentation Index: 36.0 ± 12.4 and 29.8 ± 9.0, respectively) but remained within the range for healthy sleep. This descriptive study provides novel data for the purpose of characterising sleep in elite athletes.

The effects of ionized and nonionized compression garments on sprint and endurance cycling.

The aim of this study was to examine the effects of ionized and nonionized compression tights on sprint and endurance cycling performance. Using a randomized, blind, crossover design, 10 well-trained male athletes (age: 34.6 ± 6.8 years, height: 1.80 ± 0.05 m, body mass: 82.2 ± 10.4 kg, VO2max: 50.86 ± 6.81 ml·kg(-1)·min(-1)) performed 3 sprint trials (30-second sprint at 150% of the power output required to elicit VO2max [pVO2max] + 3 minutes recovery at 40% pVO2max + 30-second Wingate test + 3 minutes recovery at 40% pVO2max) and 3 endurance trials (30 minutes at 60% pVO2max + 5 minutes stationary recovery + 10-km time trial) wearing nonionized compression tights, ionized compression tights, or standard running tights (control). There was no significant effect of garment type on key Wingate measures of peak power (grand mean: 1,164 ± 219 W, p = 0.812), mean power (grand mean: 716 ± 68 W, p = 0.800), or fatigue (grand mean: 66.5 ± 6.9%, p = 0.106). There was an effect of garment type on blood lactate in the sprint and the endurance trials (p < 0.05), although post hoc tests only detected a significant difference between the control and the nonionized conditions in the endurance trial (mean difference: 0.55 mmol·L(-1), 95% likely range: 0.1-1.1 mmol·L(-1)). Relative to control, oxygen uptake (p = 0.703), heart rate (p = 0.774), and time trial performance (grand mean: 14.77 ± 0.74 minutes, p = 0.790) were unaffected by either type of compression garment during endurance cycling. Despite widespread use in sport, neither ionized nor nonionized compression tights had any significant effect on sprint or endurance cycling performance.

Perceptual and physiological responses to recovery from a maximal 30-second sprint.

The aims of this study were to evaluate perceptions of postexercise recovery and to compare patterns of perceived recovery with those of several potential mediating physiological variables. Seventeen well-trained men (age: 22 ± 4 years; height: 1.83 ± 0.05 m; body mass: 78.9 ± 7.6 kg; and body fat: 11.1 ± 2.2%) completed 10 sprint trials on an electromagnetically braked cycle ergometer. Trial 1 evaluated peak power via a 5-second sprint. The remaining trials evaluated (a) the recovery of peak power after a maximal 30-second sprint using rest intervals of 5, 10, 20, 40, 80, and 160 seconds; (b) perceived recovery via visual analog scales; and (c) physiological responses during recovery. The time point in recovery at which individuals perceived they had fully recovered was 163.3 ± 57.5 seconds. Power output at that same time point was 83.6 ± 5.2% of peak power. There were no significant differences between perceived recovery and the recovery processes of VO2 or minute ventilation (V(E)). Despite differences in the time courses of perceived recovery and the recovery of power output, individuals were able to closely predict full recovery without the need for external timepieces. Moreover, the time course of perceived recovery is similar to that of VO2 and V(E).

Caffeine and sprinting performance: dose responses and efficacy.

The aims of this study were to evaluate the effects of caffeine supplementation on sprint cycling performance and to determine if there was a dose-response effect. Using a randomized, double-blind, placebo-controlled design, 17 well-trained men (age: 24 ± 6 years, height: 1.82 ± 0.06 m, and body mass(bm): 82.2 ± 6.9 kg) completed 7 maximal 10-second sprint trials on an electromagnetically braked cycle ergometer. Apart from trial 1 (familiarization), all the trials involved subjects ingesting a gelatine capsule containing either caffeine or placebo (maltodextrin) 1 hour before each sprint. To examine dose-response effects, caffeine doses of 2, 4, 6, 8, and 10 mg·kg bm(-1) were used. There were no significant (p ≥ 0.05) differences in baseline measures of plasma caffeine concentration before each trial (grand mean: 0.14 ± 0.28 µg·ml(-1)). There was, however, a significant supplement × time interaction (p < 0.001), with larger caffeine doses producing higher postsupplementation plasma caffeine levels. In comparison with placebo, caffeine had no significant effect on peak power (p = 0.11), mean power (p = 0.55), or time to peak power (p = 0.17). There was also no significant effect of supplementation on pretrial blood lactate (p = 0.58), but there was a significant time effect (p = 0.001), with blood lactate reducing over the 50 minute postsupplementation rest period from 1.29 ± 0.36 to 1.06 ± 0.33 mmol·L(-1). The results of this study show that caffeine supplementation has no effect on short-duration sprint cycling performance, irrespective of the dosage used.

Situations and mechanisms of non-contact knee injury in adult netball: A systematic review.

OBJECTIVES: Noncontact knee injuries in netball are a concern due to a range of negative consequences. To reduce the number of injuries, identifying the situation and mechanism of injury is important. This systematic review examined the literature reporting the situation and mechanism of noncontact knee injury in netball. DESIGN: Systematic Review. METHODS: PRISMA guidelines were followed and specific key-term combinations used to search databases. Descriptive and analytic-observational studies reporting the situation or mechanism of noncontact knee injury in females playing netball were included (evaluated using frequency counts). RESULTS: Six articles were included (combined sample 11,401). Players self-reported the situation of injury in five studies, only one study reported both the situation and mechanism of injury. Landing was the most reported situation of knee injury, representing 46.6% of all knee injuries whilst knee abduction (valgus) collapse was the most observed mechanism. Situation and mechanism of noncontact knee injury in netball were not adequately reported. CONCLUSIONS: Despite the variations in reporting methods, landing is the most common situation of injury. As only one study reported mechanism of injury, it is difficult to draw conclusions but the mechanism of noncontact knee injury in netball appears similar to those identified in other female athletes.

Caffeine, exercise physiology, and time-trial performance: no effect of ADORA2A or CYP1A2 genotypes.

The aim of this study was to investigate the influence of ADORA2A and CYP1A2 genotypes on the physiological and ergogenic effects of caffeine. Sixty-six male cyclists were screened for ADORA2A and CYP1A2 genotypes; with 40 taking part subsequently in a randomised, double-blind, placebo-controlled study. Trial 1 was used to establish the oxygen uptake-power output relationship and maximal oxygen uptake. In trials 2 and 3, participants ingested 5 mg·kg-1 of caffeine or placebo 1 h before completing a submaximal incremental cycling test, followed by a time-trial (∼30 min). Relative to placebo, caffeine led to a significant reduction in time to complete the time-trial (caffeine: 29.7 ± 1.8 min; placebo: 30.8 ± 2.3 min); but there was no effect of genotype. During submaximal exercise, caffeine reduced mean heart rate by 2.9 ± 3.7 beats·min-1, with effects dissipating as exercise intensity increased. Caffeine also significantly reduced perceived exertion by 0.5 ± 0.8, and increased blood lactate by 0.29 ± 0.42 mmol·L-1, respiratory exchange ratio by 0.013 ± 0.032, and minute ventilation by 3.1 ± 6.8 L·min-1. Nonetheless, there were no supplement × genotype interactions. In conclusion, caffeine influences physiological responses to submaximal exercise and improves time-trial performance irrespective of ADORA2A or CYP1A2 genotypes. Novelty: Caffeine affects physiological responses at rest and during submaximal exercise independent of ADORA2A or CYP1A2 genotypes. Variability in the effect of caffeine on time-trial performance is not explained by ADORA2A or CYP1A2 genotypes.

Familiarization, reliability, and evaluation of a multiple sprint running test using self-selected recovery periods.

The aims of the present study were to investigate the process of self-selected recovery in a multiple sprint test with a view to using self-selected recovery time as a means of reliably quantifying an individual's ability to resist fatigue in this type of exercise. Twenty physically active exercise science students (means ± SD for age, height, body mass, body fat, and VO2max of the subjects were 21 ± 2 yr, 1.79 ± 0.09 m, 83.7 ± 10.8 kg, 16.6 ± 3.9%, and 52.7 ± 7.2 ml·kg·min, respectively) completed 4 trials of a 12 × 30 m multiple sprint running test under the instruction that they should allow sufficient recovery time between sprints to enable maximal sprint performance to be maintained throughout each trial. Mean recovery times across the 4 trials were 73.9 ± 24.7, 82.3 ± 23.8, 77.6 ± 19.1, and 77.5 ± 13.9 seconds, respectively, with variability across the first 3 trials considered evidence of learning effects. Test-retest reliability across trials 3 to 4 revealed a good level of reliability as evidenced by a coefficient of variation of 11.1% (95% likely range: 8.0-18.1%) and an intraclass correlation coefficient of 0.76 (95% likely range: 0.40-0.91). Despite no change in sprint performance throughout the trials, ratings of perceived exertion increased progressively and significantly (p < 0.001) from a value of 10 ± 2 after sprint 3 to 14 ± 2 after sprint 12. The correlation between relative VO2max and mean recovery time was 0.14 (95% likely range: -0.37-0.58). The results of the present study show that after the completion of 2 familiarization trials, the ability to maintain sprinting performance in a series of repeated sprints can be self-regulated by an athlete to a high degree of accuracy without the need for external timepieces.

The effect of the menstrual cycle on running economy.

BACKGROUND: The aim of this study was to examine the effect of the menstrual cycle on running economy (RE). METHODS: Using a repeated-measures design, ten eumenorrheic, trained female runners (age: 32±6 yrs, V̇O2max: 59.7±4.7 mL·kg-1·min-1) completed four, weekly, identical sub-maximal and maximal incremental step tests on a treadmill to measure physiological responses across a full menstrual cycle. For phase comparison, the results from the trials that fell in the early follicular (low estrogen, low progesterone), late follicular (high estrogen, low progesterone) and mid-luteal (high estrogen, high progesterone) phases were used. RESULTS: There was a significant effect of menstrual cycle phase on RE (P=0.001), with RE in the mid-luteal (ML) phase being worse than that of the early follicular (EF) (+2.33 mL·kg-1·min-1; P=0.026) and late follicular (LF) (+2.17 mL·kg-1·min-1; P=0.011) phases. The ML phase also resulted in elevated core temperature versus the EF (+0.51 ºC; P=0.001) and LF (+0.66 ºC; P=0.037) phases, and elevated minute ventilation versus the EF phase (+3.83 L·min-1; P=0.003). No significant effects of menstrual cycle phase were found on body mass, heart rate, ratings of perceived exertion, time-to-exhaustion, maximal oxygen consumption, or blood lactate concentration. CONCLUSIONS: In the ML phase, which causes increased core temperature and minute ventilation, RE is impaired at exercise intensities that are applicable to training and performance. In physiologically stressful environments, this impairment in RE may have a significant impact on training and performance.

The effects of acute static and dynamic stretching on spring-mass leg stiffness.

OBJECTIVE: This study investigated the effect of brief static and dynamic stretching on spring-mass leg stiffness in a vertical bilateral hopping task. METHOD: 38 men and 18 women were randomly assigned to either a natural (NAT; n = 27), or maximal (MAX; n = 29) hopping group. NAT bounced at their self-selected stiffness and MAX were instructed to bounce as stiffly as possible. Hopping was performed at 2.2 Hz on a force plate. After each of four treatment conditions (no stretch, 30 s stretch, multiple (4 × ) 30 s stretch, and dynamic stretch), subjects completed three × 30 s bouts (2 min rest periods) of hopping, in a counterbalanced crossover design. Stretches were performed on: gluteals, hamstrings, quadriceps and calves. Spring-mass leg stiffness was calculated as the ratio of peak vertical force to vertical displacement during ground contact. RESULTS: The results revealed that men displayed greater leg stiffness than women (mean difference: 6.04 kN m-1; 95% likely range: 1.94-10.13 kN m-1), and that MAX produced higher stiffness values than NAT (mean difference: 10.93 kN m-1; 95% likely range: 6.84-15.03 kN m-1). Although there were no significant effects of treatment (p = 0.85) or time (p = 0.54) on leg stiffness, there was a significant treatment × time interaction (p = 0.015). Nevertheless, post hoc analyses were unable to identify where those differences were. CONCLUSION: Relative to controls, the results of this study showed that brief static stretching or non task-specific dynamic stretching does not affect spring-mass leg stiffness during vertical bilateral hopping.